EC225 crash near Bergen, Norway April 2016

[handysnaks]

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

just a shame that the MD 900 gearbox internals were made from the same batch of metal as my old Lancia Beta Coupe!! :{

[Lonewolf_50]

Excepts when it doesn't.
No kidding? Head on over to the Robbie 66 crash thread, recent, two fatalities, and the Isle of Mann thread (206), one fatality ... you can die a lot of ways.


The point being I was trying to make is that there is more than one approach to dealing with wear -- a known phenomenon in gear boxes and power trains. If another (better) means of monitoring/warning can be implemented, that's one way to address this. I am not pretending that it is the only way. It was of interest to note that this kind of feature was mentioned in the G-REDL write up, and has been a feature in the current reports coming from the investigators in Norway.


The sub text may be something along the lines of your point: if you can't come up with a better monitoring system, then you have to come up with higher safety factors / wear resistance / shorter inspection intervals.

[Geoffersincornwall]

So what's wrong with the 'dual load path' idea? If you put Kawasaki internals in the box instead of the Lancia versions in the MD product surely this would be a design that the folk who ride in helicopters would prefer? (Kawasaki make gearbox bits for the 139 etc).


G.

[Sevarg]

While we are at it, let's go back to the rotordyne. No gears needed in the "gearbox" . Dry run shouldn't be a problem just a couple of bearings to lub. Now that shouldn't be beyond the Ken of man.
Then of course there´s the noise and that's an other question.

[Lonewolf_50]

While we are at it, let's go back to the rotordyne. No gears needed in the "gearbox" . Dry run shouldn't be a problem just a couple of bearings to lub. Now that shouldn't be beyond the Ken of man.
Then of course there´s the noise and that's an other question. If you want to get rid of gears in the drive train, we have a thread here on Rotorheads discussing the all electric powered helicopter=> (http://www.pprune.org/rotorheads/426523-future-helicopter-electric.html) ... all motor needs no reduction gears! :E
Not sure if that solves the problem of getting a good sized load of people to and from oil and gas rigs in the foreseeable future ...

[Sevarg]

In the 50's the rotordyne (Fairy) could take 40 pax not sure of the range but I'm sure google knows. The tech works and it's simple always a plus. I have heardthat the noise problem was solved, mind that would be noise 60 years ago, maybe not good enough for today. Surely a bit of modern tech could sort it.
By the way an electric motor would be high speed and would still need reduction, hence gears.

[Lonewolf_50]

By the way an electric motor would be high speed and would still need reduction, hence gears. You are invited to argue that with Adam Frisch, author of the OP in the link I provided to you. (I included the evil smilie -- :E -- for a reason. ;) )


On a more serious note, if the rotordyne were the answer, why do you think the industry has not yet provided it?

[Sevarg]

Noise and from memory a hell of a lot of it. I would also guess it´s not a fuel efficient as current designs. All guesses on my part.
Sorry not able to read the link as yet, cheap phone not doing what it says it will.

[riff_raff]

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.

Lonewolf_50-

I think the subject of what upgrades/modifications can be made to existing gearbox designs that can provide significant improvement in loss of lube operation versus the cost involved is somewhat relevant to this thread, and is worth discussing a bit further. Your comment about OEMs making decisions that are a balance between manufacturing cost and regulatory requirements is correct. But I don't think the higher raw material cost of C64 is a major factor versus the benefit it provides.

Let's take a look at an example of where C64 gears may have made a huge difference. Consider the 2009 S-92 accident where the main gearbox TTO spiral bevel pinion suffered catastrophic plastic failure of the gear teeth (http://www.tsb.gc.ca/eng/medias-media/photos/aviation/a09a0016/images/photo_8.jpg) from elevated temperatures during loss of lube operation after just 15 minutes. One could argue that if the TTO spiral bevel gears were made of C64, with its much higher temperature capability, they might have continued to function long enough to prevent the crash.

Below is a table of the cost for replacement spiral bevel pinions/gears used in the UH-60 tail rotor drivetrain. The TTO pinion is $7291 and the gear is $9436. The difference in raw material cost between 9310 and C64 for the 25lb ring gear forging is probably around $250, or less than 3% of the total gear cost. In this example, raw material cost would not seem to be a significant factor. However, the total cost of manufacturing and retrofitting a dozen or more gears would likely run several hundred thousand dollars per gearbox. So the question becomes is that cost worth the added safety/reliability provided?

Here's a good NASA technical paper (http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20110023751.pdf) on the subject of C64 gears if anyone is interested.

[jimf671]

Generally, that will go beyond just raw material cost. Stronger materials are often more difficult to machine and often every process has added time and cost. Additional processes may be necessary. New materials can also bring new unforeseen problems.

[Twist & Shout]

Is there any time frame for an official update on this investigation, does anyone know?

[Never Fretter]

There have been 4 to date and the last suggested that updates will now be less frequent.

EC225 LN-OJF Accident Investigation Timeline (http://aerossurance.com/news/ec225-lnojf-investigation/)

[Lonewolf_50]

Let's take a look at an example of where C64 gears may have made a huge difference. Consider the 2009 S-92 accident where the main gearbox TTO spiral bevel pinion suffered catastrophic plastic failure of the gear teeth (http://www.tsb.gc.ca/eng/medias-media/photos/aviation/a09a0016/images/photo_8.jpg) from elevated temperatures during loss of lube operation after just 15 minutes. One could argue that if the TTO spiral bevel gears were made of C64, with its much higher temperature capability, they might have continued to function long enough to prevent the crash. Good example, I've heard a similar point being made about gears with Isotropic superfinishing but am not sure if they could claim the loss of lube protection ... but the point about changes in manufacturing requirements factoring into cost is worth keeping in mind. (Does AH/Eurocopter use ISF to their planet/sun gears in the epicyclic module?)
Here's a good NASA technical paper (http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20110023751.pdf) on the subject of C64 gears if anyone is interested. Thanks for the link and the table provided. :ok:

[The Sultan]

Riff

The 92 crash was caused by failure of the xmsn tail rotor output roller bearings which allowed the quill to move and, after it was stripped, loss of tail rotor drive. Main rotor drive was never lost.

The Sultan

[Sevarg]

Llanelli, had a read up on brushless motors and yes IF batteries can be improved I can see it would be the path to follow. I can see a problem regards the speed of the motor re the wieght. A low speed motor would require large conductors so the weight would be high, high speed motor lower weight but a gear box needed to get to, say, 400 rpm. So your back to the same problem.
All this worked out by an old brain feed on a bit to much red wine, so I wouldn't bet the farm on it.
The more I think about it the jet tip is well worth looking in to, no MRGB, as we know it, and no tail rotor system. I would say a bit more noise well worth the extra safety.
Now I guess I'll have read u on tip jets/bleed air, tomorrow, a clear head needed.

[Concentric]

However, the total cost of manufacturing and retrofitting a dozen or more gears would likely run several hundred thousand dollars per gearbox. So the question becomes is that cost worth the added safety/reliability provided?


Do you really think the benefit of the new material would be spent solely or even at all on improving safety or reliability?
Given that designers and manufacturers would probably apply the same design methods, same approach, codes and practices, same safety factors and design inputs, would they not simply arrive at either a smaller lighter component or increase the design loads on it or increase the TBO on the gearbox?

With limited experience of this new material in service, might they not risk getting caught out by the unexpected at least as much as they have already been with the 16NCD13 gears on the L2 & H225 when performance is pushed to the limit?
Is there not a statement in the conclusions section of the NASA article you linked that there was significant variation in fatigue performance (“However, due to considerable scatter in the UHS test data, the anticipated overall benefits of the UHS grades in bending fatigue have not been fully demonstrated”).

The benefits of new wonder materials will only be realised when consistency can be guaranteed. How consistent I wonder is the 16NCD13 material and the present planet gear's manufacturing processes?

[Holy Moly]

I fear that it doesn't matter if they make a new gear box out of kryptonite and dilithium crystals, the Super Puma series is DOA on emotions alone. :sad:

Nobody will want to touch it with a barge pole. The Super Puma is the new DC-10. :=

Stick a fork in it - it's done. :cool:

[SASless]

Could it be the 225 MGB Design failed to correctly assess Loading on those particular Gears/Bearings? Sometimes it is more an art form than science when trying to determine the true loading of various parts of a helicopter.

I am just suggesting there is more to designing a piece of machinery than meets the eye sometimes and we discover that limitation the hard way far too often.

Some examples....the US Army lost two UH-1's and Two Instructors and Four Student Pilots in one day due to Tail Boom failures at Fort Rucker. That led to needed Mods to the Tail Boom.

PHI in the Gulf of Mexico lost two Jet Rangers due to Transmission Mount failures in one day.

The US Army lost a couple of Chinooks to Incidence Bolt Failures on Rotor Blades.

Sikorsky had Blade problems on the A Model 76.

The Wessex had some gearbox failures.

It is not limited to just one Brand, Type, Model, or any one set of Engineers.

[Martin_Baker]

Could it be the 225 MGB Design failed to correctly assess Loading on those particular Gears/Bearings?

I have been wondering about this also. The lineage of the AS332L2/EC225 saw it go from 4 blade MR / 5 blade TR in the 332 to a 5 blade MR and 4 blade TR in the 225, this went along with substantial increases in the gross weight and MTOW.

It would be interesting to see what, if any, changes were made to the MGB along the way. Do the 332L2 and 225 have the same part number and mod status MGB, do they have the same part number planetary gears and bearing rollers?

I have heard that at some point along the way going from the SA330 to the 332L to the 332L1/L2 the MGB went from having 9 planetary gears in the primary and secondary reduction stages to having 8 planetary gears. I'm not sure if this is correct or when the change occurred but your comment about assessing the loads especially when increasing max weights is a valid one.

[AW009]

@Martin_Baker: Up to AS332L1 in both epicyclic are 9 planetary gears. With AS332L2 up to EC225EP/H225 there are 8 planetary gears. Difference between L2 and H225: H225 has more sensoric for chip-detection and HUMS, but the oil flow at the sensors is said to be reduced by the sensor plate / disk.

[riff_raff]

Riff- The 92 crash was caused by failure of the xmsn tail rotor output roller bearings which allowed the quill to move and, after it was stripped, loss of tail rotor drive. Main rotor drive was never lost.

Sultan-

In my post I stated, "...where the main gearbox TTO spiral bevel pinion suffered catastrophic plastic failure of the gear teeth from elevated temperatures...". This is a conclusionfrom theCAB investigation report A09A0016 sec. 1.12.3 (http://www.tsb.gc.ca/eng/rapports-reports/aviation/2009/a09a0016/a09a0016.asp#sec1_12_3) . From the picture of the failed TTO spiral bevel pinion included in the report section linked, most notable is that all of the teeth are missing and it does appear to be the result of severe plastic deformation. However, there is also evidence of similar type damage on both of the pinion's bearing journals which would agree with your statement about the tapered roller bearings failing. Since both the gear teeth and bearing journal damage appears to be severe plastic deformation resulting from loss of mechanical strength due to the material being heated well above its tempering temperature, it seems logical to conclude a C64 pinion would have performed much better than a 9310 gear. At the tempering temperature used with C64 gears, a 9310 gear will have experienced a reduction in tensile strength of ~35%. The loss of drive to the tail rotor would seem to be the result of the TTO pinion losing all of its gear teeth. But I may be wrong.

Lonewolf_50-

ISF of gear tooth flanks definitely provides some additional scoring margin under marginal lubrication conditions such as that experienced during loss of lube operation. The reduced mean surface roughness provided by ISF improves the min hydrodynamic oil film thickness the gear contacts can safely operate at. In case you're interested, the technical term for the relationship between hydrodynamic oil film thickness and mean height of the mating gear surface asperities is called "lambda ratio".

[Pablo332]

Ye gods you’ve got to get through a number of pages before you get to this topic.

Anyone privy to information beyond the AH solid wall of silence that SKF v Timken bearings has any relevance to good/bad 2nd stage planetary gears?

[gulliBell]

Photo of a bearing removed from an Australian Army helicopter. How a bearing can go this bad before being detected comes as a surprise to me.

http://i740.photobucket.com/albums/xx48/DTVbeejay/Screen%20Shot%202016-08-10%20at%208.44.02%20AM_zpsqf8vqxbs.png

[roscoe1]

I hope you are in no way implying this is from an Airbus product. The 206 part number on it confirms it is a Bell part. Do you have any first hand information on this, did you find it on the internet, do you know whether or not there were any chip lights, I seriously doubt they just found this at overhaul. It is of course possible but based on my experience with Bell light and mediums helicopters it is not likely this would have been undetected. This photo doesn't really even belong in this thread.

[gulliBell]

An element of the discussion is bearings in helicopter gearboxes, whether this particular bearing in #1535 came out of a AH or Bell or Robinson product, whether made by SKF (in this case) or somebody else doesn't matter. It does show the nature of damage that can occur in a failed bearing, and in that context I think shows relevance in the general discussion.

[RVDT]

I think gullibell's post is relevant.

It points out that there are not a lot of huge design differences in most helicopter MGB's.

These components are invariably not made by the OEM.

There are plenty of MGB failures that are not catastrophic and there are some that but for some grace easily could have that do not get into the public domain.

Something really obscure happened here.

There are a large number of factors in this accident and some that may be difficult to trace unfortunately, for various reasons, which will make any fix possibly beyond economic as it seems.

[etudiant]

I think gullibell's post is relevant.

It points out that there are not a lot of huge design differences in most helicopter MGB's.

These components are invariably not made by the OEM.

There are plenty of MGB failures that are not catastrophic and there are some that but for some grace easily could have that do not get into the public domain.

Something really obscure happened here.

There are a large number of factors in this accident and some that may be difficult to trace unfortunately, for various reasons, which will make any fix possibly beyond economic as it seems.



Is it really true that ' something obscure happened here'?
Au contraire, it seems obvious to me that the gearbox design has insufficient margin, based on the record.
That is a solvable problem, which AH tried to finesse after the first crash.
Can they solve it while still making a return? After the second crash, I don't think so. AH has to eat the dirt and fix the gearbox, not for the 225s sake, but to be an acceptable supplier going forward.
I recognize that AH depends on its suppliers, so that the fault is not solely that of AH, but AH blessed the final product.
Still, AH can and will surely have the suppliers eat part of the cost

[riff_raff]

It is indeed true that the bearings used in most helicopter gearboxes are manufactured by a vendor like SKF or Timken. But the bearings are made to a detailed specification supplied by the OEM.

The particular type of planet gear bearing shown in the example above is quite common with helicopter gearbox epicyclic stages. But one problem with these epicyclic stages that use more than 3 planet gears is their capability to evenly share loads between the planet gears. With the example of the EC225 output stage that used 8 planet gears, the load mismatch between the planet gears/bearings could be up to +/-25%. And the fatigue analysis for these planet gears/bearings would need to take this into account.

[Concentric]

It is indeed true that the bearings used in most helicopter gearboxes are manufactured by a vendor like SKF or Timken. But the bearings are made to a detailed specification supplied by the OEM.

The particular type of planet gear bearing shown in the example above is quite common with helicopter gearbox epicyclic stages. But one problem with these epicyclic stages that use more than 3 planet gears is their capability to evenly share loads between the planet gears. With the example of the EC225 output stage that used 8 planet gears, the load mismatch between the planet gears/bearings could be up to +/-25%. And the fatigue analysis for these planet gears/bearings would need to take this into account.

Would that +/-25% be for a brand new matched set or a mixture (after an overhaul) of new and ‘on-condition’ gears that may have used up some of their wear and fatigue lives?

In any single revolution, ovality of the sun gear or of the ring gear may affect the sharing of load over the set of planet gears. Could there be a numerical phenomenon whereby the number of gear teeth, the number of planets and the initial assembly position of the gears with respect to their individual maximum ovality axes could combine at the same position and repeat with more frequency (and reduced fatigue life) than say a similar module with 9 planets and corresponding differences in teeth numbers? It may sound a bit far fetched but it might explain how a gearbox could pass all the inspection checks at major overhaul yet fail relatively soon afterwards if that one gear repeatedly takes a higher share of loading than the others.

It shouldn’t be as difficult as cracking the Enigma code machine (another cluster of cogs) to work out if this can happen.

I still think the primary ‘cause’ will be found to be a manufacturing process producing an irregularity in the polycrystalline material but the design margins that should prevent this leading to failure do not appear to have been wide enough to compensate for manufacturing or operating margins.

[Pablo332]

Would that +/-25% be for a brand new matched set or a mixture (after an overhaul) of new and ‘on-condition’ gears that may have used up some of their wear and fatigue lives?

In any single revolution, ovality of the sun gear or of the ring gear may affect the sharing of load over the set of planet gears. Could there be a numerical phenomenon whereby the number of gear teeth, the number of planets and the initial assembly position of the gears with respect to their individual maximum ovality axes could combine at the same position and repeat with more frequency (and reduced fatigue life) than say a similar module with 9 planets and corresponding differences in teeth numbers? It may sound a bit far fetched but it might explain how a gearbox could pass all the inspection checks at major overhaul yet fail relatively soon afterwards if that one gear repeatedly takes a higher share of loading than the others.

It shouldn’t be as difficult as cracking the Enigma code machine (another cluster of cogs) to work out if this can happen.

I still think the primary ‘cause’ will be found to be a manufacturing process producing an irregularity in the polycrystalline material but the design margins that should prevent this leading to failure do not appear to have been wide enough to compensate for manufacturing or operating margins.
That would be inconvenient for AH, as they appear to have bet the Farm/reputation on it being a manufacturing problem that has caused their problems.

