EC225 crash near Bergen, Norway April 2016

[Satcomm]

This is true. However it is interesting to note what information has been leaked / drip fed, and what info has been withheld.

How do you know what information has been withheld, if it's been withheld?

[HeliComparator]

How do you know what information has been withheld, if it's been withheld?

Because for example the hours on the epicyclic since overhaul must be known but it's not been reported. Ditto the HUMS history. Maybe the relevant HUMS history is zero (probably not!) in which case say so. What maintenance activities relating to the struts? Must be known, but secret. Exactly what bits of struts were found where (ie what remained attached to the transmission decking, what was attached to the free flying bit. This must be known but the release of info on this subject has been cryptic.

WHY?

[Diversification]

Re: SLB #1251.
The SKF procedure is for spherical rollerbearings. On normal roller bearings it seems that one flange is often pressed into place after spacers and roller are in place.
Strange that we have no leaked mintenance manuals for the gearboxes.

[Self loading bear]

Diversification,

When you look at the cross section drawing of the transmission
cross section (https://www.google.nl/search?q=drawing+h225+transmission&client=tablet-android-samsung&hl=nl-NL&prmd=isvn&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjr6fnO_5vNAhWK2BoKHX67BrgQ_AUIBygB&biw=1280&bih=800#hl=nl-NL&tbm=isch&q=cross+section+ec332l2+transmission&imgrc=Bv33jtFpEf0w5M%3A)
you can see these are spherical roller bearings

SLB

[SASless]

it is interesting to note what information has been leaked / drip fed, and what info has been withheld.


Have you considered a leaky faucet might have been tightened up?

[disting]

Its a legal requirement when taking part in an investigation not to speak about any part of it to anyone outside the investigation. People leaking information do not help the investigation in any way. It is very frustrating to be on the inside of an investigation and seeing some of the rubbish that is put forward by armchair investigators and the media, but having the professionalism not to break the investigation rules. When the facts are fully known, they will be released.

[birmingham]

This is true. However it is interesting to note what information has been leaked / drip fed, and what info has been withheld.
It is certainly pretty clear that the suspension bar theory still needs clarification. It still hasn't been ruled out as the primary causal event. I'm assuming they do not yet have enough evidence to stand up a chain of events and have decided to say nothing. Both Airbus and the AIBN have been very quiet since 1 June report and CHC have only mentioned the commercial aspects/redundancies.

[Pi1ot]

This seems like an interesting article: Airbus-sjef frikjente girboksen. 12 dager senere kom rapporten som indikerer det motsatte - Tu.no (http://www.tu.no/artikler/airbus-sjef-nektet-for-at-det-kunne-vaere-feil-pa-girboksen-like-etter-ulykken/348418)

Could someone please help translating the article and linked document?

[turboshafts]

Because for example the hours on the epicyclic since overhaul must be known but it's not been reported. Ditto the HUMS history. Maybe the relevant HUMS history is zero (probably not!) in which case say so. What maintenance activities relating to the struts? Must be known, but secret. Exactly what bits of struts were found where (ie what remained attached to the transmission decking, what was attached to the free flying bit. This must be known but the release of info on this subject has been cryptic.

WHY?

I fully agree with HeliComparator!

Seeing in the light of how the bereaved from former accidents
are feeling towards the openness of the investigation, it is high time
that there is put some pressure on it!

Not to leak, but to be frank, humble and correct in the statements made.

Up until now I have found several contradictions in the info stated by CHC
Also the need to have a public advisor present, and thus is hesitating to
the most extent to confirm or make clear any of the questions asked by the press.

This is not alone only the case with CHC, but also Statoil and
as well AH.

[Apate]

Using Google Chrome translate feature reveals:

SF is composed of representatives from the government, helicopter operators, oil industry, Avinor, unions and others involved in the offshore sector.

They have met three times after the accident with EC225 helicopter that crashed outside Turøy 29 April.

In the second extraordinary meeting on 20 May, attended by several representatives from Airbus Helicopters, including their security chief.

According to the minutes , he ruled out that events are similar in character to the accidents in 2009 and 2012.

In 2012 an emergency landing two EC225 in the North Sea with wrecked Main Gear Box (MGB) with crack in the same place on the shaft.

In 2009 overthrew a AS332L2 after MGB failed due to fatigue fracture on one of the planetary gears in the second stage of the episyklisme module.

But in the interim report from the Accident Investigation Board Norway (AIBN) from June 1, it is pointed precisely at a similar fatigue fracture in one of the planet wheels of one of the planetary gears.

- Airbus Helicopters (AH) argues that it is not found traces of overheating in MGB. AH do not think the problem lies in the MGB, but must be found outside. That is why AH believes that one can not add design of MGB assumed that the helicopter should not be airworthy, according to the minutes of helicopter safety forum.

At this time argued helicopter manufacturer remains that mistake by one of the hangers, specifically attached to the MGB suspension bar, was a likely trigger for the main rotor loosened.

In the minutes it emerged that Norwegian expertise find it difficult to understand that too much torque on fixing bolts to support braces on MGB should be able to cause a break in the support structure.

- This position Airbus Helicopters had taken, was solely founded on proprietary research. We are critical of the factory as much has been leaning in one direction instead of being more open in an early exploration phase, says SF leader Anders Røsok to TU.

TU has asked Airbus Helicopters question whether they still believe that the primary cause of Turøy accident is outside the MGB.

A spokesman for the helicopter manufacturer says the TU that the only thing they will be quoted on now, is that they work closely with the Norwegian Accident Investigation Board and that they do not rule out some causes.

In conversation also shows that Airbus did not entirely agree with SF-abstract. Their version is that the message on May 20 was that it was too early to draw parallels to the 2009 accident, not to categorically reject any similarities.

TU mentioned last week that the reconditioned main gearbox, which was installed in the accident helicopter on January 17, was subjected to "rough treatment" and had to return to the workshop before installation.

This is among several things AIBN now look more closely at, and which also was the topic of helicopter forum, shows the minutes.

- SF wanted to know what was done by transport damage in Australia. AH explained the process when this transmission came into the AH for repair. They were further asked whether it was possible to see the strip down the report by the overhaul of the MGB. AH would check up.


The highlights are mine.

Note that the box was overhauled/repaired by AH, if the text is correct.

[Heliflyger]

This seems like an interesting article: Airbus-sjef frikjente girboksen. 12 dager senere kom rapporten som indikerer det motsatte - Tu.no (http://www.tu.no/artikler/airbus-sjef-nektet-for-at-det-kunne-vaere-feil-pa-girboksen-like-etter-ulykken/348418)

Could someone please help translating the article and linked document?

The article is referring to a meeting in SF which is a forum for helicopter safety with representatives from Norwegian caa, helicopter oprators, oil companies and unions etc.
AH participated in this meeting may 20 and claimed there is no sign of overheating in the mgb and therefore the cause has to be outside the mgb.
AH means design is not a basis for grounding the aircraft.
The representatives from the norwegian expertise finds IT hard to understand that overtorque of the bolts attatching the suspensjon bars can cause the suspension stucture to break.
Tu.no has questioned AH if they still belive the cause is outside the mgb, a AH spokesman says they are working closely with aibn and will not exclude any causes.
SF wanted to know what AH had done with the mgb they had repaired after a transport damage in Australia,
AH representatives explained the process after the mgb came in for repair, SF asked for the strip down report after the pepair/overhaul. AH answered they would check this out

[turboshafts]

This seems like an interesting article: Airbus-sjef frikjente girboksen. 12 dager senere kom rapporten som indikerer det motsatte - Tu.no (http://www.tu.no/artikler/airbus-sjef-nektet-for-at-det-kunne-vaere-feil-pa-girboksen-like-etter-ulykken/348418)

Could someone please help translating the article and linked document?

Very interesting.
It is nothing directly new, except they refer to the meeting protocol of
ekstraordinært møte i Samarbeidsforum for helikoptersikkerhet på norsk kontinentalsokkel (SF). That has been published.

(extraordinary meeting in cooperationforum for helicopter security on norwegian continental shelf - SF)

Here is the interesting part:

Utenfor MGB
– Airbus Helicopters (AH) hevder at det er ikke funnet spor av overopphetning i MGB. AH tror ikke problemet ligger i MGB, men må finnes utenfor. Det er derfor AH mener at en ikke kan legge design av MGB til grunn for at helikopteret ikke skulle være luftdyktig, heter det i referatet fra helikoptersikkerhetsforumet.

På dette tidspunktet framholdt helikopterprodusenten fortsatt at feil ved et av opphengene, nærmere bestemt festet til MGB suspension bar, var en sannsynlig utløsende årsak til at hovedrotoren løsnet.

I referatet kommer det fram at den norske ekspertisen synes det er vanskelig å forstå at for mye tiltrekkingsmoment på festebolter til støttestagene på MGB skal kunne forårsake brudd i støttestrukturen.

– Denne posisjonen Airbus Helicopters hadde inntatt, var utelukkende fundert på egne analyser. Vi er kritiske til at fabrikken i så stor grad har lent seg i én retning i stedet for å være mer åpen i en tidlig undersøkelsesfase, sier SF-leder Anders Røsok til Teknisk Ukeblad.


Outside of MGB

Airbus helicopters state that there is no trace of overheating of MGB.
AH does not believe that the problem lies within MGB, but has to be found outside. That is why AH means that one cannot hold design of MGB reason for the helicopter not to be airworthy, it is stated in the report from the helicopter security forum.

At this point the helicopter producer still claims, a failure to one of the fasteners, more specifically, the mount for the fastener of the MGB suspension bar, was a probable reason that the main rotor came loose.

In the report it is said that the Norwegian expertise find it difficult to understand that too much fastening torque to the fastening bolts of the suspension bar, should cause a crack in the support structure.
This position that Airbus Helicopter had taken, was solely based on own analyses. We are critical that the factory in such large grade have leant towards one direction instead of being more open in an early stage of the investigation, says SF leader Anders Røsok to Teknisk Ukeblad.

[Diversification]

SLB #1267
You are right about the bearings being spherical. Thanks for the link to the drawing.

[Apate]

Hi turboshafts, you said

Up until now I have found several contradictions in the info stated by CHC

Care to elaborate, rather than make unsubstantiated statements yourself??!!!

[birmingham]

Using Google Chrome translate feature reveals:




The highlights are mine.

Note that the box was overhauled/repaired by AH, if the text is correct.
I assume the SF meeting was held a little before evidence was apparently found of a fatigue crack in the epicyclic. However, we now have two separate maintenance related events;

1. Fitting of suspension bolts/ possible over torque related fatigue crack,
2. Damage to and repair of the MGB.

So did a failure related to 1 actually occur and precede a failure related to 2 or vice versa?

Was the fatigue/damage apparently found in the MGB initiated inside or outside the aircraft?

They should have all the maintenance records, do they now have enough bits and pieces for the metallurgy, finite element analysis etc?

The stakes are incredibly high even by the standards of an air accident enquiry.

Sorting out the wood from the trees will be a complicated process.

[turboshafts]

Hi turboshafts, you said


Care to elaborate, rather than make unsubstantiated statements yourself??!!!

To get the whole context you should eventually look back a few pages.
but here are some points I made earlier

Claiming that helicopter had not have problems
(media reports that there where multiple abrupted flights in the days before.

If it had nothing to do with the accident they could tell (and score PR trust)
what is was.

Gearbox TBO is not aligned with what is told here 4400 hr vs 2000 hr

CHC state has nothing to do with MGB, not wanting to tell if unit is new
or overhauled, where MGB is beeing repared etc.

(if there was secrecy in the above topics, they SF report would not have been made public)

Interview is coming weeks after accident, with support of PR advisor,
and indeed not conciliating the hope to let any uncertainties be clarified.

I understand times are hard for CHC as well, but these contradictions
are making it worse for everyone involved.
And it does not give the needed trust this situation deserves.

[Apate]

Sorry turboshaft I've been reading this from the start and you're simply making some of this up. I've no idea what you motivation is, but I suggest you think before you type!

To take each of your points - when did they claim the "helicopter had not had any problems"?

MGB TBO. You take a statement from someone (who could be a 12 year old school boy for all you know!) on this forum that the TBO is 2000 as gospel and immediately conclude that CHC are lying. Interesting approach!

Finally Interview is coming weeks after accident, with support of PR advisor,
and indeed not conciliating the hope to let any uncertainties be clarified.. Now I know English isn't your first language, but I don't even know what you are on about :ugh:
In any case, is this a "contradiction", which is what you were asserting?

[turboshafts]

Sorry turboshaft I've been reading this from the start and you're simply making some of this up. I've no idea what you motivation is, but I suggest you think before you type!

To take each of your points - when did they claim the "helicopter had not had any problems"?

MGB TBO. You take a statement from someone (who could be a 12 year old school boy for all you know!) on this forum that the TBO is 2000 as gospel and immediately conclude that CHC are lying. Interesting approach!

Finally . Now I know English isn't your first language, but I don't even know what you are on about :ugh:
In any case, is this a "contradiction", which is what you were asserting?

Simmer down lad,

I am not claiming anyone lying.

a contradiction simply meaning there are two different explanations.
I did not say that I conclude to either one of those.

I am trying to get the facts straight, those few that exist

What is the TBO MGB for commercial flight with the EC225?
2000 hours or 4400 hours?

It was claimed to be problem free and had flown 6 commercial flights the same day without indications of anything wrong.
Then it came clear of the problems and abrupted flights in the days before.
After that, those two "stories" are merged and told chronologically, but not before.

If you need a PR advisor when speaking to the press
I would assume there is a significant risk of stepping on the wrong foot.
The questions where so easy, they hold back and now they are answered officially anyway.
That is a contradiction if there is no information behind that could put responsibility on the shoulders of CHC

keep up the constructive tone:
I think Airbus should be praised for finding the root cause so quickly. What a shame the AIBN and AAIB, Norwegian and UK CAA are all taking SOOOOO long to come to a similar conclusion

and be consecutive
So many 225 fan boys falling for the Airbus ploy of deflection.

[henra]

SF wanted to know what AH had done with the mgb they had repaired after a transport damage in Australia,


That is an interesting part!
What kind of transport damage was that? Would be interesting to know if the epicyclic gears have been replaced afterwards. Roller bearings do take shocks VERY personal when not turning. With the design of the epicyclic gears acting as outer race of the roller bearing I would be thoroughly worried about any shock load while static and not replacing the epicyclics.

[Concentric]

This is my first posting on this forum, having followed it for several years and learned a lot from some very knowledgeable folks. Since I am an engineer and SLF and not a professional pilot I have been reluctant in the past to comment, but for the subject of this thread I believe there was nothing that pilots could have, or should have, done to prevent the crash. It was clearly a failure of engineering somewhere along the line whether that was design, manufacturing, inspection, materials, maintenance or assembly.

I will not be the only member to have their personal theory as to how the accident occurred but I will make the following simple observations and ask a few questions.

Firstly, with reference to the AIBN Preliminary Report dated 27/5/16, Figure 4 shows the broken upper end of the front suspension bar which has clearly fractured in a ductile manner from a gross tensile overload, evidenced by the elongation of the male eye. Any suggestion that it was not properly pinned at either end or that the lower connecting lug bolts were incorrectly torqued contradicts the evidence. The bar must in fact have been very well restrained and under a tensile force much greater than its design load before it failed in this manner, assuming it was made of the correct material. For anything not designed to, other than the pins and bolts, to have transmitted this force is, frankly, far-fetched. For the front bar at least, it would also appear that the direction of loading was close to its normal arrangement as the pin is not bent and failure was across minimum tensile section.

Secondly, the ATC radar plot (Figure 1) gives a timeline and some indication of groundspeed of LN-OJF. The radar returns are at approximately 4 second intervals and the (straight line) distance covered between 09:54:44 and 09:54:48 is only about 50% of that covered in the preceding 4 seconds. If I have scaled off the map correctly, the initial groundspeed appears to be approximately 148 knots but the average groundspeed for the 4 seconds after 09:54:48 appears to be approximately 74 knots (it could be higher if the aircraft followed an S-turn). The CVFDR is reported to have shown everything ‘normal until a sudden catastrophic failure developed in 1-2seconds’.

The (average) groundspeed after 09:54:48 scales as approximately 52 knots, by which time, taking the wind direction (190 – 200degrees) and final position of the MRH into account, the MRH had probably separated from the aircraft. Thereafter the fuselage would be a ballistic projectile with only air resistance having any effect on its groundspeed. Within the 4 seconds after 09:54:44 the aircraft had decelerated from 148 knots to slightly over 52 knots regardless of flight path. It is even possible it could have been during just the last 2 seconds of that interval.

This would appear to be a very high rate of horizontal deceleration (up to 2.5g) in addition to normal ‘g’ and any additional vertical acceleration and/or rotational acceleration. I will leave it to the professionals to suggest whether this is within normal airframe loading limits and how a helicopter can be made to decelerate this rapidly. Presumably it requires a very severe flare and the rotor to be attached? On top of mast axial loading such a rotation must impart a moment to the top of the gearbox, increasing load on the front suspension bar.

Thirdly, Figure 7 and Figure 9 show how the epicyclic external ring gear burst open across both 1st and 2nd stages around the 4 o’clock position directly adjacent to an M/R servo location. What would be the effect of a planet gear or fragment bursting out and breaking the right hand rear servo?

Fourth, the aft RH and LH suspension bars and all pins appear to have stayed together and the logical conclusion is that the bolts connecting the lugs to the airframe failed. The AH EASB 53A058 requested operators to check, and report back to AH, torque measurements on the airframe lug mounting bolts. Checking the torque is a safety measure; reporting torque figures from across the world could be construed as something else.

Presumably these bolts are designed to take the full design load of the suspension bar, crucially when the geometry is as per the normal arrangement. If designed on the same basis as the front bar the bolts should be capable of resisting failure load of the upper eye. The rear bars did not fail although the LH upper lug looks a little bent. Its lower pin is the only one photographed fitted – does that imply it has bent and could not be removed? Could it have been the last to fail?

If the geometry changes, for example if the front bar has already failed and the mast tilts backwards, the bolts could be subjected to prying action, overloading them in rapid succession. The EASB does not show how long these bolts are. If they are fatigue critical and are required to retain pre-tension they should have as long a length as practical, preferably with L/d> 5 (where L = clamp length; d = diameter). If they are very short they could fail without significant bending of the brackets. As an aside, are there dissimilar materials between the bolts, lugs and airframe? Given the short time since the last MGB and MRH replacement I am not suggesting corrosion would be responsible but it is an interesting design feature.

Failure of the rear bolts, assuming they were new and correctly fitted along with the MGB, is highly suggestive that they failed later in the sequence of events through tensile failure and not fatigue and therefore were not the initial cause.

The AIBN’s latest report of 1 June 2016 points to the very serious possibility of fatigue failure of a 2nd stage planet gear. It is fortunate they recovered 2 parts of this gear with 4 fracture faces. The missing fragments will eventually be found although corrosion may by then have destroyed some of the evidence of beach marks.

I think the AIBN should be commended on how open they have been to date. It would appear that some of their public updates have been forced by the unusual and less than cautious behaviour of Airbus Helicopters in making their own opinions public, independently of the official investigation. I think the AIBN’s open approach will be appreciated by the relatives of those killed in this latest human tragedy and in G-REDL. As an engineer, I know that every day is a school day and I feel for the design engineers at Airbus and maintenance engineers at CHC. What normally works, on this occasion and possibly one previous hasn’t, and they need to understand why that is the case. Above all, it is important to be earnest.

So there you go, that’s my first tuppence worth!

[n305fa]

I fully agree with HeliComparator!

Seeing in the light of how the bereaved from former accidents
are feeling towards the openness of the investigation, it is high time
that there is put some pressure on it!

Not to leak, but to be frank, humble and correct in the statements made.

Up until now I have found several contradictions in the info stated by CHC
Also the need to have a public advisor present, and thus is hesitating to
the most extent to confirm or make clear any of the questions asked by the press.

This is not alone only the case with CHC, but also Statoil and
as well AH.


I'd just like to say a couple of comments re the above and helicompartor.

The AIBN is the investigation authority, no-one else. They areinvestigating a significant, complicated (beyond our laymans understanding)accident without all of the evidence available. Everything they publish is as a result of comprehensive expert analysis of factual evidence available to the investigation, not us. To suggest that they are 'hiding' (my paraphrase) facts shows a very clear misunderstanding of the process of air accident investigation.

Issues relating to immediate airworthiness are published when the evidence and analysis shows that the airworthiness of an aircraft type is in question. All of the issues that may show 'deficiencies' will be investigated and reported as appropriate in the final report.

[Apate]

I am trying to get the facts straight, those few that exist

That one is easy, lay off the speculation and wait for the AIBN report. Simples!!!!

[buzz66]

I see the Gearbox Transport is gaining traction.
I would imagine IF ANY significant stress to the box was caused by Transport damage to cause the Gearbox to fail WITHOUT warning. It would start at the Epicyclic Ring or Conical housing. I think the Epi Ring would fail well before the Conical Housing.
This is a more plausible cause than a Sus Bar Event.

AH are going to have to go to extreme lengths to be able to say everything that did after receiving the alleged transport damaged Gearbox, was in no way the root cause of the failure. Common sense would dictate this Box was Eddy Current, & NDT'ed to death above and beyond a normal Gearbox overhaul, or was it?

[HeliComparator]

I'd just like to say a couple of comments re the above and helicompartor.

The AIBN is the investigation authority, no-one else. They areinvestigating a significant, complicated (beyond our laymans understanding)accident without all of the evidence available. Everything they publish is as a result of comprehensive expert analysis of factual evidence available to the investigation, not us. To suggest that they are 'hiding' (my paraphrase) facts shows a very clear misunderstanding of the process of air accident investigation.

Issues relating to immediate airworthiness are published when the evidence and analysis shows that the airworthiness of an aircraft type is in question. All of the issues that may show 'deficiencies' will be investigated and reported as appropriate in the final report.
I suggest that you are making most of that up because you don't actually know. Not out of malice, of course. What you say is as it should be, however you fail to address the issue that some quite complex pieces of information, pictures, titbits etc have been released whilst some very basic facts, easily available without any need for interpretation, have not been released. Until that can be explained I'll remain a bit suspicious.

[OnePerRev]

This is my first posting on this forum, having followed itfor several years and learned a lot from some very knowledgeable folks.


Concentric,
Nice first post.
On a 'rumor network' such as this, we find both wild speculation based on agenda and emotion, and then sometimes a little educated insight.. Thank you for the latter. Professionals here are seeking advance knowledge, exploring the circumstances to improve safety for the entire industry, across models. So in that sense it is worth doing. We just have to balance what the active investigation professionals are telling us, with due respect.


