EC225 crash near Bergen, Norway April 2016

[Heliflyger]

Originally Posted by Pi1ot

This seems like an interesting article: Airbus-sjef frikjente girboksen. 12 dager senere kom rapporten som indikerer det motsatte - Tu.no

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]

Originally Posted by Pi1ot

This seems like an interesting article: Airbus-sjef frikjente girboksen. 12 dager senere kom rapporten som indikerer det motsatte - Tu.no

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]

Originally Posted by Apate

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]

Originally Posted by Apate

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
In any case, is this a "contradiction", which is what you were asserting?

[turboshafts]

Originally Posted by 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 . Now I know English isn't your first language, but I don't even know what you are on about
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:

Originally Posted by Apate

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

Originally Posted by Apate

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

[henra]

Originally Posted by Heliflyger

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]

Originally Posted by turboshafts

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]

Originally Posted by n305fa

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]

Originally Posted by Concentric

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]

Originally Posted by OnePerRev

......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 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]

Originally Posted by 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.

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.