Anyone got information on AH SKF/Timken good/bad belief?

[OnePerRev]

Agree that the Bell pinion photo is relevant, but it may have helped initially if it explained that it was a different product.


Spalling is a quite normal "wearout" mode in gear or bearing designs. It is actually a form of metal fatigue itself at just below the surface of contact due to contact stress. It can initiate at asperities, or even surface damage from dents, handling, or debris going through the system. It progresses from smaller pits into larger flakes. Often a small pit, or beginning spall, will not produce a significant chip enough to be indicated, although they will usually stick to the magnetic detector commonly found on most aerospace transmissions. The progressive nature of the spall produces more chips, which will accumulate, and bridge the gap on the detector. My 50 cents guess was that the one in the photo was detected in such manner.


Spalls will progressively worsen in the direction of the contact, which also means that examination can sometimes pinpoint the initiating location, such as a dent.


Issue with the subject mishap pinion is that the raceway spall produced high stress concentration enough to produce a secondary fatigue made, which became catastrophic. Probably was not ever predicted.


If someone were so inclined, they could compare the rim thickness of the two examples, as a ratio of tooth size. Suspect the Bell version is inherently thicker, thus more stiff, thus less relative bending stress. Thus, less likely to experience a secondary rim fracture fatigue. Now of course that is 20,000 foot view, without any real calculation of stress due to load. There should be a stress level that the 225 pinion should be able to tolerate, even with surface spalls present. What makes this questionable now is that the local stress is probably higher than predicted due to unknown reasons, and it may be that by the time the questions are answered, it may point out that the gearbox design is over-rated for power capability.

[riff_raff]

Would that +/-25% be for a brand new matched set or a mixture (after an overhaul) of new and ‘on-condition’ gears that may have used up some of their wear and fatigue lives?

In any single revolution, ovality of the sun gear or of the ring gear may affect the sharing of load over the set of planet gears. Could there be a numerical phenomenon whereby the number of gear teeth, the number of planets and the initial assembly position of the gears with respect to their individual maximum ovality axes could combine at the same position and repeat with more frequency (and reduced fatigue life) than say a similar module with 9 planets and corresponding differences in teeth numbers? It may sound a bit far fetched but it might explain how a gearbox could pass all the inspection checks at major overhaul yet fail relatively soon afterwards if that one gear repeatedly takes a higher share of loading than the others.

It shouldn’t be as difficult as cracking the Enigma code machine (another cluster of cogs) to work out if this can happen.

I still think the primary ‘cause’ will be found to be a manufacturing process producing an irregularity in the polycrystalline material but the design margins that should prevent this leading to failure do not appear to have been wide enough to compensate for manufacturing or operating margins.

AGMA 6123-B06 table 8 provides planet gear mesh design load factor recommendations based on numbers of planets, gear accuracy grade, application, mounting arrangement/flexibility, pitch line velocity, etc. The EC225 output stage would seem to fall under "application level 3" which recommends using a mesh load design factor of 1.30 for the "heaviest loaded planet". These are load factors used for design/analysis of the gear system, are based on accumulated industry experience, and tend to be conservative. However, obtaining even load sharing when you have a large number of planets (ie >4) and a very lightweight, flexible supporting structure, can be extremely difficult in practice.

Here is a good article on the issue of planet gear load sharing analysis (http://www.gearsolutions.com/article/detail/6224/epicyclic-load-sharing-map-application-as-a-design-tool) if you're interested in reading more about it.

[Concentric]

AGMA 6123-B06 table 8 provides planet gear mesh design load factor recommendations based on numbers of planets, gear accuracy grade, application, mounting arrangement/flexibility, pitch line velocity, etc. The EC225 output stage would seem to fall under "application level 3" which recommends using a mesh load design factor of 1.30 for the "heaviest loaded planet". These are load factors used for design/analysis of the gear system, are based on accumulated industry experience, and tend to be conservative. However, obtaining even load sharing when you have a large number of planets (ie >4) and a very lightweight, flexible supporting structure, can be extremely difficult in practice.

Here is a good article on the issue of planet gear load sharing analysis (http://www.gearsolutions.com/article/detail/6224/epicyclic-load-sharing-map-application-as-a-design-tool) if you're interested in reading more about it.

Interesting article, thank you. The 225 planet carrier certainly looks like it has low enough stiffness to share the load well over 8 planets.
Just compare it against the industrial planet carrier on the cover photo of the article (pdf download version).

One significant drawback of making the pins and carrier 'flexible' is that it puts a greater share of planet load on the upper bearing race. That effect on the raceways could easily outweigh any benefit to the gears of having carrier/pin flexibility especially as the bearing load distribution becomes more unequal as torque increases.

Doubtless this will all have been factored into the original fatigue design(?). It should be evident in higher occurrence of spalling in the upper races than lower ones.

[turboshafts]

Is there any other reason the upper stage is significantly
wider than the lower

There must as well be a reason related to fatigue
that they don´t stiffen the conical housing any more.

but anyways, if a stiff conical housing would prevent MRA detatch from AC
but in its lifetime using 2-3 gearboxes more, it would be worth it.

[jimf671]

TS,
Power is Torque times Speed. At high speeds, in stages near the engine, lower torque is experienced so single stage reductions and smaller gear sets are adequate. As you get nearer rotor speed, torques become very large, epicyclics make more sense as way of spreading load across many components, and facewidth typically increases as torque increases.

[riff_raff]

Interesting article, thank you. The 225 planet carrier certainly looks like it has low enough stiffness to share the load well over 8 planets.
Just compare it against the industrial planet carrier on the cover photo of the article (pdf download version).

One significant drawback of making the pins and carrier 'flexible' is that it puts a greater share of planet load on the upper bearing race. That effect on the raceways could easily outweigh any benefit to the gears of having carrier/pin flexibility especially as the bearing load distribution becomes more unequal as torque increases.

Doubtless this will all have been factored into the original fatigue design(?). It should be evident in higher occurrence of spalling in the upper races than lower ones.

Concentric,

Load sharing is always a problem with any type of gear drive where torque is split into several parallel paths. The most recent example being problems with the torque-split arrangement used on the new CH-53K main rotor gearbox. The CH-53K MRGB uses a set of torsionally flexible quill shafts with spline teeth at each end that provide a very precise vernier-type angular index adjustment at assembly. In theory, this adjustment feature should compensate for any manufacturing tolerance errors and produce the required load distribution between the parallel gear paths. In practice, it proved more difficult than Sikorsky's gearbox designers anticipated.

Load distribution between epicyclic planet gears has also been a chronic problem with large wind turbine transmissions. Here is an interesting tech paper from Timken (http://www.timken.com/es-es/solutions/windenergy/Documents/FlexpinBearingPaper.pdf) that describes their flexible planet pin concept.

[turboshafts]

TS,
Power is Torque times Speed. At high speeds, in stages near the engine, lower torque is experienced so single stage reductions and smaller gear sets are adequate. As you get nearer rotor speed, torques become very large, epicyclics make more sense as way of spreading load across many components, and facewidth typically increases as torque increases.

Radial load from the rotor mast is transferred through the upper planet carrier
and onto the planetary gear. So to even transfer the load on to the gears there is a flex in the system.
I am sure that the higher loading distributed through the gears are accounted for in the design, and thus the gear tooth width.
The gears does not only handle the input torque as you suggest.

My point is that this allowable flex in the system. While probably increasing the individual gear life, is a great risk that the rotor will detach from AC if the gearbox breakdown.

the explanation confirms my previous point why not having 10 suspension bars and ultimately prevent the rotor share-off if the gearbox breaks down.

It could as well be a coincidence and the reason for only having
3 susp bars is only to save money and they thought it would be enough.

[Concentric]

Radial load from the rotor mast is transferred through the upper planet carrier
and onto the planetary gear.

Is it though? I think if you look more closely you may find a bearing locating the 2nd stage carrier in the centre of the 'lid' of the epicyclic transmission module. Or is that only an oil seal? The location however of this bearing is dependent on integrity of the epicyclic casing below it. Have another read of post #1507. It may make more sense now why I was suggesting an additional load path around (from above to below) the epicyclic.

The 1st stage carrier does look to be floating. As jimf671 points out this carries less torque. As far as I am aware, no 1st stage planet has catastrophically failed in flight although AH have found cracks in at least one removed from service according to the G-REDL report.


http://www.aereo.jor.br/wp-content/uploads//2014/04/novo-projeto-do-eixo-do-EC225-EC725-recorte-2-a-partir-de-imagem-Airbus-Helicopters-c%C3%B3pia.jpg
Also the suspension bars locating the upper mast bearing are unlikely to have contributed in any way to the fatigue crack in the planet gear that propagated to failure. Three bars is determinate and an ideal way of locating something with predictable distribution of loads. On this aircraft they failed as a consequence of gearbox breakup, they were not a cause of it. Once the lower location is lost, no number of bars at the upper bearing will prevent the mast pivoting. The bars can take axial loads only (i.e. in their own axis), normally tensile.

[jimf671]

In a drawing provided on the thread about the 2012 UK ditchings, one can clearly see a substantial roller bearing mounted in the lower web of the conical housing that supports side forces from the second stage planet carrier and the splined mast inside it.

225-coupeBTP.jpg Photo by FBav | Photobucket (http://s1340.photobucket.com/user/FBav/media/225-coupeBTP.jpg.html)

[Concentric]

This may be a little off topic but since the 2012 UK ditchings were mentioned and we have a couple of good gearbox cutaway drawings at hand, it may be of interest to note the bearing arrangement on the bevel gear shaft. One at the bottom and two (one thrust; one radial roller?) above the bevel gear. What would have been the load distribution after the shaft broke half-way up?
I think it may have been fortuitous that the EMLUB warning system gave a false warning...
Does this perhaps explain AH's immediate interest in the bevel gear shaft in the Bergen crash?
Apologies for going off topic and if this was covered in a 2012 thread, but it is a quiet day. So far.

[turboshafts]

in any case as long as there is a rigid fit between rotor
mast and 2nd stage planet carrier it will take up radial load.
the bearing in the bottom of the conical housing will take up some load.

that was the principle of the load distribution that we just talked about!

even if you say there is enough radial play in the planetary bearing/gear to completely unload the 2nd carrier of any radial load from the rotor mast
it will be taking up the load as long as it is driven


Also the suspension bars locating the upper mast bearing are unlikely to have contributed in any way to the fatigue crack in the planet gear that propagated to failure. Three bars is determinate and an ideal way of locating something with predictable distribution of loads. On this aircraft they failed as a consequence of gearbox breakup, they were not a cause of it. Once the lower location is lost, no number of bars at the upper bearing will prevent the mast pivoting. The bars can take axial loads only (i.e. in their own axis), normally tensile.

That is not what I am saying.

Picture yourself, the AC with rotor mast and MRA, but without the MGB.
Is it a rigid construction that could carry the load of the AC? No.
That is what I am talking about. If the MGB is a rigid part of the MRA
and MGB fails shattering the housing, the Rotor will detach.

In order to do this, you need to make a gearbox with a stiff housing.
Possibly add 7-10 susp bars.

The stiff housing is increasing load on individual gears and reducing lifetime of them, but if it could allow a total break-up of MGB without sacrificing the rigidity of the rotor assembly, in my view that would be a life-saving solution because it would allow to autorotate without the MGB

In the same way as twin-engine, emergency lubrication etc are needed.
There is no saying against a multiple failing MGB cannot be a rigid part of the AC airworthy capability.

So I dont say that either susp bars, conical housing or gears broke first.
I am saying the should never break together.

[turboshafts]

Btw,

in the Nasa report and Bell report that I linked to (earlier in this thread)
there was even a test showing the rigidity of the conical housing with respect to
the gear failure.

The next thing about only 3 susp bars would also possible be ground resonance dampening.
Any thoughts on that?

[etudiant]

A redesign as suggested by 'turboshafts' would not be inexpensive either structurally or financially.
AH would very likely rather accept reduced performance placards rather than spending a lot to get the same end performance.
Seen that the major operators for the type going forward are governments and the military, such a rerating would also be less disruptive.

[riff_raff]

in any case as long as there is a rigid fit between rotor mast and 2nd stage planet carrier it will take up radial load.
the bearing in the bottom of the conical housing will take up some load.
that was the principle of the load distribution that we just talked about!
even if you say there is enough radial play in the planetary bearing/gear to completely unload the 2nd carrier of any radial load from the rotor mast
it will be taking up the load as long as it is driven

That is not what I am saying. Picture yourself, the AC with rotor mast and MRA, but without the MGB. Is it a rigid construction that could carry the load of the AC? No. That is what I am talking about. If the MGB is a rigid part of the MRA and MGB fails shattering the housing, the Rotor will detach. In order to do this, you need to make a gearbox with a stiff housing. Possibly add 7-10 susp bars. The stiff housing is increasing load on individual gears and reducing lifetime of them, but if it could allow a total break-up of MGB without sacrificing the rigidity of the rotor assembly, in my view that would be a life-saving solution because it would allow to autorotate without the MGB. In the same way as twin-engine, emergency lubrication etc are needed.
There is no saying against a multiple failing MGB cannot be a rigid part of the AC airworthy capability.
So I dont say that either susp bars, conical housing or gears broke first. I am saying the should never break together.

From what I can see in the online images available, the mast bearing arrangement in the conical housing appears to be a back-to-back pair of preloaded tapered roller bearings. This bearing arrangement provides excellent stiffness and load capacity in radial/axial directions, and also for moments out of the plane of rotation. The spline joint between the lower end of the rotor shaft and the output epicyclic stage planet carrier is likely not a "rigid" connection. These types of spline connections (fillet root, side fit) are usually made with a small amount of clearance between the mating teeth, and have a small amount of radial play when assembled. A small amount of radial play in the spline joint would seem necessary to prevent an over-constrained condition in the rotor mast bearing set.

[Concentric]

Turboshafts

A redesign as you suggest with a stiff casing could, to describe it in a term you will understand better than most, result in a 'schlimmbesserung'. Not only would the stiffness increase be counter to load sharing among planet gears but by containing fragments in a space designed only for gears' running clearances you could jam up the gearbox with equally catastrophic consequences.
You are getting there, recognising the need to secure the bottom of the mast after epicyclic failure, but there are more practical ways of achieving this than an array of up to 10 suspension bars.
I can think of 2 practical solutions, one of which is particularly elegant. It would not surprise me if AH are already working on one, or even both.
It is probably too late for the offshore market but it can be made safe again. Probably in a similar timescale to the bevel gear shaft redesign and replacement.

[Concentric]

Load distribution between epicyclic planet gears has also been a chronic problem with large wind turbine transmissions. Here is an interesting tech paper from Timken (http://www.timken.com/es-es/solutions/windenergy/Documents/FlexpinBearingPaper.pdf) that describes their flexible planet pin concept.

Thanks riff for another interesting read. :ok:
That IFB looks much superior to the AH planetary arrangement, on so many levels:
- Enabling use of taper roller bearings,
- Preloading the bearings,
- Reversing the angle of the bearings from ‘dihedral’ to ‘anhedral’,
- Increasing material in the rim, giving a stronger ring in bending.

It is a great pity that technology was not around when the L2/225 epicyclic module was designed.

[turboshafts]

Turboshafts

A redesign as you suggest with a stiff casing could, to describe it in a term you will understand better than most, result in a 'schlimmbesserung'. Not only would the stiffness increase be counter to load sharing among planet gears but by containing fragments in a space designed only for gears' running clearances you could jam up the gearbox with equally catastrophic consequences.
You are getting there, recognising the need to secure the bottom of the mast after epicyclic failure, but there are more practical ways of achieving this than an array of up to 10 suspension bars.
I can think of 2 practical solutions, one of which is particularly elegant. It would not surprise me if AH are already working on one, or even both.
It is probably too late for the offshore market but it can be made safe again. Probably in a similar timescale to the bevel gear shaft redesign and replacement.

I am clearly not an expert in the field of helicopter gearboxes,
but the same problems is apparent in all automatic gearboxes.
They do not have the same amount of planetary gears,
but they do have "stiff" housings. The same accounts for automotive differentials.

I will go back in citate the Nasa conical housing test that I referred to.

Yes I agree there could probably be more solutions to this that is smarter than my suggestions, I was not trying to come up with a final solution, but rather to prove my point. And I realize as well, making the mast completely stiff to the AC would probably allow for much more frequent ground resonance problems as long as the AC has stiff landing gears and not a flexible undercarriage.

Riff_raff

If the planet carrier is unloaded, what is actually
contributing to the load-sharing? Only the input torque?

I don´t agree to that the splines are not a rigid fit.
it is probably a very rigid fit. otherwise it may suffer from
severe failure due to the nature of the vibrations acting directly on the shaft.
loose fit, normally leads to small spot weldings on the shaft and finally overheating. in this case the splines are running completely in oil.
but to say that the splines are a loose fit that unloads the ring carrier I have problems to understand. How are they preloaded? How do you see that the lower bearing is tapered? In any case i would say that the bearing of this size would not be able to take any axial load at all. given the size of it

[Pablo332]

The splines are a clearance fit, otherwise you couldn’t fit the head to the box.

[Self loading bear]

Statoil had reviewed it's own organisation and response procedures.

Statoil investigation (http://m.offshoreenergytoday.com/#newsitem-214088)

The pdf link at the bottom of the article is missing. Should be possible to find in on the web but in Norwegian anyway.