I had not noticed the distortion on the suspension bar fitting eye, I would concur that it was overloaded at time of failure. It is of course possible that a fatigue started there prior to final overload, but we probably would have heard about that already from AIBN.


I would not put much faith in mapping direction of rotor departing based on the location found. We saw the video of it like a maple seed or boomerang, not much of a direct glide path. Otherwise, your general theory of a flare makes sense. For that matter, it has already been speculated that the rotor moved back first and blades struck the tail and tail rotor.


So it comes back to the gearbox. The first report showed two pinion fracture surfaces, one looks darker than the other. Also, the smearing to the integral race is discolored differently than the rest. The lab guys are no doubt evaluating relative amounts of corrosion, and discoloration. Don't be surprised if this box had corrosion internally prior to the crash.

[Satcomm]

Why would anyone suspect this may be due to transport damage of the gearbox? Maybe if you had any idea of what the damage may have been, then maybe, just maybe you could speculate.

But without knowing what happened, then you have no grounds to speculate. This could be something as simple as damaged threads of the generator/alternator studs. It could also have been bounced off the back of the transport trailer going down the highway ... Tumbling down the highway, smashing through a couple construction barriers and eventually coming to rest at the bottom of a lake. Either way, it was sent back to AH (despite the rumours on here of heli-one) and I'm sure was inspected/repaired accordingly.

[Satcomm]

HC,

Because for example the hours on the epicyclic since overhaul must be known but it's not been reported. Ditto the HUMS history. Maybe the relevant HUMS history is zero (probably not!) in which case say so. What maintenance activities relating to the struts? Must be known, but secret. Exactly what bits of struts were found where (ie what remained attached to the transmission decking, what was attached to the free flying bit. This must be known but the release of info on this subject has been cryptic.

I guess I can see your point and I must admit I would like for the aibn to come out with some of the above details but at the same time, they must not feel it is pertinant information for the general public at this point.

Here's my take for what it's worth.

The epicyclic TBO hours will be somewhere less then the TBO, and that's all that really matters. As far as I know, we do not know the MGB or MRH hours at this point either. I believe it is turboshaft that has been pushing the MGB TBO. Seeing how it came from AH overhaul and was installed in January, who cares, it is no where near TBO. If the TBO was 1000 hours, let alone 2000 or 4400, it would not be at TBO.

The HUMS must not be telling to much or the AIBN would not be able to say that current means the detect failure are not adequate. If there was an obvious vibration trend or chips detected in the days/weeks on HUMS prior to the accident then I think they could state that it was detectable and avoidable.

We all know there was a substantial amount of suspension bar maintenance prior to the accident. Both the MGB and MRH were replaced in the months prior. This is in no means abnormal maintenance, they have to be disconnected to remove these major components. I do believe it was stated early on that there were no "human misinterpretions", so one should assume this maintenance was performed correctly.

As far as what was still connected to where, you seen the pics of the wreckage correct?? It's not only if the fitting was still attached to the deck or not. If not, was it the cause, was it ripped off as a result of the cause or was it detached when the aircraft hit the the ground at 13000 +feet/min. All this I'm sure they have highly trained individuals working very hard to figure out. Can only imagine the amount of speculation on here if they just said all 4 bolts were sheared off!

Just my thoughts

[riff_raff]

......So it comes back to the gearbox. The first report showed two pinion fracture surfaces, one looks darker than the other. Also, the smearing to the integral race is discolored differently than the rest. The lab guys are no doubt evaluating relative amounts of corrosion, and discoloration. Don't be surprised if this box had corrosion internally prior to the crash.

It seems quite possible that it may have started in the gearbox epicyclic stage based on the public source information I have seen. I still don't understand why debris from the planet bearing outer race spall was not picked up by the lube oil chip detector. A race surface spall large enough to initiate a rim fracture should have generated a significant amount of ferrous debris. I took another look at the oil flow path from the output stage planet gear spherical roller bearing down to the sump. In the sketch attached I traced the oil flow path in green. One thing that caught my attention is the oil tray just below the first stage planetary carrier. It forms a ledge around the inner perimeter of the housing, and based on the inboard location of the drain opening in the tray it seems that. Due to the close proximity of the rotating carrier surface just above, windage will impart a significant swirling motion to the return oil draining onto the tray, causing it to pile up around the housing wall. The high velocity swirl motion in this return oil will cause denser ferrous debris particles to separate and collect on the inner housing wall and upper tray surfaces. This type of dynamic oil debris separation (http://www.tedecoindustrial.com/diag.htm) is quite effective and is actually used in many aircraft lube oil systems. One thing that would be interesting to see is if there was significant amounts of ferrous debris trapped in this location around the upper perimeter of the oil tray.

As always, just pure speculation from someone (me) with no detailed knowledge of this gearbox design.

[TylerMonkey]

Re: Concentric
" Thirdly, Figure 7 and Figure 9 show how the epicyclicexternal ring gear burst open across both 1st and 2ndstages around the 4 o’clock position directly adjacent to an M/R servo location.What would be the effect of a planet gear or fragment bursting out and breakingthe right hand rear servo ? "

Could damage to a servo theoretically cause a cyclic change so abrupt that it could over stress the front suspension strut and cause it to fail ? That might explain the fast horizontal fuselage deceleration you described. I know the answer is not within our grasp but it is one possible sequence of events that would explain why/if the strut failed after the event started.
Seems there is possibly evidence (failure under extreme tensile load) that the strut was intact when the event started, which would make it more unlikely that the strut failed first and that caused the event.
Interesting post.

[buzz66]

Why would anyone suspect this may be due to transport damage of the gearbox? Maybe if you had any idea of what the damage may have been, then maybe, just maybe you could speculate.

But without knowing what happened, then you have no grounds to speculate. This could be something as simple as damaged threads of the generator/alternator studs. It could also have been bounced off the back of the transport trailer going down the highway ... Tumbling down the highway, smashing through a couple construction barriers and eventually coming to rest at the bottom of a lake. Either way, it was sent back to AH (despite the rumours on here of heli-one) and I'm sure was inspected/repaired accordingly.
Any Transport Damage will lead to speculation.

Just as you are speculating on the idea that I don't know the details of the Transport damage, if I did I wouldn't be putting it in print or anywhere else that could land my butt in Court

You know the word "Rumor" features heavily in the Name of this Forum.

Just for your info, the Alternators are NOT mounted to the gearbox by studs. It's held in Place with a Clamp...It does have a locating Pin thou, and provision for oil cooling, but I get your point.

[buzz66]

Re: Concentric
" Thirdly, Figure 7 and Figure 9 show how the epicyclicexternal ring gear burst open across both 1st and 2ndstages around the 4 o’clock position directly adjacent to an M/R servo location.What would be the effect of a planet gear or fragment bursting out and breakingthe right hand rear servo ? "

Could damage to a servo theoretically cause a cyclic change so abrupt that it could over stress the front suspension strut and cause it to fail ? That might explain the fast horizontal fuselage deceleration you described. I know the answer is not within our grasp but it is one possible sequence of events that would explain why/if the strut failed after the event started.
Seems there is possibly evidence (failure under extreme tensile load) that the strut was intact when the event started, which would make it more unlikely that the strut failed first and that caused the event.
Interesting post.
I like the theory.
I'm pretty sure any servo damage caused from an exploding gearbox would be easily identified, due nature of the damage, especially when compared to the other 2 Servo's

[n305fa]

I suggest that you are making most of that up because you don't actually know. Not out of malice, of course. What you say is as it should be, however you fail to address the issue that some quite complex pieces of information, pictures, titbits etc have been released whilst some very basic facts, easily available without any need for interpretation, have not been released. Until that can be explained I'll remain a bit suspicious.

HC

Re your comments, fortunately what I said was based on experience of being directly involved in a significant accident investigation, it wasn't made up. The investigation releases information for two reasons, to provide the general public and media with information on the progress of the investigation and secondly to publisise issues of immediate airworthiness concern. Obviously the AIBN will not publish everything they have analysed and "closed off" it would be a waste of investigation resources which are better directed at the significant issues of the investigation.

[buzz66]

HC,



I guess I can see your point and I must admit I would like for the aibn to come out with some of the above details but at the same time, they must not feel it is pertinant information for the general public at this point.

Here's my take for what it's worth.

The epicyclic TBO hours will be somewhere less then the TBO, and that's all that really matters. As far as I know, we do not know the MGB or MRH hours at this point either. I believe it is turboshaft that has been pushing the MGB TBO. Seeing how it came from AH overhaul and was installed in January, who cares, it is no where near TBO. If the TBO was 1000 hours, let alone 2000 or 4400, it would not be at TBO.

The HUMS must not be telling to much or the AIBN would not be able to say that current means the detect failure are not adequate. If there was an obvious vibration trend or chips detected in the days/weeks on HUMS prior to the accident then I think they could state that it was detectable and avoidable.

We all know there was a substantial amount of suspension bar maintenance prior to the accident. Both the MGB and MRH were replaced in the months prior. This is in no means abnormal maintenance, they have to be disconnected to remove these major components. I do believe it was stated early on that there were no "human misinterpretions", so one should assume this maintenance was performed correctly.

As far as what was still connected to where, you seen the pics of the wreckage correct?? It's not only if the fitting was still attached to the deck or not. If not, was it the cause, was it ripped off as a result of the cause or was it detached when the aircraft hit the the ground at 13000 +feet/min. All this I'm sure they have highly trained individuals working very hard to figure out. Can only imagine the amount of speculation on here if they just said all 4 bolts were sheared off!

Just my thoughts
Not true...I have been directly involved in 2 X EC225 gearbox changes and several AS332 Gearbox changes.
In both the EC225 gearbox removals the forward Sus Bar was never removed from the Aircraft. Only the upper attachment on the forward Bar was disconnected. This is due to the nature of the firewall from memory and it differs from the AS332 gearbox installation, in a lot of ways, this is just one example.
The Engines of these Aircraft come out very easily and quickly. You are looking at around 200 man hours to change the Gearbox, so those quick release Pit Pins sure save heaps of time....I really think the Frogs don't get it sometimes.

[HeliComparator]

HC

Re your comments, fortunately what I said was based on experience of being directly involved in a significant accident investigation, it wasn't made up. The investigation releases information for two reasons, to provide the general public and media with information on the progress of the investigation and secondly to publisise issues of immediate airworthiness concern. Obviously the AIBN will not publish everything they have analysed and "closed off" it would be a waste of investigation resources which are better directed at the significant issues of the investigation.
Your post seems a bit of a non-sequitur. What you are saying is what should happen, which is not necessarily the same as what is happening. In the accident investigation I was involved in (not AAIBN) no information was released for public consumption until the report was produced. However AAIBN seem to be releasing information selectively, the question is what is behind the selection process.

[Concentric]

I like the theory.
I'm pretty sure any servo damage caused from an exploding gearbox would be easily identified, due nature of the damage, especially when compared to the other 2 Servo's

Consider also the location of M/R servo parts found in relation to the flight path.

[Concentric]

Concentric,
I had not noticed the distortion on the suspension bar fitting eye, I would concur that it was overloaded at time of failure. It is of course possible that a fatigue started there prior to final overload, but we probably would have heard about that already from AIBN.

I would say it is highly unlikely there was any fatigue crack in the suspension bar fitting eye. Both sides have failed at the same place and there is no distortion suggestive of one side failing appreciably earlier. The ductile nature of this material is evident on both sides.

[CertGuy]

Concentric,

Nice to see some engineering insight to this. Very well thought out, and presented.

Cert

[crunchingnumbers]

Concentric:

Yes really good to see some engineering insight into this. I don't fly the EC225/332and never have but it is always interesting to read Pprune posts from those knowledgeable in the industry. Thank you.

[Satcomm]

Buzz66,

Just for your info, the Alternators are NOT mounted to the gearbox by studs. It's held in Place with a Clamp...It does have a locating Pin thou, and provision for oil cooling, but I get your point.

You are right ... Lol. Been a while since working on the puma but how could I forget those clamps. Usually not too bad going on but could be a pain at times to get the self locking bit to release coming off. I said gen/alt because many on here I'm sure have only been around the Sikorsky products and only refer to an alternator when talking about cars. Well now that you have corrected me, let me say maybe then it could be as simple as damage to the alternator mounting flange (where the clamp goes) ;)

forward Sus Bar was never removed from the Aircraft. Only the upper attachment on the forward Bar was disconnected.

Where I could from, this is still considered maintenance to the suspension bar. Hence why I stated disconnecting suspension bars, not removing. I too have been involved in several AS332 gearbox changes, but will admit, never a 225.

[JohnDixson]

Are the planetaries replaced at overhaul, do they have a fatigue life, or are they on-condition?

[SASless]

Nice to see some engineering insight to this. Very well thought out, and presented.

If Engineers had wanted to work with their hands instead of their Brains.... they would have been Pilots instead of Engineers.:E

[Satcomm]

If Engineers had wanted to work with their hands instead of their Brains.... they would have been Pilots instead of Engineers.

Was nice to see a little engineering insight and also equally nice to see someone try to throw a little humour in as well. Pilots and work in the same sentence ... Thank you for the laugh this morning!

[Concentric]

If Engineers had wanted to work with their hands instead of their Brains.... they would have been Pilots instead of Engineers.:E

I'll take that as a compliment, thank you Sir! This particular engineer has never been afraid to get his hands dirty when necessary but has never had the delicate touch to be a (successful) pilot. I have the greatest respect for you guys in the front seats.

[n305fa]

Are the planetaries replaced at overhaul, do they have a fatigue life, or are they on-condition?

The OH life of the MGB including epicyclic is 2500 hrs on the EC225, the planets have an ultimate life of 5000 hrs from memory.

[n305fa]

Your post seems a bit of a non-sequitur. What you are saying is what should happen, which is not necessarily the same as what is happening. In the accident investigation I was involved in (not AAIBN) no information was released for public consumption until the report was produced. However AAIBN seem to be releasing information selectively, the question is what is behind the selection process.

HC

You and I obviously have had different experiences of accident investigation, all of the ones I've been directly involved with, or on the sidelines of have followed the process I've described regarding the release of info. You have obviously had a different experience. Lets leave it at that.

[turboshafts]

The OH life of the MGB including epicyclic is 2500 hrs on the EC225, the planets have an ultimate life of 5000 hrs from memory.

Here is my summary on TBO.

The MGB had a total flight time of 2300 hours before OH according to the PR agency Zync reports to media. (Incl 4 extensions of TBO, recorded in OEP)
Zync has also reported TBO is 2000 hours.

17. of January this was changed to a new unit. According to reports in the media.
At time of accident this unit had 1300 flying hours .

CHC Helikopterserice CEO claims during press conference they follow a maintenance program which says the gearbox is sent to a supplier for maintenance at 4400 hours. It could be wrongly cited, we are here talking about something else.

What is not clear is that Zync claims the AC had a new approval after 17 th of January for the MGB change. There is still no documentation stored in OEP about this. (until the accident it should at least be protocolled)



Firstly, with reference to the AIBN Preliminary Report dated 27/5/16, Figure 4 shows the broken upper end of the front suspension bar which has clearly fractured in a ductile manner from a gross tensile overload, evidenced by the elongation of the male eye. Any suggestion that it was not properly pinned at either end or that the lower connecting lug bolts were incorrectly torqued contradicts the evidence. The bar must in fact have been very well restrained and under a tensile force much greater than its design load before it failed in this manner, assuming it was made of the correct material. For anything not designed to, other than the pins and bolts, to have transmitted this force is, frankly, far-fetched. For the front bar at least, it would also appear that the direction of loading was close to its normal arrangement as the pin is not bent and failure was across minimum tensile section.



It could be also a scenario, that the rear susp bars are sheared off the fuselage
(on picture in prel report it looks like this).
Then it could be the remaining front susp bar could already be in such torsion
that the upper mount have recieved all of the bending torque, of the rotor on its way loose.


Secondly, the ATC radar plot (Figure 1) gives a timeline and some indication of groundspeed of LN-OJF. The radar returns are at approximately 4 second intervals and the (straight line) distance covered between 09:54:44 and 09:54:48 is only about 50% of that covered in the preceding 4 seconds. If I have scaled off the map correctly, the initial groundspeed appears to be approximately 148 knots but the average groundspeed for the 4 seconds after 09:54:48 appears to be approximately 74 knots (it could be higher if the aircraft followed an S-turn). The CVFDR is reported to have shown everything ‘normal until a sudden catastrophic failure developed in 1-2seconds’.

The (average) groundspeed after 09:54:48 scales as approximately 52 knots, by which time, taking the wind direction (190 – 200degrees) and final position of the MRH into account, the MRH had probably separated from the aircraft. Thereafter the fuselage would be a ballistic projectile with only air resistance having any effect on its groundspeed. Within the 4 seconds after 09:54:44 the aircraft had decelerated from 148 knots to slightly over 52 knots regardless of flight path. It is even possible it could have been during just the last 2 seconds of that interval.

This would appear to be a very high rate of horizontal deceleration (up to 2.5g) in addition to normal ‘g’ and any additional vertical acceleration and/or rotational acceleration. I will leave it to the professionals to suggest whether this is within normal airframe loading limits and how a helicopter can be made to decelerate this rapidly. Presumably it requires a very severe flare and the rotor to be attached? On top of mast axial loading such a rotation must impart a moment to the top of the gearbox, increasing load on the front suspension bar.



If we look at the take-off rate of climb, it is not much different to
the rate of deceleration before the incident. (Which could indicate a free fall)
I wouldnt put too much certainty in the recorded speed on the radar readings.
It could well be that the resolution is not small enough to include the exact speed
upon impact. The radar plots I have looked at (flightradar24) you see the
last recording is about 52 knots. It could well be the last recording upon ground impact. (That occured before the last recorded point on the radar)

In the very first reports of the accident in the a newspaper.
there where also an amateur video of the incident. You can see the aircraft coming
in at altitude, huge mechanical noise, the rotor shear of (not in focus on the film)
and there is a black cloud upon impact. The video then focus on the separated rotor flying its own way. (the same film after this moment is still public)
I refer to this only to avoid speculation of this part. I would say it came
in at normal altitude (400-600 m on the film) before it dropped
After seeing this I was in total shock.

[birmingham]

1300 hours in about 3.5 months is about 12 flying hours per day seven days per week.
With the current economic climate are NS shuttles really averaging this? it seems very high to me. I don't fly the NS but a couple of years back S92s world wide average less than 1000 hours per year each. I know the NS schedules are v demanding but are they as high as that? With all the associated maintenance is that even possible?

[ericferret]

1300 would be about the top end for a years flying on the North Sea.

If you look on G-INFO you can calculate the average hours for a UK aircraft. I doubt the Norwegians are any different.


GINFO Search Results Summary (http://publicapps.caa.co.uk/modalapplication.aspx?catid=1&pagetype=65&appid=1&mode=summary&aircrafttype=EC225)

Further to this it seems to me that there is a lack of understanding about the terminology.

As an example from above

"17. of January this was changed to a new unit. According to reports in the media.
At time of accident this unit had 1300 flying hours ".

1300 since new, since overhaul or since repair? Without knowing which, the figure means nothing.

The way components are tracked on aircraft can mean that a component that has 5000 hours consists of the data plate and the log book with every other item being replaced and therefore having lower hours. Without sight of the log cards you cant tell a thing.

[turboshafts]

Luftfartstilsynet: Ulykkeshelikopteret skiftet girkasse og rotor i år - Helikopterstyrten i Hordaland - VG (http://www.vg.no/nyheter/innenriks/helikopterstyrten-i-hordaland/luftfartstilsynet-ulykkeshelikopteret-skiftet-girkasse-og-rotor-i-aar/a/23671517/)

"I løpet av perioden fra 17. januar og frem til ulykken hadde helikopteret rundt 1300 flytimer, opplyser CHC Helikopter Service til VG gjennom kommunikasjonsbyrået Zync."

My transl:

"During the period from 17th of January until the accident the helicopter had around 1300 flying hours, informs CHC Helicopter Service to VG, through the PR-agency Zync."

So according to the article it is 1300 flying hours since January 17th when the gearbox was changed.

[Satcomm]

So according to the article it is 1300 flying hours since January 17th when the gearbox was changed.

Well, I guess that sums it up!! We have found the problem. 1300 hours of flying in 3.5 months, poor maintenance staff didn't even have time to check the oils, let alone download HUMS.

I can tell you without a doubt turboshaft, either the PR staff have it wrong or the news have reported it wrong. Don't think anyone on here can verify a helicopter in any type of operation that would be on track for 4000 + hours per year. As others have said, 1300 hours would be a decent year ... I have seen aircraft doing upwards of 2000 but they were super busy aircraft.

[turboshafts]

Here are all TBO from the EC225 spec sheet

http://airbushelicoptersinc.com/images/products/ec225/ec225-tech_data_2009.pdf


Let's go through some dates again (from oep.no)

09.12.2014 Approval of extended TBO

03.12.2015 Approval of extended TBO

so a year between those dates. The extended TBO is 100 hours.
So either inbetween 2014 and 2015 the MGB was changed. Or the AC flew
less than 100 hours.

18.12.2015 Second approval of extended TBO

Then the MGB was changed 17th of January 2016.

The changed MGB had 2300 hours.
Estimating from the 2014 date, could be MGB was changed
around January 2015 and flew 2300 hours until January 2016.

Between the 3rd and the 18th is 15 days.
And the TBO is extended with 100 hours. 100 hours - 15 days
Fits with 2300 hours a year, but is off course just speculation.

But I agree 1300 hours in 3.5 months doesn't sound realistic

[EESDL]

This is a Rumour Network.
It is not a place for logical, knowledgeable and pragmatic reasoning!
I enjoyed your first post and is the main reason I continue to look at this website as, sometimes (actually, more often than not to be honest) I learn something different about the industry we are in.

One of the things I have learnt is that companies will say and do anything to 'cover ar5e'.
For purely personal reasons I regard CHC (the company and culture) as a despicable company - and yet all employees I have met have been hard-working and professional.
To employ a PR company to provide a vague polish/spin on such a matter is also despicable and lacks credibility - much like when another company described a crash as a 'water landing'!

I guess what I am trying to say is - the speculation on this site is more credible than anything I have heard uttered from the OEM and Operator thus far. The 'manoeuvring' has been contemptible and no doubt confused/elongated the process.

The 'sludge' theory which was deemed one of the root causees for REDL was addressed by redesign - is someone suggesting that that was a 'red herring/window dressing' or maybe the re-introduction was rushed last time - when the airframes were desperately required?

