EC225 crash near Bergen, Norway April 2016

[birmingham]

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.
The EADS requirement to only fly with the non occurrence type of planetary must have provided a large number of components that can be analysed. What we have here is a specific failure mode not yet fully understood. We still have no idea whether this is a design issue, some type of manufacturing problem or a couple of one off unique occurrences such as the truck accident story. And that's the problem - we can't restore confidence until we know definitively why this happened. Premature statements from the manufacturer and some unfortunate PR hasn't helped. If it turns out the design itself is safe the public will require an explanation they can understand clear and simple. Hopefully the recent discovery of additional parts will help this happen.

[riff_raff]

Epicyclic 2nd stage gear found!

Actually, that is the planet carrier. There are no planet gears present, but there is a single planet gear inner bearing race still attached at the 3 o'clock position. You can also see what remains of one of the tabs used to retain the planet gear inner bearing races at the 2 o'clock position. Took a significant amount of axial force to tear all those planet gears off the carrier pins.

[Concentric]

Took a significant amount of axial force to tear all those planet gears off the carrier pins.
riff,

One might assume it took a similar magnitude of axial force to break 4 tabs on REDL as you can see in the photo below (Source AAIB Report 2-2011) but it is interesting that its gears stayed on and there seems to have been a limit to the axial displacement of the inner races – possibly contact with the 1st stage carrier?

Of course, the axial force component on LN-OJF may well have been much, much larger than that needed to just break these tabs.

I think the major difference was in whether the larger gear fragments went outwards between planet cluster and ring gear (G-REDL) or inwards between the cluster and the sun gear (LN-OJF). All consequential to the root cause – fatigue failure of a planet gear.

[birmingham]

HC, as you predicted the next fatal incident was indeed an s92 sadly killing an Irish Coastguard crew who were only there to rescue others. At this very early stage no information is available as to what was the cause. I am sure that unless evidence of technical failure is found the S92s will keep flying. If it transpires there was a technical reason and a grounding of S92s as well as 225s is necessary it will be seriously testing for the oil and gas people. For everyone's sake let's hope they can establish the facts quickly. Another sad reminder, if it were needed, of how dangerous helicopter ops can still be.

[HeliComparator]

HC, as you predicted the next fatal incident was indeed an s92 sadly killing an Irish Coastguard crew who were only there to rescue others. At this very early stage no information is available as to what was the cause. I am sure that unless evidence of technical failure is found the S92s will keep flying. If it transpires there was a technical reason and a grounding of S92s as well as 225s is necessary it will be seriously testing for the oil and gas people. For everyone's sake let's hope they can establish the facts quickly. Another sad reminder, if it were needed, of how dangerous helicopter ops can still be.
Much as I like to score points with SAS on the S92 vs 225, I do hope this latest isn't a sudden catastrophic failure as that would seriously scupper N Sea ops. But it does show the dangers of having pretty much a one-horse town.

Obviously we have no idea yet but if it turns out to be CFIT during an instrument approach in bad weather, it does raise the question of whether one sort of fatal accident is worse than another. I'm thinking that, e.g. the Sumburgh L2 accident could have happened to both an L2 and an S92, but not to a 225. What if this accident could not feasibly have happened to a 225?

From the pilots' point of view, we hate the idea of a sudden rotor detachment as it's out of our control. Even though the probability of a CFIT is perhaps greater, we dismiss that as being something that couldn't happen to us because we are competent. And yet it still does.

From the passengers' point of view, I doubt that such a distinction is made since either scenario is out of their control.

[jimf671]

Whatever the details, in the last few weeks the principle that if a type does all the work then it has all the accidents seems to be settled.

[725_driver]

SA less, one advice, do not stay at the bar before posting...

[212man]

Ok, what am I missing here?
The Safety Recommendation document relating to the accident concerning AS332L2 Super Puma, G-REDL has been updated. (March 17th 2017)

When I look at the document: https://assets.publishing.service.gov.uk/media/58cba972e5274a16e8000036/G-REDL_SR_Header_V1.pdf

The latest comments I see are still from 2015.

[birmingham]

an update from the AIBN is due later this month I believe

[Non-Driver]

Confirmed for this Friday:

https://www.aibn.no/About-us/News-archive/The-Helicopter-Accident-near-Turoy-Invitation-to-press-conference-in-connection-with-the-publication-of-a-preliminary-report

[birmingham]

Much as I like to score points with SAS on the S92 vs 225, I do hope this latest isn't a sudden catastrophic failure as that would seriously scupper N Sea ops. But it does show the dangers of having pretty much a one-horse town.

Obviously we have no idea yet but if it turns out to be CFIT during an instrument approach in bad weather, it does raise the question of whether one sort of fatal accident is worse than another. I'm thinking that, e.g. the Sumburgh L2 accident could have happened to both an L2 and an S92, but not to a 225. What if this accident could not feasibly have happened to a 225?

From the pilots' point of view, we hate the idea of a sudden rotor detachment as it's out of our control. Even though the probability of a CFIT is perhaps greater, we dismiss that as being something that couldn't happen to us because we are competent. And yet it still does.