SLB

[jimf671]

www.statoil.com/no/NewsAndMedia/News/2016/Downloads/Granskingsrapport – Helikoptersikkerhet i Statoil.PDF

[Shell Management]

Time they followed Shell Aircraft;)

[SASless]

Care to enlighten us to which you refer?

Seems you are always a bit light on facts,data, and evidence to back up your posts!

[OnePerRev]

Does anyone have an English translation of this document?

[Self loading bear]

"The Turøy helicopter accident investigation report will be made available as soon as possible."

Watch this site:
http://www.statoil.com/en/NewsAndMedia/News/2016/Pages/Report23Sept2016.aspx

SLB

[roundwego]

It's a Statoil report produced to make sure they don't come out with too much **** stuck to them. Nothing much to do with the technical issues relating to the failure. Ignore it; its for PR purposes only.

[roundwego]

As to following SAI, I wouldn't rely on them for a good lead.

[212man]

As to following SAI, I wouldn't rely on them for a good lead.

Anything specific you can point to? I assume you know of their role in the introduction of HUMS, HFDM, improved helideck lighting and, soon to come, optimised envelopes for H-TAWS to increase warning time of CFIW?

[bigglesbutler]

I assume you know of their role in the introduction of HUMS, HFDM I thought Bristow did that off their own back way back when and prior to anyone else?

Si

[212man]

I thought Bristow did that off their own back way back when and prior to anyone else?


Jointly funded initiatives with the CAA and BHL, with HUMS driven by the BV234 accident (on contract to Shell).

[bigglesbutler]

OK fair nuff, it was before my time and I only heard snapshots from a few people when I first joined.

Si :D

[JulieAndrews]

All large oil companies have various management structures to kid themselves they are doing it the 'Safeway'.
The Statoil 'report' was a joint ar5e-covering and PR exercise that contributes nothing to the safety argument.
Likewise, Shell Aviation can employ as many 'inspectors' and 'Aviation Safety Advisors' as they can justify; but it will be Shell Commercial that calls the shots.
As far as introducing up-to-date Helideck lighting - you must be referring to decks before my time.......
For example; latest 'Clipper' deck was introduced well after the design of 'new' Helideck lighting was agreed, and it was still allowed to be commissioned with 'old-spec' lighting!
Be careful what you say SM, it was only after the industry embarrassed the CAA into taking action did 'updates' - which had previously been left on the shelf as they were only examples of 'best practice' - start to be 'mandated'.
You are still using out-of-date aircraft when you could been leading the field and insisting in OEMs to provide 'modern' machines - but then that would cost more and it is only a 'taxi' to get plumbers to work and no one has insisted in the past..............
You might regard yourselves as 'leaders' in the Energy Transport sector but you are all well behind the fixed-wing world. That might have been acceptable in the days of the mad rush to extract the black stuff but you have no excuse now and will find it difficult to hide behind a wall of Safety Cases when the lawyers ask "why not" when it was simply a matter of spending a bit more of the green stuff.......

[212man]

'Safeway' is a supermarket......
Shell Aviation makes fuels and lubricants.....
You are still using out-of-date aircraft Currently we only use AW139/189, S92 and AH175, but happy if you can point us to some more modern types...

[EESDL]

There are no other options.
It is only recently that such an aircraft like the 175 has come to market.
The 175 was not Shell's first choice.
Please do not pretend that the 92 and latest rash of AWs are 'modern' designs.
However, you have probably been in the industry for so Long that you can be forgiven for thinking 'modern' means having true Class 1 performance.
And well done for picking-up in the typos, keep doing that and all should be well with the world ;-)

[212man]

There are no other options.
It is only recently that such an aircraft like the 175 has come to market.


You appear to be making the same point as me.

[Never Fretter]

Most of the research projects Shell have co-funded are long in the past.

On the most recent, on TAWS (fixing an inadequate system that they had stubbornly insisted was introduced prematurely!), I'm told that their contribution was a token figure AFTER others had already funded inital work, but enough to get their name on the credits.

So where are Shell using the 175?

[bladegrabber]

Shell M &212 man
Care to give us evidence of what really SAI funded and how much ?

Thanks
B.G

[212man]

Most of the research projects Shell have co-funded are long in the past.

On the most recent, on TAWS (fixing an inadequate system that they had stubbornly insisted was introduced prematurely!), I'm told that their contribution was a token figure AFTER others had already funded inital work, but enough to get their name on the credits.


Not sure the facts bear that statement out!
http://i202.photobucket.com/albums/aa50/S92ctc/HTAWS%20Funding.jpg

So where are Shell using the 175?

They're not, but is approved and useable if tendered.

[Cyclic Hotline]

Please do not pretend that the 92 and latest rash of AWs are 'modern' designs.

I realize that I may not be the smartest person participating, but what exactly are these missing "modern" designs you are referring to?

[Shell Management]

If the warning project is going ahead it does look like someone else put in 9 times what Shell did.:\:eek:

They're not, but is approved and useable if tendered.

Ah yes I used to enjoy those long trips to exotic locations being wined and dined by OEMs. :)

Margarine was a great place to visit for the EC155 and EC225 approvals.:p

[EESDL]

Sorry Cylic, what I meant is that in aviation 'Modern' does not mean what is available from the manufacturers but what could be available from technology currently available.
I guess CAA's recent pointer that the industry could go a long way to lead this and to help themselves in the process.
It's encouraging to see such overt 'hinting' or even 'wrist slapping' from the authorities - I guess they are getting fed-up of the industry taking the £iss!
I'm out of it now but I understand from what has been published that the industry is still dragging its feet over various issues - or has the CAA got it wrong?

[ericferret]

http://publicapps.caa.co.uk/docs/33/CAP1386_OffshoreHelicopterProgressReport2016.pdf

[Lonewolf_50]

Gentlemen, I will suggest that some of these posts really belong in the "end of the 225" thread or one of the threads on the oil industry/helicopter support thereof. We seem to have drifted from the more pressing concern of accident details and reports pertaining thereunto. (I confess, I found the linked 2016 report of interest).

[Tatischeff]

As you have all probably seen it in the press, EASA withdrew on friday the flight restrictions on 225LP and 332L2.

You can find below the related inspections asked by EASA to perfom safe flights :
EASA Safety Publications Tool (http://ad.easa.europa.eu/ad/2016-0199)

[TommyL]

So AH got EASA to lift the ban...****ing joke that's what it is!! No regards for personnel, money talks as usual. Just spit the victims relatives in the face, why don't you!! Well, the flying piece of junk is gone forever from the Norwegian sector anyway, thank god. But I feel for the poor souls who has no choice other than the puma.

[Nadar]

EASA have effectively banned the use of the type of second stage planet gears involved in the accident(s?). Any 225LP and 332L2 with that type og second stage planet gears have to replace them with the other type to fly again.

I'm not knowledgeable enough about this to evaluate if that is enough to deem it safe or not, but it's not like they just waited for the dust to settle and then let things continue as if nothing happened.

[etudiant]

This reminds me of the early years of the Cessna Conquest, which included some fatal crashes because of design flaws that were not corrected but only patched.
Cessna eventually had to redesign the entire tail assembly and the aircraft never achieved its full market potential.


As I read the EASA document, it simply notes that one type of planetary gear configuration has lower stress levels and better reliability than the other, so it must now be used.
It conceded that 'the root cause of the failure is still not fully understood'.


Perhaps that is pragmatic air safety regulation, but it seems more like military than commercial in orientation.

[Sanus]

What is going on with EASA?

They are going against the advice of both the UK and Norwegian CAA's, who are arguably the most experienced airworthiness authorities regarding offshore helicopters in the world.

EASA agree with the UK & Norwegian CAA's that the cause of the latest 225 accident is not understood yet. But even so EASA are prepared to take a risk and allow it to fly commercially, although admittedly with fairly restrictive daily maintenance.

This is not joined-up governance. Some people have suggested this is curiously advantageous timing for Airbus just before Helitech week. For all our sake's let's hope the EASA decision is based more on fact than political expediency.

[Mee3]

If it is political, some nation should be happy they get someone to share the blame and keep their industry.

[birmingham]

What is going on with EASA?

They are going against the advice of both the UK and Norwegian CAA's, who are arguably the most experienced airworthiness authorities regarding offshore helicopters in the world.

EASA agree with the UK & Norwegian CAA's that the cause of the latest 225 accident is not understood yet. But even so EASA are prepared to take a risk and allow it to fly commercially, although admittedly with fairly restrictive daily maintenance.

This is not joined-up governance. Some people have suggested this is curiously advantageous timing for Airbus just before Helitech week. For all our sake's let's hope the EASA decision is based more on fact than political expediency.
Unbelievable - three agencies two opinions and no explanation as to why they disagree. There is no place for politics in safety.

[Frying Pan]

Alas though there is politics for taking us into needless wars.

I think the place of safety though is too often clouded with the commercial and financial desires of those above. It does to me give the impression that this aircraft has one (another) last chance to not kill more people.

[Concentric]

I would be curious to know what AH understand by the term “reliability”.

"There are two configurations of planet gear within the current type design. In depth review of the design and service data showed that one configuration has higher operating stress levels that result in more frequent events of spalling, associated with rolling contact fatigue, while the other exhibits better reliability behaviour. By limiting the type design to the gear configuration with lower stress levels and better reliability and specifying a reduced life limit, combined with more effective oil debris monitoring procedures and other operational controls, an acceptable level of safety can be restored."

They state that one type has more frequent events of spalling but the certification of the H225 and Super Puma range MGB is reliant on magnetic chip detection. The problem identified by AIBN is that one 2nd stage planet gear fractured without prior warning by chip detection. Similarly the only warning on G-REDL was one single chip detected and referred to AH for advice. According to the AAIB Report 2/2011 section 1.18.3, the advice later given by AH when a chip of planet gear raceway was detected on another aircraft, G-REDN, in March 2011 (23 months post G-REDL and long after magnets were all removed from oil separator plates) was to continue to fly and monitor, which it did for another 87 FH until further chips were detected. It is fortuitous that G-REDN survived and it is therefore important to know what type, A or B, was its planet gear.

As far as published investigation reports go to date, no gear fragment recovered from either crash exhibited notable spalling. So, if operators replace these planet gears with ones that are even less likely to give prior warning by particles from raceway spalling, how exactly does that improve reliability? It seems there are 2 possible failure modes, one with spalling and one without.

What AH appear to be doing is attempting, desperately, to perpetuate the myth that the only cause of fatigue cracks can be spalling, and spalling extensive enough at that to be detected before a crack propagates to failure (which in the case of G-REDL the AAIB estimated the total time of crack propagation from initiation to failure as “possibly more than 100 flying hours”). The thing you have to ask yourself, punk…

[noooby]

Well said Concentric!

As a nobody who used to overhaul a lot of AH epicyclics, I find it difficult to believe that AH seem to think the gear will spall before the inner race. The inner race has the load concentrated in one area, whereas the gear is rotating, spreading the load.

If the gear really does spall before the inner race and then this spalling has the possibility of inducing a fatigue failure, then there is definitely something wrong with their gear design/metallurgy.

The inner race should be spalling well before anything shows up on the gear, producing lots of nice flakes to set off the appropriate alarm, before anything catastrophic happens.

I'm not saying it doesn't happen, but I never saw an epicyclic gear with spalling. The inner race would lunch itself and contaminate the gear, leaving it with a pitted look, but not spalling on the gear itself.

[turboshafts]

then we also come back to that of interpreting the facts...

I still don´t agree to the fact that LN-OJF had "no" spalling Before the breakdown.

the pics shown are as well spalling evident and exactly in the same shape
and position related to the depth of the nitrated Surface as with the G-REDL.

what can be said is that it is claimed that no significant spalling had occured
during the time the box was installed in LN-OJF

moreover, we don´t know if there was spalling at an earlier stage of overhaul, since the MGB was inside the TBO of checking and replacing the gears.

moreover, I Think we should say, we don't know... but AH knows

what we also don't know is the reason that the two types of gears are produced.. we also don't know how many TBO each gear set have had, in total with the H225.

lets's get the facts straight Before we go into that discussion.

it might be that many many of the 225's that are not operated by British or Norwegian would not in the next year(s) be in the flight time of MGB TBO.

I would assume that AH knows this, and that is the reason EASA is allowing it to fly.. But of course, they would never say that in the ongoing
investigations, or to any customers that have bought this chip maker of a french disaster.

I would not be suprised if the old gear-sets have passed many more flight hours and TBO's than the other one..


It is still nonetheless disrespectfull to the victims and their families to
still play with Dirty hands and not telling the truth

[Concentric]

I still don´t agree to the fact that LN-OJF had "no" spalling Before the breakdown.
I should say that I did not mean to imply in my post that there was ‘no’ spalling (i.e. zero) on the recovered fragments, but rather 'no notable spalling' and not enough to be detected. To my mind a notable or significant extent of spalling would be similar to that shown in Fig 33 in the AAIB report 2/2011 and that was associated with a crack that had not yet reached fracture. My personal experience is with much larger machinery bearings where spalling would often be measured in several square inches.
The extent of spalling in the CT scan Fig 6 in the AIBN preliminary report is minimal in comparison to Fig 33.

[Hompy]

Anybody else find it interesting that the French president was so annoyed that Poland cancelled an order for 50 225s that he cancelled a trip there? This within days of EASA lifting a flight ban on the type. Amazing coincidence......

France's Hollande scraps Poland trip over lost Airbus deal
http://www.bbc.co.uk/news/world-europe-37586911

[Concentric]

Anybody else find it interesting that the French president was so annoyed that Poland cancelled an order for 50 225s that he cancelled a trip there? This within days of EASA lifting a flight ban on the type. Amazing coincidence......

France's Hollande scraps Poland trip over lost Airbus deal
France's Hollande scraps Poland trip over lost Airbus deal - BBC News (http://www.bbc.co.uk/news/world-europe-37586911)
Perhaps he was expected to make the journey in an EASA225(‘B’) as a show of confidence in the type but he is a reader of PPrune? Not like a politician to look after their own skin…Comment allez-vous, Francois?;)

[riff_raff]

Well said Concentric!

As a nobody who used to overhaul a lot of AH epicyclics, I find it difficult to believe that AH seem to think the gear will spall before the inner race. The inner race has the load concentrated in one area, whereas the gear is rotating, spreading the load.

If the gear really does spall before the inner race and then this spalling has the possibility of inducing a fatigue failure, then there is definitely something wrong with their gear design/metallurgy.

The inner race should be spalling well before anything shows up on the gear, producing lots of nice flakes to set off the appropriate alarm, before anything catastrophic happens.

I'm not saying it doesn't happen, but I never saw an epicyclic gear with spalling. The inner race would lunch itself and contaminate the gear, leaving it with a pitted look, but not spalling on the gear itself.

noooby,

Your point about a sector of the planet gear bearing inner race (which is fixed wrt radial loads) being subject to most fatigue cycles is correct. And normally one would expect this to be the most likely location for contact fatigue spalling to occur. But there can be other problems that would cause the planet gear to suffer the type of radial fracture propagating outward from a race surface spall like this example.

First, it is not possible to pre-load the type of spherical roller bearing used in this case. So there will normally be some amount of radial clearance present. If this radial clearance is excessive, the gear rim will be subject to greater reverse cyclic bending loads than it was designed for. Think of a rotating cylinder subject to opposing local inward radial loads as it gets squeezed between the ring and sun gear. The planet gear race surface will experience a tension/compression load cycle every 180 degrees of rotation, adding to the normal contact stresses. If the fatigue/fracture analysis of the planet gear did not consider a condition with excessive radial clearance in the bearing, this problem would not have been exposed. Normally, the analysis assumes the bearing is manufactured within certain tolerances.

[Concentric]

noooby,

Your point about a sector of the planet gear bearing inner race (which is fixed wrt radial loads) being subject to most fatigue cycles is correct. And normally one would expect this to be the most likely location for contact fatigue spalling to occur. But there can be other problems that would cause the planet gear to suffer the type of radial fracture propagating outward from a race surface spall like this example.

First, it is not possible to pre-load the type of spherical roller bearing used in this case. So there will normally be some amount of radial clearance present. If this radial clearance is excessive, the gear rim will be subject to greater reverse cyclic bending loads than it was designed for. Think of a rotating cylinder subject to opposing local inward radial loads as it gets squeezed between the ring and sun gear. The planet gear race surface will experience a tension/compression load cycle every 180 degrees of rotation, adding to the normal contact stresses. If the fatigue/fracture analysis of the planet gear did not consider a condition with excessive radial clearance in the bearing, this problem would not have been exposed. Normally, the analysis assumes the bearing is manufactured within certain tolerances.
A good clear description. If I may add a little:

There are further complexities that would make analysis of stresses in these gears a difficult 4D problem when considering fatigue. The squeezing described above is not equal but rather the 'cylinder' is wrapped around 3 quarters of the bearing. All the clearance bunches up behind the bearing (in advance of the bearing as it orbits the sun gear) which will happen once in 360 degrees. So you have effects once per rev and effects twice per rev of the planet.

The 2 races of rollers per gear are inclined and bear against the concave inner surface of the gear (the outer raceway of the bearing). As well as radial forces, these also impart axial tensile forces into the body of the gear around the loaded sector creating axial tensile stresses that vary with the thickness of the 'cylinder'. The opposite effect occurs on the inner race which is axially compressed.