[ericferret]

Turboshafts

The document you have produced there is a seven year old sales brochure.
As the document says it is based on data from 2008.
How about producing the figures from the latest version of the maintenance program.
At least then we can be sure what we are looking at.

[Noiseboy]

The box could have had 1299 flying hours when fitted, no reason to assume it was a new or zeroed box, simply a serviceable part which was fitted to replace a gearbox which needed to come off. It could easily have come from another machine undergoing some other sort of heavy maintenance.

I'm also confused by the idea that specific authorisation is needed to carry out standard maintenance such as changing a gearbox, to get extensions yes, but I would not expect to see any external requests to comply with routine procedure.

[Concentric]

EESDL,


This is a Rumour Network.
It is not a place for logical, knowledgeable and pragmatic reasoning!


Give a man a break, I’m new here!

Seriously though, and to others who have expressed their appreciation, thanks. I didn’t intend to speculate too much but rather just to look at officially released evidence as an engineer and ask questions that others may hold the answers to, or at least to set some minds thinking. If that comes across as promoting a particular theory then that is incidental but perhaps inevitable.

I make no comment about commercial interests, for they are what they are.

Re- the ‘sludge theory’, don’t you mean G-REDW and the vertical shaft failure? I thought G-REDL was fatigue crack propagation in a 2nd stage planet gear thought to originate from raceway spalling. The only re-design I recall after REDL was removal of the row of magnets and trimming of the oil collector plates.

Re-introduction of the EC225 fleet with daily inspections of the vertical shafts and some lube oil spray mods may not have been an ideal solution but it was pragmatic and no further failures of vertical shafts occurred before they were all replaced with the re-designed ones. Fixing the wiring on the EMLUB warning system was something that could have prevented G-CHCN having to set down on water (just a week after I flew in it, incidentally. Shame, it had nicer seats!).

I should point out that my experience is in general offshore/mechanical/structural engineering not specifically aviation though I have probably spent a couple of thousand hours in the back of the Puma family of helicopters since those wonderful days when the welcome sight of a Puma or ‘Tiger’ on the helideck meant getting home quicker than in an S-61 and ‘enjoying’ music through the ear defenders (invariably some Driller’s choice of Country &Western).

[Concentric]

If we look at the take-off rate of climb, it is not much different to
the rate of deceleration before the incident.


If any helicopter I am travelling in accelerates vertically from take-off at a rate of 0 - 100mph in 4 seconds I think I would be having a word with the PF as my 2nd top priority.:yuk:


I calculated the groundspeeds simply from scaling the distances on the map and dividing by the time elapsed between radar returns. Speed before 09:54:44 approx. 152 mph; speed after 09:54:48 approx. 54 mph. I have no idea how accurate the chart produced by AIBN is but it is a pretty large scale as you can see by the houses.

[ericferret]

There seems to be a lack of understanding in relation to normal working practises within the aircraft maintenance environment. Components can be new, overhauled, repaired or
used serviceable. The same applies to sub components within an assembly.

[Apate]

Eric, turboshafts seems to be stuck in some strange "conspiracy theory" surrounding MGB TBOs. Personally I'm bored with his ramblings and will simply ignore his postings from now on.

[albatross]

As an aside -- in the late 80s I had an engine failure with an Arial engine in an Astar due to an internal gear failure. The auto went fine and the seat cushion was eventually removed safely.
The cause of the failure was, as best as I recall, that "it was believed that during the engine assembly the gear had been dropped causing a stress point that later propagated into a crack which led to a gear failure."

[turboshafts]

Eric, turboshafts seems to be stuck in some strange "conspiracy theory" surrounding MGB TBOs. Personally I'm bored with his ramblings and will simply ignore his postings from now on.

No,

I referred only with CHC and AH info,
mostly as an answer to n305fa.

The arguments against that info is fully equitable.

Thanks

[Satcomm]

Turboshaft,

I just don't think anybody knows where you are tryi to go with the TBO thing. You keep talking about the extensions on the MGB that was removed. That gearbox is gone to overhaul, with no incident and is not in question. We got that. Then the 1300 hours since January, which is not possible, but even it was, you have already stated the TBO to be 2000. Meaning the gearbox in question would still be 700 hours shy. It is possible that a gearbox with 1300 hours was installed, as already mentioned, but that gearbox would still no likely make it to 2000 hours in 3.5 months either. I'm sure some of the other guys can pipe in, but I'm use to the average yearly hours on an offshore aircraft being between 1000-1500.

Maybe you need to explain exactly what you are getting at rather then going off about extensions. Extensions are a normal part of the aviation industry.

[buzz66]

All the Gear's in the Box have an ultimate life.

The TBO on these Gearbox's already have ridiculous low hours as it stands, making this Aircraft a very expensive Aircraft to maintain on a good day.

What I would like to know is just what percentage of the Planet's or Epicyclic's make Ultimate Life, if any?
Does the Gearbox Log Book specify the Actual hours of all the discreet Components or only module's within.
Did the TBO goes down as a precautionary thing, or is around 2,000 all the Epicyclic can handle before it begins to wear?
I can't help thinking a dedicated Bearing for the Planet's instead using the Gear as an outer race would prevent these issue's.
It still freaks me out when I see the Epi Ring form part of the Gearbox Structure.

[riff_raff]

Are the planetaries replaced at overhaul, do they have a fatigue life, or are they on-condition?

Typical design practice with aircraft gearboxes is to design the flight critical power gears for unlimited fatigue life in bending at max continuous torque and something like L2 reliability. The reason for this is to avoid having a gear tooth fail from bending fatigue. The planet gears of a simple epicyclic present an especially difficult situation with regards to tooth bending fatigue, since the teeth are subjected to a full reverse bending load every 180deg of rotation.

However, the gear teeth are not designed for unlimited surface contact fatigue life. Gear tooth surface contact durability is similar to that of rolling element bearings. Surface pitting is the most likely failure mode, which progresses slowly and is easy to detect long before it presents a serious problem. The ability to readily detect surface pitting of gear teeth and bearing surfaces long before it becomes a problem is what allows an on-condition service life approach to be used.

[Tatischeff]

Turboshafts

The document you have produced there is a seven year old sales brochure.
As the document says it is based on data from 2008.
How about producing the figures from the latest version of the maintenance program.
At least then we can be sure what we are looking at.
Hello everybody ! This is my first post on this topic that I read from the beginning.

@ ericferret :

About MGB and Epi TBO, the last update was done by AH on January and give 2000 FH for both Epi module and main reduction module, with a margin of 200 FH. (If it can remove unnecessary speculation).

[JohnDixson]

Thanks, Riff-Raff. A previous poster cited an " ultimate " life for the gears at 5000 hours. I assume he meant the fatigue life or Component Replacement Time (CRT ). Can one assume that the gears are exposed to accelerated load testing, multiple samples, a three sigma curve reduction etc? Assuming this or a similarly rigorous procedure to support the 5000 hour life is in place, there must be some hard work going on at AH to discover what resulted in two fatigue failures well within the CRT for the part. Unless I missed it, there hasn't been any information at all regarding the failure surface striation count, i.e., how long the crack existed prior to failure. There are a couple of posts on this thread that may/may not point toward a factor affecting the gear loads, but I'd guess that by now, the AH transmission people are way beyond that sort of speculation.

[triskele]

re concentrics' excellent first post...if one of the rear suspension rods failed it is likely the hull would flare, could this bring the disc into brushing contact with the engine intake screens? The ground pics of the disc show light damage a short distance from the hub on 4 blades, but looking at the blurry shots of the disc floating down, there appear to be similar dings in the blades at the same positions, ie before the disc hits the ground?

[OnePerRev]

Thanks, Riff-Raff. A previous poster cited an " ultimate " life for the gears at 5000 hours. I assume he meant the fatigue life or Component Replacement Time (CRT ). Can one assume that the gears are exposed to accelerated load testing, multiple samples, a three sigma curve reduction etc? Assuming this or a similarly rigorous procedure to support the 5000 hour life is in place, there must be some hard work going on at AH to discover what resulted in two fatigue failures well within the CRT for the part. Unless I missed it, there hasn't been any information at all regarding the failure surface striation count, i.e., how long the crack existed prior to failure. There are a couple of posts on this thread that may/may not point toward a factor affecting the gear loads, but I'd guess that by now, the AH transmission people are way beyond that sort of speculation.

John,
Don't know about the published CRT as others are posting about, but we can assume that the fatigue approach is NOT as you say for gears. It is close, however. The standards have not changed much in this area, in general it is a 140% overtorque test that is conducted in a rig. This equates to just under 3 sigma for steel. The load can be reduced further for multiple specimens. It is intended for tooth bending loads. Not sure what was done on this box, how much credit if any was taken for legacy assemblies. Nor do we know what other loads are considered. In the pinion, the cracks shown are not tooth bending, but initiate at the bearing integral race (our guess based on the released photos).
I concur that AH engineers are scrambling, regardless of what the press releases are saying.. in addition to experts from their transmission source, as I understand that it is completely outsourced, including design.
On the loads, Also agree as you suggest that there may be an anomaly, a previously not understood load source affecting the epicyclic, beyond that which it was certified to.

[JohnDixson]

OneP: Thanks for the correction re gear qual as opposed to main shaft, push rods, servo loads and the like.

It reads like you are well educated re gearbox qual. Admitting to be too lazy to go back and see who posted it, but there was some chat re how those three rollers came to be missing. Is that a realistic possible result of the wrenching forces at work during the initial event? If not, would a gear eccentricity under load produce 1P eccentric loads ( Gear 1P, not main rotor 1P ) which could be a factor to weigh? Sounds pretty far out, perhaps.

[RVDT]

John D,

There is a previous post that points out that the gear can be just tilted and the rollers are then only retained by the separator cage.

There is not a huge difference in the MGB design basics throughout the whole
family right back to the Alouette as you would expect, just bigger.

I have worked with an overhaul guy on AS350 MGB's and he used to pop the
bearing rollers out when we changed a bevel module for a quick look at the inner race.

AS 350 shown below - pretty much the same.

http://www.airwork.co.nz/imageGallery/components/as350-355/DSC_0456.jpg

[OnePerRev]

Thanks John,
Seems to me the roller is probably secondary - The carrier deformation indicates that tremendous inertial forces were in play which could cause pinion deformation and roller ejection. but it could have gone either way. Early, we postulated that the pinion fractures could be the same reason, but the evidence of fatigue tells us otherwise. You are probably on to something about eccentricity. What is strange about this arrangement is the spherical bearings. They allow the pinion to float, but if the alignment of the sun to ring is held, then why need it. The first stage sun gear wear makes it look like a crown gear, but an ugly crown. It some point prior to SHTF, this gear was not aligned correctly with all of the pinions. It could be that a pinion was tilted so we can't say what one was 'wrong'. That goes back to the roller/ raceway..
Something tells me that, in absence of HUMS record, an acoustic analysis of the CVDR would indicate a rising background noise corresponding to epicyclic origins. AIBN does not have to tell us that yet now do they.

[JohnDixson]

RVDT and One-P, thanks for the illuminating education. Good thought re the acoustic signature, and the AH group is undoubtedly all over that if the evidence is usable and shows anything. The idea of eccentricities or even gear resonances is probably getting a good look. The CH-47A production prototypes at the Army Aviation Test Board at Ft Rucker had at least two incidents ( 1962-3 ) where the engine nose box literally exploded and the parts were ingested into that engine, making a further mess and resulting in unplanned landings, one on the Officers Club Golf Course. Traced to a gear resonance and the short term fix was to change the Nr from 204 to 230. Stuff happens.

It's a bit surprising to read some of the "End of the 225" thread posts. I may be a former member of what the AH folks probably refer to as the Evil Empire, but having been involved in a few of these particularly thorny investigations, I'm actually quite sympathetic to the situation facing the operations and test troops there. Two failures in so many hours suggests patience.

[BedakSrewet]

John,
Don't know about the published CRT as others are posting about, but we can assume that the fatigue approach is NOT as you say for gears. It is close, however. The standards have not changed much in this area, in general it is a 140% overtorque test that is conducted in a rig. This equates to just under 3 sigma for steel. The load can be reduced further for multiple specimens. It is intended for tooth bending loads. Not sure what was done on this box, how much credit if any was taken for legacy assemblies. Nor do we know what other loads are considered. In the pinion, the cracks shown are not tooth bending, but initiate at the bearing integral race (our guess based on the released photos).
I concur that AH engineers are scrambling, regardless of what the press releases are saying.. in addition to experts from their transmission source, as I understand that it is completely outsourced, including design.
On the loads, Also agree as you suggest that there may be an anomaly, a previously not understood load source affecting the epicyclic, beyond that which it was certified to.

Having done the SA330 ( Puma ) course in 1970, I remember that the MGB was designed and manufactured by FIAT AVIAZONE.

[riff_raff]

Thanks, Riff-Raff. A previous poster cited an " ultimate " life for the gears at 5000 hours. I assume he meant the fatigue life or Component Replacement Time (CRT ). Can one assume that the gears are exposed to accelerated load testing, multiple samples, a three sigma curve reduction etc?

One fatigue analysis case used to design helicopter transmission components like gears/bearings/etc is based on a composite (cubic mean) of the various speed/load operating conditions and times over a typical mission profile. The 5000 hour number is likely a minimum design requirement at the composite speed/load condition. There are also other fatigue analysis cases considered, such as OEI and max torque, that involve far lower numbers of load cycles.

As for qualification tests performed on an MRGB, take a look at FAR 27.923 (http://www.ecfr.gov/cgi-bin/text-idx?node=14:1.0.1.3.13#se14.1.27_1923).

[Cyclic Hotline]

Having done the SA330 ( Puma ) course in 1970, I remember that the MGB was designed and manufactured by FIAT AVIAZONE.
You are absolutely correct BedakSrewet, this transmission was indeed designed and manufactured by Fiat Aviazone. I seem to remember it was all the parts painted blue on the SA330 and subsequent evolution of helicopters that originated there. As another poster earlier noted, this organization evolved into Avio, which is of course now owned by General Electric. GE in turn is further involved in the leasing activities affected by the CHC actions, as well of course as the manufacturer of the CT7 engines in the S92. You couldn't make this stuff up if you tried!

[RVDT]

riff_raff,

As for qualification tests performed on an MRGB, take a look at FAR 27.923.

???? EC225 is a Transport Category aircraft so you would need to apply Part 29 requirements. You may find it a little more extensive.

[BedakSrewet]

You are absolutely correct BedakSrewet, this transmission was indeed designed and manufactured by Fiat Aviazone. I seem to remember it was all the parts painted blue on the SA330 and subsequent evolution of helicopters that originated there. As another poster earlier noted, this organization evolved into Avio, which is of course now owned by General Electric. GE in turn is further involved in the leasing activities affected by the CHC actions, as well of course as the manufacturer of the CT7 engines in the S92. You couldn't make this stuff up if you tried!

Indeed Cyclic Hotline. One of my ( Dutch ) colleagues referred to it as 'KLM blue'. The lawyers will have a 'field day' ( years ) once they commence legal action against AH and the OEM of the MGB.

[JohnDixson]

Thanks, Riff Raff,

I did look at my 1999 copy of AC 29-2C ( just assuming that something similar applied to the EC225 design/qual effort ), which provides the test/qualification methods the FAA expects to see that support compliance with the basic FAR Pt 29. In this case 29.923, and those procedures look like they pertain to the tie down aircraft endurance runs etc, so the underlying requirement would remain as One-P described, a design to 140% of max load. There is a statement I found offering an alternative test to 10-7th cycles with an appropriate power spectrum. Does that square with where you were going?

[OnePerRev]

29.923 is endurance, which evaluates wear and general durability - different than fatigue. Fatigue comes from 29.571. The regulation does not specify handling any different for gears, but the AC does have an entire section on gear fatigue. It is intended, as it states, to be specifically for gear tooth bending, however it does mention that "fatigue damage other than tooth fatigue should be considered for test validity and the integrity of the affected part confirmed as necessary" The pinion rim failure mode should now, if it was not originally, be considered a catastrophic failure mode. This would then necessitate that the fatigue evaluation be conducted for it using the non-gear guidance -which will be quite complicated. Why? besides multiple specimen, 3 sigma, the initiation is coming from a bearing integral raceway. This gets tricky now, as the puma family is not certified to the latest damage tolerant standards, so the evaluation could simply assume surface finish as new. A little bearing wear, lubrication concerns, and/ or load changes, make this a complicated scenario. If there is no replacement time for the pinion, then they could be re-using pinions at overhaul with an unknown number of hours. Of course we still don't know if this is an early symptom, or the root cause.

[albatross]

WOW...used to think I was not terribly bright but the last few posts lead me to believe I am the burned out bulb on the old "connected in series" xmas tree light string.
Thanks for posting the interesting stuff.

[JohnDixson]

Only mentioned that as Riif Raff had referenced it above.

Your explanation of the implications of the pinion failure mode as a catastrophic failure and to be treated as such against the updated damage tolerance standards, if accepted, will certainly increase the sales of Pepto-Bismol in certain sectors of the industry. Gets back to waiting for the AIB and AH people determining the underlying cause and progression of the failure.

[Heliflyger]

This came from AH this afternoon
15/06/2016
[EC 225]
"E"ASB 05A049 TIME LIMITS - MAINTENANCE CHECKS – Main rotor drive - Check of the Main Gearbox (MGB) oil filter and chip detectors, limitation of the epicyclic modules. - Rev0
Through this ALERT SERVICE BULLETIN, Airbus Helicopters introduces the following precautionary measures for helicopters which are not subject to EASA Airworthiness Directive No. 2016-0104-E: - inspection of the MGB oil filter and chip detectors after the last flight of the day, - identification of the epicyclic modules which have been involved in an unusual event since new or Complete Overhaul, for a return for Complete Overhaul.
Download EASB / TA document

[terminus mos]

It seems that the MGB transport supply chain is under the spotlight as it may be a contributing factor here. Could the fix be relatively simple?

[FC80]

It seems that the MGB transport supply chain is under the spotlight as it may be a contributing factor here. Could the fix be relatively simple?

Yeah. Sounds like it - a wee 'fragile' sticker on the crate and it'll be grand.

:hmm:

[Apate]

So we have an MGB that has to be treated like a crate of eggs?

I've watched freight forwarders handle goods, and it usually ain't pretty. How is anyone at each end of the supply chain (operator or MRO facility) meant to know exactly what has happened to the crate during transit?

Oh dear, what a mess!!

[lowfat]

Impact Indicators | G-Force & Go/No-Go Monitoring Devices that Alert to Mishandling | ShockWatch (http://shockwatch.com/products/impact-and-tilt/impact-indicators)

simple really

[buzz66]

I can see the future as we speak.
All you Aerosexual Aviation Freaks will love this.

Lets start with the acronym first.

SCRTVDL

"Self Contained Real Time Vibration Data Logging" for anyone who gives a half a flying f.u.c.k. about the transport of anything worth more than they can afford to lose.

You can buy this Bad Boy on EBAY right now
LUTRON BVB-8207SD 4 Channels Vibration Meter Recorder Real Time Data Recorder



So for just $1250 US you can shove the Overhaul cost of your next Engine or Gearbox right up the Shipping Company's you know what.
This reply started out as a joke, but you watch the concept become reality.

[RVDT]

You might be a bit late out of the blocks there buzz.


http://shockwatch.com/wp-content/themes/shockwatch/timthumb.php?src=http://shockwatch.com/wp-content/uploads/2016/03/Spec_ShockDot_600x600.png&w=600&h=600

[buzz66]

Yeah I saw the previous post after I wrote, but yeah fair call.
It's a simple no go indicator but I think it needs a bit more than that.

It's not uncommon for a Gearbox to sit on the back of a truck for extended periods of time on less desirable Roads here in Australia. I would think an AIR Ride Truck would be mandatory?
Would a Truck with Bad Vibs @ X frequency over X Time be OK with the residual oil as protection..?.....you would think so.

This is where you need to see the big picture. If in transport an item is subject to what might be considered undue stress. The Shock Dot won't depict when it happened.
This is bad news for Greedy Corporations that want to pin the blame on someone.:=

What you need is my solution so the World's balance of true Distortion & Greed remain intact and keep everyone happy. :O
The Shock Dot is far to Practical, Simple, & Reliable to ever be put in place in Aviation. :ugh:
The other problem with your solution is the "Made in USA"...:E

[212man]

I think it was more than a 'rough ride' or handling.......

[terminus mos]

FC80

Yeah. Sounds like it - a wee 'fragile' sticker on the crate and it'll be grand

Thanks for your contribution, very valuable.

[500e]

Sarcasm TM ? :hmm:

[SASless]

What kind of Container does CHC use for Shipping the Gearbox to/from the Overhaul Facility?

[Apate]

All MGBs are shipped in OEM provided containers

[AW009]

@Apate; Is this a warranty or only an eyewashing?

[albatross]

I have never seen a MGB shipped at CHC in anything but the OEM container.
Same goes for engines ect.

[krypton_john]

Wrap it up in several layers of bubblewrap - she'll be right mate!

[albatross]

Ref this ..does the requirement to remove the oil filter everyday raise any red flags with you guys..thats a lot of removals and reinstalls IMO

This came from AH this afternoon
15/06/2016
[EC 225]
"E"ASB 05A049 TIME LIMITS - MAINTENANCE CHECKS – Main rotor drive - Check of the Main Gearbox (MGB) oil filter and chip detectors, limitation of the epicyclic modules. - Rev0
Through this ALERT SERVICE BULLETIN, Airbus Helicopters introduces the following precautionary measures for helicopters which are not subject to EASA Airworthiness Directive No. 2016-0104-E: - inspection of the MGB oil filter and chip detectors after the last flight of the day, - identification of the epicyclic modules which have been involved in an unusual event since new or Complete Overhaul, for a return for Complete Overhaul.
Download EASB / TA document

[jimf671]

Good question considering the history of another member of the class. Anyone able to post illustrations of the filter and fixings and tell us the materials used?

[Frying Pan]

If the MGB can't handle road transport should it really be in a helicopter?

[SASless]

Shucking Rotorheads and Oil Filter issues.....uh oh!:uhoh:

[Satcomm]

Sasless,

Shucking Rotorheads and Oil Filter issues.....uh oh!

Don't believe they are suggesting filter issues. Chip detectors are obviously not doing the job well enough so requiring a physical inspection now. Luckily, the filter on the puma is much more maintenance friendly then others. The ground run/leak check is more of a pain then the actual inspection.

[Arnie Madsen]

Inner bearing races and outer bearing races are made from hard brittle material and can easily be cracked with a moderate blow from a hammer or dropping it or whatever. I have seen mechanics remove (industrial) bearings faster than anyone using the best pullers , he would place a rag over the bearing (to prevent flying fragments) , carefully position a dull punch or chisel on the race , then deliver a careful moderate blow with a hammer and the bearing would crack.