As was revealed in the G-REDL accident report, the barrel shaped rollers only truly 'roll' at one position over their length, with some of the contact under loading conditions involving some sliding and frictional force components that had not originally been considered in the design and which can lead to a crack radiating outwards.

Whilst we can envisage these forces and stresses, actually calculating and combining them all accurately requires sophisticated software tools. Even then there have to be certain assumptions made regarding utilisation load spectra, load sharing, temperature effects etc. and the validity of assumed boundary conditions in any model. Then you have to consider material and manufacturing consistency that the whole model is based on. Factors that affect the various heat treatments have previously been discussed.

[Geoffersincornwall]

As a mere pilot these technical explanations appear to reveal a situation in which the manufacturers of these gearboxes know from the outset that they are full of imperfections due to the very concepts behind their design. They then rely on being able to detect the inevitable failure courtesy of the infamous chip detector system. When this detection mechanism is found to have holes in it surely that puts the whole design philosophy behind this type of gearbox into question. How can the certification authorities support the notion that all is well in the helicopter transmission business? Is this behind the UKCAA and NCAA approach? How come the EASA experts don't get it? What kind of world are we living in?

G.

[TipCap]

Tell you what, Geoffers, whilst I miss flying terribly, I am glad I am now retired!!

TC

[riff_raff]

As a mere pilot these technical explanations appear to reveal a situation in which the manufacturers of these gearboxes know from the outset that they are full of imperfections due to the very concepts behind their design. They then rely on being able to detect the inevitable failure courtesy of the infamous chip detector system. When this detection mechanism is found to have holes in it surely that puts the whole design philosophy behind this type of gearbox into question. How can the certification authorities support the notion that all is well in the helicopter transmission business? Is this behind the UKCAA and NCAA approach? How come the EASA experts don't get it? What kind of world are we living in?

Geoffers-

As Concentric pointed out, the analysis of this particular bearing case is a very complex non-linear problem. Even with the best computational analysis tools currently available, there are lots of assumptions and simplifications that must be used to make the analysis practical. Normally the assumptions and factors-of-safety used tend to give a very conservative result. But sometimes a "perfect storm" of problems occurs that the analysts did not consider, and the result can be what we witnessed in this situation.

Don't blame the gearbox designers. They seemed to have done a professional job designing this gearbox given the engineering tools available at the time, and meeting existing certification requirements.

[Geoffersincornwall]

riff
The manufacturers employ gearbox designers who presumably know about the shortcomings of making an epicyclic gearbox, which, if I have understood the situation, is one that harbours basic conceptual floors given the manufacturing tolerances currently achievable. Small imperfections are magnified by the very nature of the relationship between sun, planet and ring gears when under load. It seems that the design philosophy is that 'we know it's going to break but we will replace/overhaul it BEFORE it breaks. Premature failure will be detected by HUMS (or equivalent) and by monitoring for debris using a system that gathers debris on a sensor and indicates the presence of debris to the end user.

Seems to me (pilot remember) that a gearbox overhaul period is a major key element. It may also be that existing gear wheels are NDT'd and returned for another spell at the sharp end at overhaul and not swapped for a complete new set. The TBO, in my simple mind, should be a fraction of the period before a test article produces debris. Say... half that period. (what methodology to calculate TBO's is used currently???).

So that brings into question the certification criteria with regard to initial TBO and overhaul protocols. Presumably the authorities have their own experts in gearbox design so the manufacturers cannot 'snow' the pen-pushers with a scientific overload. Can we use the lessons of the 225 to change the certification criteria.

History can teach us some lessons. As a type enters maturity the TBO's are extended as much as possible so reducing the safety margins in pursuit of reducing the costs of ownership. At the same time new types put pressure on manufacturing facilities so older types may have their vitals farmed out to sub contractors. I think Sikorsky have had that as an issue over the years with the S61 and S76. Sub contractors can cut corners to make money, particularly when i comes to the detailed checking of components. Who's to know if you check one in five instead of every one. One in 100 instead of one in 10.

So history sets us up to fail unless the rules are changed or existing rules properly enforced.

Seems to me that we need to invest in a little more reality from every organisation involved.

[Fareastdriver]

TC. You and me. both.

[Lonewolf_50]

riff
Seems to me (pilot remember) that a gearbox overhaul period is a major key element. It may also be that existing gear wheels are NDT'd and returned for another spell at the sharp end at overhaul and not swapped for a complete new set. The TBO, in my simple mind, should be a fraction of the period before a test article produces debris. Say... half that period. (what methodology to calculate TBO's is used currently???).

History can teach us some lessons. As a type enters maturity the TBO's are extended as much as possible so reducing the safety margins in pursuit of reducing the costs of ownership. At the same time new types put pressure on manufacturing facilities so older types may have their vitals farmed out to sub contractors. I think Sikorsky have had that as an issue over the years with the S61 and S76. Sub contractors can cut corners to make money, particularly when i comes to the detailed checking of components. Who's to know if you check one in five instead of every one. One in 100 instead of one in 10.

Geoffers
TBO is typically driven by the life limited component with the lowest fatigue life, be it a gear, a bearing, a shaft, what-have-you. The fatigue life is calculated based on the loads modeled and then the safety factors ...
A variety of other things arise which lead to "on condition" overhaul decisions, which means that something didn't reach the predicted MTBF/TBO. It is in the ability to detect "on condition" conditions -- wear, pitting, fretting, corrosion, ect. -- that an on condition decision is made. If conditions are hidden or masked, as appears to be the case with this crash, a surprise failure, rather than "graceful degradation" is what the aircrew are confronted with.

A TBO change as a design matures would, in a perfect world, be based on parts or components remaining serviceable beyond its initially predicted/calculated fatigue life.


I am not sure I understand your point on broad brush TBO changes. Over time I'd expect them TBO to go down, not up, as parts age, and wear, and as actual replacement intervals are discovered in service (as compared to design/calculated fatigue life).

[Geoffersincornwall]

LoneW. - My only knowledge of TBO's is in association with a new product where conservative TBO's are set on day one and the manufacturer seeks to grow those as real world experience increases. I didn't realise that they could be reduced as a type aged.

I guess the gearbox designers are struggling with weight issues so how much metal goes into the vital components is clearly a critical part of the design. Well, here is one pilot that would beg the designers to put 15kg (my flight bag) of metal back into the gearboxes or any where else where margins have been pared to the bone.

G.

[jimf671]

"We don't know what we don't know yet."

[Lonewolf_50]

LoneW. - My only knowledge of TBO's is in association with a new product where conservative TBO's are set on day one and the manufacturer seeks to grow those as real world experience increases. I didn't realise that they could be reduced as a type aged.

I guess the gearbox designers are struggling with weight issues so how much metal goes into the vital components is clearly a critical part of the design. Well, here is one pilot that would beg the designers to put 15kg (my flight bag) of metal back into the gearboxes or any where else where margins have been pared to the bone.

G.
Geoffers: our experience seems to vary, so I suppose it may very much depend on the model, the safety factors used, and what they see in service. My comments are biased by my experience, so let's not pretend that my model is universal, and your experience has now taught me something.

Thank you.

[RVDT]

Goffers,

Both and/or any case of TBO/Finite life can change in the life cycle of most models. It more than likely starts out low as you say then increases with empirical evidence then inevitably it possibly goes down again as MTOW's increase during the life cycle of the type. ATA Chapter 4 and 5 are normally constantly changing.

Or not.

As usual being the customer we probably get about 1% of the real picture.

The "code" written in manufacturer service bulletins between the lines is "priceless" in some cases.:rolleyes:

[Mel Effluent]

Geoffers,

Just before my son started his course in mechanical engineering, I vividly remember his professor (the head of department at the University) quoting this:

"Engineering is the art of modelling materials we do not wholly understand, into shapes we cannot precisely analyse, so as to withstand forces we cannot properly assess, in such a way that the public has no reason to suspect the extent of our ignorance."

Apparently this was taken from a lecture by a distinguished engineer in 1946. We have made lots of progress since then, but I doubt that the fundamental truth has changed.

[Geoffersincornwall]

A very appropriate observation.

What does that say about the regulator's position in this conundrum? It would seem to be a thankless task. I wonder if they were aware that there were two different quality gearwheels in service? If not, should they have known? Were AH as open about the situation as they should have been?

Some might suggest that passengers have been sacrificed on the alter of commercial expedience.

I would join TipCap in being happy that I don't have to fly the line any more. Life as a pilot is getting ever more complex with RNP, PBN, LVP, CDFA, TCAS II, EGPWS-30, ADS-B all adding to future intellectual demands when training budgets are increasingly under pressure and our helicopters becoming more and more complex. Add to that any lack of confidence in our ability to arrive in one piece and I wonder if the pilots of tomorrow are going to be as enthusiastic as I was when I signed up to jollying around the oggin day and night, fair weather and foul, chasing submarines in a single engine Wessex at 150 feet?

Ah well......

G. :}

[Concentric]

Does anyone know what the actual latest TBO is for the H225 MGB epicyclic module? All I seem to be able to find is that it has been reduced to“ less than half” what it was previously.
[Edit: See correction in post #1616]. At one time (2009) the TBO was 2000FH but under the Maturity Plan had a target of 3000FH.

So, what was previously measured in the thousands is now measured in hundreds.
That is obviously applicable to epicyclic modules fitted, or retrofitted, with the supposedly superior type B planet gear/bearing. I find it slightly odd that, given the possibility of subsurface fatigue cracking, only the TBO is reduced but there is no mention of any revised Service Life Limit? Has this also been reduced and if so, to what?

How exhaustive will overhauls of these gearboxes now be to guarantee them for the next TBO interval? Will each planet gear need to be radiographed or CT scanned for the smallest possible inclusion or micro-defect? Or would they only further examine a gear if it shows signs of spalling, since AH’s faith still appears to hang on that premise?

Who would meet the cost of these enhanced and more frequent inspections and the maintenance time necessary to remove the modules from the aircraft and refit them?

I am also curious as to AH’s ‘confidence’ in the effectiveness of the MCD devices fitted to their MGB system. Mandating inspections of the oil filter and all these MCDs at 10FH intervals seems to suggest that these elusive ‘spalling particles’ can miss MCDs at the epicyclic, at the MGB sump and at the oil cooler (I assume the filter is placed, logically, after the cooler?).

[vfr440]

Spot-on Concentric; a very cogent rationale. I agree totally (and am only an LAE with some limited exposure to TCH design & testing parameters) and they were in USA ~ VFR

[Concentric]

I heard from AH that it was being reduced to 1500 FH which is not as much of a reduction as you would suggest.
Thanks. My source for "less than half" was this: https://www.easa.europa.eu/newsroom-and-events/news/easa-lifts-temporary-flight-suspension-super-puma-helicopters

On re-reading it I now see it actually referred to Service Life, not TBO, so it answers one of my questions. Apologies for any confusion (mine).

So what was, and now is, the Service Life limit?
[Edit: According to previous posts (way back) the SLL used to be 5000 when the TBO was 2000. Without an absolute SLL figure available, we can reason that "less than half" will be <2500, but if the TBO has also been reduced to 1500 as Insider revealed, then for practical purposes since the planet gear cannot be replaced at <2500 without full stripdown of the module it will effectively have to be replaced at each and every TBO, therefore 1500. "Less than half" therefore becomes effectively 0.3, so the life of the component will now be less than one third of what it was. AIBN reported the gearbox on the crashed aircraft had 1340 FH since new, but that of course was with type A planet gears. We do not know how MUCH better the design or manufacture of type B planet gears is by comparison. All these additional inspection measures do not seem to suggest that the difference was all that much.]

Is flying hours the best measure of fatigue loading spectrum on a helicopter gearbox or would some additional parameter like say Torque Hours be more relevant, assuming instrumentation can log this (maybe HUMS already does?).

[Fareastdriver]

I can remember the period in the mid eighties when the logging if flight hours changed . Up to that point flying time for both crew and machine was logged from moving for the purpose of take off to shutting down the rotors. It was then changed to the crew logging it as before but only actual flight time being recorded for the aircraft. Concern was raised that all the running time, which could be quite extended in certain circumstances, was ignored despite concerns that there was a fair amount of stress and wear going on.

These objections were overridden for the obvious financial reasons.

On the fixed wing side engine running time is on the clock and various stages of power are recorded. The wings don't do a lot on the ground so taxiing and suchlike can be ignored. Are we right using the same criteria for helicopters?

[fagin's goat]

Fareastdriver: That is a very wise point and I think you really are onto something there.
Geoffers: as ever spot on about TBO and the 'growth of complexity' issues. I very much endorse your idea of swapping your 15 Kg of bumf for 15 Kg of metal in the MRGB!

[Sevarg]

Fareast, I seem to remember that the Times in the techlog remained start to rotor stop but the MSLS, which they oil companies were billed from, used TO to landing. Could well be wrong as memory isn't what it was.

[EESDL]

If your rotors are running then your engines are running - does not matter if your wheels are not moving.
EASA is quite clear on what must be recorded.
It matters not a jot what the customer wants recorded - that is for those who fudged the contract to decide.

[AAKEE]

For the TBO times and inspection intervalls it's the actual flight time that what is counts. At least in my job, and all the other flying i did.


EASA/JAR etc. 'flight time' is to regulate the time the crew puts in their logbooks.

[212man]

If your rotors are running then your engines are running - does not matter if your wheels are not moving.
EASA is quite clear on what must be recorded.
It matters not a jot what the customer wants recorded - that is for those who fudged the contract to decide.

Have you actually read a maintenance manual?

[Fareastdriver]

I don't know if it has changed but when I was flying offshore the computerised MSLS was filled in with the actual flying times so running time and deck time was not charged to the customer. This information went down to engineering and these times were inserted by the technical computer into the aircraft records. I never filled in tech log times apart from start to stop with two dashed lines in between.

On overseas operations without a computerised MSLS system where the customer was charged for everything the tech log times were taken from the weight on wheels readout of the HUMS.

On a boring day the times could be up to an hour apart.

[Geoffersincornwall]

In Brazil the customer is charged from first engine start to engines stopped. Regrettably I believe the biggest oil company has returned to the system of allocating a time limit for each flight. This fosters a 'hurry-up' and corner cutting V-NE attitude in the hope that penalties can be avoided.

G.

[msbbarratt]

What is going on with EASA?

.
.
.

This is not joined-up governance. Some people have suggested this is curiously advantageous timing for Airbus just before Helitech week. For all our sake's let's hope the EASA decision is based more on fact than political expediency.

I've been wondering about that. When it was decided that the ECC225 could fly with one inspection per flight, I found myself questioning the mathematical basis for such a position. No reliability calculation can ever be that accurate, there must be error bars on the graph. And the thing about errors in a calculation whose answer was 1 is that you have to allow for the physical reality being < 1. Which means that you're going at some point to have 1 less landing than take off. Oh, look.

Now to me the 1 inspection per flight directive suggested that someone somewhere too important to be questioned was not performing a reliability calculation. A calculation with that result is mathematically indefensible. Had they calculated it they would have realised that and recognised the future danger (and not just to crew and passengers, their own personal reputation and career future would be at stake) inherent in such an answer.

So was someone somewhere just, well, guessing? Going on a hunch? Folding to commercial pressures and hoping for the best?

If nothing else I hope we never see such a situation arising ever again.

[Pablo332]

If your rotors are running then your engines are running - does not matter if your wheels are not moving.
EASA is quite clear on what must be recorded.
It matters not a jot what the customer wants recorded - that is for those who fudged the contract to decide.

Could you provide more details please. As AH would appear to be in contravention of this requirement.

[oleary]

I recall we did a job one time that involved a 20 minute wait on one leg.

The bean counters decided it was better to just sit at ground idle rather than shut down and start up again.

A argument ensued about component time so we asked Sikorsky.

They said, "Running a 61 at ground idle or flat pitch full RPM generates no significant flight loads", so .... don't log it as component time.

[gulliBell]

I've never recorded engine operating time in the technical log. Clients get invoiced engine operating time, the boss pays for maintenance based on component (flight) time recorded in the technical log.

[Fareastdriver]

Running a 61 at ground idle or flat pitch full RPM generates no significant flight loads

I can go along with that. I think the concern comes when taxiing, especially in strong wind conditions and when on a helideck in near 60knot winds.

[maeroda]

I remember in CHC Global on AW139 the costumer was charged block time + time with wheels on platform.
Same CHC but in Netherlands, costumer was charged block time only.
Different family I work, different habits I find!

[EESDL]

Oops - comment made as a result of a recent employer's training department trying to tell me that off/on blocks was the time that went in my logbook.
It was not until I queried who do I put as 'Captain' in the incident report if I was sat on the deck in the machine and a bird flew into the rotors...........
It goes without saying that techlog times are different but you might be surprised what is asked not to be recorded.

[Camp Freddie]

Pilots log - rotor start to stop
Tech log - airborne time
Customers pay for what ever formula is agreed,
That's it isn't it 🤔

[Nescafe]

Pilots log - rotor start to stop
Tech log - airborne time
Customers pay for what ever formula is agreed,
That's it isn't it

Got it in one.

[jimf671]

Glad that's over. :E

[Concentric]

https://www.verticalmag.com/news/airbus-helicopters-sued-three-companies-h225-situation/#sthash.esg0Blh2.dpuf

link copied from other thread for discussion (for pablo332)

[Pablo332]

https://www.verticalmag.com/news/airbus-helicopters-sued-three-companies-h225-situation/#sthash.esg0Blh2.dpuf

link copied from other thread for discussion (for pablo332)
Thank you. For some reason I couldn’t find the thread in the 4 pages of Rotorhead threads. Now I can answer my own question.

[Pablo332]

Could anyone confirm the alleged bad -07 part number was manufactured by FAG and the alleged good -06 part number was manufactured by Timken?

[Non-Driver]

Could anyone confirm the alleged bad -07 part number was manufactured by FAG and the alleged good -06 part number was manufactured by Timken?

Given the litigation already starting, particularly with AH view of "defamation" I wouldn't advise anyone to answer that question TBH, only insiders at AH would be privy to that information and it wouldn't be wise to put one of them in a vulnerable position.

[Pablo332]

Does anyone know if it was a -06 part number that was the cause of the G-REDL accident?

[Concentric]

It is difficult to say (even for those who know, perhaps) if it was an -06 gear/bearing that failed in G-REDL. The people who should know that are the UK AAIB.

In their report 2-2011, (page 51 Section 1 – Factual Information), Figure 21 shows a photograph of the remaining 7 gears still attached to the 2nd stage carrier. A number of those gear/bearings can be seen in the photo to carry a particular manufacturer’s markings, though that on the inner race of the failed gear is less distinct but similar in position and spacing. In Figure 22 the AAIB showed a “complete undamaged gear for reference”. This can clearly be seen to carry the part number (7 o’clock position) ending 3335-06. The inner race does not appear to carry manufacturer’s markings, unlike those in the previous photo.

At the time this report was published that did not appear to be significant. However in the light of AH mandating the removal from service of all epicyclic modules containing one or more of specific planet gear/bearing part numbers (and return of those to AH for gear replacement), some searching questions need to be asked. Evidently one operator (currently involved in a law suit against AH) chose to hang on to some of those parts and conduct their own examinations.

So, if the failed gear was a type -06 and the reference gear clearly an -06, why would AH maintain the -06 as the only authorised part?

Or, if the failed gear was actually a type -07 (or an -02, -03, or -05 as detailed in EASB 63A030), was the AAIB aware in 2011 that there were differences in the parts and specifically as stated in the above EASB?

“-The detailed design of the planet gear bearing has an increased damage tolerance.
-Modeling and calculation reveal a lower load level on the external race of the planet gear bearing.
-In-service experience shows enhanced reliability”.

The report (1.16.2, page 60) states that “a detailed analysis, using advanced methods, was undertaken by the helicopter manufacturer to build a three-dimensional stress model of the component. A separate analysis tool was used for the Hertzian stresses”

Given the stated differences in damage tolerance and reliability in the EASB, which part number did the manufacturer model and analyse for the AAIB?

The REDL investigation had access to two planet gears from other L2 MGBs (why not EC225s with their higher loading?). These had been “previously sectioned” by the helicopter manufacturer (ref P62) but it does not state when. Which part number was that sectioned 2nd stage planet gear/bearing?

I do not expect anyone on here to answer those questions but I sincerely hope that the Norwegian AIBN and other involved agencies do seek those answers.

[NorthSeaTiger]

https://www.eveningexpress.co.uk/fp/news/local/north-sea-helicopter-crash-no-correlation-previous-accident-investigators-say/

[Concentric]

For busy people who don't read past headlines, the "previous accident" referred to was the road transportation accident, not the previous (or any similar) helicopter crash. To equate one with the other is sloppy journalism, as is the statement "The crash was the first fatal helicopter incident involving the offshore industry in 19 years." In the Norwegian sector, possibly.

[cyclic]

We don't do newspapers in the North East.

[GenuineHoverBug]

A very brief statement (https://www.aibn.no/Luftfart/Undersokelser/16-286) on their website yesterday goes something like:

... The investigation so far has shown that the accident was the result of a fatigue fracture in one of the eight second stage planet gears in the main gear box, a failure with clear similarities with the crash off the coast of Scotland in 2009 with G-REDL. The fatigue crack developed without this being captured by the existing required or supplementary warning systems.

The investiagation is complex and with a broad scope. So far, the metallurgical studies has had the major focus. That is efforts to map and understand how the fatigue crack initiated and developed. This work is not yet completed.

Currently, the main focus of the AIBN investigation is the certification of the main gearbox and the robustness of the previous and current design requirements. This includes follow-up of safety recommendations given by the AAIB in connection with the accident with G-REDL and an assessment of the continuous follow-up of the gear box reliability. This work requires a close collaboration with the responsible parties, primarily the helicopter manufacturer and EASA.

The scope and complexity of the investigation means that it is not yet possible to estimate a date for when the final report is completed. The investigation continues with the same high activity. The Aviation Authorities in Norway and Europe are continually updated about the investigation.

AIBN intends to publish a new preliminary report on the 29 April 2017, unless significant new discoveries necessitates a preliminary report earlier.

[SASless]

... The investigation so far has shown that the accident was the result of a fatigue fracture in one of the eight second stage planet gears in the main gear box, a failure with clear similarities with the crash off the coast of Scotland in 2009 with G-REDL. The fatigue crack developed without this being captured by the existing required or supplementary warning systems.

Where does that take us?

Shy of small enough bits breaking off the Gear is there anyway the existing detection and monitoring systems would ever work to prevent such a thing from leading to a Catastrophic failure?

[G0ULI]

The existing systems for monitoring gearbox degradation have demonstrably failed twice with fatal results. The environment in the North Sea is probably harsher than the designers appreciated, with more frequent shock loading of drivetrain components accelerating fatigue crack spreading once a chip or stress point has been formed.

Other areas where helicopters operate in harsh conditions seem to have more stable bad weather. Wind speeds may be higher, but they are more constant. Temperatures also tend to remain more stable over a period of weeks or months. The North Sea can be relatively temperate on day and below freezing the next. Similarly wind speeds are very variable ranging from dead calm to a full storm in a matter of a couple of hours with frequent gusts and squalls.

As usual the planetary gear components need to be hard to prevent wear while being ductile to absorb shock without fracturing. Selective heat treatment and surface hardening are the usual methods used to try and deliver both properties in ine component. A modern day version of damascus steel techniques from the middle ages used to manufacture swords that could cut without snapping when they hit armour. While x-ray, ultrasound and eddy current testing can give an indication that the components have been correctly manufactured, only destructive testing can provide absolute proof. So there is no way of providing an absolute guarantee that every component is flawless.

Chip monitoring and measurement of metallic waste contamination in the gearbox oil filters only works if conducted at frequent intervals and all the chips are actually collected. Even a single hardened metal chip can cause extremely rapid catastrophic destruction of a gearbox if it falls into the mesh between the planetary gears.

As it stands, this gearbox is operating too close to the technical limits of current metallurgy. Either the design needs to be radically changed or the operating limits downgraded, which would severely reduce the operation capabilities of the helicopter.

[Pablo332]

It just doesn’t make any sense the unbiased pen pushers of EASA have declared the aircraft safe.

Why does this meddlesome non-member (and one soon to be non-member of the EEC) insist on rocking the boat? Money is at stake, sales are not doing well.

Think of the common cause you safety first out landers.

[212man]

Very good points raised, Gouli

I'm afraid I disagree. Aircraft flying the North Sea normally sit overnight in hangars and are started up soon after being pulled out, so they're not cold soaked in low temperatures. Once started and at operating temperature, it's pretty irrelevant what the oat is. Wind? Explain to me how that can be considered a harsh environment - last time I checked there were rarely 155kt winds in that area, which is what the 225 spends most of its airborne time experiencing. Operating regime? What; flying in a straight line for two hours, hovering for a few seconds and landing? I think this is a better example of a harsh operating environment, with a much more diverse range of dynamic and structural flight loads:
https://m.youtube.com/watch?v=oGUbPdc5CI0

[Pablo332]

Where does that take us?

Shy of small enough bits breaking off the Gear is there anyway the existing detection and monitoring systems would ever work to prevent such a thing from leading to a Catastrophic failure?
Who knows AH are willing to give it a shot.

Don’t think of it as a flight, think of it as expanding the envelope of human knowledge, who could resist?

[SASless]

I found the first video to be a bit boring....but my Orang Tabby Cat, "JR Mewing" was intrigued and kept trying to catch the Rotor Blades flashing by at the top of the screen!

I would think the North Sea thing is being over blown beyond the Gearbox loading being fairly high but constant for long periods of time.

The stress on a Gearbox in Underslung work like Logging would be far greater in stresses I would imagine.

[cyclic]

The military don't fly their aircraft at MAUM and MCP everyday. Bear in mind that the 225 struggles into the air at 11t. AH don't have anyone who truly understands the oil and gas environment particularly the North Sea. Their luck ran out in 2009 and they are still struggling to understand why. They are still mystified why 2 national authorities are uncomfortable with the lack of a solid explanation. Let's remember in both fatal accidents they did everything they could to initially blame the operator. In fact, in 2012 they did the same and were reluctant to admit there was a problem with the MGB design until a different operator ditched a second aircraft. Sorry, a successful water landing according to AH. I think they make great helicopters but as a business when things go wrong, their arrogance is still outstanding. Perhaps it is cultural.

[occasional]

Wind? Explain to me how that can be considered a harsh environment - last time I checked there were rarely 155kt winds in that area,

I have a friend who sold windmills made and tested on the Bay of Biscay coast.
He tried selling them in the Scottish Islands and found that the windmill blades could not cope. Apparently the instantaneous stresses suffered by the blades were much higher in Scotland although the overall environment did not appear to be that different.

[Pablo332]

The military don't fly their aircraft at MAUM and MCP everyday. Bear in mind that the 225 struggles into the air at 11t. AH don't have anyone who truly understands the oil and gas environment particularly the North Sea. Their luck ran out in 2009 and they are still struggling to understand why. They are still mystified why 2 national authorities are uncomfortable with the lack of a solid explanation. Let's remember in both fatal accidents they did everything they could to initially blame the operator. In fact, in 2012 they did the same and were reluctant to admit there was a problem with the MGB design until a different operator ditched a second aircraft. Sorry, a successful water landing according to AH. I think they make great helicopters but as a business when things go wrong, their arrogance is still outstanding. Perhaps it is cultural.
Hear,hear.

[G0ULI]

With prevailing winds from the southwest, the North Sea is downwind of the UK. After passing over the UK, the wind is more turbulent than wind blowing in off unobstructed ocean. The effects of Welsh mountains can be seen in cloud patterns over Norfolk even though the mountains are hundreds of miles away and not particularly tall by global standards. That is why I make the point that air turbulence in the North Sea is different to that in many other areas.

[SASless]

During the Trials Programs for various HUMS systems and aircraft.....did any Air Tests take place with well instrumented Aircraft that might have yielded Test Data to support your proposition that rough air might be playing a role in unusual stresses upon Gearboxes?

[Nigerian Expat Outlaw]

Assuming that was the problem, how has "rough air" (is that a new term ?) on the North Sea been overcome historically ? It's not exactly a new phenomenon. Surely it was windy and turbulent when Wessex was flying offshore ?

NEO

[G0ULI]

I don't have any aircraft test data but there have been well documented cases of off shore wind turbines experiencing significantly higher wear and failure rates than the designers anticipated, especially gearbox failures. So there is a potential indication that North Sea air turbulence is greater than is commonly assumed. The latest wind turbines are built significantly stronger than the original designs.

[212man]

Maybe it was a particularly smooth and benign 7 years during which I flew on the N. Sea, but I don't recall any markedly rough conditions as a rule . Windy; yes, turbulent sectors on some 'rigs'; yes, but not during normal flight. Conversely, I've had MGB low oil pressure captions come on in the cruise in other arenas.....

I would politely suggest the 'rough air' theory is a non-starter.

[SASless]

Enroute offshore on the North Sea....perhaps I was just lucky but Turbulence was a non-issue....Icing and some other things were.

As to mechanical turbulence off some of the Platforms and Rigs when the Wind got up.....yes sure but as 212Man opined....other places I have flown have shown themselves to be far more violent and prevalent than the North Sea ever was.

[occasional]

I would politely suggest the 'rough air' theory is a non-starter.

You and SASless may well be illustrating the problem rather than rebutting the argument.

The windmill designers were presumably equally convinced that they had taken the conditions into account when completing their designs. It needed strain gauges on the windmills to convince them otherwise.

[SASless]

In case you missed it...five posts before yours....I asked if there were any Test Data from Flight Tests or Proving Tests that would support Gouli's suggestion that unstable air over the North Sea might be playing a role.

He said he knew of none.

We did not "rebut" his argument but offered a response each based upon first hand experience.

You might read back through the thread and see where several of us have questioned the design criteria the AH Gearbox uses and question if ALL of the possible stresses and loads have been considered adequately.

Instead of playing Don Quixote....what are your thoughts to Gearboxes on Helicopters in flight and exactly how rough air might affect them as compared to Windmills firmly attached to the surface?

[G0ULI]

In considering possible external factors for the gearbox failures I was making the assumption that the AH engineers had factored in all of the normal stresses and strains to be expected in flight.

There is a possible alternative which may not have been picked up by the monitoring programs.

Continuous vibration monitoring is great at picking up sudden changes in vibration levels. A sudden jump indicates that something in the rotating system has changed. Visual inspection is usually sufficient to identify the fault at that stage.

However constant vibration at a particular frequency that does not change over time is considered to be fine and a good sign that everything is functioning normally. This view may be totally wrong. Vibration at infrasound frequencies of 10-20Hz has been proved to cause embrittlement of metal and other substances.

Helicopters being a collection of vibrating rotary parts, a constant level of vibration at around 20Hz might be accepted as perfectly normal if it doesn't change over time. The vibration is however slowly degrading certain components. Rotors could delaminate, gearboxes fail, fastening bolts suddenly snap under load.

A rotor blade starting to delaminate should be detected very quickly. Failed fastenings should also be picked up during standard walkaround inspections. Internal gearbox components are hidden away and difficult to assess without a full strip down.

The point being that if infrasound is a factor there may well be no indication of impending failure until a gear tooth or something else actually snaps off.

Interestingly these sound frequencies frequently cause feelings of foreboding and discomfort in humans exposed to them.

[SASless]

Some of us must be exceedingly susceptible to that malady!:uhoh::oh:

I think I am one of them....many a time I have had those exact feelings over the Years. Sometimes while in helicopters too.

[birmingham]

The only thing that can really be taken from the AIBN statement is they haven't yet established why the fatigue occurred with a sufficient level of confidence to agree that the removal of one type of planet gear assembly and adding a more rigorous check regime, will be sufficient to restore safety margins. They remain out of step with the European Agency, the US and the manufacturer. The update merely tells us they will continue with their work. This is a tough one - no guarantees of prevention combined with no guarantees of detection - different payers with very different opinions about the degree of risk involved in returning the aircraft to service as is.

[riff_raff]

There is a possible alternative which may not have been picked up by the monitoring programs.....Continuous vibration monitoring is great at picking up sudden changes in vibration levels. A sudden jump indicates that something in the rotating system has changed....

The approach of using vibration monitoring to detect the condition of gears or rolling element bearings has been researched by the rotorcraft industry for many years. One thing that makes it difficult in practice is the extremely complex acoustic environment existing in the typical MRGB having dozens of gears and bearings.

Ferrous debris detection systems work well if engineered properly. So I think they will continue to be used for the foreseeable future.

[The Sultan]

Gouli

What you state is correct in most cases. However, the jump in vibe may occur with no meaningful time between jump an failure. Additionally, HUMS has always been basically worthless for planetaries. Early report from CAA showed it had a 70% chance of missing a problem or generating a false positive. Since then it has not improved.

Robust chip detection and crew alerts are the best bet to catch a planetary issue. If someone had taken the chips seriously REDL would not have happened.

The Sultan

[Concentric]

The only thing that can really be taken from the AIBN statement is they haven't yet established why the fatigue occurred with a sufficient level of confidence to agree that the removal of one type of planet gear assembly and adding a more rigorous check regime, will be sufficient to restore safety margins. They remain out of step with the European Agency, the US and the manufacturer. The update merely tells us they will continue with their work. This is a tough one - no guarantees of prevention combined with no guarantees of detection - different payers with very different opinions about the degree of risk involved in returning the aircraft to service as is.
I think we can draw a few other things from the latest AIBN statement (https://www.aibn.no/Aviation/Investigations/16-286), not the least of which is that there will be a further preliminary report issued on 29th April, the anniversary of this tragedy. Respect.

[G0ULI]

I have been following developments in vibration monitoring for thirty years. Works great in large static machine installations, not quite so well in complex highly mobile vehicles that are subject to constantly changing external conditions.

Hindsight being a wonderful thing, I can easily envisage that certain signs were picked up in advance of the failure but not recognised for what they were because they appeared "normal", or were buried in the noise.

I am still also of the opinion that there is something different about North Sea operations compared to other areas. Whether it is weather conditions or long passages with relatively constant power settings followed by high energy manouvers to land, or some other factor, I don't have any evidence to say.

Living only a mile south of Norwich International Airport I do get to see an awful lot of helicopter movements every day. Fascinating machines, but you wouldn't get me up in one!

[birmingham]

I think we can draw a few other things from the latest AIBN statement, not the least of which is that there will be a further preliminary report issued on 29th April, the anniversary of this tragedy. Respect.
Agreed, but with the anniversary of the event approaching, it is clear they only understand "what" happened. Without a definitive answer to "why" they will be unable to provide recommendations which if implemented would make for safe travel. To still be at this stage more than nine months on is rare in my experience. Usually if the exact reason for failure cannot be found and there are no other occurrences in other units tested, investigators with follow EADS and AH's line of return to service then monitor closely. Here, because we have had two fatal incidents and they have low confidence in current advance detection methods they have held back. They say that their main investigative tool is the metallurgy and this is ongoing. Ironically part of the problem seems to be the low rate of occurrences. In all the millions of cycles as far as we know this has only happened twice. This means that the bearings are inherently very reliable. The problem, of course, is that on the two occasions when they are known to have failed it resulted in such tragic accidents.