That is why I was surprised to see the outer race incorporated into the gear on the EC225 , I always thought gear teeth should be less brittle and the bearing should have its own outer race pressed in. Reading the fine print it sounds like they use different hardening for the inside of the gear (race) so obviously they have figured out a way to make it work and are obviously much more knowledgeable than I am

Mostly I wanted to point out that impact damage or shipping damage has some merit in this discussion. Actually I think it would most likely happen pre-installation , the gear was dropped or impacted in some way to start a microscopic crack

I repeat my surprise while watching a (careful) mechanic disintegrate a bearing race with a light hammer blow , it breaks like glass , pieces fly all over the place.

[bluesafari]

Arnie,

Am surprised to hear your experience of seeing a bearing shatter with a light hammer blow, was that bearing from a helicopter MGB?

re the transit damage to MGB - was it in the correct transit container? MGB are usually pretty well mounted inside them. Would be interested to see the damage to container and gearbox, anybody have pictures?

BS

[Deux Cent Vingt Cinq]

If the MGB can't handle road transport should it really be in a helicopter?

What if it was involved in a road traffic accident?

[Arnie Madsen]

Am surprised to hear your experience of seeing a bearing shatter with a light hammer blow, was that bearing from a helicopter MGB?No , they were industrial bearings but if I could get a bunch of time expired MGB gears I would sure beat them up to see how brittle or malleable they are.

[Miles Gustaph]

I have an epicyclic gear complete with bearings on my desk, and given the ongoing discussion and it's in-visual line to my computer screen I have just decided to satisfy my curiosity to see if it it will break when hit with a hammer.

I don't know what alloy it's made of or what they do to harden it but it didn't break and I don't recommend anyone doing it either.

It does however satisfy my curiosity about this ongoing discussion and a personal theory that if it was going to break easily it would have done so years ago from the abuse it regularly receives by 'accidentally' falling on the floor due to enthusiastic dusting.

[G0ULI]

The OP specified a dull punch or chisel was placed against the bearing to provide a point load and that this was then hit with a moderate blow. Just hitting the bearing with a hammer is unlikely to shatter it as the blow is distributed over too wide an area.

Similar principle to hammering a nail into wood. Hit the wood with a moderate blow with a hammer and little or no damage. Concentrate the energy into the point of a nail and it penetrates the wood easily.

[Fareastdriver]

In the days when cars had rear axles that was the way you got the old wheel bearing off; then pressing a new one on.

[voando]

Probably off-thread sorry but was fowl at the time: RTA lowloader carrying S76 (all less blades) colliding with swerving articulated trailer filled with live chickens; re-named KFC ........

563

564

[turboshafts]

Radial roller bearings outer races are heated up and pressed oval in a die when mounting the balls.
They would not crack with a hammer hit. The standard bearing material is 100Cr6 and has a surface hardness of around 60 HRC.

here are two interesting reports that gives a bit more insight in the materials used

https://www.google.de/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0ahUKEwi9i8qQh7DNAhXKIMAKHRynD9wQFggcMAA&url=http%3A%2F%2Fntrs.nasa.gov%2Farchive%2Fnasa%2Fcasi.ntrs. nasa.gov%2F19800016828.pdf&usg=AFQjCNFP44R72_lPqM4UEQf7KKQa9p8YTg&bvm=bv.124817099,d.ZGg&cad=rja

https://www.google.de/url?sa=t&rct=j&q=&esrc=s&source=web&cd=12&ved=0ahUKEwi9i8qQh7DNAhXKIMAKHRynD9wQFghSMAs&url=http%3A%2F%2Fwww.dtic.mil%2Fdtic%2Ftr%2Ffulltext%2Fu2%2F p000703.pdf&usg=AFQjCNHA_2QmDeD2BtruNbI7Ggy55GFPZw&bvm=bv.124817099,d.ZGg&cad=rja

And here it refers the material of the 332L2 planet gear outer race material:
Fractured Gear | Flight Safety Foundation (http://flightsafety.org/aerosafety-world-magazine/february-2012/fractured-gear)
Subsequent testing determined that the particle was not silver or cadmium but 16NCD13 steel, planet gear outer race/gear material.

[buzz66]

Probably off-thread sorry but was fowl at the time: RTA lowloader carrying S76 (all less blades) colliding with swerving articulated trailer filled with live chickens; re-named KFC ........

563

564
Gota feel sorry for the Chickens and the Truck

[Nadar]

Not sure how relevant this is, but I recently had to remove the inner race from a BMW rear wheel drive axle that just wouldn't move using any bearing puller available to me. It didn't split easily, I had to cut (with a Dremel) almost through the race and then use a hammer and chisel in the groove. After quite a lot of (hard) hammering it finally cracked. I'd say that's a long way from cracking simply from a moderate blow. It all comes down to the alloy and hardening process used, and I doubt (or hope not) that they would make the epicycle bearings in a MGB to "a lower standard"/more brittle than the wheel bearings on a car.

[twisted wrench]

Voando: Note this event with the S76 and the chicken truck happened about 8 years ago.

[riff_raff]

The planet gear teeth and bearing outer race surface are case hardened by carburizing. The spherical bearing rollers and inner race are through hardened bearing steel. The cage is quenched and tempered alloy steel with a coating like silver electroplating.

The article linked by turboshaft was very interesting. Learned quite a bit about actual maintenance procedures used by commercial operators.

The following comment caught my attention, "Although the particle was removed from the epicyclic chip detector, maintenance personnel did not remove the epicyclic module or recover any particles that might have accumulated on the magnets that were part of the gearbox separator plate." This is something I had asked about in previous posts. Whether the gearbox separator plate arrangement was trapping ferrous debris from the epicyclic stages contained in the return oil flow.

[Lonewolf_50]

@riff raff: it is useful to specify that the maintenance personnel you refer to are not related to the Bergen Crash, but the crash in 2009. What the maintenance details were, or weren't, in the case of this crash have yet to be reported as part of the current investigation. (I realize you understand this, but some of our readers may not).

[Arnie Madsen]

Originally Posted by turboshafts

Radial roller bearings outer races are heated up and pressed oval in a die when mounting the balls.
They would not crack with a hammer hit. The standard bearing material is 100Cr6 and has a surface hardness of around 60 HRC.

here are two interesting reports that gives a bit more insight in the materials used

https://www.google.de/url?sa=t&rct=j...,d.ZGg&cad=rja (https://www.google.de/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0ahUKEwi9i8qQh7DNAhXKIMAKHRynD9wQFggcMAA&url=http%3A%2F%2Fntrs.nasa.gov%2Farchive%2Fnasa%2Fcasi.ntrs. nasa.gov%2F19800016828.pdf&usg=AFQjCNFP44R72_lPqM4UEQf7KKQa9p8YTg&bvm=bv.124817099,d.ZGg&cad=rja)

https://www.google.de/url?sa=t&rct=j...,d.ZGg&cad=rja (https://www.google.de/url?sa=t&rct=j&q=&esrc=s&source=web&cd=12&ved=0ahUKEwi9i8qQh7DNAhXKIMAKHRynD9wQFghSMAs&url=http%3A%2F%2Fwww.dtic.mil%2Fdtic%2Ftr%2Ffulltext%2Fu2%2F p000703.pdf&usg=AFQjCNHA_2QmDeD2BtruNbI7Ggy55GFPZw&bvm=bv.124817099,d.ZGg&cad=rja)

And here it refers the material of the 332L2 planet gear outer race material:
Fractured Gear | Flight Safety Foundation (http://flightsafety.org/aerosafety-world-magazine/february-2012/fractured-gear)
Subsequent testing determined that the particle was not silver or cadmium but 16NCD13 steel, planet gear outer race/gear material.That is the type of info we need, thanks

I am a layman and speak as a layman but when a chip is produced in a MRGB it is not because a gear is too soft but because it is too hard (brittle)

Obviously soft steel gears would not be used because they would wear out quickly so they harden them to a point where they have a long life at the risk of being brittle and designers walk a fine line trying to find the best balance.

In an earlier post I gave some (poor) examples of witnessing bearing races shatter from impact and I did not make my point properly so I will try a different slant ...

If planetary gears were made of mild steel we could place them on an anvil and hammer them flat and they would never crack or break .... but if they were made of hardened steel they would never bend or distort , they would shatter into several pieces

The failed gears in these MRGB's are never deformed , they break into several pieces as the photos show.

[birmingham]

According to the AIBN/AH timetable they should now have some of the initial metallurgy and be trying to make sense of what it tells them. I would think it is going to be a difficult job to prove the chain of events - so many variables in the equation.

[n305fa]

That is the type of info we need, thanks

I am a layman and speak as a layman but when a chip is produced in a MRGB it is not because a gear is too soft but because it is too hard (brittle)

Obviously soft steel gears would not be used because they would wear out quickly so they harden them to a point where they have a long life at the risk of being brittle and designers walk a fine line trying to find the best balance.

In an earlier post I gave some (poor) examples of witnessing bearing races shatter from impact and I did not make my point properly so I will try a different slant ...

If planetary gears were made of mild steel we could place them on an anvil and hammer them flat and they would never crack or break .... but if they were made of hardened steel they would never bend or distort , they would shatter into several pieces

The failed gears in these MRGB's are never deformed , they break into several pieces as the photos show.

From the REDL report the epicyclic planets are made of the following steels: Gear/outer raceway 16NCD13, rollers M50, inner race M50.

The REDL gives the reasons for the different materials and details manufacture.

From experience a normal spalling failure would start on the inner race if all of the materials were the same due to the increased loading of the inner race. The gear/outer race on the 225 planet is a "softer" material due to the load cycle of the gear teeth, therefore there is a tendency of the 225/332 planets to start with outer race spalling

[turboshafts]

That is the type of info we need, thanks

I am a layman and speak as a layman but when a chip is produced in a MRGB it is not because a gear is too soft but because it is too hard (brittle)

Obviously soft steel gears would not be used because they would wear out quickly so they harden them to a point where they have a long life at the risk of being brittle and designers walk a fine line trying to find the best balance.

In an earlier post I gave some (poor) examples of witnessing bearing races shatter from impact and I did not make my point properly so I will try a different slant ...

If planetary gears were made of mild steel we could place them on an anvil and hammer them flat and they would never crack or break .... but if they were made of hardened steel they would never bend or distort , they would shatter into several pieces

The failed gears in these MRGB's are never deformed , they break into several pieces as the photos show.

Arnie you are right and I take your Point.

However, there are several types of heat treatment that can be done to
a steel.

When you say hardened and brittle. There are several types of hardening.
I assume you mean through-hardened.
If you take a normal Construction steel and harden it, that is about
what you would get a brittle steel.

but for gears there could be several heat-treatments depending on the type of application.

you have through hardening, case hardening, quenching, carburizing etc.

through hardening is normally not favourable on a gear,
allthough in low-cost Products in may also be used.

if you have a carburizing steel, you heat treat it to
make the core though and the outer Surface hard.
If you look at the Pictures of the broken gears from the preliminary report,
you can actually see that the gears are lightly oval from deformation Before they crack.

you can see from the reports I linked the different characteristics of the failure modes in a gear cog.

what is evident here is fatigue cracks.
from my understanding is not occuring due to overload of the gear
but after a number of repeated cycles Close to it´s yield strength
it will sooner or later start to spall or crack

anyway after looking again at the epi pics from AIBN,
with out any chip detection alarm. oil pressure?

[riff_raff]

From the REDL report the epicyclic planets are made of the following steels: Gear/outer raceway 16NCD13, rollers M50, inner race M50. The REDL gives the reasons for the different materials and details manufacture. From experience a normal spalling failure would start on the inner race if all of the materials were the same due to the increased loading of the inner race. The gear/outer race on the 225 planet is a "softer" material due to the load cycle of the gear teeth, therefore there is a tendency of the 225/332 planets to start with outer race spalling

Good post.

16NCD13 is equivalent to AMS 6263 (9315), and the material is likely supplied in the form of a roll forged ring. This material is carburized, quenched, and tempered at a temperature that gives optimum core strength for the intended operating conditions. There is large difference between the case and core hardness.

You are also correct about the loaded sector of the inner race surface being the most likely area to experience a spalling failure under normal conditions. The inner race is fixed with respect to the applied radial load, the roller/race profile contact is convex/convex, so there is one small area of the race surface in-line with the load vector that is subject to a large number of load cycles at high stress every time a roller passes by.

The bearing roller/race contact is hertzian, and as noted, the most common failure is a race surface spall initiated by a sub-surface shear fracture. One very important consideration with carburized rolling element bearing race surfaces is ensuring the case depth after finish grinding is adequate for the hertzian contact conditions. The depth of max shear stress from hertzian contact must lie well within the very high strength carburized case. If the depth of max shear stress lies at the case/core transition or even within the core, a sub-surface shear fracture initiated spall will occur fairly quickly.

There are also a couple issues that can produce a local area of reduced strength in the gear/race material. One is excessive heating of the material during grinding operations that causes local de-tempering. This is fairly easy to do if the grinding is not performed carefully, since the gear material (9315) is tempered at a fairly low temperature (typically <400degF). Of course, there are normally NDI procedures used after finish grinding to check for this problem. Another potential cause of de-temper is excessive local heating of the gear/race material during operation, due to lack of cooling oil flow, or abnormal function of the bearing such as skidding/sliding.

One reason the inner race and rollers of this bearing were made from M50 is that M50 can operate at much higher temperatures (>500degF) without loss of strength/hardness.. There are some new carburizing gear alloys that have recently become available, such as C64, that can operate at very high temperatures (~900degF) without significant loss of strength/hardness. So we'll likely see greater use of these alloys in new gearbox designs.

[cteneto139]

The KFC S76 happened here in Brazil...

[cteneto139]

Am I understanding right???? Are they considering the transportation as potential factor?

[birmingham]

Am I understanding right???? Are they considering the transportation as potential factor?
Yes but only in so much as they have to understand the entire history of the MGB (among many other things). Transport damage is one of many factors they have to consider - standard procedure I would imagine

[msbbarratt]

This info on steels, bearings, etc. is excellent.

But isn't it time for a reality check? It seems clear that the combined talent of the design authority, crash investigators, regulators and operator maintenance staff is unable to fully understand or control what is happening to these aircraft. Whatever it is that we know about materials, operating conditions, wear rates, etc, that knowledge is inadequate in this case.

I know that the aviation sector is generally run with great maturity and care by all those involved, and takes pride in knowing all aspects of aircraft behaviour and how to operate safely.

However for this type they imposed a regime of intensive examination after every flight, after a few other accidents occurred. To me that sounds like "we don't really, truly know what's happening, so we'll sample the gearbox condition at every opportunity and maybe find out". In retrospect that's probably going to look like a bad idea.

The most important part of the investigation will be its focus on how it came to this.

[Miles Gustaph]

Msbbarratt: "We don't really, truly know what's happening, so we'll sample the gearbox condition at every opportunity and maybe find out"
I don't see this as a very constructive comment and feel that this is fundamentally a miss-understanding of aviation and expectations of performance.
While any fatality is a horrendous occurrence I feel that it is important to understand that there is a lot about aviation we, as a species, don't understand.

Firstly, there are no professionals out there who look to put people in danger!
As an industry we are dealing with a truly amazing level of variables and we, as an industry, don't know what we don't know!
More importantly there are whole rafts of everyday aviation based upon best practice, consistency of outcome and historical approaches, we do this because of the law of unintended consequence, specifically if we stray of the established line we will be less certain of the outcome. Unfortunately this means that as an industry we do tend to have to learn a lot of 'new' things as a result of accidents, ideally not fatal ones and as an industry we have what must be the ultimate in hazards that we manage on a daily basis, gravity and it is an unforgiving mistress. So when something new, novel or different occurs we are all very lucky when we learn it without loss of life.

As an industry we model, plan, design, re-design, review those plans and re-designs, train, retrain and retrain some more until we understand our machines as much as is possible. We build test models and prove that they work as best as we can, to the limit of technical knowledge and skill. We then manufacture them and expose them to thermal ranges from -50 degrees to +50 degrees, stress loads that would rip a house apart, moisture, people and a truly vast number of other variables. As a result we can't, hand on heart tell you what we will find in a few years’ time when we pull it apart for a big maintenance check, we can't tell you what will happen if several really obscure failure modes happen at the same time, we can’t guarantee a zero accident rate.

It is this fundamental inability to control the aviation operating environment in its totality that separates us from other disciplines. I have talked with mechanical engineers who are critical of the aviation industry and its perceived inability to produce gearboxes that never fail. Ask them to explain how they would manufacture a gearbox that is a primary part of a large, variable load path, is subjected to a horrible amount of vibration and doesn’t weigh as much as a truck. And if it goes wrong could kill a dozen plus people, I haven't heard a credible answer yet.
Saying aviation shouldn’t have accidents is not an ideology that anyone in aviation would argue with, it is however easier said than done.

On a positive note, we have embraced our deficiencies and compensate. Due to our high levels of regulation and consistency of approach, once a failure mode is established the whole industry has the ability to enact the corrective action to reduce the possibility of re-occurrence in a very short space of time. But we do this one failure mode discovery at a time.

But is the aviation industry every going to be able say 'X will never have an accident'. No, and it is this that needs to be understood. We can only reduce the probability of one happening.

[Lonewolf_50]

It is this fundamental inability to control the aviation operating environment in its totality that separates us from other disciplines. I have talked with mechanical engineers who are critical of the aviation industry and its perceived inability to produce gearboxes that never fail. Ask them to explain how they would manufacture a gearbox that is a primary part of a large, variable load path, is subjected to a horrible amount of vibration and doesn’t weigh as much as a truck. And if it goes wrong could kill a dozen plus people, I haven't heard a credible answer yet.
Miles, well said, but I'll add a different angle to this point. Even fixed wing design and production folks often don't "get" how helicopter design and production and operation is orders of magnitude more complex/difficult. (Per pound, it's about 10x as expensive to create a helicopter than a fixed wing aircraft). The continual interaction in all three axes of loads, on the flight controlling surfaces and on the airframe, as well as the vibration problem to sort out, complicates achieving MTBF goals.

Wear and fatigue are facts of life. Where the commercial market finds itself bumping into sharp edges is in seeking to increase MTBF for major dynamic components while also chasing that weight reduction problem. If you have to change the main transmission every 500 hours, as opposed to every 2500 hours, has a big impact on how well your transport service operates, or if it even survives. Designing and maintaining in good health the critical systems is a never ending effort.

The other matter, and IMO the critical matter in a mature aircraft, is how the system is set up to warn the operator of impending failure or in many ways present wear and tear as "graceful degradation." What makes this accident such a shock to the system is the few seconds of warning and then it all came apart on a fairly mature aircraft design.

Monitoring of dynamic component health and usable signs of things wearing out: that's were accident prevention may learn something valuable when this accident is fully understood.

[AW009]

Just have a look in Latest Engine Problem May Impact Airbus A400M Delivery Plans (http://www.defense-aerospace.com/articles-view/feature/5/173461/latest-engine-problem-may-impact-airbus-a400m-deliveries.html) and in http://www.pprune.org/9416209-post174.html
(http://www.pprune.org/rotorheads/578953-end-225-a-9.html#post9416209)

[Lonewolf_50]

Just have look in Latest Engine Problem May Impact Airbus A400M Delivery Plans (http://www.defense-aerospace.com/articles-view/feature/5/173461/latest-engine-problem-may-impact-airbus-a400m-deliveries.html) and in http://www.pprune.org/9416209-post174.html (http://www.pprune.org/rotorheads/578953-end-225-a-9.html#post9416209)
With warmest regards, neither of those is on topic for this thread, which addresses a fatal helicopter accident. The A400M's engine problems don't seem to be related, as the 225's engines do not appear to be a culprit in this accident. (As far as we know today) . Your other post has to do with automobile transmissions, in the "end of 225" thread.
I believe you have already gone on record in this thread with a dislike for AB and AB's helicopter division. We get it. ( I have no dog in that fight ...)

[AW009]

@all: Arn't we relatively shure that the upper epicyclic module of H225 / AS332L2 MRGB with only 8 planet wheels might be one of the culprit?

That's really not a question of dislike or like of ABH, that's a question of design, layout, choose of material, metallurgy, tempering, finishing and tribology in transmisson technology and in general, no matter where the gearbox is installed. Gearboxes always are characterized by 3-dimensional dynamic and static loads.

Sorry, I have flown in my life too many AB/EC/AS/SA & SE helicopter types and have a little bit to much grey cells instead of being put in the corner by a submitted general aversion to some very good HC and to be accosted by shallow arguments of a lad who obviously missed a good upbringing.

Argumentes like "my wife doesn't like the Mini, … Cars only function in two dimensions unless one is stunt driving for a movie. Their altitude design spec is 0 feet AGL, … The A400M's engine problems don't seem to be related, as the 225's engines do not appear to be a culprit in this accident, … your other post has to do with automobile transmissions“ and I don't "fight with dogs", are unimpeachable evidence for a smart-aleck phrase monger, who didn’t latch on to the point that MRGB of H225 and PGB of TP400-D6/A400M are of the very same manufacturer and therefore a close technical fit is given.

Blustering to be an engineer (in profile) provocates not only the question „which sort of engineer?“ (*),but also due to beforesaid highly intelligent statements the question „Is the vaguest notion of gear technology and of mechanical engineering given?
--------------------------------------------
(*) Many pilots are also „engineer“ and commonly with an university degree.

[JohnDixson]

AW, in post 1389 are you saying/implying that the same gearbox manufacturer makes both the engine/prop box on the A400 and the main box on the 225?

[AW009]

John Dixson: Sorry, but this is very right, very well proofed and system immanent.

[birmingham]

AW009 I think your point is entirely valid. EADS is suffering badly from these issues and the problem has reached the point where the engineering needed to resolve them may no longer be commercially viable. The 400 has reduction gearbox issues and the C130J doesn't. Both the S92 and EC255 have had reduction gearbox issues but the EC225's appear overwhelming. Unfortunately even if this accident enquiry decides that the suspension bar failed initiating the tragedy, the discovery of more fatigue issues with the planetary is a massive blow. Also if we are making automotive comparisons the;"it's too complicated - you laymen don't understand it's just the way it is, s*** happens" response is reminiscent of British Leyland in the 1970s (and we know what happened to them).BTW I am a fan of many EADS products especially the A320/330s that I have had a lot of time in, but we need to address reality here; Look who makes the Mini Cooper now!