[industry insider]

Gouli

I am still also of the opinion that there is something different about North Sea operations compared to other areas. Whether it is weather conditions or long passages with relatively constant power settings followed by high energy manouvers to land, or some other factor, I don't have any evidence to say.

With 30+ years flying and operating helicopters in most parts of the oil and gas world, I disagree with you. When distance is taken into account, long range operations have basically the same flight profiles and short range have basically the same flight profiles (and HUMS readings) worldwide.

I am sure that you know that the helicopter operations on your "doorstep" is short range different, and lots of landings and take offs. Arguably, that should be the most stressful in terms of cycles and torque applications.

[G0ULI]

Industry insider

Thanks for the comments, that is the sort of practical feedback that I was interested in. :ok:

[Concentric]

Agreed, but with the anniversary of the event approaching, it is clear they only understand "what" happened. Without a definitive answer to "why" they will be unable to provide recommendations which if implemented would make for safe travel. To still be at this stage more than nine months on is rare in my experience.
If you recall, REDL happened on 1 April 2009 but the official report 2-2011 was not published until 24 November 2011, some 32 months later. That report left several loose ends. I believe the Norwegians intend to complete that unfinished business.

[ericferret]

The crash report for LN-OPG took over 4 years and I suspect that while that accident was as tragic the investigation was not as complex. Could be a long wait.

[Hilife]

I am still also of the opinion that there is something different about North Sea operations compared to other areas.

As I recall, most of the S-92 MGB housing foot cracking (severing & radial) occurrences some six or seven years back, were happening in the North Sea sector and when the OEM dug a little deeper to understand why this was, it was noted that crews were routinely pulling more Tq than in the GoM or Far East.

If my memory serves me well, in addition to Phase II/III housing replacements, the OEM also sent out AS/Tq recommendations to the operators.

More Tq = more fatigue/stress.

[birmingham]

If you recall, REDL happened on 1 April 2009 but the official report 2-2011 was not published until 24 November 2011, some 32 months later. That report left several loose ends. I believe the Norwegians intend to complete that unfinished business.
I suspect so too! With REDL the type was cleared for flight well ahead of the final report though

[jimf671]

North Sea ops are in a 'hostile environment' (regulators' definition, not mine) and is in an area where the level of existing aviation infrastructure is very high, there is a large pool of aircrew, and highly developed industrial and transport infrastructure.

Does this mean that there is a mix of challenging conditions and competition that does not occur anywhere else?

[SASless]

I suppose flying off Newfoundland has similar conditions if you think about it.

Remember back when the Helicopter Services S-61's had their Blade Spindle problems and Bristow did not and it was found there was a difference in the way the two Company's Procedures differed that played a role in those losses?

[jimf671]

Newfoundland certainly joins Scotland and three or four other places as having the greatest wind and waves 'resources' in the world. In terms of population and major human infrastructure, maybe a bit like a bigger version of the NW Highlands and a bit more out there than the North Sea. I wonder whether the North Sea's proximity to major highly developed human infrastructure allows a pace of operation that has some effect on the aircraft that we haven't yet seen measured.

[tistisnot]

Would Global companies not have noticed the disparity in total annual hours per airframe throughout their regions if the pace of ops was so different?

[EESDL]

Insider - after the first rotorhead departed, Eurocopter made quite a deliberate point that it was only in NS that MC Tq/power was used for such extended periods of time - I appreciate it should not matter how long the 'period' under MC was in usual certification processes - but history now seems to indicate that MC might not mean MC when it comes to an overstretched MRGB design??
The 'slick' presentations had a summary of user hours/SOP power settings mapped out for all to see (I suggest to show potential buyers that the risk was restricted to NS practice of using the aircraft limits).

[cteneto139]

Good Morning Dear Friends,

Greetings from Brazil! Following since the very beggining the 225 Crash case, few days ago I was asked about how many companies/countries are, currently, using 225 in civilian/off shore services. Then, I am seeking for answers. Would you mind to inform me? (off course, I already did a search in Google, etc. and did not find anything regarding that.)
Thank you in advance for your attention.

Best regards,

[gnow]

The only operator that I know still using the L2 and Ec225 is in Vietnam Helicopters operating off from Vung Tau. In Malaysia our clients are still not using the machine.

[cteneto139]

Thnk u!!!!

[Pablo332]

The only operator that I know still using the L2 and Ec225 is in Vietnam Helicopters operating off from Vung Tau. In Malaysia our clients are still not using the machine.
This obviously can’t be true as my local AH representative assures me the only people not flying are UK and Norway, is this not the case?

[212man]

No, has he heard of Malaysia and Australia?

[Nigerian Expat Outlaw]

And Africa !

NEO

[SASless]

How many hours did the two gearboxes have that failed?

How much of a margin would be appropriate to guarantee safety?



Rumour is that the UK CAA will lift the grounding within a couple of weeks, maybe for a further trade off in MGB TBO hours.

[birmingham]

How many hours did the two gearboxes have that failed?

How much of a margin would be appropriate to guarantee safety?
I'm assuming that as per AH/European/US conditions they will only be using the type of epicyclic that hasn't resulted in catastrophic failures. If so it will be interesting to see if any decision to allow a return is based on a better understanding of the bearing failure on the crash aircraft than was previously reported. Realistically not a lot will change anytime soon as few UK aircraft are likely to return to service in the short term.

[Concentric]

How many hours did the two gearboxes have that failed?

How much of a margin would be appropriate to guarantee safety?
G-REDL's MGB had accumulated 4467 hrs since new and the planet gears had accumulated 3623 hrs since new. Together they had accumulated 2354 hrs since last overhaul.

LN-OJF's MGB had accumulated 1080 hrs before it was installed in that aircraft and 1340 hrs total since new at the time of the accident.

Setting a safety margin based on such a small sample of data and considering differences in maximum loading between L2 and H225 variants would be extremely difficult, in my opinion, not to mention differences in flight profiles. Maybe HUMS data could give a little insight into the latter variations.

[The Sultan]

OJF's xmsn reportedly had been dropped which invalidates total time as useful measure.

[Democritus]

According to the BBC Scotland News website today, the European Aviation Safety Authority (Easa) has asked operators of EC225 and L2 aircraft to carry out one-off inspections of the gearbox.

Further helicopter checks ordered after Norway crash - BBC News (http://www.bbc.co.uk/news/uk-scotland-north-east-orkney-shetland-39106837)

[212man]

One-time inspection and flush of the oil cooler for MGBs with more than 300 hours.

[birmingham]

One-time inspection and flush of the oil cooler for MGBs with more than 300 hours.
any ideas what they are trying to establish? I would think there are very few if any still operating in Europe

[KiwiNedNZ]

"The crash report for LN-OPG took over 4 years and I suspect that while that accident was as tragic the investigation was not as complex. Could be a long wait."

Question for those familiar with accident investigation - why does it take four years for a report to be issued - what actually goes into its compilation that takes so long.

[G0ULI]

There is an initial investigation at the site and examination of wreckage a while later to attempt to establish the cause. Various components are sent for metallurgical testing, electronics are examined for saved data, flight data recorders are downloaded and interpreted.

Where component failure is identified it may be subjected to further independent testing because in many cases involving scientific investigation the results are subject to interpretation by experts. Different experts may arrive at different conclusions despite being presented with essentially the same findings.

Then there is a need to determine whether any human factors are involved in maintenance or operation of the equipment.

Were there any other administrative failings that led to improper maintenance or other failings.

In every case where a problem is identified, individuals and organisations are offered the opportunity to respond and challenge or justify the findings. This may involve legal procedings through civil courts which are notoriously long winded affairs.

A final draft of the report is prepared and sent to all parties concerned for any final comments or challenges before publication.

A complex investigation being completed and a final report published can easily take four years, especially if several parties are extremely interested in avoiding any blame for an incident.

Although the civil investigation can take a long time, any criminal charges arising will generally take even longer, as that investigation is generally not allowed to proceed until the civil process has been exhausted.

Obviously the reason for all accident investigations is to improve safety and to prevent a recurrance. It is perfectly possible to issue orders grounding aircraft for urgent rectification work to be carried out well before any formal report is issued if the problem identified is serious enough.

[Concentric]

any ideas what they are trying to establish? I would think there are very few if any still operating in Europe
So, what if they find such particles? – Conclude that the Type B gear/bearing spalls at or before 300 FH? That wouldn’t be good, would it?

Or, what if they don’t find any? – Eureka!? Or maybe ‘Hey Presto’? The Type B’s are safe??? Try again at 600 FH, 900 FH etc…?

For the 300 FH to have significant meaning the cooler would have to have been flushed when the MGB/epicyclic module/2nd stage planet gears were installed. Is that normal procedure? If not, I don’t think the specific FH would be the important factor here. How about flushing the MGB casing too?

In exchanging all Type A planet gears for Type B’s last year, AH must have accumulated a large sample of used Type A's for metallurgical inspection. Perhaps the answer is that this latest measure is to now, selectively, acquire a sample of Type B’s that have begun to spall and put them under the microscope too.

[Pittsextra]

So, what if they find such particles? – Conclude that the Type B gear/bearing spalls at or before 300 FH? That wouldn’t be good, would it?

Or, what if they don’t find any? – Eureka!? Or maybe ‘Hey Presto’? The Type B’s are safe??? Try again at 600 FH, 900 FH etc…?

Sounds logical. Did we get to the bottom of the process that identified a batch of drive shafts in a previous event?

[Impress to inflate]

EVEN if all the authorities grant permission for the 225 to fly under their OAC's, who's to say the oil workers and their unions will allow them to board the machine. I know it's a "tainted" machine in their eyes, they have no trust in it.

You can be rotors running about to pick up a load of Pax but if they have been told NOT to board then you can't force them, this is something AH along with the agencies don't get. Look back at the BV234, sat in hangers in ABZ and ENZV

[S92PAX]

I think you have hit the nail on the head there Impress.
I used to accept the risks of travelling to and working offshore. However the events of the last few years have given me the impression that to the Puma/225 manufacturers are more concerned with profits than the lives that their machines are entrusted with.
I think I might have reluctantly got back into a 225, but my family are adamant that I don't. I respect their decision and have spent the last year retraining in case I need to change jobs. Nearly everyone I know offshore feels the same, it is about time AH realised this and moved on. The 225 is dead and finished. (Hopefully)

[jimf671]

... the Puma/225 manufacturers are more concerned with profits than the lives that their machines are entrusted with. ...

Unlikely, since the H225 is still the safest helicopter in its class of all time. That sort of record does not usually happen by chance. All of the alternatives either have worse accident records or are so new that we have no idea what the future holds.

[HeliComparator]

I think you have hit the nail on the head there Impress.
I used to accept the risks of travelling to and working offshore. However the events of the last few years have given me the impression that to the Puma/225 manufacturers are more concerned with profits than the lives that their machines are entrusted with.
I think I might have reluctantly got back into a 225, but my family are adamant that I don't. I respect their decision and have spent the last year retraining in case I need to change jobs. Nearly everyone I know offshore feels the same, it is about time AH realised this and moved on. The 225 is dead and finished. (Hopefully)
I understand that these things aren't based on rationality, but I wonder if your family has considered that the S92 has had one fatal accident, and the EC225 has had one fatal accident, and it is therefore completely illogical to have a fear of one type and not the other. My feeling is that they are victims of the hysteria and hype that apply to accidents "in our back yard" vs the disinterest in accidents that happen far far away.

[S92PAX]

I know it may be slightly irrational but it is definitely not hysteria.
The complete lack of confidence comes from the multiple failures of the same components. I accept we don't live in an ideal world but I would have hoped that any failure would be learned from and reliability improved. AH appears to want to get them in the air with a sticking plaster on as soon as possible. I base this on the shaft problems, how many times where we assured it was fixed, and the mgb catastrophic failure occuring twice? What has changed to make this once reliable and trusted aircraft so bad?
You also have to realise that it is unacceptably cramped for 19 people. It may be ok in the front seats but when you cant walk after two hours because there is absolutely no room to move in some of the seats you start to look for reasons not to fly in them. This is a really serious problem that the operators are unwilling to address.

[Concentric]

HC,

Would you care to explain your own rationality in separating the EC225 from the rest of the Super Puma AS332 family, even though Airbus Helicopter groups them together as variants in their sales material? Also, would you care to list the variants that use the same epicyclic transmission module as the 225 and, specifically, that used 2nd stage planet gears with Part No’s. 332A32-3335-00 and -02 to -07 inclusive? Would you care to explain why AS332L2 variants are currently grounded in Norway and UK?


jimf671,

Would you care to share your statistical analysis, also with definitions of ‘safe’, ‘safest’ etc.? e.g. Fatal accident, potentially fatal accident etc.

S92PAX’s comment referred to the manufacturer of the product, not the product itself or any nit-picking derivative/variant/colour of it. The behaviour of AH following the Bergen crash supports his assertion, would you not agree? Or do you actually believe somebody forgot to put a pin in a suspension bar?

[HeliComparator]

HC,

Would you care to explain your own rationality in separating the EC225 from the rest of the Super Puma AS332 family, even though Airbus Helicopter groups them together as variants in their sales material? Also, would you care to list the variants that use the same epicyclic transmission module as the 225 and, specifically, that used 2nd stage planet gears with Part No’s. 332A32-3335-00 and -02 to -07 inclusive? Would you care to explain why AS332L2 variants are currently grounded in Norway and UK?


jimf671,

Would you care to share your statistical analysis, also with definitions of ‘safe’, ‘safest’ etc.? e.g. Fatal accident, potentially fatal accident etc.

S92PAX’s comment referred to the manufacturer of the product, not the product itself or any nit-picking derivative/variant/colour of it. The behaviour of AH following the Bergen crash supports his assertion, would you not agree? Or do you actually believe somebody forgot to put a pin in a suspension bar?



The poster I was replying to, said his family wouldn't let him fly in a 225, the L2 wasn't mentioned. I was merely replying in that context. There is an awful lot that is different between the 225 and other Super Puma variants but of course the epicyclic is shared with some other variants as you suggest.

It boils down to, if say we went back to flying the EC225 on the N Sea in equal shares with the S92, 175 and 189, whether the next fatal accident would certainly be on an EC225 due to an epicyclic issue. I suggest it almost certainly wouldn't be. More likely it will be pilot error (S92 - its had plenty of near misses) or as yet unknown design flaw (175 and 189).

But that of course is a logical, rational, evidence-based argument. Decisions made in the modern way, ie by ignorance, scaremongering and Facebook, are likely to reach a different conclusion.

[etudiant]

The poster I was replying to, said his family wouldn't let him fly in a 225, the L2 wasn't mentioned. I was merely replying in that context. There is an awful lot that is different between the 225 and other Super Puma variants but of course the epicyclic is shared with some other variants as you suggest.

It boils down to, if say we went back to flying the EC225 on the N Sea in equal shares with the S92, 175 and 189, whether the next fatal accident would certainly be on an EC225 due to an epicyclic issue. I suggest it almost certainly wouldn't be. More likely it will be pilot error (S92 - its had plenty of near misses) or as yet unknown design flaw (175 and 189).

But that of course is a logical, rational, evidence-based argument. Decisions made in the modern way, ie by ignorance, scaremongering and Facebook, are likely to reach a different conclusion.
What is the evidence based argument here?
Is it fatal accidents/flight hour in the North Sea theater?
Is it not equally evidence based to argue that the 225 has had 2 very unusual failures which remain unresolved, versus none such for the other 3 contenders?

In fixed wing aviation, aircraft that lose a lifting surface get grounded until the cause is resolved. The same logic should apply to rotary wing products.

[HeliComparator]

The evidence base is the fatal accidents and flights hours - not particularly in the N Sea. You say the 225 has had 2 very unusual failures - which two are you referring to? There has only been one fatal accident. The S92 has had a fatal accident, only "resolved" by ensuring the pilots are fully aware of the aircraft's failure to meet its certification requirements. The other 2 contenders are pretty new on the scene and not yet proven. If your contention is that a brand new helicopter fresh from certification is bound to be safe since it has had zero accidents (and zero hours) then both I and history disagree with you. Has there ever been such a helicopter?


I am not suggesting that the EC225 should return to service until after the NAAIB report is published and any required corrective action taken. What I think is foolish is to say that "I'll never fly a 225 again, regardless of anything" whilst also saying "Oooh look, a shiny new 175 / 189 (etc) - can't wait to spend hours in one of those!"
The whole idea that a brand new type is by definition totally safe, is incredibly naive.

[nowherespecial]

But HC, you forget that people only care about the global safety record of an aircraft if the global safety record refers only to accidents/ incidents in the North Sea in a time period determined by self interest! :)

Keep you balanced and logical argument to yourself, some sense might break out otherwise...

(tongue in cheek if that hasn't come across in text)

[jimf671]

No great complexity. The number of accidents and number of fatalities is pretty basic.

As stated by others, some of that is not in the North Sea so can be filed under "Don't f3ckin want to think about it."

[SASless]

Unlikely, since the H225 is still the safest helicopter in its class of all time.


I suppose I might just be getting senile.....but could you prove that Statement of Fact by providing comparative Statistics that underlie your assertion of that?

[jimf671]

THE HISTORY?
Most long-established helicopter types in this class have been involved in hundreds of incidents involving hundreds of fatalities. One type had 33 known accidents, 16 fatal accidents, 116 fatalities in 2016 alone but operates in many territories where reporting is less than thorough. I couldn't count total fatalities because I kept losing count around 2700. Even the much-loved S-61 (incl SK) has been involved in over 400 fatalities and in spite of a much reduced fleet size, accidents, including fatalities, were still happening in 2016.

NEW ERA?
As stated above, we're really looking at S-92, H225, H175 and AW189. Helicomparator has made plain his view on new types and I agree with his position.

For the S-92 (13 years service), I can find 18 accidents (9 of which were in the North Sea), 2 of which involved fatalities, and 18 fatalities, 1 of which was military/paramilitary not involving enemy action.

For the H225/725 (13 years service), I can find 9 accidents, 3 of which involved fatalities, and 21 fatalities. Of the fatalities, 1 was military/paramilitary in training not involving enemy action and 7 were military/paramilitary resulting from enemy action.

H225
The H225/725 therefore appears to have a low number of accidents for an aircraft that has been in both civilian and military service for a substantial period including considerable intense public transport activity, SAR, and military/paramilitary use during warlike operations. It had been in service for 10 years before a fatality occurred and in service for 12 years before a fatality occurred during public transport operations. In comparison to the nearest comparable modern type, its history of stability on floats, means of escape, control of noise and vibration, and gearbox run-dry characteristics are superior. Fatalities in public transport operations are fewer but only through the chance number of POB at the time.

[gasax]

Those numbers do not look very robust. Fatalities are something of the 'luck of the draw' in that the number of occupied seats varies considerably - both up to a maximum of 21 (inc aircrew).

More importantly airframe safety is generally measured in fleet hours. In 60 seconds googling I find the S-92 fleet has approximately 1,000,000hrs (not sure about the military / civil split) and the last quoted 225 fleet hours were around 350,000 which tends to turn those 'statistics' on their heads.

It is however very noticeable that none of the official assessments actually split accident rates into types - a fundamental failing given the topic of this discussion!

FWIW the earlier 332 type have circa 4.3 million hrs.

[bigglesbutler]

last quoted 225 fleet hours were around 350,000

Sorry don't believe that is correct.

Si

[212man]

Indeed - from the Airbus H225 portal:


Did You Know?
H225/H225M operators: more than 35
Operating countries: 25
Total number of H225/H225Ms delivered: nearly 270
Total in-service H225/H225M helicopters: approximately 260
2015 H225/H225M flight hours: 111,900
Total H225/H225M cumulated flight hours: 546,100

[Twist & Shout]

For me, as an ex EC225 pilot, the number of accidents, flight hours, and fatalities are just statistics. Of mild interest, and of low trustworthiness.

The thing that makes me not want to get into an L2 or EC225 is the fact that they have had several similar failures that have never been adequately explained. Failures that result in certain death for all on board. Failures the manufacturer has proven a willingness to lie about.

I'd fly in a Comet if it had upgraded oval windows. I'd love to fly in a Concord. I'd even fly an experimental helicopter.

IMHO, flying an L2/EC225 is playing Russian Roulete. Statistics could probably indicate approximately how many chambers are empty. History has proven at least one is loaded.

[gasax]

Thaks for the update 212. So S-92 circa 1,000,000 hrs, H225 546,100 hrs - that is at least something to base the numbers on! And makes them look pretty similar......

[TylerMonkey]

I have not flown yet on the S-92 , but I have flown to oil rigs on the Puma series a few times. Some comments here equate one fatal accident each on the 92 and the 225 as being a reason not to fear one machine over the other. As SLF I would not take any comfort in those statistics if I had a choice of which machine to board. One 92 broke 2 filter studs and still presumably had time to ditch in control ( hindsight is always 20/20 unfortunately) , but the 225 ( and G-REDL before it ) both suffered instant and unrecoverable failures that will remain etched in the public's memory. I would never belittle a worker or crew who refuses to fly the Puma series just because someone feels they don't really understand the flight hours and statistics vrs other types.

[Aluminium Mallard]

Comparing accident statistics for different machines is pointless.

The one that that should never ever be allowed to happen is the main rotor head departs during flight!

I would expect if an airliners wings fell off in strait and level flight and then it was "fixed" only to happen again a short time later that type would never fly again.

The gearbox should be able to fail without losing the rotor head. I would rather see this on a specification sheet than all the run-dry toss.

[HeliComparator]

I would never belittle a worker or crew who refuses to fly the Puma series just because someone feels they don't really understand the flight hours and statistics vrs other types.

I would. If they decide that the risks of offshore flying are too great for them, then fair enough, their choice. But if they decide they don't want to fly a specific type just because it is the most recent one to have an accident, but are quite happy to fly one that crashed a few years ago and/or far far away, then they are irrational and foolish and I have no problem telling them so. In fact it's my duty to. If we allow irrational and foolish decisions to go unchallenged then we are setting the human race up to fail.

[Evil Twin]

If we allow irrational and foolish decisions to go unchallenged then we are setting the human race up to fail.

Unfortunately, I think we've been doing that for an awfully long time and are paying the price, aviation is not an island in that case.... Back to the thread. Excuse my flippant comment.

[Mel Effluent]

[QUOTE]I would expect if an airliners wings fell off in strait and level flight and then it was "fixed" only to happen again a short time later that type would never fly again./QUOTE]

+1

[Fareastdriver]

But if they decide they don't want to fly a specific type just because it is the most recent one to have an accident,

But the S92 in Newfoundland didn't have an accident. It crashed because the emergency drills weren't followed.

[ericferret]

The rosy view of the fixed wing world is at variance with the facts.

https://en.wikipedia.org/wiki/Boeing_737_rudder_issues

"This was only the fourth time in the NTSB's history that it had closed an investigation and published a final aircraft accident report where the probable cause was undetermined."

I bet just about everybody has flown on one of these aircraft without knowing that there was a potential problem. Millions of passengers flown in aircraft with a potential fatal flaw.

What did any of the European safety agencies do?
Not much, far too much money at stake.
The operators were given years to modify the aircraft and it was clear that some of them would be time expired before they were modified.

[TylerMonkey]

But the S92 in Newfoundland didn't have an accident. It crashed because the emergency drills weren't followed.

+1 . . . . . . . .

[Hilife]

Jim, I don’t know if you were bullied at school by a Sikorsky employee, but you clearly don’t like the S-92, but to comment on your post #1708 (and I stand to be corrected if wrong), I would contest your findings regarding fatal and non-fatal S-92 accidents.

No I don’t work for Sikorsky, but to be fair to all sides in the debate on platform safety by type, other than Cougar 91, I am not aware of another S-92 accident resulting in fatalities, so I suspect you are referring to the Saudi Civil Defence incident in which a civil defence officer fell out the door from around 700 feet during an air show display in Riyadh.

This incident had absolutely nothing to do with the S-92’s design or airworthiness, and unfortunate as it was for this individual who died from his injuries, it cannot be classified as an S-92 accident as you suggest, so to include this incident in your stats, is as meaningful as also attributing blame to Sir Isaac Newton.

Going back to the Cougar 91 accident and noting HeliComparator’s comment, "The S92 has had a fatal accident, only "resolved" by ensuring the pilots are fully aware of the aircraft's failure to meet its certification requirements" comment (if it didn’t HC, it would not have an FAA and EASA Airworthiness Certificate).

Evidently there is more heat than light regarding this accident, as the CVR transcript reveals clearly that post the MGB oil pressure warning light illumination observed by the pilots, and having followed the Emergency Procedures check list, the co-pilot declared that they were in a "Land Immediately Situation", to which the captain agreed, but indicated his intention to stop the descent at 1000 feet, at which point the co-pilot acknowledged the pilots decision, but again repeated that they were in a "Land Immediately Situation", AND, that the Emergency Checklist was complete.

The captain levelled out at 800 feet, but did not respond to the co-pilots second declaration that they were in a "Land Immediately Situation". Tragically 11 minutes after the initial warning of indications of a MGB oil problem, 17 occupants drowned due to the very high rate of descent/impact with the water.

Looking back at the West Franklin Platform accident/incident in December and to quote a CHC statement: "We can confirm that one of S92s operating from Aberdeen experienced unexpected control responses during the final stages of a landing at an offshore platform.

The crew responded immediately in accordance with their training and the aircraft was successfully landed and shut down; there were no reported injuries amongst the passengers or the crew".

Reading the AAIB interim report suggests to me that in spite of the uncommanded high rate of turn (up to 30 degrees per second) at just 4 foot above the helideck during final approach, with the helicopter at one point pirouetting around the left-hand MLG, the crew were able to maintain enough control to land the S-92 safely with no rollover or injuries to crew and passengers, so to me it suggests a more inherently stable platform far less prone to rollover than say other models, so a positive safety point.

I would also point out that although the investigation is ongoing, the aircraft's HUMS system worked as per design and identified a problem with the tail rotor system some 4.5 hours before the accident, this being that the Tail Gearbox Bearing Energy Analysis limit had been exceeded and that this data was downloaded the previous day.

Coming back to your stats. An accident can be defined as an unintended event resulting in damage or harm. I’m not so sure the failure of a vespel spline adapter or oil pump should be defined as an "Accident", as such I would suggest most of the 18 accidents you refer to were really just engineering/crew/operational incidents.

As for S-92 flight-hours, this time last year the S-92 fleet exceeded one million flight hours, and with some 275 aircraft flying worldwide and with the 332L2/H225’s grounded in the North Sea, I’d suggest current totals are likely to be between 1.1 to 1.2 million flight hours for the S-92, so that’s twice the 225 hours, and some.

Again getting back to safety of a specific airframe model and to quote a Sikorsky press release this time last year, "Along with accomplishing this (one million flight hours) in an impressively short time of less than 12 years, the S-92 helicopter also asserts a best-in-class safety record with an accident rate of 0.20, which is 1/10th the U.S. Civil Multi-Turbine engine helicopter rate".

There you have it Jim, "Best-in-Class".

I’d have to say HeliComparator, I take heart at your strong defence of the 225 and although grandfathered up the yin-yang (which in itself is not such a bad thing), yes in general it is an excellent performing platform and so too are Eurocopter (never going to get used to AH), who make some iconic helicopters.

However, looking back at the numerous MGB incidents in the North Sea, two of which have been un-survivable due to catastrophic failure of the MGB (unlike the Cougar 91 accident, in that there was no time for the crew to manage the situation) and also the two incidents of incorrect system operation/indication of the emergency water glycol system, which resulted in the crew ditching the helicopters (this in itself may well have been a blessing in disguise for all those on-board, as would you want to be flying for 30-minutes post loss of oil pressure knowing that the oil pump drive shaft had separated and was rattling around the gearbox sump), the uprated 332L2 and 225 MGB’s clearly have design issues that I suspect will not be addressed by senior management (another problematic area) and engineers to the satisfaction of the passengers in the back.

[RVDT]

Hilife,

When did you last read FAR Part 29?

Specifically 29.927 Additional tests. (c) Lubrication system failure.

As the aircraft does not meet "extremely remote" i.e. 10-7 per AC 25-1309 as proven it is required to comply with the second
part of the paragraph which it also does not to this day.

The certification requirement overrules any BS that you put in the RFM.

[Mee3]

Jim, I don’t know if you were bullied at school by a Sikorsky employee, but you clearly don’t like the S-92, but to comment on your post #1708 (and I stand to be corrected if wrong), I would contest your findings regarding fatal and non-fatal S-92 accidents.

No I don’t work for Sikorsky, but to be fair to all sides in the debate on platform safety by type, other than Cougar 91, I am not aware of another S-92 accident resulting in fatalities, so I suspect you are referring to the Saudi Civil Defence incident in which a civil defence officer fell out the door from around 700 feet during an air show display in Riyadh.

This incident had absolutely nothing to do with the S-92’s design or airworthiness, and unfortunate as it was for this individual who died from his injuries, it cannot be classified as an S-92 accident as you suggest, so to include this incident in your stats, is as meaningful as also attributing blame to Sir Isaac Newton.

Going back to the Cougar 91 accident and noting HeliComparator’s comment, &quot;The S92 has had a fatal accident, only &quot;resolved&quot; by ensuring the pilots are fully aware of comment (if it didn’t HC, it would not have an FAA and EASA Airworthiness Certificate).

Evidently there is more heat than light regarding this accident, as the CVR transcript reveals clearly that post the MGB oil pressure warning light illumination observed by the pilots, and having followed the Emergency Procedures check list, the co-pilot declared that they were in a &quot;Land Immediately Situation&quot;, to which the captain agreed, but indicated his intention to stop the descent at 1000 feet, at which point the co-pilot acknowledged the pilots decision, but again repeated that they were in a &quot;Land Immediately Situation&quot;, AND, that the Emergency Checklist was complete.

The captain levelled out at 800 feet, but did not respond to the co-pilots second declaration that they were in a &quot;Land Immediately Situation&quot;. Tragically 11 minutes after the initial warning of indications of a MGB oil problem, 17 occupants drowned due to the very high rate of descent/impact with the water.

Looking back at the West Franklin Platform accident/incident in December and to quote a CHC statement: &quot;We can confirm that one of S92s operating from Aberdeen experienced unexpected control responses during the final stages of a landing at an offshore platform.

The crew responded immediately in accordance with their training and the aircraft was successfully landed and shut down; there were no reported injuries amongst the passengers or the crew&quot;.

Reading the AAIB interim report suggests to me that in spite of the uncommanded high rate of turn (up to 30 degrees per second) at just 4 foot above the helideck during final approach, with the helicopter at one point pirouetting around the left-hand MLG, the crew were able to maintain enough control to land the S-92 safely with no rollover or injuries to crew and passengers, so to me it suggests a more inherently stable platform far less prone to rollover than say other models, so a positive safety point.

I would also point out that although the investigation is ongoing, the aircraft's HUMS system worked as per design and identified a problem with the tail rotor system some 4.5 hours before the accident, this being that the Tail Gearbox Bearing Energy Analysis limit had been exceeded and that this data was downloaded the previous day.

Coming back to your stats. An accident can be defined as an unintended event resulting in damage or harm. I’m not so sure the failure of a vespel spline adapter or oil pump should be defined as an &quot;Accident&quot;, as such I would suggest most of the 18 accidents you refer to were really just engineering/crew/operational incidents.

As for S-92 flight-hours, this time last year the S-92 fleet exceeded one million flight hours, and with some 275 aircraft flying worldwide and with the 332L2/H225’s grounded in the North Sea, I’d suggest current totals are likely to be between 1.1 to 1.2 million flight hours for the S-92, so that’s twice the 225 hours, and some.

Again getting back to safety of a specific airframe model and to quote a Sikorsky press release this time last year, &quot;Along with accomplishing this (one million flight hours) in an impressively short time of less than 12 years, the S-92 helicopter also asserts a best-in-class safety record with an accident rate of 0.20, which is 1/10th the U.S. Civil Multi-Turbine engine helicopter rate&quot;.

There you have it Jim, &quot;Best-in-Class&quot;.

I’d have to say HeliComparator, I take heart at your strong defence of the 225 and although grandfathered up the yin-yang (which in itself is not such a bad thing), yes in general it is an excellent performing platform and so too are Eurocopter (never going to get used to AH), who make some iconic helicopters.

However, looking back at the numerous MGB incidents in the North Sea, two of which have been un-survivable due to catastrophic failure of the MGB (unlike the Cougar 91 accident, in that there was no time for the crew to manage the situation) and also the two incidents of incorrect system operation/indication of the emergency water glycol system, which resulted in the crew ditching the helicopters (this in itself may well have been a blessing in disguise for all those on-board, as would you want to be flying for 30-minutes post loss of oil pressure knowing that the oil pump drive shaft had separated and was rattling around the gearbox sump), the uprated 332L2 and 225 MGB’s clearly have design issues that I suspect will not be addressed by senior management (another problematic area) and engineers to the satisfaction of the passengers in the back.

They are both grown out of a stretch, have just as much hanky panky fix, and fail at critical frame and MGB attaching points. Having more luck does not make a helicopter safer than the other. The latest one was lucky enough not to smash the deck and killing everyone including ground crew.

[jimf671]

... ... Having more luck does not make a helicopter safer than the other. ... ...

Right with you there.


I have stated in several fora that BOTH the S-92 and the H225 are part of a new generation of safer helicopter. The numbers support that. You can cut and slice it and spin it any way you want but I tried to lay out the whole picture.


Do I hate the S-92? No, I love it compared to the S-61/SK because I know how much safer our guys are hanging from it with all that power and those nice new 21st century toys. :ok:

What's my beef with Sikorsky? Nothing, other than being able to see through their teflon coating. :ugh: (Seahawks in a few weeks: really looking forward to that. :ok:)

[Lonewolf_50]

(Seahawks in a few weeks: really looking forward to that. :ok:) Good birds, hope you have a long and enjoyable time flying them.

[terminus mos]

They are both grown out of a stretch, have just as much hanky panky fix, and fail at critical frame and MGB attaching points. Having more luck does not make a helicopter safer than the other. The latest one was lucky enough not to smash the deck and killing everyone including ground crew.

No ground crew, it's an NUI

[jimf671]

Lonewolf 50,
We (under one or other of my hats) get some all-too-short interesting experiences to add a bit of variety and save our weary legs. AW189 SAR last week, Seahawk, later maybe 532 Cougar if I can swing it.