So while allegedly off subject - anyone else worry that geared-fan engines for the A3** and B737-* NEOs may bring unwanted complexity to what are currently astonishingly safe and reliable aircraft, after all, these puma gearbox problems also appeared relatively late in the life of a successful design?

[buzz66]

Surely from here Oil Company's will start with the basics.

1. He who has the best Gearbox run dry times (no cheating e.g. Glycol)
2. Best Single Engine performance

The AW189 does over 60 mins with no Glycol, now that's a Gearbox!

[The Sultan]

Buzz

And the Bell 429 4 hours.

[Brother]

Buzz

The AW189 does over 60 mins with no Glycol, now that's a Gearbox!

Yes, but its a shame that the airframe is having trouble coping with it and the fuel capacity and burn restrict range.

Run dry, run wet, glycol or no run dry, down here in Oz, we need 92s (and 225s) to fly the long haul routes.

[Variable Load]

AW do make good gearboxes. Having toured the factory at Vergiate on a couple of occasions I have to say their transmission workshop is very impressive. The EH101 MGB is a beast!

[Margins]

And the Bell 429 4 hours

It looks a little too much, at what torque level?

[jimf671]

... ... reminiscent of British Leyland in the 1970s (and we know what happened to them). ... ...

Ouch. With a handle like birmingham, presumably you can recall the Lord Stokes one about not being in the business of making cars for the secondhand market. But they were always rubbish at cars. Trucks and industrial machinery were what they were good at. That is where there truly is a comparison with the Super Puma. Just as the 225 is an upgrade of the 330, in the UK, a very large proportion of the trucks delivering your internet shopping are an upgrade of 70s and 80s Leylands with DAF written on the front. The Sud Aviation stuff has Airbus written on it but it's not helping at the moment.

[turboshafts]

This info on steels, bearings, etc. is excellent.

But isn't it time for a reality check? It seems clear that the combined talent of the design authority, crash investigators, regulators and operator maintenance staff is unable to fully understand or control what is happening to these aircraft. Whatever it is that we know about materials, operating conditions, wear rates, etc, that knowledge is inadequate in this case.

I know that the aviation sector is generally run with great maturity and care by all those involved, and takes pride in knowing all aspects of aircraft behaviour and how to operate safely.

However for this type they imposed a regime of intensive examination after every flight, after a few other accidents occurred. To me that sounds like "we don't really, truly know what's happening, so we'll sample the gearbox condition at every opportunity and maybe find out". In retrospect that's probably going to look like a bad idea.

The most important part of the investigation will be its focus on how it came to this.

I think you are right

to me it's both a technical and a cultural problem,
combined with a control authority regime that is reactive.

In other countries outside Europe, there is much more focus
on precaution to fault modes. Not only on aircraft as well as in other businesses, simply because the culture/law systems allows to put the responsibility on the manufacturer alone.
For sure it creates an environment of political correctness that is not always
smooth and easy to work with, but if it avoids accidents it´s worth it.

It induces also serious research on government funded platform, that
has absolutely no comparison elsewhere.

[Apate]

In other countries outside Europe, there is much more focus on precaution to fault modes.

Having worked in SE Asia and N America, as well as having a good grasp on what happens in S America and Africa, I have to say I have no idea what you're talking about!!

If anything Europe is over regulated.

Do you wish to provide examples to support your statement?

[riff_raff]

Here's something interesting to consider regarding the level of technology used to design the typical main rotor gearbox. Take the example of the AS332 MRGB failure in April 2009. The gearbox was designed prior to 1993. And the accident investigation was performed in 2011, around two decades later. If you take a look at the very sophisticated finite element fracture analysis study work described in the 2011 accident report, you'd appreciate that this level of analysis capability was far more advanced than what was available to the gearbox designers in 1993.

The various types of failure modes and the fundamental process behind each one, have been understood by gearbox designers for many years. But remember that the gearbox conforms to a design that was certified many years ago, and represented the acceptable level of safety and reliability required by government regulations.

[AW009]

Looking back at 1993 as @riff_raff did, the Super Puma family has a lot of ‘constructive gray areas’ that never have been really ‘rayed’ with reference to the current certification criteria and to a present state of technique and science.
To summarize:

• E.g.: Rotor suspension by 3 suspension bars instead of 4 or 5 (redundancy & harmonics) and also ‘zero# redundancy by the discontinuous rotor mast and by an extensive ‘de-axation / outlining’ between bevel gear and upper ‘rotor shaft bearing’ in the conical housing?

• Suspicious fixing and securing of the suspension bars with bolts, Nappy Pins (Fokkernadeln) and Washer (not chamfered)?

• The ring gears of the planetary gear modules are simultaneously with the outer housing structure of the MRGB (compare PGB of TP400D6)?

•The inner parts of satellite mesh gear wheels are direct possession of outer bearing races of the roller bearings?

•No continuous rotor mast with axial and radial bearings at highest and lowest end and not non-positive to the bottom of MRGB, thus the forces and moments can not transferred direct via the bedplate of MRGB into the transmission and engine deck of the cell. Compare S61 SEA KING (https://www.youtube.com/watch?v=F9wnzBaE24s) and S60B SEAHAWK = S92 SUPER HAWK (http://aasf1-ny.org/4-Standards/Documents/PUBLICATIONS/StudentHandouts/UH60%20Powertrain%20and%20Rotor%20System.pdf, there D6 & D7))?!

•The bevel gear butt with welded shaft, might be of similar resistance to torsion-, shearing- and tensile forces as tp)?

• Etc., etc., ….

Times are gone for (Super) Puma!

Therefore AIRBUS should better clean his mess, instead of a permanently creating knocking sayings and new excuses. This is pure reality – absolutely no bashing - and seems identical also to other AC types of AIRBUS (e.g. NH90 and AS400M having a state of technology and a certification base of the 90th).

In military aviations AS/EADS/ABH always had been a ‘purveyor to H.M.’, but in professional commercial aviations being a market leader, finds its end in reliabilty, in operational and technical flight safety and not only in terms of economic and defense politicaly utilitarian national and subjective yardsticks.

That is a fact the French quys in their ’laissez faire’ never have understood and now they have to pay the bill in an international ’hardball scenario’ of lessee and lessors. The next fate of ABH will be to become a central ‘Second Hand Shop’ for PUMA and this might become a very large one, if ABH wouldn’t change its philosophy fundamentally.

[Concentric]

Here's something interesting to consider regarding the level of technology used to design the typical main rotor gearbox. Take the example of the AS332 MRGB failure in April 2009. The gearbox was designed prior to 1993. And the accident investigation was performed in 2011, around two decades later. If you take a look at the very sophisticated finite element fracture analysis study work described in the 2011 accident report, you'd appreciate that this level of analysis capability was far more advanced than what was available to the gearbox designers in 1993.

The various types of failure modes and the fundamental process behind each one, have been understood by gearbox designers for many years. But remember that the gearbox conforms to a design that was certified many years ago, and represented the acceptable level of safety and reliability required by government regulations.

Whilst it may well be that the gearbox conforms to a design certified several years ago it should also be remembered that following two bevel gear shaft failures, both resulting in precautionary ditchings with no serious injury, Airbus Helicopters extensively re-designed that shaft and these have now been retro-fitted into all of the offshore fleet.

So it would appear there is a precedent at AH for today’s analytical methods to be used to analyse stress distribution in older components and to redesign them and have them approved against (original?) certification requirements.

The big question is, did AH make any design changes to the 2nd stage planet gears following the 2009 accident and AAIB Safety Recommendation 2009-075 to “review the design, operational life and inspection processes of the planet gears” ? The TBO for the epicyclic module appears to have remained at 2000FH.

[Lonewolf_50]

AW009-Minor point regarding your linked .pdf ... it is explicitly for the UH-60A Black hawk, not a Seahawk and not an S-92. (Seahawk is SH-60B, albeit derived from the S-70/Blackhawk basic design. It has more in common (IDGB and carrier assembly) with UH-60L than the A. Your larger point is taken and understood if we read = (which is "equals") to be read like "very similar; based on the same design philosophy." Your pointing to those illustrations for an example of a kind of design works well to illustrate your point.

[Tatischeff]

‘zero# redundancy by the discontinuous rotor mast and by an extensive ‘de-axation / outlining’ between bevel gear and upper ‘rotor shaft bearing’ in the conical housing?

AW009, I looked at the plans and I do not understand where you see a misalignment ?
As for the rotor mast, I do not see what you mean by "discontinuous" ?

(I am not a neophyte but you may know more than I do)

[n305fa]

A new update has been released pointing towards the failure of the second stage planet gear as being the most probable cause of the accident

http://www.aibn.no/Aviation/Investigations/16-286?iid=20104&pid=SHT-Report-Attachments.Native-InnerFile-File&attach=1

[Pi1ot]

From the report:

"Main Gearbox history: The main gearbox (MGB) was received from Airbus Helicopters after modification, inspection and repair before it was installed in LN-OJF 15 January 2016. At the time of installation, the MGB had accumulated 1 080 hrs since new. At the time of the accident, it had accumulated approximately 1 340 hrs since new."


"Examinations of these parts show that one of the fracture surfaces can be described as being close to 100% fatigue."

" It is considered unlikely that this fatigue crack propagated as a consequence of a structural break-up of another component."

"Even though some differences are observed when comparing the LN-OJF accident with the G-REDL accident, the fatigue fractured planet gears, however, show clear similarities."

"The AIBN is aware that the gearbox was involved in a road accident in 2015. The gearbox was inspected, repaired and released for flight by the manufacturer before it was installed in LN-OJF in January 2016. Whether there is a link between this event and the initiation and growth of a fatigue fracture, is being investigated."

"AIBN will also look into the follow-up of safety recommendations issued after the Super Puma accident in Scotland in 2009 (https://www.gov.uk/aaib-reports/2-2011-aerospatiale-eurocopteras332-l2-super-puma-g-redl-1-april-2009)."

The last statement is very interesting. Does anyone know if all the safety recommendations have been satisfactory actioned and closed? To my knowledge, they did not change the design, and the monitoring systems have remained the same after the 2009 accident.

[n305fa]

I guess the response to the safety recommendations are in one of the AAIB annual reports

[Concentric]

"AIBN will also look into the follow-up of safety recommendations issued after the Super Puma accident in Scotland in 2009 (https://www.gov.uk/aaib-reports/2-2011-aerospatiale-eurocopteras332-l2-super-puma-g-redl-1-april-2009)."

The last statement is very interesting. Does anyone know if all the safety recommendations have been satisfactory actioned and closed? To my knowledge, they did not change the design, and the monitoring systems have remained the same after the 2009 accident.

Not only the design of planetary gearing and monitoring systems but also Safety Recommendations 2011-045 and 2011-046 concerning the use of g-switches which can lead to the premature removal of power to CVFDR systems. I do not think the cessation of recording on the 2009 accident has actually been satisfactorily explained.

[AW009]

That was it for the planetary gears of the H 225 / ASs 332 L2 Super Puma and AS 532 U2 Cougar.

AHF is confrontated by a redesign, retesting, reevaluation and recertification of Super Puma MRGB

Eeek, in PGB of TP400-D6 planetary gears are installed, which seems to be constructed and produced exactly in the very same manner!

And if after G-REDL nothing had been changed due to the safety recommandations by AHF, they are sucide canditates in present stressed (offshore) markets.:uhoh:

[FNTC]

From the last report:

"Scenarios under consideration as part of this investigation have included failure of a suspension bar attachment or failure of the MGB conical housing as the initiating event. The investigation activities since the previous report do not suggest that either of these scenarios were the initiating event."

This puts Airbus' earlier statements in a very weird light...

[FNTC]

Norwegian article with several statements from Halvorsen from ABIN:
Havarikommisjonen: Dette forårsaket helikopterulykken - Bergens Tidende (http://www.bt.no/nyheter/innenriks/Havarikommisjonen-Dette-forarsaket-helikopterulykken-3622024.html)

He says the gear box had been in a road accident in Australia, and gotten damaged, and then sent to Airbus, who checked it and approved it for use.

Also he says that there was nothing that could have been done, maintenance wise, to discover this fatigue crack.

"- Det betyr at vi mener dette var en feil som var umulig å detektere med vanlige vedlikeholdsrutiner, sier Halvorsen."
Translation: "This means that we are of the opinion that this was a fault that was impossible to detect using ordinary maintenance routines, says Halvorsen"

[ARRAKIS]

There is a new version of the AIBN preliminary report published today.
Investigation of helicopter accident at Turøy near Bergen in Hordaland county, Norway | aibn (http://www.aibn.no/Aviation/Investigations/16-286)

Arrakis

[lowfat]

Seems quite clear...

29 April 2016 the Main Rotor Head (MRH) and mast suddenly detached from an Airbus Helicopters H225 enroute from Gullfaks B to Bergen Airport Flesland. The helicopter impacted on a small island east of Turøy. All 13 people on board perished.

On 28 June 2016 a preliminary report is published to disseminate findings from the ongoing investigation.

At this stage of the investigation, the AIBN finds that the accident most likely was a result of a fatigue fracture in one of the eight second stage planet gears. It appears that the fracture has propagated in a manner which is unlikely to become detected by existing mandatory or supplementary systems for warning of an imminent failure.

Scenarios under consideration as part of this investigation have included failure of a suspension bar
attachment or failure of the MGB conical housing as the initiating event. The investigation activities
since the previous report do not suggest that either of these scenarios were the initiating event.

What initiated the fracture has not yet been determined.



Over to you Airbus.... seems those 225 ashtrays are going to be sat on the ground for some considerable time..

[212man]

Echoes of G-BJVX

[FNTC]

"June 28, 2016

Airbus Helicopters takes note of the AIBN’s preliminary report update and welcomes the significant progress made by the investigation. We continue to focus our efforts on providing assistance to the investigation team and the authorities as they work toward the identification of the accident root cause.
In parallel, we are putting precautionary measures in place to support our global customers and address potential initiating events."



Norway-Statement - Airbus Helicopters (http://www.airbushelicopters.com/website/en/ref/Norway-Statement_347.html)


Too bad for them that their very strange statement from May 27th is still on the same page:
"Out of these seven scenarios, only one – the failure of the attachment of a suspension bar – can be assessed as probable by Airbus Helicopters, based on the information available to date." :ugh:

[AW009]

@Tatischeff: By looking on http://isambardkingdom.com/wp-content/uploads/2012/01/Power-Gear-Box-1.jpg I see three axles / drive shafts and a virtual rotor mast discontinuous (fr. discontinue), meaning four machine elements one upon the other,


don’t see any continuous (fr. continue) rotor mast,



don’t see it’s axial and radial bearing at bottom / sump of MRGB,



don’t see its upper bearing in the conical housing,



and see only a bevel gear and two epicyclic modules,



which are worst ‘axial and radial bearings' to prevent disalignment..

By this your questions and your non-neophyte ’disalignment’ (= tous les côtés sur la ligne entre deux points) will find an answer by technical and constructively facts.:)

[roscoe1]

Is there any information out there about the nature of the road accident? Was the transmission in a container? Was there external damage to the case components? Was the truck destroyed? I would think it would have to be a significant accident to initiate a fracture of internal gearbox components. Is it correct that the inspection and repair by AH prior to the installation in January was the inspection required due to the road accident? Why was the transmission being transported at that time (with continued time on it)? How extensive were their repairs and more importantly, what did they inspect (how deep did that go)? If that is the case then 260 hours elapsed between the road accident and the failure. I have no doubt that anything can happen during shipping. I've seen fork lift holes in blade boxes, engine cans that have rolled over and been severely dented and seen the gyro we were waiting for AOG fall off the top of a stack of boxes the delivery person was carrying. His comment was "If you think that was bad, you should come to our warehouse sometime". If it turns out that there is any correlation, it makes a viable argument to what we sometimes see as OEMs being overly cautious when they say "you have to overhaul that component as if it were a sudden stoppage/hard landing incident" even when we know it wasn't that bad. I think any OEM is out on a limb if they are willing to comply with the minimum they think is necessary for an incident scenario that may be unusual or uncommon. Of course, I have no idea if that was the case. Just another part of this nasty puzzle.

[GenuineHoverBug]

Some of what has been said by AIBN representatives about the road accident as far as I have seen is:

-The gearbox received some unkind treatment and had to be repaired.
-The accident happened in Australia in last year.
-The gearbox was transported on a small lorry, which had an accident and the gearbox fell/came off the lorry.

[AnFI]

lowfat "the accident most likely was a result of a fatigue fracture in one of the eight second stage planet gears."

does anyone see whats fundamentally wrong with that? EIGHT second stage planetary gears !! In the cause of engine redundancy, madness !

anyone in authority got a maths o level?

[turboshafts]

I don´t understand this statement:

"Also, the HUMS appears unable to identify symptoms of such degradation in the epicyclic module"

From the G-REDL report, it is quite clear that there was abnormal HUMS readouts in the days before the accident.´
But it was not known how to interpret the data,
that showed increased vibrations. According to Eurocopter the debris should be determining the Health of the gearbox and not the HUMS readouts.

So it is strange to me no HUMS readouts on LN-OJF. Still no mention about the problems with the helicopter in the days before the accident.

Would be interesting to understand why AIBN concludes on the HUMS?

What about the chip detectors?

I already read that Visual inspection of gears are done at 2000 hours. up to that spalling can occur, that is not dangerous to the gearbox operation.


"The main gearbox (MGB) was received from Airbus Helicopters after modification, inspection and repair before it was installed in LN-OJF 15 January 2016. At the time of installation, the MGB had accumulated 1 080 hrs since new"

Why is the gearbox modified, inspected and repaired by Airbus at 1080 hours?

I am disappointed in AIBN, a very weak preliminary report
with vague statements.

[FNTC]

"Why is the gearbox modified, inspected and repaired by Airbus at 1080 hours?"

Because it was damaged after falling of a truck/lorry during a road accident in Australia...

"The AIBN is aware that the gearbox was involved in a road accident in 2015. The gearbox was inspected, repaired and released for flight by the manufacturer before it was installed in LN-OJF in January 2016."

[AW009]

@AnFI: AS 332 L1 has 9 plantetary gears and obviously that's the 'less sensitive' construction.

Math? Perhaps Planetengetriebe (http://www.tgabathuler.ch/_/Weblinks/Animation/Antrieb/Planetengetriebe_Graz.html) & ZAR5 Planetengetriebe (http://www.hexagon.de/zar5_d.htm) & http://www.hexagon.de/zip/zar5_d32.zip
will be a first help.

[birmingham]

Two points on the latest AIBN report ...

(1) I may be naive but these latest updates from AIBN have rather shocked me. Not because of what they reveal but in respect to the original AH statement about the suspension assembly. I genuinely believed that to put that out with all its inevitable effects AH must have had access to the engineering equivalent of a smoking gun. If AH have made a genuine mistake they should explain why and clarify why they made those remarks on their website. Some folks at CHC must have been through hell because of it.

(2) It confirms that systems for detecting fatigue cracks don't always work as required and without further design modifications that the Super Puma remains unsafe to fly. These will presumably be applied at some stage in the military versions but the civil version? Is there the demand or will this machine now be retired? It's reputation is clearly utterly beyond repair in the NS whatever AH do now.

[birmingham]

Can't be a Sus Bar failure because the Gearbox split in 2 parts.
Sus Bar or Pin failure would see the Barby Plate and whole gearbox leave the scene. Almost has to be major Gear failure internal to the Gbox.
I bet my bottom dollar they are the bits they want to still find.
... looks like you might be correct

[Tatischeff]

By looking on Isambard's Lad | The sun shines out of the Engineers (http://isambardkingdom.com/wp-conten...Gear-Box-1.jpg) I see three axles / drive shafts and a virtual rotor mast discontinuous (fr. discontinue), meaning four machine elements one upon the other,
- don’t see any continuous (fr. continue) rotor mast,
- don’t see it’s axial and radial bearing at bottom / sump of MRGB,
- don’t see its upper bearing in the conical housing,
- and see only a bevel gear and two epicyclic modules,
- which are worst ‘axial and radial bearings' to prevent disalignment..

AW009, thank you for explaining you view, but I'm a little disappointed by its support (a very simplified block diagram). :hmm:

Is there a real (reliability) matter with a discontinuous rotor mast as you say ?
The mast is held in position by a double conical bearing mounted in O at the top of the conical housing, and by the contact of the teeth of the second stage planet carrier.
By the facts, we can say with relative confidence that the mast design and holding is not the issue and has proved its reliability on others H/C.

I don't think that hyperstatism ever did well with the wear resistance ...

[Nadar]

I don´t understand this statement:

"Also, the HUMS appears unable to identify symptoms of such degradation in the epicyclic module"

From the G-REDL report, it is quite clear that there was abnormal HUMS readouts in the days before the accident.´
But it was not known how to interpret the data,
that showed increased vibrations. According to Eurocopter the debris should be determining the Health of the gearbox and not the HUMS readouts.

I think it's pretty clear. You must see this sentence in context of the previous:

AIBN believes that a sub-surface crack has propagated without creating a significant amount of magnetic debris from spalling. Also, the HUMS appears unable to identify symptoms of such degradation in the epicyclic module.
They are saying that there were no warning signs before the accident neither from the chip detectors or HUMS for LN-OJF. They see this as a "certification flaw" as the certification was based on the premise that a fatigue crack would produce a warning from at least one of these systems.


So it is strange to me no HUMS readouts on LN-OJF. Still no mention about the problems with the helicopter in the days before the accident.

Would be interesting to understand why AIBN concludes on the HUMS?

What about the chip detectors?

What they are saying is that there were no warnings from the chip detectors or HUMS. That implies that they have checked the previous HUMS readouts. If I recall correcly, the HUMS data for the accident flight determined to be lost since these data aren't stored (but kept in RAM only which loose all information when it looses power).

The reason the problems the previous days aren't mentioned must be that it's seen as irrelevant to this accident. This is a preliminary report with just the current status of the major investigation areas.

When it comes to the chip detectors, they say this:

No findings indicate any malfunctions to the magnetic debris detection system on LN-OJF, or fail to follow procedures for visual inspection and checks before flight. Neither are there any records of magnetic debris findings from inspections made since the gearbox was installed on LN-OJF in January 2016.
That seems pretty clear to me.


I already read that Visual inspection of gears are done at 2000 hours. up to that spalling can occur, that is not dangerous to the gearbox operation.

This is not what I read in the report. Quite the opposite, they say that the design philosophy assume that a spalling will not develop into a fracture because of the material properties, but that this accident indicates that this assumption is wrong:

An essential design philosophy regarding a possible failure inside the epicyclic module has been that propagation of a crack would be suppressed by the compressive surface stress. Thus a crack in the surface area should grow outboard and create spalling that would produce magnetic debris, which will be detected on the magnetic plugs (chip detectors). The optional HUMS1 is an additional means for detecting developing degradation.

"The main gearbox (MGB) was received from Airbus Helicopters after modification, inspection and repair before it was installed in LN-OJF 15 January 2016. At the time of installation, the MGB had accumulated 1 080 hrs since new"

Why is the gearbox modified, inspected and repaired by Airbus at 1080 hours?

This is clearly stated in the report. It was repaired/modified/inspected and approved for use by AH after being sent there as a result of the road accident in Australia were the gearbox was damaged.


I am disappointed in AIBN, a very weak preliminary report
with vague statements.
Not as I read it. I think it's perfectly clear in the areas being addressed. That all remote, unlikely connections aren't included is to be expected as it is preliminary and the investigation is still ongoing.

[Nadar]

Two points on the latest AIBN report ...

(1) I may be naive but these latest updates from AIBN have rather shocked me. Not because of what they reveal but in respect to the original AH statement about the suspension assembly. I genuinely believed that to put that out with all its inevitable effects AH must have had access to the engineering equivalent of a smoking gun. If AH have made a genuine mistake they should explain why and clarify why they made those remarks on their website. Some folks at CHC must have been through hell because of it.

As I have stated before, I don't give much for any statement or report by any commercial organization. The reason is that the actual truth is so far down on their list of priorities. I doubt it was a "mistake", it was a gamble, probably a relatively desperat gamble, and it failed.

[Concentric]

Now that the focus is squarely on the planet gears, investigators will doubtless be looking into all aspects of their design, manufacture, assembly and operation.

I am just going to throw this speculative idea up in the air for consideration.
Is it possible there may have been hydrogen embrittlement of the gear material? I noted from AAIB report 2-2011 that the carburised gear raceway is chemically etched before final polishing.

I am not a materials specialist but I wonder if a combination of materials susceptibility, environment and stress have combined with the presence of diffused hydrogen trapped underneath the carburised layer to initiate a defect and cyclic stress has done the rest? Spalling might or might not occur.

[Lonewolf_50]

@Concentric: if that's the case, than one might worry about a whole batch of gears made when that serial number (the failed one) was manufactured ... if one wasn't baked for hydrogen embrittlement relief, how many others weren't? (Caveat: this response is solely related to Concentric's "what if" question, and is not an assessment of factual evidence revealed so far regarding the material condition of gears in the accident aircraft).

[SansAnhedral]

Hydrogen embrittlement is certainly a very important concern in all metallic rotorcraft components. Halogenated cutting fluids can cause this issue while machining metallic parts and there is nearly no way to test for this effect in a fatigue lab setting.

Some OEMs learned this the hard way (http://www.ntsb.gov/about/employment/_layouts/ntsb.aviation/brief2.aspx?ev_id=20100602X63138&ntsbno=CEN10FA291&akey=1)

All that said, the fracture pattern from hydrogen embrittlement is fairly telltale, and it does not appear to be the case on these gears.

[Concentric]

@Lonewolf_50:

My question was purely hypothetical as you know, and proposed on the observation that hundreds of these planet gears have been manufactured and not failed catastrophically in the same application. But this one did fail, so why? Transit damage might be one answer and is being further investigated but other answers may also exist. Fatigue obviously has propagated a crack but it would need a source, which could be quite small, probably outside the residual compressive stress zone from the carburising, and if so might not cause sufficient spalling at an early enough stage to be detected. That seems to be what AIBN are reporting.

I would not rush to the conclusion that there exists a ‘bad batch’ of components and with the affected type(s) currently grounded any worrying would be commercial and not safety based. The failed bevel gear shaft of G-REDW was initially put down to a bad batch with roughly drilled holes and we know the rest of that story.

The manufacture of these safety critical gears would be subject to many controls and inspections. Baking would most likely be among them and that process would be tightly controlled (possibly empirically), but I don’t know how you could actually determine the removal of hydrogen had been homogeneous and irreversible. Is baking done only after carburising or also after etching for final polishing?

There are so many factors that need to be achieved in a complex manufacturing system to make this gearbox safe. The holes in the Swiss cheese do not necessarily need to be concentric, just the slightest overlap may do it, like a build up of tolerances. That the AS332 up to L1 variant has never suffered this fate once in 4m hours says a lot for the system, but does the L2/EC225 just occasionally nudge one cheese a little too far?

[Concentric]

Hydrogen embrittlement is certainly a very important concern in all metallic rotorcraft components. Halogenated cutting fluids can cause this issue while machining metallic parts and there is nearly no way to test for this effect in a fatigue lab setting.

Some OEMs learned this the hard way (http://www.ntsb.gov/about/employment/_layouts/ntsb.aviation/brief2.aspx?ev_id=20100602X63138&ntsbno=CEN10FA291&akey=1)

All that said, the fracture pattern from hydrogen embrittlement is fairly telltale, and it does not appear to be the case on these gears.

Thanks for your feedback. My thoughts (in my hypothetical scenario) were that the hydrogen embrittlement would not be across the bulk of the fracture surface but just at the source. Would the interstitial carbon restrict diffusion of hydrogen out through the hardened raceway?

[msbbarratt]

@Miles Gustav,

I don't see this as a very constructive comment and feel that this is fundamentally a miss-understanding of aviation and expectations of performance.

...

Firstly, there are no professionals out there who look to put people in danger!

Well, if a constructive comment helps, the regulators should always ask themselves whether the conditions they impose are sensible. Mandating a deep technical inspection of a critical component after every flight is at tacit admission of a lack of faith in that component, an acknowledgment that within the timescale of a flight it might fail. Regulators should in future apply poppycock filters to their advice.

As for professionals deliberately putting people in danger, we'll of course they don't do that. But circumstances (commercial pressures, can do attitudes, etc) have a nasty way of resulting in a conspiracy of optimism, and it's the regulator's job to spot those and put a stop to them. I think what's happened here is that the regulator has not acknowledged that they have the power to prevent aviation as well as the duty to enable it.

[AnFI]

"the AS332 up to L1 variant has never suffered this fate once in 4m hours"

doesn't go far in establishing 1x10^-9 scale safety
#provesnothing #

"the regulators should always ask themselves whether the conditions they impose are sensible."
#haha

[turboshafts]

I think it's pretty clear. You must see this sentence in context of the previous:
They are saying that there were no warning signs before the accident neither from the chip detectors or HUMS for LN-OJF. They see this as a "certification flaw" as the certification was based on the premise that a fatigue crack would produce a warning from at least one of these systems.


What they are saying is that there were no warnings from the chip detectors or HUMS. That implies that they have checked the previous HUMS readouts. If I recall correcly, the HUMS data for the accident flight determined to be lost since these data aren't stored (but kept in RAM only which loose all information when it looses power).

The reason the problems the previous days aren't mentioned must be that it's seen as irrelevant to this accident. This is a preliminary report with just the current status of the major investigation areas.

When it comes to the chip detectors, they say this:
That seems pretty clear to me.


This is not what I read in the report. Quite the opposite, they say that the design philosophy assume that a spalling will not develop into a fracture because of the material properties, but that this accident indicates that this assumption is wrong:

This is clearly stated in the report. It was repaired/modified/inspected and approved for use by AH after being sent there as a result of the road accident in Australia were the gearbox was damaged.


Not as I read it. I think it's perfectly clear in the areas being addressed. That all remote, unlikely connections aren't included is to be expected as it is preliminary and the investigation is still ongoing.


Thanks for your detailed answer and citations!

If there where no HUMS readouts, how can they conclude it is not a sufficient way of monitoring?

In G-REDL there was indeed seen several HUMS readouts,
some of them failed to cause the attention of the engineer because
the datacard was incorrectly loaded.

So no reading, or not an abnormal reading, is not definitely answered yet?

When it comes to no chip detection, if that is the case it is indeed a strange condition.
For the 300 flight hours done on LN-OJF the gearbox had, it can´t be argued against.
But what about the 1080 hours before?
Do we know already that the gearbox had 1300 hours without any flaws at all? No.

We also know that the individual gears are not due to visual inspection before 2000 hours of operation.

Also, if they claim that it have proven against the theory that spalling does not induce any chips, it could be because the gear had already induced spalling and left the surface in such a shape that a crack would be induced.
It was then shipped out to LN-OJF

We can clearly see that the gears on the pictures have spalling.
especially the bottom left.
from the gear starts to get light pitting, which may cause hairthin
cracks in the surface, it will also soon start to spall.
Can´t say how long, but with normal lubrication and temperature it should have at least been ok for 300 hours.

So again, I don´t feel that the report brings a clear view to several
relevant aspects that should have been cleared out until now.

For sure there maybe reasons to hold off the information, until
further investigations are done, but still if the conclusion is that the gear is without warning cracked causing the gearbox total seizure. I don`t believe it.
And person with experience in risk assessement and engineering should not believe it either.

Concentric: I agree with your theory, it could be the underlying reason it happened.
And that could also be the reason they changed the material on the bevel gear from 16NCD13 to 32CDV13 to allow nitrating.
Especially in relation to the crack-prone area near the welding.
However, that should have been a failure mode, that they are perfectly aware of. Seeing the process a gear goes through during manufacturing,
it is not very likely to be a problem with only 1 gear.
And even if it was, the way we can see the surface pitting on the other gears, and also cracks due to deformation, if not occured in aspects of the gear development and certification, that process is for sure useless

[n305fa]

Thanks for your detailed answer and citations!

If there where no HUMS readouts, how can they conclude it is not a sufficient way of monitoring?

In G-REDL there was indeed seen several HUMS readouts,
some of them failed to cause the attention of the engineer because
the datacard was incorrectly loaded.

So no reading, or not an abnormal reading, is not definitely answered yet?

When it comes to no chip detection, if that is the case it is indeed a strange condition.
For the 300 flight hours done on LN-OJF the gearbox had, it can´t be argued against.
But what about the 1080 hours before?
Do we know already that the gearbox had 1300 hours without any flaws at all? No.

We also know that the individual gears are not due to visual inspection before 2000 hours of operation.

Also, if they claim that it have proven against the theory that spalling does not induce any chips, it could be because the gear had already induced spalling and left the surface in such a shape that a crack would be induced.
It was then shipped out to LN-OJF

We can clearly see that the gears on the pictures have spalling.
especially the bottom left.
from the gear starts to get light pitting, which may cause hairthin
cracks in the surface, it will also soon start to spall.
Can´t say how long, but with normal lubrication and temperature it should have at least been ok for 300 hours.

So again, I don´t feel that the report brings a clear view to several
relevant aspects that should have been cleared out until now.

For sure there maybe reasons to hold off the information, until
further investigations are done, but still if the conclusion is that the gear is without warning cracked causing the gearbox total seizure. I don`t believe it.
And person with experience in risk assessement and engineering should not believe it either.

Concentric: I agree with your theory, it could be the underlying reason it happened.
And that could also be the reason they changed the material on the bevel gear from 16NCD13 to 32CDV13 to allow nitrating.
Especially in relation to the crack-prone area near the welding.
However, that should have been a failure mode, that they are perfectly aware of. Seeing the process a gear goes through during manufacturing,
it is not very likely to be a problem with only 1 gear.
And even if it was, the way we can see the surface pitting on the other gears, and also cracks due to deformation, if not occured in aspects of the gear development and certification, that process is for sure useless

Turbo shafts

Just a couple of points

REDL s HUMS was analysed by both the AAIB, EC and the system manufacturer, all of who concluded that the CIs observed gave no prediction of catastrophic failure of the 2nd stage planet gear. There were also issues with the epicyclic chip detection system which called its correct function into question

We may not know the history of the MGBs 1300 hours since overhaul, but you can be absolutely sure that the AIBN and AH do, it probably hasn't been reported because there is nothing of significance.

You can't predict how long the gear should run as the complete gear is not available to fully quantify the damage to the raceway as (I assume) you do not know enough about the gears operational load cycle, effect esn of lubrication, rate of damage progression etc.

SPalling Is the progressive failure of a bearing surface due to rolling contact fatigue, surface damage continually increases, as does particle production. Carburisation of the surface introduces comressive stresses in the bearing surface, to a depth of about 2mm. Spalling in this area will result in particle release from the raceway but not crack progression into the body of the gear/outer race. THence the use of MCDs as the primary method of detecting epicyclic deterioration (HUMS doesn't work well due to the constant movement of the planets relative to the accelerometers).

The 225 and 332 have plenty of history of detecting spalling of planet gears without catastrophic failure, therefore it is possible that this failure is not due to normal spalling. If a crack forms at the interface of the carburised layer, or in the body of the gear it will only be detectable when it breaches a surface and results in particles being released. This was what the AAIB theorised with REDL and may be a factor in the accident.

Re the jamming of the gearbox, the epicyclic ring gear damage suggests that something was entrained between a planet gear and the ring gear which burst the case, If the epicyclic had jammed the ring gear and planets would have had significant stripping of gear teeth. There was no suggestion that the REDL MGB jammed

[Apate]

turboshafts:

If there where no HUMS readouts, how can they conclude it is not a sufficient way of monitoring?

Prior to the accident flight the Airbus HUMS system was serviceable and being analysed IAW company and customer procedures, AH guidance and regulation.

AIBN are indicating that HUMS did not detect any anomalies, which is the reason for their statement "HUMS appears unable to identify symptoms of such degradation in the epicyclic module."

Where did you get the idea from that there were no HUMS readouts?

[megan]

Certainly going to be interesting to see the root origin of the failure.

Reminded of the fan disc failure in a DC-10. Was found the disc had been machined from a piece that came from the near end of a billet, which was found to contain inclusions. Fix, discard the ends of the billet.

In the early 60's worked in a shop manufacturing steam turbines for ships. For the gear cutting shop battery back up was supplied to the cutters/grinders. Once a cut/grind on a tooth was begun it was not permitted to be interrupted, for it introduced a point of future failure.

[GenuineHoverBug]

For those who have not seen it:

EASB - MAIN ROTOR DRIVE - Epicyclic module Replacement of the epicyclic module second stage planet gears:

Summary:
For helicopters which are not subject to EASA Airworthiness Directive No. 2016-0104-E, this ALERT SERVICE BULLETIN requests that you identify the P/Nos. of the epicyclic module second stage planet gears and replace the module if its planet gears have the P/Nos. concerned.

Compliance:
Airbus Helicopters renders compliance with this ALERT SERVICE BULLETIN mandatory.
...

SIN No. 3053-S-00- Update on EC225LP accident in Norway dated April 29th:

-Deleted-

[SansAnhedral]

So the Rev B planet gear bearing is expected not to show the mystery non-spalling fatigue crack growth that should have never occurred in the original version.

Metallurgically, I suspect there is little to no difference between them. If it was a material-driven failure, the lower loads observed may serve only to delay the onset of this undetectable failure.

I do very much wonder exactly what "In service experience shows enhanced reliability" means

[turboshafts]

turboshafts:
Where did you get the idea from that there were no HUMS readouts?


If I recall correcly, the HUMS data for the accident flight determined to be lost since these data aren't stored (but kept in RAM only which loose all information when it looses power)

This is what Nadar wrote. I asked a question, wether it is clearly known if there are no HUMS readouts, or no abnormal readouts.


You can't predict how long the gear should run as the complete gear is not available to fully quantify the damage to the raceway as (I assume) you do not know enough about the gears operational load cycle, effect esn of lubrication, rate of damage progression etc.


That´s is why there is an immense amount of durability testing of components.
I would tend to agree with you if it was a completely new design, but this design has operated for years with 1000's flying hours. If you look at the failure modes and
wear prior to failure modes, you are able to accurately predict the life of components, adding a safety factor to it.


THence the use of MCDs as the primary method of detecting epicyclic deterioration (HUMS doesn't work well due to the constant movement of the planets relative to the accelerometers).


The accelerometers are able to measure vibration frequency. As I understood
monitoring a given treshold for the frequency should tell you if it is abnormal operation. It might be the case, exceeding my knowledge, if the G-REDL
and LN-OJF has different positioning of the accelerometers?


The 225 and 332 have plenty of history of detecting spalling of planet gears without catastrophic failure, therefore it is possible that this failure is not due to normal spalling. If a crack forms at the interface of the carburised layer, or in the body of the gear it will only be detectable when it breaches a surface and results in particles being released. This was what the AAIB theorised with REDL and may be a factor in the accident.


Read the REDL report closely. The length of the spalling close to where the crack started is very similar on the two gears


Re the jamming of the gearbox, the epicyclic ring gear damage suggests that something was entrained between a planet gear and the ring gear which burst the case, If the epicyclic had jammed the ring gear and planets would have had significant stripping of gear teeth. There was no suggestion that the REDL MGB jammed

If you look at the outer ring gear of the secondary stage planet,
you will clearly see that on G-REDL it is broken on the same place as on LN-OJF.
What is different as I see it is the fair amount of teeth crushing on the sun gear of the LN-OJF.

In both cases the outer ring is cracked open.
In both cases 1 gear is cracked into several pieces.

Such a failure is fairly stochastic. If there was a piece of the failed gear that
broke and jammed between itself and the sun gear on LN-OJF which cracked
open the case and on G-REDL it jammed between itself and the outer ring gear.

[riff_raff]

I am just going to throw this speculative idea up in the air for consideration. Is it possible there may have been hydrogen embrittlement of the gear material? I noted from AAIB report 2-2011 that the carburised gear raceway is chemically etched before final polishing. I am not a materials specialist but I wonder if a combination of materials susceptibility, environment and stress have combined with the presence of diffused hydrogen trapped underneath the carburised layer to initiate a defect and cyclic stress has done the rest?

Carburized surfaces of the planet gear that get finish ground after heat treat are given a surface temper etch inspection procedure (AMS 2649 or similar) to check for manufacturing damage such as overheating (re-hardening or over-tempering) caused by abusive grinding, or to detect areas of local discontinuous carburization. The surface temper etch inspection is performed after finish grinding but prior to any honing/lapping/polishing operations on the surface. The etchant used is typically a 3-5% nitric acid solution with an anti-smut additive containing hydrochloric acid. Immediately after etching the parts are cleaned with an alkaline solution followed by hot water rinse. After inspection the parts are given hydrogen embrittlement relief baking (AMS 2759/9 or similar). The time between etching and baking should be less than 24 hours.

So the short answer to your question is that it is possible there may have been some hydrogen embrittlement issues from the temper etch inspection, but only if the procedures were not performed correctly.

[n305fa]

This is what Nadar wrote. I asked a question, wether it is clearly known if there are no HUMS readouts, or no abnormal readouts.



That´s is why there is an immense amount of durability testing of components.
I would tend to agree with you if it was a completely new design, but this design has operated for years with 1000's flying hours. If you look at the failure modes and
wear prior to failure modes, you are able to accurately predict the life of components, adding a safety factor to it.



The accelerometers are able to measure vibration frequency. As I understood
monitoring a given treshold for the frequency should tell you if it is abnormal operation. It might be the case, exceeding my knowledge, if the G-REDL
and LN-OJF has different positioning of the accelerometers?



Read the REDL report closely. The length of the spalling close to where the crack started is very similar on the two gears


If you look at the outer ring gear of the secondary stage planet,
you will clearly see that on G-REDL it is broken on the same place as on LN-OJF.
What is different as I see it is the fair amount of teeth crushing on the sun gear of the LN-OJF.

In both cases the outer ring is cracked open.
In both cases 1 gear is cracked into several pieces.

Such a failure is fairly stochastic. If there was a piece of the failed gear that
broke and jammed between itself and the sun gear on LN-OJF which cracked
open the case and on G-REDL it jammed between itself and the outer ring gear.

Turbo shafts

Re the prediction of remaining gear life with spalling present, I was referring to your assertion that the gear should have lasted 300 hours, not the ability of the design team to predict residual life based on certification testing.

The use of case mounted accelerometers to measure deterioration in epicyclic planet gears is close to impossible, the planet system is inherently noisy, any defect in a planet race and hence the signature it produces is constantly changing position in relation to a fixed accelerometer, the planet rotates around the ring gear and it is also rotating about its mounting point. HEnce current research programs to try to develop a monitoring system that can defect epicyclic deterioration.

The REDL report clearly states that no spalling was present on the bits of the failed gear recovered, if there was spalling it would have been on the 25% of the gear not recovered. The only evidence of spalling was the particle recovered on 25 March and the evidence it gave.

Jamming means that a section of the gearbox monentarily stopped rotating, If you read the REDL report there is no suggestion of jamming and the latest AH report into OJF says that there is no evidence of jamming. The REDL report talks about debris being "entrained" between the remaining planets and ring gear.

[Concentric]

Off Topic – The fascinating thing in the ‘Pink Panther’ series of films is that the culprit is invariably caught, in the end.

On Topic – So now there is consensus that (probably) suspension bars were pinned. Connecting bolts were (probably) torqued. Now AH EASB mandates removal of all 2nd stage planetary gears of one design (there were 2 – who knew?).

The EASB does not stipulate what is to be done with the removed planetary gears, does it? Send them back to AH? Or forward to AIBN for scanning and testing to see if they yield any ‘gems’ or hold any clues so sought after?

[Concentric]

@riff_raff:

Thank you for that enlightening explanation of the carburizing and etching processes. It illustrates well the point I mentioned about complex processes required to achieve a safe finished product, and that is just one such process.

Who would imagine that to control dimensions of the bearing raceway and hardened layer that so many chemical and thermal processes would also be required, some of which to counteract potentially harmful effects of a preceding process?

[AnFI]

Concentric
You are spot on. I was chilled to read the number of critical processes that are required. So many opportunities for error.

That process has to happen how many times (eight of those gears) and as you say thats before you mention all the bearings, raceways and other processes.

I dare say if you add up all the processes, from ensuring that no one has a biro in their pocket at the foundary (non melting ball can cause component failure) to design, to regulatory errors, to assembly for all components in series.

Far from saying that these things are safe it is an absolute miracle that they are as safe as they are, showing what an amazingly reliable job all the characters involed are performing despite the whole exercise being so inherently dangerous.

2 crew performing the softest of flying tasks goes some way to

Serial risk of 1000 processes, maybe 10000? Still hoping to acheive 1x10^-9? daft unrealistic nonsense

[birmingham]

Concentric
You are spot on. I was chilled to read the number of critical processes that are required. So many opportunities for error.

...

Serial risk of 1000 processes, maybe 10000? Still hoping to acheive 1x10^-9? daft unrealistic nonsense
Concentric/AnFi

Given the complexity of the manufacturing process and the many steps necessary to ensure that a pristine product performs safely, it struck me as odd that a unit that had been damaged in a road accident was repaired and returned to service.