[HeliComparator]

Hilife - some good points but marred by a few too ...

When dispassionately observed by a neutral bystander, it is obvious that the S92 doesn't meet FAR29.927. That it still retains its certification is only down to politics and economics.

If your argument that the S92 is "best in class" is based on a Sikorsky press release, could you please send me some of what you are on, it seems fun.

As to the Newfoundland crash being an accident only as a result of the pilots' incorrect actions, there is some truth in that but bearing in mind the weather, it seems unlikely that a ditching in accordance with the RFM wouldn't have resulted in some loss of life. What riles in that accident is that Sikorsky knew perfectly well that the MGB didn't have the required dry run ability and yet they pushed it hard both in their publicity and on here as having it. If they didn't lie directly, there was clearly intent to mislead. We will never know to what extent this influenced the pilots' decisions.

I am not trying to make out that the 225 is wonderful and the 92 is a dog from a safety point of view (only from an operational point of view!) but both types have had fatal accidents, both types have had a few "near misses" any of which could, but for luck, have been fatal. So I don't see a big difference in their airworthiness. Where the 225 lost out to the 92 was only in that the rotor head detachment was caught on video whilst the 92 smashing into a raging ocean wasn't. And if we look at the most likely cause of the next accident - pilot error - the 225 wins hands down in its level of pilot-supporting automation vs the 1980s autopilot tech in the 92.

[212man]

...but bearing in mind the weather, it seems unlikely that a ditching in accordance with the RFM wouldn't have resulted in some loss of life.

I've never bought into that argument. G-TIGK autorotated without a tail rotor onto 6-7m seas and 30 kts, Cougar 491 was faced with 2.5m seas and 30 kts, and the ability to land with power.

[HeliComparator]

I've never bought into that argument. G-TIGK autorotated without a tail rotor onto 6-7m seas and 30 kts, Cougar 491 was faced with 2.5m seas and 30 kts, and the ability to land with power.
Maybe so, but there are other variables in play. The S92 only had SS4 floats which put it pretty much on or slightly over the limit. And I don't think the crew had the actual SS figures at the point of possible ditching. Can you tell from 800'? TIGK was outside its SS limit but remained upright - however to extrapolate that all helicopters will be happy ditching above their SS doesn't seem a valid argument. Newfie air and water temperatures significantly lower than TIGK's - perhaps only an issue if you get wet! And time to rescue would have been much longer I think, since TIGK ditched very near a platform whereas I think the S92 was somewhat in the middle of nowhere. And the design strategy that means you can't inflate the floats until AFTER you ditch seems ludicrous for a "best in class" helicopter! Surely, depending on the exact timing of when you hit the button, the chances of overturning on ditching are increased? Presuming you are clear thinking enough to do it as icy water is coming in through the floor!

Anyway, the fact remains that there was a very avoidable technical problem and the crew decided not to ditch. I suggest some of the above factors were contributory to that decision.

I can't help feeling that if the crew with the first vespel spline problem had followed the RFM and ditched, and if the S92 plopping unscathed into a clearing in Borneo (thank heavens for deforestation) had been flying over the N Sea, it might be the S92 that has the bad social media profile.

[212man]

And the design strategy that means you can't inflate the floats until AFTER you ditch seems ludicrous for a "best in class" helicopter

I'm pretty sure I would ignore that bit of the RFM!

I can't help feeling that if the crew with the first vespel spline problem had followed the RFM and ditched, and if the S92 plopping unscathed into a clearing in Borneo (thank heavens for deforestation) had been flying over the N Sea, it might be the S92 that has the bad social media profile

Agreed - in fact there was a second emergency landing in Brunei too, 4 months after the one you describe (vespel spline failure followed by churning). It was on its way to Bandar airport to take a senior manager offshore and landed 7 nm short in a chicken farm!

[jimf671]

Hang on a minute. So how many S-92 incidents have there really been?

[212man]

So how many S-92 incidents

Define incidents?

[Twist & Shout]

Can someone list the fatal S92 crashes, where whilst airborne the the machine suffered a failure that left the crew with no options, and all onboard no chance of survival whatsoever?

We are all aware of several tragic examples of the above involving the L2/EC225.

I don't fly S92s or have any vested interest.
I do know what I would do if I suffered a loss of MRGB pressure if the ECL stated "land or ditch immediately."
I also know what I'd do if the main rotor system detached at altitude, unfortunately.

[HeliComparator]

Can someone list the fatal S92 crashes, where whilst airborne the the machine suffered a failure that left the crew with no options, and all onboard no chance of survival whatsoever?

We are all aware of several tragic examples of the above involving the L2/EC225.

I don't fly S92s or have any vested interest.
I do know what I would do if I suffered a loss of MRGB pressure if the ECL stated "land or ditch immediately."
I also know what I'd do if the main rotor system detached at altitude, unfortunately.
So if you are going to lump the L2 accidents with the 225 ones to try to make your case more convincing, can we lump Blackhawk accidents with the S92 ones?

But anyway I think you are missing the point. We are looking at hundreds of thousands of hours for both fleets, with a minuscule proportion of flights being problematic. Whether a major incident or accident becomes a fatal one is largely down to luck, so to get a handle on the relative safety you need to look at the big picture, and consider the basics of probability theory. If one (hypothetical) type has numerous "near misses" but no fatals (by luck) and the other has unblemished record except for one unlucky fatal accident, which is the safer?

It's akin to saying that you only want to fly a brand new type with zero hours on it, because it hasn't got a history of any fatal accidents.

[jimf671]

Define incidents?

An incident or occurence, where an 'occurrence means any safety-related event which endangers or which, if not corrected or addressed, could endanger an aircraft, its occupants or any other person.'

And including places that the Press and Journal, Aftenbladet and the Grimsby Telegraph do not report from.

[SASless]

One thing is for sure....HC is going to talk up the Head tosser and talk down the other.

He is at least consistent in his opinion.

What really gets to him is the 92 continues flying in all the oil patches and his favorite ride has become financial drains on every operator that owns or leases the 225.

Evidently the licensing authorities, operators, AND the customers see things much differently than does HC.

[Twist & Shout]

HC
I'm not trying to make "my case more convincing".

I'm trying to point out there have been several unexplained* catastrophic failures# of the same component which is fitted to L2 and EC225 model helicopters (a component type not fitted to L or L1 models).

I'm unaware of similar component failures# in S92 aircraft. I'm genuinely asking if there have been any.

HC, are you saying components shared between Blackhawks and S92s have failed giving all on board no chance of survival?

Just to be clear. I'm not saying any type of helicopter is statistically less safe than any other.
I guess, like most pilots, I can accept the risk of being killed or worse, by something that couldn't be foreseen. But am mortified at the thought of getting back in an EC225 and having the rotor system detach. Which is a twice proven possibility.


*Considered unexplained, let alone rectified, by most in the aviation community, includeding several aviation authorities.
#Failures which kill all on board despite any level of pilot intervention or "luck".

[gasax]

The fact that we are having this 'discussion' sort of says it all. The relevant authorities have been very careful (if would seem) to not get into type specific assessments - hence this toing and froing. If they had there would at least be a solid factual basis to work from.
I know pilots who fly (or rather flew!) both. Each had their preferences, but when you come down to very big chunks flying off or losing control then the situation is pretty serious. Telling a captive workforce to put 'its' big boy pants on' or immediately pointing to the machines maintenance are tactics which add a lot of smoke and fire to the situation and the first victim are the facts.
Will the 225 return to offshore service? Without a pretty impressive effort from AH it seems unlikely, at least not in the next couple of years. In contrast the Sikorski response to the loss of control incident seemed textbook and does not seem to impacted workforce confidence.
Those things by themselves almost tip the argument, regardless of the content of the actual incident.
As to EASA clearing the type for flight? Before the incident investigation reports? Only the French would even think of doing that!

[HeliComparator]

HC
But am mortified at the thought of getting back in an EC225 and having the rotor system detach. Which is a twice proven possibility.


Well once proven for a 225, but never mind! Anyway I am not suggesting that everyone jumps back into a 225 right now. Even though the probability of a rotor head coming off again is probably much less than the probability of another sort of accident, it is of course sensible to wait until we know exactly what the cause of the problem was and there is a satisfactory remedy. But my point is that if those two criteria are met, the only reason not to fly it again seems to be its trial and guilty verdict by social media, hysteria and general ignorance.

[HeliHenri]

As to EASA clearing the type for flight? Before the incident investigation reports? Only the French would even think of doing that!

EASA and FAA have approved last year (october and december) the return to service of the Airbus Helicopters H225 and AS332 L2 .
.

[HeliComparator]

One thing is for sure....HC is going to talk up the Head tosser and talk down the other.

He is at least consistent in his opinion.

What really gets to him is the 92 continues flying in all the oil patches and his favorite ride has become financial drains on every operator that owns or leases the 225.

Evidently the licensing authorities, operators, AND the customers see things much differently than does HC.

Yes you are right about the financial drain, wrong that my view differs from the authorities, operators and customers right now. As I've just said, I think it is correct to keep the aircraft grounded until the cause and solution are implemented.

But whilst of course the weakest link in the chain dominates, in many other ways the 225 is the far better machine, from the pilot's point of view at least. But of course you wouldn't know, you haven't flown either machine.

[SASless]

HC,

You are correct that I have not flown either machine.

That being said....plain ol' commonsense tells me that the 225 has killed two Crews and Passenger loads of people as a result of shucking the entire Main Rotor System (both apparently from very similar causes) in a very short interval of time.

The 92 on the other hand, has not had a fatal accident that can legitimately be attributed to the Aircraft. In the Cougar crash the Crew did not follow the Checklist and the prolonged flight after that decision is what resulted in the Fatalities.

You can brag about the 225 automation all you wish....but until the things can keep their Rotorheads on.....then it is not the better machine no matter how you want to think it so.

Face it....the 92 is out there earning its living and the 225 is not.

So tell me....just why do you keep to that same old position?

Everything argues against your position.

We saw the Wessex removed from Civil Use post numerous fatal crashes did we not.....anyone that flew the Wessex loved it. But....it was removed from service.

I see the 225 thing much the same as the Wessex in how it all turned out.

Your loving how the 225 flew...versus your opinion of the 92.....that has nought to do with which aircraft is the better as Pilot Satisfaction is but one criteria of many that would determine the relative merits of various aircraft.

I personally rate the ability to retain the Rotorhead far more important than having a magic autopilot system. At the end of the Day I want to be stood at the Bar with a Pint in my hand and not plucking at a Harp.

[HeliComparator]

SAS, yes of course keeping its head is quite important! I don't see anything that argues against my position - which is that the 225 shouldn't be flown until it can learn to keep its head on. But if it can, it will once again be a far better helicopter than that old rehashed dog of an S92. If not - well what a shame.

Anyway I would be careful about crowing too much, the next fatal N Sea accident is not going to be a grounded aircraft is it!

[SASless]

Just like the Lotto....you don't have a ticket...you cannot play....or win or lose!

[Pablo332]

AH say there is now no problem, do you share this view?

[Pablo332]

SAS, yes of course keeping its head is quite important! I don't see anything that argues against my position - which is that the 225 shouldn't be flown until it can learn to keep its head on. But if it can, it will once again be a far better helicopter than that old rehashed dog of an S92. If not - well what a shame.

Anyway I would be careful about crowing too much, the next fatal N Sea accident is not going to be a grounded aircraft is it!
AH say there is now no problem, do you share this view?

[birmingham]

Comparisons of the various types of helicopter, while interesting, aren't really helpful...

The problem is that MRG has failed causing two hull losses and the loss of the lives of all on board. After two incidents and major technical investigations we do not yet have a fully developed understanding of the failure mode, a package of modifications to prevent its recurrence, or a workable system to detect the failure once initiated.

After the second incident the manufacturer initially and publically concluded that MRG failure was not likely and suggested the investigation of the suspension bar assembly and a thorough review of maintenance records. Then debris was recovered which enabled the AIBN to conclude that the two incidents did indeed result from similar events in the epicyclic of the MRG. The investigators publically disagreed with the manufacturer and some of the regulators over allowing the type to return to service with increased inspections.

Many passengers lost confidence taking the view that there is a serious unresolved issue which as things stand might result in a third incident.

Some here have labelled them ill informed, hysterical even stupid; led on by a sensationalist press.

The customer may not be an expert, sometimes the packaging may sound sensational even hysterical - however he may also have a valid point!

[HeliComparator]

AH say there is now no problem, do you share this view?
I don't know enough about it to have an opinion, but clearly the CAA don't agree with AH or EASA. I think it is sensible to wait for the NAAIB report at the very least.

[HeliComparator]

Some here have labelled them ill informed, hysterical even stupid; led on by a sensationalist press.

The customer may not be an expert, sometimes the packaging may sound sensational even hysterical - however he may also have a valid point!

I have labelled them thus, but not for the reasons you imply. I think it is perfectly reasonable to want to wait for the steps you mention in the middle part of your post. What is foolish is to say that they will never set foot in an EC225 again regardless of anything, whilst being quite happy (relatively!) to fly in a brand new and unproven type.

[gasax]

Actually this is the crux of the matter;

Comparisons of the various types of helicopter, while interesting, aren't really helpful...

The problem is that MRG has failed causing two hull losses and the loss of the lives of all on board. After two incidents and major technical investigations we do not yet have a fully developed understanding of the failure mode, a package of modifications to prevent its recurrence, or a workable system to detect the failure once initiated.


So there is one type that has done this. And it's manufacturers response has been to squirm and dissemble.

How does it compare? Well I have a technical interest because this newer 'safer' generation of helicopters seems to be anything but that.

One seems to have issues, some possible caused by marketing hype and the rest by measures which need to be sorted out (4.5 hrs warning and no actions????) and one has what appears to be a fundamental problem which it's manufacturers just want to 'go away'.

[Mee3]

After the second incident the manufacturer initially and publically concluded that MRG failure was not likely and suggested the investigation of the suspension bar assembly and a thorough review of maintenance records. Then debris was recovered which enabled the AIBN to conclude that the two incidents did indeed result from similar events in the epicyclic of the MRG. The investigators publically disagreed with the manufacturer and some of the regulators over allowing the type to return to service with increased inspections.

Conclusion came before they even find evident is what makes this investigation fishy from the beginning. Claiming MGB failure subsequently teared off the suspension bar which also proved to be false by simulation.

[212man]

Epicyclic 2nd stage gear found!
https://www.aibn.no/About-us/News-archive/The-EC-225-LP-helicopter-accident-near-Turoy-Norway-Discovery-of-parts

https://www.aibn.no/Aviation/Investigations/16-286?iid=21799&pid=SHT-Report-Attachments.Native-InnerFile-File&r_n_d=61177_&attach=1

[Holy Moly]

was found in the sea between the area of the main rotor separation and the crash site.

Amazing work to locate that. Whether it will be of much use in the analysis aft that long time in the sea will be interesting. Where are all the planet gears? Fired out radially in all directions along the path of destruction?

[BluSdUp]

I have with great interest followed this accident thread.
Can any of you with experience please comment on how this important finding might help solve or prove the likely cause of the failiure .
I have to say I am very happy to see the Norwegian Navy finding this important part.
Respectfully
Cpt B

[Fareastdriver]

How did the planetary support ring get bent; especially where two spigots seem to have lost there bearings before it went into the sea.

[Concentric]

Pretty straightforward really, FED, one or more chunks from the failed gear get carried forwards by the faster rotating sun gear and get entrained between the sun and those next 2 planet gears. With nowhere else to go it pushes the 'spigots' (or carrier pins) outwards causing the carrier to bend and the ring gear to burst.

It appears to have happened quicker and with a lot more energy than REDL where 7 planets and the inner race from the 8th stayed with the carrier.

It is not clear from the other photo (Close-up of the inner race from the failed planet gear) (https://www.aibn.no/Aviation/Investigations/16-286) posted by AIBN whether it is showing the loaded arc or the reverse side of the inner race. Once cleaned up, if there is no evidence of pitting it would suggest little or no spalling of the outer race prior to fracture.

[atakacs]

I muss say I am very impressed by the recovery of this admittedly very important piece of evidence so long after the fact.

[roscoe1]

I'm surprised it took 10 days to release the information that it was found. Love to see the details of how they found it. I had thought the search was long over or at least over. Was Airbus supporting the continued effort to find the parts or was it all AIBN? Makes you wonder if they can find this how hard could it be to find MH370. I guess a lot harder.

[Twist & Shout]

Well once proven for a 225, but never mind! Anyway I am not suggesting that everyone jumps back into a 225 right now. Even though the probability of a rotor head coming off again is probably much less than the probability of another sort of accident, it is of course sensible to wait until we know exactly what the cause of the problem was and there is a satisfactory remedy. But my point is that if those two criteria are met, the only reason not to fly it again seems to be its trial and guilty verdict by social media, hysteria and general ignorance.
HC
I think we are having parallel arguments, rather than totally disagreeing with each other.

We both agree, that we wouldn't like to fly (in) a machine that has a known fault. A fault that can't be mitigated or compensated for.

Personally, after what has been claimed by AH up to now, I'm disinclined to believe anything they say, especially in regards a "fix". Apparently within 24hrs of the Norwegian tragedy, there was "no problem" that wasn't "caused by maintenance issues". Disgraceful.

Once the problem has been fixed, and scrutinized by an independent authority, Ill happily fly the Super Doopa Puma again.