Now I know we have no idea whether it was a contributing factor and clearly we can't just throw away expensive kit at the drop of a hat, but safety critical components with very limited opportunities for redundancy such as an MGB? If such a thing receives a shock loading outside of its normal operational environment which causes damage which needs to be repaired, surely it would be prudent to write it off as an insurance loss. I am not familiar with the overhaul that was carried out but it would be close to impossible to ensure the safety standards inherent in the manufacturing process or a routine overhaul from normal wear and tear.

[Brucci2000]

This is my first post - thanks to everyone over the 73 pages for an informative read.

I'm interested in the latest revelation about the two types of second stage gears - it raises these questions:

1. Did the two types exist prior to the REDL accident and if so why was analysis of the differences not a feature of the AAIB investigation? Which type was REDL using?

2. If the second type post-dated the REDL accident, why was it introduced, and if it was a quiet response to internal AH findings with respect to REDL, why was the immediate retrofit of the second type not mandated?

[Concentric]

This is my first post - thanks to everyone over the 73 pages for an informative read.

I'm interested in the latest revelation about the two types of second stage gears - it raises these questions:

1. Did the two types exist prior to the REDL accident and if so why was analysis of the differences not a feature of the AAIB investigation? Which type was REDL using?

2. If the second type post-dated the REDL accident, why was it introduced, and if it was a quiet response to internal AH findings with respect to REDL, why was the immediate retrofit of the second type not mandated?

You ask a couple of very good questions. I think it raises further questions too.

I do not mean this as criticism of the AAIB but if you look at their report on G-REDL, section 1.18.2 it states that:

“Data provided by the helicopter manufacturer indicated that between 2001 and 2009 there were nine recorded cases of planet gear spalling on the AS332 L2 (see Table 2)”

and then goes on to add that:

“The information provided by the manufacturer regarding the number of planet gear rejections due to spalling was incomplete. During the investigation anecdotal evidence was provided that indicated that overhaul facilities disposed of rejected gears without routing them for investigation”.

As the EC225 and AS332L2 are widely reported to share the same epicyclic gearbox module, isn’t it surprising that only data on L2 gears with spalling was considered relevant? Was the Type 2 gear introduced for the EC225 to use exclusively, therefore considered to not be relevant to the 2009 investigation? Something doesn’t add up here.

[turboshafts]

You ask a couple of very good questions. I think it raises further questions too.

I do not mean this as criticism of the AAIB but if you look at their report on G-REDL, section 1.18.2 it states that:

“Data provided by the helicopter manufacturer indicated that between 2001 and 2009 there were nine recorded cases of planet gear spalling on the AS332 L2 (see Table 2)”

and then goes on to add that:

“The information provided by the manufacturer regarding the number of planet gear rejections due to spalling was incomplete. During the investigation anecdotal evidence was provided that indicated that overhaul facilities disposed of rejected gears without routing them for investigation”.

As the EC225 and AS332L2 are widely reported to share the same epicyclic gearbox module, isn’t it surprising that only data on L2 gears with spalling was considered relevant? Was the Type 2 gear introduced for the EC225 to use exclusively, therefore considered to not be relevant to the 2009 investigation? Something doesn’t add up here.

From the report:
Components rejected, in operation or during overhaul, were inspected in accordance with the Continued Airworthiness programme. Those which were considered to show new or unusual failure modes were then routed by the manufacturer to its materials laboratory for further analysis. However, the laboratory did not have the capacity to carry out an investigation of every component rejected during gearbox overhaul. When the Continued Airworthiness programme for the AS332 L2 was initiated it was determined, based on previous operational history, design calculations and the maintenance programme requirements, that damage to the planet gear outer race would not adversely affect the continued airworthiness of the helicopter. Therefore, planet gears which had been rejected for spalling were not routinely routed to the laboratory for additional investigation.

I think that was more of a capacity problem, rather than not of interest.
It is disturbing though, that they did not take action to investigate every one of them.

But the failure risk experienced on the L2 was assessed on the 225 by means of
decreasing the TBO.


Re the prediction of remaining gear life with spalling present, I was referring to your assertion that the gear should have lasted 300 hours, not the ability of the design team to predict residual life based on certification testing.

Sorry I don't follow you. I'm referring to the given running time and the TBO.
So 1080 to 2000 hours is 900 hours. It ran 300 hours until failure from last
modification, inspection and repair, whatever that means. According to the certification testing, it could have some spalling at 2000 hours that would not lead to catastrophic failure.

[Brucci2000]

Concentric,

Yes - I hadn't considered that the "second type" might have originated in the 225 (then possibly been distributed in L2s as units get swapped for overhaul). I guess the casual treatment of the rejected gears during 2001-9 may come down to not expecting them to fail suddenly, or regarding spalling as normal wear and tear.

The AAIB report, whilst thorough, didn't conclude why these gears suffer fatigue in the way they do. This led to some fairly woolly recommendations about assessments of continued airworthiness etc. It appears to me as if AH have then stood by their design and put extra monitoring requirements in place rather than doing much research into the component suitability.

[Lonewolf_50]

Concentric/AnFi

Given the complexity of the manufacturing process and the many steps necessary to ensure that a pristine product performs safely, it struck me as odd that a unit that had been damaged in a road accident was repaired and returned to service.

Now I know we have no idea whether it was a contributing factor and clearly we can't just throw away expensive kit at the drop of a hat, but safety critical components with very limited opportunities for redundancy such as an MGB? If such a thing receives a shock loading outside of its normal operational environment which causes damage which needs to be repaired, surely it would be prudent to write it off as an insurance loss. I am not familiar with the overhaul that was carried out but it would be close to impossible to ensure the safety standards inherent in the manufacturing process or a routine overhaul from normal wear and tear. Neither you nor I knows what "repaired" means for that gear box. It covers a lot of ground. The details of that may or may not be in the final report.
What was disassembled?
How far down was the gear box taken down?
What was inspected?
What was found damaged?
What was replaced?
What was repaired?
Not enough information to assess the return to service decision.


As to "write it off and collect the insurance" -- that's one way to go. But doesn't that decision depend on what you found out once you opened up the gear box and assessed what was or wasn't damaged after that transportation accident?

[n305fa]

From the report:
Components rejected, in operation or during overhaul, were inspected in accordance with the Continued Airworthiness programme. Those which were considered to show new or unusual failure modes were then routed by the manufacturer to its materials laboratory for further analysis. However, the laboratory did not have the capacity to carry out an investigation of every component rejected during gearbox overhaul. When the Continued Airworthiness programme for the AS332 L2 was initiated it was determined, based on previous operational history, design calculations and the maintenance programme requirements, that damage to the planet gear outer race would not adversely affect the continued airworthiness of the helicopter. Therefore, planet gears which had been rejected for spalling were not routinely routed to the laboratory for additional investigation.

I think that was more of a capacity problem, rather than not of interest.
It is disturbing though, that they did not take action to investigate every one of them.

But the failure risk experienced on the L2 was assessed on the 225 by means of
decreasing the TBO.



Sorry I don't follow you. I'm referring to the given running time and the TBO.
So 1080 to 2000 hours is 900 hours. It ran 300 hours until failure from last
modification, inspection and repair, whatever that means. According to the certification testing, it could have some spalling at 2000 hours that would not lead to catastrophic failure.
Turbo shaft
Sorry, I got the wrong end of the stick about your comment on the running time, please accept my apologies.


Re the two types of planet gear, the 2nd stage planet gears are produced by two manufacturers, and they have done since the L2 was certified. Obviously the outer dimensions of the gear are identical as are the method and dimensions of the location to the second stage planet carrier. I don't know what the differences are in terms of raceway profiles, bearing roller design etc. You can also "mix and match" gears from each manufacturer within the module so you could end up with different manufacturers gears in the same epicyclic stage / module

[birmingham]

Neither you nor I knows what "repaired" means for that gear box. It covers a lot of ground. The details of that may or may not be in the final report.
What was disassembled?
How far down was the gear box taken down?
What was inspected?
What was found damaged?
What was replaced?
What was repaired?
Not enough information to assess the return to service decision.


As to "write it off and collect the insurance" -- that's one way to go. But doesn't that decision depend on what you found out once you opened up the gear box and assessed what was or wasn't damaged after that transportation accident?

My point was why bother. These events will be very, very rare and it is virtually impossible to be certain the repair has covered all bases. A significant deceleration impact might initiate a future fatigue crack in almost any of the critical components that would be extremely difficult to detect.

I am not suggesting it for all the components in the helicopter but a helicopter MGB I would argue is something where those risks need not be taken. Just reject those which have been exposed to such exceptional events.

If you owned a single engined light aircraft and the repair shop accidentally dropped the engine a metre or so during overhaul and damaged it would you accept it back after repair or would you feel safer if they replace it with a new one? That is what insurance is for.

[TylerMonkey]

This event in Oz transporting the MGB is interesting in regards to claiming insurance and scrapping the freight. If it was a serious crash / deceleration ( wish we knew those details ) what would you gain by returning the unit into service even after inspection and refurb ?

Reminds me of the COUGAR ACE that listed off Alaska carrying 4800 Mazda cars with water damage to some decks and cars hanging on their chains at 60 deg angles for days. Ship was righted and towed to Portland . Mazda decided to have all 4800 cars crushed to avoid any getting sold or on the road. Expensive yes, but it covered their butt in the future.

[albatross]

I think the reported damage to the MGB and subsequent repair at AB will be a big factor in the ongoing investigation. I assume that this avenue is being followed.
I posted previously of an engine failure in a single engine helicopter with the determination that the root cause was believed to be that an internal gear had been dropped during assembly causing damage to the gear leading to it's in flight failure. It was interesting day for me.
Much as many think they should be privy to all information I fear they will have to wait for the final report.

[riff_raff]

@riff_raff: Thank you for that enlightening explanation of the carburizing and etching processes. It illustrates well the point I mentioned about complex processes required to achieve a safe finished product, and that is just one such process. Who would imagine that to control dimensions of the bearing raceway and hardened layer that so many chemical and thermal processes would also be required, some of which to counteract potentially harmful effects of a preceding process?

Concentric-

Glad to help. I found your question regarding potential hydrogen embrittlement of the planet gear quite interesting, so I looked into it.

It indeed seems ironic that an inspection procedure intended to detect material damage from a previous manufacturing process could itself potentially produce damage to the material. Also consider that the hydrogen embrittlement relief relies on strict adherence to a controlled process to ensure quality. This requires every person involved to maintain accurate documentation/records of their work. With the hydrogen embrittlement relief baking of these planet gears, even something as simple as how the gears are positioned in the furnace can be important.

Hydrogen embrittlement in steel parts is often associated with finishing processes such as electroplating. Copper plating (AMS 2418 type 2 or similar) is often used with carburizing to mask surfaces that don't require case hardening. The copper plate masking is sometimes removed after heat treat using a chemical stripping process. And plating specs (such as the one noted above) usually require the stripping method to be defined as part of the approved process, and state that the process shall not produce hydrogen embrittlement in the part. But as noted above, this only works when the controlled process is strictly adhered to by everyone involved.

[turboshafts]

Klare likheter mellom to fatale Super Puma-ulykker - Tu.no (http://www.tu.no/artikler/klare-likheter-mellom-to-fatale-super-puma-ulykker/349103)

Here they claim that the cracks have propagated from the same surface deterioration/spalling.

However they say, spalling from G-REDL but no spalling from LN-OJF.

I am not sure about if the article is correctly citing AIBN.

Because the picture they refer to showing the crack propagation is a
simulation/calculation done by AH and not an actual analysis of the cracked gear

The article cites AH, are currently testing how the impact of a similar road accident could affect the gearbox and epicyclic module.

The last statement, don´t understand it. Why would they need to do such
a test, if the gearbox was completely stripped, checked and overhauled after the accident?

[roscoe1]

I am curious where you got your information that " gearbox was completely stripped, checked and overhauled after the accident". The only statements I've seen are that it was inspected and repaired. Not sure anyone but the company, AH, or the insurer would actually know what that means. Obviously it was not overhauled because it was installed with continued time, not zero time since overhaul.

[noooby]

AIBN will also know what was done. Work Order is recorded on the log card. Go to AH, pull the Work Order and there you have everything that was done to the MGB after that incident.

Easy.

[riff_raff]

Lots of reports to read regarding this issue. Interesting that AH says one planet gear design has better reliability than the other. Yet they have not established the root cause of the planet gear that failed. If the root cause was a manufacturing problem, all of the planet gears and bearings would likely need to be replaced again.

[JohnDixson]

This morning's Aviation Week Network, in an update on the 400M program, notes that AH is assisting with resolution of their prop gear box issues. ( same gearbox supplier, I believe ).

[Arnie Madsen]

original post by megan
Certainly going to be interesting to see the root origin of the failure.

Reminded of the fan disc failure in a DC-10. Was found the disc had been machined from a piece that came from the near end of a billet, which was found to contain inclusions. Fix, discard the ends of the billet.

In the early 60's worked in a shop manufacturing steam turbines for ships. For the gear cutting shop battery back up was supplied to the cutters/grinders. Once a cut/grind on a tooth was begun it was not permitted to be interrupted, for it introduced a point of future failure.original post by riff raff
Lots of reports to read regarding this issue. Interesting that AH says one planet gear design has better reliability than the other. Yet they have not established the root cause of the planet gear that failed. If the root cause was a manufacturing problem, all of the planet gears and bearings would likely need to be replaced again. My thinking too ... the other day I pulled some numbers out of the air .... fleet of 200 machines X 8 planetary gears = 1,600 gears .... changed every couple thousand hours there could be way over 5000 of those gears manufactured and only 1 would have to be off-spec and fail

Hopefully someone more knowledgeable on total-fleet-hours and total-gears-manufactured can improve my numbers .

[AnFI]

buzz: "Surely from here Oil Company's will start with the basics.

1. He who has the best Gearbox run dry times (no cheating e.g. Glycol)
2. Best Single Engine performance"

That would be a single engined aircraft but the authorities won't allow it.

[The Sultan]

AnFi

Glycol is a valid means to reach the 30 minute requirements. Design mistakes which effectively neutralized this type of system (a sensor designed to report failure when the system is working and led to two ditchings) are not acceptable. This sensor screwup may point to systemic issues at AH (supported by the latest crash) which should cause operators to look elsewhere for aircraft, just not for a glycol loss of lube backup.

The Sultan

[SASless]

You miss the point....using Glycol is not the same as a genuine Run Dry capability just as assuming there shall always be some trapped Oil in the Gearbox (such as in the S-92 original assumptions).

The goal would be to have a gearbox that can be run at Cruise Power for 30 Minutes with no oil, glycol, or fluid of any kind.

The question I would pose is what does the Crew do if there is no landing site within that 30 Minute Range and the Sea State exceeds the Certification Limit of the Emergency Floatation System particularly in very cold air and water temperatures and rough seas?

Why have a 30 minute run dry time if a safe landing (Ditching) can be made and SAR resources are available to retrieve the Crew and Passengers in a timely manner?

Are we perhaps chasing the wrong Horse?

[turboshafts]

I am trying to understand how the rotor mast are supported in the sun gear
and how the bearing loads would be if the rotor came out of control as a result of a crack in the conical housing leading to conical housing separation.

This question is supported by the fact that the secondary planetary gear carrier where the sun gear is attached is significantly bent, which could be a reason that the rotor mast upper mounting on the conical housing is no longer supporting the upper side forces of the rotor mast. (The rotor mast is inclined before separating from the sun gear)

this could be supported by the fact that there was no HUMS and magnetic plug readouts supporting any problems related to the MGB operation before the accident.
there are no indications that supports an actual gearbox jamming (from what I read and heard)

Would it be a possible scenario that the conical housing failed first?
And this is caused by a damage due to the rough handling that is not discovered?

there are two things that I find points towards this

the direction of the helicopter in relation to the direction of the rotor
after the separation from the aircraft.

if there was only a shearing of the gearbox, while the rotor still in a motion horisontal to the aircraft and MGB mounting plate
the rotor would also spin horisontal to that after separation due to the strong gyro forces.

If there was a breakdown of the upper bearing of the rotor mast and conical housing could this have lead to the rotor spinning out of control?
and if it was still supported by the lower bearing could this explain why the outer ring gear casing is broken, and whythe planetary gear carrier is bent?

if you look at the angle of the rotor on the videos available
it is nearly 45 degrees to the horisontal which a helicopter would normally travel.

would there be any serious argument against such a scenario?

[TylerMonkey]

The rotor only continues to spin after separation because it is driven by air from below as it falls ( as in autorotation). The tilt up 45 degs you mention is a result of this change as far as I know.
Open to suggestions ....

[riff_raff]

You miss the point....using Glycol is not the same as a genuine Run Dry capability just as assuming there shall always be some trapped Oil in the Gearbox (such as in the S-92 original assumptions). The goal would be to have a gearbox that can be run at Cruise Power for 30 Minutes with no oil, glycol, or fluid of any kind. The question I would pose is what does the Crew do if there is no landing site within that 30 Minute Range and the Sea State exceeds the Certification Limit of the Emergency Floatation System particularly in very cold air and water temperatures and rough seas? Why have a 30 minute run dry time if a safe landing (Ditching) can be made and SAR resources are available to retrieve the Crew and Passengers in a timely manner? Are we perhaps chasing the wrong Horse?

These are all valid points. And there is currently a big effort underway to improve loss of lube capability of rotorcraft gearboxes.

First, let's consider what the real problem is when an MRGB operates under loss of lube conditions. The primary functions of the lube oil are to reduce friction and provide cooling of the bearings and gears. What causes failure of gears/bearings with loss of lube is the combination of increased friction heat generation and a greatly diminished cooling capability. If the gear/bearing materials are heated much beyond their tempering temperature, they begin to lose strength. The reason for a loss of lube back-up system using glycol injection rather than oil is because glycol provides better cooling. There are also new gear materials (like C64) that can operate at very high temperatures (~900degF). This will significantly improve loss of lube capability as these materials become more widely used in new designs.

Regulatory agencies such as the FAA have also recognized that their certification requirements need improvement. I think the loss of lube qual test procedure will become far more rigorous, including increasing the time requirement beyond 30 minutes.

Lastly, one change I would like to see the FAA implement is for every certified gearbox design in production to undergo a formal design review every few years using the most current analysis tools/techniques available. This analysis technology improves at a very rapid pace, and this proactive approach could likely reveal many potential problems that were missed in the original design analysis.

[Lonewolf_50]

Lastly, one change I would like to see the FAA implement is for every certified gearbox design in production to undergo a formal design review every few years using the most current analysis tools/techniques available. This analysis technology improves at a very rapid pace, and this proactive approach could likely reveal many potential problems that were missed in the original design analysis.
But our sales would plummet! (https://youtu.be/lUh9Djcxgjs?t=146)

Getting industry buy in to a never ending cost center over and above current cert requirements puts a very hard edge on "the continuous improvement model" -- for all that I agree on periodic review to get after some of those difficult trade offs that have to be made to get anything built.

(I also suspect that any analysis short comings come more from the bean counting side than the design team side ...)

[henra]

Lastly, one change I would like to see the FAA implement is for every certified gearbox design in production to undergo a formal design review every few years using the most current analysis tools/techniques available.

That is probably a good idea from a safety perspective. But:
- It would be quite expensive: Who pays for it?
- It probably wouldn't have caught this one. Using the planetary gears as bearing outer races is not an immediately visible safety hazard. It becomes one since material properties of a gear and a bearing race are somewhat similar but in detail not identical. A planetary gear with a separate bearing race inside could similarly break apart, e.g. if the bearing fails. Admittedly the latter design would put one more layer between potential problem and disaster. In that way a review of the redundancy concept might indeed have caught this design as lacking one layer of redundancy.
It is a bit sad to see that both manufacturers of the two only available (competitive) Types in this Heli category used technical trickery in order to shave weight. Sikorsky used a clever paragraph in order to circumvent the necessity for a more massive MGB/Gears that would have the mass to run dry for 30 minutes. AH tried to squeeze every ounce of the MGB by using the gears as outer races and putting the lift load through a mere 3 suspension bars.
Might be the downside of the cut- throat nature of competition in the O&G industry.

[The Sultan]

SAS,

Glycol is an acceptable means to meet the regs and far superior to the 92's PowerPoint presentation promises which should never been accepted by the regulators.

The Sultan

[bladegrabber]

SAS,

Glycol is an acceptable means to meet the regs and far superior to the 92's PowerPoint presentation promises which should never been accepted by the regulators.

The Sultan

As a recreational heli pilot, self loading freight and oil service company worker who regularly travels offshore internationally, I would suggest we should be able to rely on aircraft which don't need / rely upon secondary 'get you home ' lube systems . How about we all get together, stop bitching and demand from the manufacturers an aircraft that has robust and reliable components, adequate warning systems which allow you professional pilots to pop the machine down in a safe condition and go back to the bar and celebrate with your relieved and grateful pax? Or would that be too boring ?

BG

[SASless]

As usual you miss the point and pay scant attention to what was posted.

My contention was "Run Dry" should be exactly that..."Dry"!

I suppose you are ignorant to the the contents of the S-92 Emergency Checklist and the Cougar Accident Report....as evidenced by your post.....or are you just trolling again?

[AAKEE]

@SASless My contention was "Run Dry" should be exactly that..."Dry"!


So by this You mean that the FAR29 goal of run dry is that it has to be dry, and not the ability to continue to fly safe if all MGB oil leaves the MGB ?


Then loss of one engine literally meaning it has to fall of the A/C ?




Yes, I know...the term is 'One Engine Inoperative'. But also, in FAR29(29.927) I don't think they use the term "Run Dry".


By the way, why does it matter how the manufacturer is keeping A/C able to safe continue to fly ?

[The Sultan]

Bladegrabber

The 30 minute is to give enough time to land "safely" after loss of primary lube. Secondary glycol is fine, the 429's case reservoirs that trap oil after most has bled out is better as it has been demonstrated to allow around four hours at flight powers. Run dry to my knowledge is not a requirement. It is loss of primary lube/oil due to seal/line/filter failure where the bulk of the lube is lost.

SAS, by any measure the 12 minutes a 92 can last before catastrophic failure is inadequate.


The Sultan

[SASless]

The question is when we use these descriptions the words should accurately describe what we are talking about.

I see "Run Dry" should mean just that...."dry".

Did not Sikosky test a 92 MGB using the isolation concept and only terminated the test when the MGB had lasted longer than the max fuel endurance of the aircraft?

If a Glycol system fails to work as advertised, be it in cooling or just an indication that is working....then that machine has no "Run Dry" capability in reality.

So...if you want use some descriptive wording....or a design concept that requires coolant or trapped oil....is that a "Run Dry" Design?

[[email protected]]

I can't think you will ever get a MRGB to actually run completely dry for any significant time - too much load and too much heat to dissipate.

The UK mil Sea Kings had an emergency lube system which had an additional sump and used the torqumeter pumps to provide pressure to the top bearings in the MRGB following a double MRGB pump failure or significant oil leak - it certainly gave you more than 30 mins.

Sasless - that S-92 'isolation' concept was flawed since it didn't cover the detachment of the filter due to poor design. Without oil the S-92 MRGB failed at between 11 and 12 minutes.

[dangermouse]

Well the 101,139 and 169 have 30 mins with no additional lube system and the 189 has 50 mins, so it does seem possible....

DM

[212man]

the 189 has 50 mins

But has back up lubrication of the input modules....

[Self loading bear]

Interesting discussion.
i personnally dont bother so much,
Actual run dry or trapped oil (Bell?) Is obvious best (non complicated)
Back-up systems are ok for me as long as they are proven to work when needed.
let's get back on topic?

SLB

[SASless]

Crab,

You make my point for me.

The test by Sikorky allowed an extra delay in isolating the system....then carried on and was called off after the max fuel endurance was reached. They were testing their engineered system for certification and it worked fine. But we all know the rest of the story which enforces my position that if we say "Run Dry" it should mean "DRY".

Even those other "Trapped" fluid designs sound good but just as in the 92...the question has to be asked about even rare to the point of being an act of God kind of failure shifts you into being in a "DRY" situation.

If the drain plug were to remove itself by mystical reasons....would that cause a loss of lubricant? Sounds far fetched but then who would have guessed the 92 thing would happen? Lots of experts AFTER the fact knew of course but it made it into Service before it presented itself.

[[email protected]]

Sasless - agreed but the FAA were fooled by it which is worrying.

[turboshafts]

emergency or run dry capability does not help if the rotor falls off.

the problem here as I see it is to find a system that
in case of severe MGB failure, does not shear the rotor of the AC.

the weakest point on the LN-OJF was that the failure led to rotor
shear-off. no matter what else is broken on the AC this should not happen
Could it be avoided with 7 susp bars? 10? Don´t know.

a run dry capability would only cover one failure mode.
What is needed here is a system robust enough to cover every failure mode

[SASless]

Crab.....the Sikorsky folks did not "fool" anyone.....the System fooled everyone including those administering the system.

If you recall my previous posts about what it is going to take to make things genuinely better....it will require a dropping of shields by everyone involved in the "system"....and a clean sheet review of processes, concepts, standards, and procedures.

Plainly, like every Chain....there are weak links.

Identifying the factors that lead to these weak links is the first step.

Let's look back over the Years....and all the changes that have been made that were seen to be "cures" but in time were found not to have done what they were supposed to do.

We have HUMS, Oil Analysis, Chip Plugs and all sorts of other ways of monitoring MGB's (for example) and despite a Fatal Accident involving the loss of a Rotor Head....and efforts to remedy the problems found by the investigation of that Crash....we now have another one where it is seen that we still do not have it right yet.

Engineers, with good intentions, saw the 92 Oil Filter Assembly to be fine...as did the FAA and other Authorities but we found despite all the folks involved in the process....there were real issues.

We see the same thing with the EC MGB....lots of very good and diligent folks sought and found a problem and did what they thought would end that situation.

Sadly, we are Humans....and therefore are prone to make mistakes.

Who, where, when, why, what, and how those mistakes are made is the issue we need to consider.

Sikorsky made a mistake thinking there would always be oil in the 92 Gearbox.

EC thought revamping the method by which their Gearbox is monitored would be the fix.

The authorities affirmed the two companies thinking.

Operators did as well.

So the question is.....how do we make the system truly effective?

[Pablo332]

I can't think you will ever get a MRGB to actually run completely dry for any significant time - too much load and too much heat to dissipate.

The UK mil Sea Kings had an emergency lube system which had an additional sump and used the torqumeter pumps to provide pressure to the top bearings in the MRGB following a double MRGB pump failure or significant oil leak - it certainly gave you more than 30 mins.

Sasless - that S-92 'isolation' concept was flawed since it didn't cover the detachment of the filter due to poor design. Without oil the S-92 MRGB failed at between 11 and 12 minutes.
Could you give us a bit more info on the torqumeter pumps. If memory serves me correctly the main purpose of the emergency lube (separate electrical pump, S61) was to service the plain metal bearings of the engine high speed input.

[riff_raff]

Getting industry buy in to a never ending cost center over and above current cert requirements puts a very hard edge on "the continuous improvement model" -- for all that I agree on periodic review to get after some of those difficult trade offs that have to be made to get anything built

I was proposing conducting periodic design review/validation in specific areas where new analysis tools/techniques can provide a more accurate result than those used in the original certification analysis work. The analysis/validation work can be performed by any qualified organization, public or private. As for funding, in the US this should come from the FAA or NASA. Making use of technology to improve aircraft safety is one of their primary mandates. This analysis/validation effort would be fairly limited in scope in any given year, and could easily be accommodated by the FAA or NASA budgets. I think spending 0.1% of NASA's $18B+ annual budget on ensuring safety & reliability of the existing commercial rotorcraft fleet is a much better use of taxpayer money than sending space probes to Jupiter.

As for the cost impact to OEMs, if the result of the validation/analysis work demonstrates a solid case for implementing changes to the design certified by the FAA, then the FAA and OEM both should share the cost to correct the situation.

A great example of how recent technology developments can greatly improve the loss of lube capability of a legacy MRGB design, is shown in this presentation from 2009 describing the significantly increased high-temperature performance offered by the new C-64 gear steel alloy versus the existing gear steel alloys X-53 and 9310. The 500+degF increase in tempering temperature limit provides a huge advantage in loss of lube conditions. C64 did not even exist when the EC225 MRGB design was certified.

[buzz66]

The Truck Driver transporting that Gearbox in Australia died in the Accident.
So that will give you a good idea of what happened to the gearbox.

It's very possible the Conical housing was the initial cause. We may never know.

The fact the Gearbox was never scrapped, simply comes down to Greed!
Risk Analysis is a tricky game to play. Get it wrong and all of a sudden hundreds if not thousands of lives are effected and Millions if not Billions of loss come into play.
Those that get to play God in this way only ever get punished by way of the Karma God. It's a sad unaccountable World we live in.

Sikorsky made a mistake thinking there would always be oil in the 92 Gearbox.
Rubbish, this is a classic example of Greed and poor risk analysis at best

[birmingham]

The Truck Driver transporting that Gearbox in Australia died in the Accident.
So that will give you a good idea of what happened to the gearbox.

It's very possible the Conical housing was the initial cause. We may never know.




buzz66 ... hearing this was a fatal accident and already knowing the unit was damaged (they said some kind of, as yet unidentified, repairs were carried out) compounds my initial surprise that the MGB was returned to service.

Presumably the module in G-REDL had not been in a serious road accident or similar damage situation. Given that in both (flying) accidents the second stage planet gear appears to have failed, the news that road accident damage may, or may not, have contributed to the Bergen accident will be hard to establish in any definitive sense. Even if it can be it will hardly restore the reputation of the MGB design.

[riff_raff]

It is actually not unusual for salvaged aircraft components to be returned to service. If they pass inspection requirements, they can be sold as used replacement components. Quite often perfectly serviceable commercial aircraft are purchased and parted-out because they are worth more as spare parts. A used large commercial helo MRGB in serviceable condition is probably worth a couple hundred thousand dollars.

[Thridle Op Des]

Despite there being no certainty about the source of the failure trajectory in this case yet, the whole question of engineering and design intent is still worth reflecting on.

We can always look back and cite S76 lightning struck MRBs, OEM repaired pressure domes on B747s, Shuttle O rings and brand newish A380 wings (though there is a scurrilous story that Filton told Toulouse that oversize rivets would be an issue into machined rib feet before design release - but I digress). These things - whether an Apple iPad or a helicopter MGB have to make compromise decisions when the design phase is initiated. These considerations about compromise usually have some sort of cost associated with the discussion - it's unavoidable - even human lives have an applied value that is considerably lower than that chosen by the nearest and dearest. This could be termed 'greed' and perhaps rightly so. But as the examples indicated at the top show, there is some person who finally signs off on a decision on the behalf of some organisation. I am sure if any organisation had an inkling that what they sign off on would potentially ground a fleet, then there would be some sort of design review. Sadly none of us are granted this futuristic revelation.

In 99.9999 times out of a hundred there are no implications or comeback. We get to focus on the 'accident porn' and assess where things went wrong - afterwards.

Given the number of B212 skid sets I abused in my years, I suspect that if a cross bar had been clattered against the side of a ship or pushed out the back of an Antonov and it was later fastened to something I later flew, I am almost certain that there would be no implication. How many times could you radiographically slice and inspect a post 'sudden stop' transmission before everyone is satisfied that three years down the line, all will be well?

We are all in the risk business, its not pleasant being confronted with those moments where the risk assessment did not flag an event and you trip over the 1 in whatever accident probability. My drive to work has a hundred fold risk of an accident over my next flight to Kuwait or Houston (actually probably a bit more here), my personal focus remains obstinately on the flight and not the drive.

Take care out there

TOD

[[email protected]]

Pablo - if memory serves, there was a pressure valve in the MRGB line that opened when the normal gearbox pressure dropped - this allowed the feed from the torquemeter pumps (Tq meters worked on oil pressure) to be diverted to both the high speed inputs and the top of the MRGB. No electrical pump required.

Sasless, the FAA accepted SAC's assertion that, since all the oil pathways were inside the MRGB on the S92, there couldn't be a catastrophic loss of oil - that got them a pass/bye/wild card so they didn't have to meet the 30 mins test. Surely someone with such responsibility as the FAA engineers must have asked the question about the filter housing since that was clearly the only external element and should have been subject to some failure mode analysis. To the cynical, it seems like a fudge by a US federal department to help a large US company get their product into the market.

[SASless]

Looks and reality can be quite different.

What we know for sure is it was a flawed design that was approved by every Authority, all of whom will very quickly roll a shoulder and point to someone else.

This gets back to my assertion that the current system that allows things like this to happen is flawed and needs its own overhaul.

[Lonewolf_50]

@riff_raff What aircraft have C64 gears in them at present, that you are aware of?

[Nadar]

My drive to work has a hundred fold risk of an accident over my next flight to Kuwait or Houston (actually probably a bit more here), my personal focus remains obstinately on the flight and not the drive.

This isn't really on topic, but I can't help it, I have to give a comment to the "flying is safer" claim. I'm not afraid to fly at all and think the risk is reasonable under normal circumstances. But, I see the comparison of flying vs driving "risk" as cynical propaganda from whoever makes money on aviation - not a fact. I'm pretty sure they do something "creative" like comparing number of accidents per travelled distance (or even worse, per "passenger distance" which means to multiply the actual distance travelled with the number of passengers) when coming up with these numbers.

That doesn't really give a fair or even interesting basis for risk comparison for many reasons. The typical air trip is much longer than the typical road trip. I'm pretty confident that the comparison looks very different if you for example compare the risk of death per trip.

There are also other factors of the equation. The survivability of an accident with a car is much higher than with an airplane. Most technical faults on a car isn't critical, you can usually just stop. On an aircraft that might not be true, you have to trust whoever designed and manufactured the aircraft much more than with a car.

I think the fact that you have much less influence on the outcome also makes us consider flying more risky, even though that isn't expressed through statistics. When you drive a car you can to a large extent decide the risk yourself. In an aircraft you're to a larger degree depending on procedures made by someone else that you just have to trust that is safe. To me at least, the degree of control I have if something bad happens is a vital part of my risk assessment.

I'd also say that the "quality" of the drivers is much higher on aircrafts than in a car. If you lowered the bar for flying an aircraft to the same level as for driving a car, we would have a LOT of accidents. That impacts the statistics, but doesn't really apply when you compare the risk when the same person drive a car or fly a plane.

I don't intend to take this off-topic by making this a discussion, my point is simply that I think our brains has some good reasons for judging flying more risky than driving.

Here is a couple of links for anyone interested in the subject:
Flying Or Driving: Which Is Safer? (http://www.science20.com/gerhard_adam/flying_or_driving_which_safer)
Driving Versus Flying: The Debate Is Settled! | Observer (http://observer.com/1998/03/driving-versus-flying-the-debate-is-settled/)

[Satcomm]

Most technical faults on a car isn't critical, you can usually just stop.

MOST technical faults on a aircraft are not critical either, you can usually just continue as normal and land as planned. Unfortunately there will always be (no matter what aircraft/automobile) unforeseen faults that cause tragedy .... It's simply the nature of the beast. Anyone that thinks it can be 100% fail safe are just fooling themselves.

I will admit the rotorhead detaching is hard to accept. However, in both, the 330 and 332 instances of the past, both aircraft showed signs and provided time to correct. This one seems different in that manner (though we may find out more in the final report).

[Hot and Hi]

When you drive a car you can to a large extent decide the risk yourself. In an aircraft you're to a larger degree depending on procedures made by someone else that you just have to trust that is safe. To me at least, the degree of control I have if something bad happens is a vital part of my risk assessment.

...

Here is a couple of links for anyone interested in the subject:
Flying Or Driving: Which Is Safer? (http://www.science20.com/gerhard_adam/flying_or_driving_which_safer)
Driving Versus Flying: The Debate Is Settled! | Observer (http://observer.com/1998/03/driving-versus-flying-the-debate-is-settled/)
True enough. But it reminds me of the well known statistic that the large majority of motor vehicle drivers believe they are above average drivers ;-)
Illusionary Superiority (http://nrs.harvard.edu/urn-3:HUL.InstRepos:8954812)
By the way, if anybody reads your first citation, please also read the comments of the author (scroll to the end way past the links with the curvaceous girls). There the author admits that he miscalculated when he stated in his initial paragraph that the 'usual' stats where off by a factor of 66!

[buzz66]

True enough. But it reminds me of the well known statistic that the large majority of motor vehicle drivers believe they are above average drivers ;-)
Illusionary Superiority (http://nrs.harvard.edu/urn-3:HUL.InstRepos:8954812)
By the way, if anybody reads your first citation, please also read the comments of the author (scroll to the end way past the links with the curvaceous girls). There the author admits that he miscalculated when he stated in his initial paragraph that the 'usual' stats where off by a factor of 66!


There is a book called Freakonomics
In this book it tells the Big Picture.
Hour for Hour in an Aircraft seat compared to a Car seat you are more likely to die. Statistics don't lie.
I don't know of to many people who spend more time in an Aircraft compared to a Car.
I have personally been in 2 Aircraft that had to do forced Landings.
Apart from a Flat tyre I have never had to pull over in a car because of mechanical problems, and I spend far more time in a car than an Aircraft.

[AnFI]

if duplicating were actually a good idea then surely duplicating the gearbox would make sense ?
each engine could have it's drive split and drive into each gearbox
each gearbox could independently drive the rotor mast
there would of course be a ton of freewheel units and run-dry oil pumps so every eventuality would be covered

no dafter than carrying 2 engines

the failure rate would be 1x10^-64 so at least in theory nothing can go wrong

[riff_raff]

@riff_raff What aircraft have C64 gears in them at present, that you are aware of?

Lonewolf_50-

I don't know of any MRGB designs that use C64 gears. However, the AW609 MRGB does use X-53 gears, primarily for improved loss of lube capability. The main reason that C64 is not currently used is because it was just developed a couple years ago. Bell studied upgrading existing gearboxes with C64 gears under the recent FARDS program. (https://www.researchgate.net/publication/267490964_New_High_Performance_Gear_Steels_for_Rotorcraft_Tr ansmission_Applications_FerriumR_C61_and_Ferrium_C64)

Upgrading existing MRGBs with C64 gears in certain locations where potential for scoring is high under loss of lube operation (such as spiral bevel or output stage planet meshes) would be a very cost effective approach. While the C64 (AMS 6509) raw material is currently around 2-3 times the $/lb cost of 9310 (AMS 6265), it does provide some advantages in manufacturing processing. One important advantage is that C64 is designed to use a much cleaner gas quench instead of an oil quench.

[SASless]

Riff_Raff,

There are a lot of Pilots sitting at their computer....looking at the screen....and wondering what language you are speaking!

If you and those like me are going to have commonality of definition....you shall have to go back to four letter words and arm waving!:oh:

I got lost back in the time I was expected to know all the interworking of a cereal bowl compass in order to use an RMI for figuring out what direction I was going.:ouch:

[riff_raff]

Riff_Raff, There are a lot of Pilots sitting at their computer....looking at the screen....and wondering what language you are speaking! If you and those like me are going to have commonality of definition....you shall have to go back to four letter words and arm waving!:oh:
I got lost back in the time I was expected to know all the interworking of a cereal bowl compass in order to use an RMI for figuring out what direction I was going.:ouch:

Sorry, didn't intend to confuse you or anyone else. Just tried to provide an answer to Lonewolf_50's specific question.

If it's any help, the simple version of what I posted is as follows. There is an advanced type of alloy gear steel called C64 that has recently been developed which can safely operate at temperatures ~500degF higher than steel gear alloys used in current gearboxes. Using this advanced steel alloy to upgrade certain gears of existing main rotor transmissions could likely provide a significant increase in loss of lube performance, at a reasonable cost.

Does that explanation make sense to you?

[bigglesbutler]

Splendid riff_raff thank you ��

[Concentric]

It sounds like the new materials being developed and becoming available will push the capabilities of new rotorcraft into areas where older types will struggle to compete, with evolutionary upgrades no match for fresh design (except perhaps where those types can demonstrate a long service history with very few if any major accidents).

Where will that leave aircraft such as the H225 and AS332L2? Were it not for two accidents, both apparently caused initially by fatigue fracturing of a planet gear of ‘current spec’ 16NCD13 material, we might not be discussing the merits or feasibility of changing this material and the H225 might have a healthier future. Was the planet gear material in the SA330 or AS332 up to L1 variant the same as in the L2 and EC225, I wonder?

In visualising what may have gone wrong in these 2 similar accidents in the moments following planet gear fracture, it has struck me that AH really put all their eggs in one basket depending on these gears not to fail.

My interpretation of the G-REDL accident and report 2/2011 is that it wasn’t simply the failure of one gear that brought the aircraft down. In photo figure 21, the other 7 gears look pretty serviceable and should have been able to accommodate the small increase in load share if that was the only design consideration.

It wasn’t simply that the ring gear split at the 5 o’clock position either, as seen in Figure 20. There would probably have been enough of the remaining attachment of the epicyclic casing at that moment to keep the mast in place and some measure of pitch control possible.

However, the way that successive bolting around the epicyclic casing would subsequently fail as trapped debris worked its way around the module, would lead to the lower bearing in the conical housing becoming displaced. Thereafter the loss of control and breakup sequence would have been very quick.

This thread discussion has wandered interestingly to a side issue of “run-dry” capability and, learning of some posters past military experiences, I began to understand there are other reasons apart from the condition of the North Sea why you might not want to make an immediate landing, for loss of oil or other cause.

It is not unusual in military aircraft to provide, at the cost of some increased weight, some ‘armoured’ protection for critical components against hostile action. Even civilian turbine engine casings will be designed to contain a certain degree of blade shedding.

So could not AH have provided some means of preventing larger items of debris from a fractured planet gear from becoming entrained in the gear meshing? I know there is not a whole lot of room between planets but I wonder if some sort of guarding built into the carrier design might delay the break up of the planet gear by bending forces; retain debris including rollers from escaping into the other workings of the gearbox; and keep debris from elsewhere out from the planet itself. The critical objective would be to keep debris out of the sun gear (especially) and the ring gear meshing. Planet gear tooth damage might be tolerant to an extent.

If this could buy just a few minutes to make an emergency descent and landing I think the extra weight would be worth it. Indeed, I am surprised that certification does not demand it.

To be fair to AH, the recommendations in AAIB report 2/2011 were to review the design of the planet gear, not the consequences that actually bring down the aircraft. If you don’t ask the right question you probably will not get the right answer.

If guarding of the planet gears is beyond engineering capability then could not the bottom of the conical housing be provided with independent location, in principal not unlike the upper lift housing? Some sort of external brackets between MGB and conical housing, 3 as a minimum and possibly close to M/R servos to limit deflection of a burst ring gear from breaking or jamming a servo?

If my questions sound a bit dumb it is because I am not an aviation ‘insider’. My contribution to aviation is mostly as moveable ballast, so if instructed to I will respectfully go and sit at the back and buckle up!

[Geoffersincornwall]

If my memory serves me well the MD 900 series employ a design that shares the flight and rotational loads through two separate load paths. Is this so? and if it is, why don't we employ that standard across the board.

If the certification standards included this requirement we might see some more robust designs that are damage tolerant when critical components fail.

G.

[ericferret]

Thats correct and it goes back to the Hughes 500 so it is 1960's technology.

[Lonewolf_50]

SASless: I understood riff, but it helps that I was an engineering major so the terms aren't foreign to me. :E

The cost differential riff mentioned is a non-trivial issue when considering whether to upgrade / replace. Any manufacturer for a civil or military contract has to account for lead times for exotic / specialty alloys, and the cost versus customer requirements (and regulatory requirements) -- a balancing act that goes into any final design or upgrade decision. Part of the reason I asked is due to a different topic related to gear wear resistance (super finishing) that I understand Boeing uses on some gears in the Apache ... but we are going off topic so I'll stop there. (Either of those choices are open to AH as the final evaluation of their gears is put into print).


@Concentric: an interesting line of inquiry in your post, but for most operators, the key metric is that as components wear an indication/warning of wear or impending failure gives them a chance to change a component before failure. I am not sure that a design "to deal with it once the gears come apart" is what the industry wants. The "hey, this one's beginning to wear/lose material" trigger gets the box off the aircraft before these critical parts fail.

[vfr440]

Yes, correct Geoff - 2 x separate load-paths. As Eric says, 'old' technology, but proven, and yes, also, read across from the Hughes 500. Keep it simple (K.I.S.S) ~ VFR


If my memory serves me well the MD 900 series employ a design that shares the flight and rotational loads through two separate load paths. Is this so? and if it is, why don't we employ that standard across the board.

If the certification standards included this requirement we might see some more robust designs that are damage tolerant when critical components fail.

G.

[Nadar]

The "hey, this one's beginning to wear/lose material" trigger gets the box off the aircraft before these critical parts fail.
Excepts when it doesn't.

Humans ofter overestimate their own level of control over things, personally I prefer robust design over overconfidence in monitoring systems as a general principle. That doesn't mean that I think monitoring systems shouldn't exist, it's just not wise to think one has all eventualities covered - because one never has.