From the passengers' point of view, I doubt that such a distinction is made since either scenario is out of their control.
From what the investigators have told us would seem some form of CFIT incident is much more likely here - no evidence so far of any technical failure

[albatross]

Glad to hear that the new report is coming out. Hopefully it will shed some new light on this tragic event.

JOKE
Ok we need to divide our responses to the upcoming report.
Need volunteers for various groups. Tasking for each group, A to G, outlined below.
A) Reject any and all findings.
B) Correct any grammar, spelling or punctuation errors.
C) Explain why the 225 is the safest, most comfortable and longest range helicopter in the world.
D) Trash the S-92.
E) Call everyone else mouth drooling idiots.
F) Accept the report and compliment those who prepared it on their dedication and professional conduct.
G) The largest group ..to argue with groups A, B, C, D, E and F.
CLOSE JOKE

[helicrazi]

You forgot group (H) - god complex.

Looking forward to the report, hopefully it will give more answers than questions...

[albatross]

Helicrazi
Rotorheads is a forum that is the epitome of politeness and rational debate when compared to some other forums.
There is one forum on PPrune where posting "Great sunrise today, going to be a great day for flying!" will start a fight that will go on for 20-30 pages. Friendships will be torn assunder, reputations trashed, and folks will be challenged to duel to the death.

[sinnon7]

https://www.energyvoice.com/oilandgas/north-sea/137628/super-puma-ban-remain-place-following-latest-crash-report/

Super Puma ban to remain in place following latest crash report...

[birmingham]

https://www.energyvoice.com/oilandgas/north-sea/137628/super-puma-ban-remain-place-following-latest-crash-report/

Super Puma ban to remain in place following latest crash report...
As it says the AIBN is obliged to publish this report within a year of the accident.
It does seem that despite a huge effort we still only know what happened, not yet why.

“CAA UK and CAA NO continue to work closely on agreeing the next steps required to be sufficiently satisfied in order to remove our Operational Safety Directives.

“Developments on the lifting and the detection capability look promising and we are hopeful that after obtaining further information we will be closer to removing our directives. At this time however the directives remain in place.”

It would obviously be much easier for them if a specific reason for the failure could be established.

[FNTC]

New preliminary report out today.

https://www.aibn.no/Aviation/Investigations/16-286

"The observed failure mode in this accident, i.e. crack initiation and propagation with limited spalling, seems to differ from what was expected or foreseen during the design and certification of the main rotor gearbox. The fracture propagated in a manner which was unlikely to be detected by the maintenance procedures and the monitoring systems fitted to LN-OJF at the time of the accident."

[birmingham]

AH has recently added a "Super Puma Information Centre" section to its website. This gives a lot more detail from them and information on the programme to return the H225 and H215 to service. This shows that out of the 341 aircraft affected 49% are now back in service whereas in O&G it is only 15%. Obviously one fact in this is location as many of those 127 are located in UK/Norway where they are formally grounded. The site show the hours being accumulated by the flying aircraft and the total hours accumulated by the types to date. It acknowledges that while they know what happened and have been able to introduce measures to mitigate the risk of a recurrence that more investigation needs to take place to understand why as FNTC noted "in a manner which was unlikely to be detected by the maintenance procedures and the monitoring systems fitted to LN-OJF at the time of the accident".

The failure mode was not what would be expected and despite a huge technical effort there is still no obvious "smoking gun". The metallurgical understanding of the events is now very thorough and it would seem that further work here offers the best chance of getting to the bottom of this one.

[Lonewolf_50]

Tasking for each group, A to G, outlined below.

I think you left out the group that needs to advocate UAV/unmanned transport modes.
On a more serious note ...
The fracture propagated in a manner which was unlikely to be detected by the maintenance procedures and the monitoring systems fitted to LN-OJF at the time of the accident." Addressing that is critical to restoring confidence in the aircraft. If you don't get a hint/warning that 'things are going wrong in the box full of metal gears' you don't get the chance to fix, or replace, that critical component. Ouch. (Best wishes to the engineers/designers in coming up with a mode/tool/kit that can address this "graceful degradation" issue).

[Twist & Shout]

AH has recently added a "Super Puma Information Centre" section to its website. This gives a lot more detail from them and information on the programme to return the H225 and H215 to service. This shows that out of the 341 aircraft affected 49% are now back in service whereas in O&G it is only 15%. Obviously one fact in this is location as many of those 127 are located in UK/Norway where they are formally grounded. The site show the hours being accumulated by the flying aircraft and the total hours accumulated by the types to date. It acknowledges that while they know what happened and have been able to introduce measures to mitigate the risk of a recurrence that more investigation needs to take place to understand why as FNTC noted "in a manner which was unlikely to be detected by the maintenance procedures and the monitoring systems fitted to LN-OJF at the time of the accident".

The failure mode was not what would be expected and despite a huge technical effort there is still no obvious "smoking gun". The metallurgical understanding of the events is now very thorough and it would seem that further work here offers the best chance of getting to the bottom of this one.

My bold. I see these statements as contradictory.
If you don't know why it happened, how can you mitigate the risk of recurrence?

[birmingham]

My bold. I see these statements as contradictory.
If you don't know why it happened, how can you mitigate the risk of recurrence?

They know what happened so they can definitely mitigate the risk - one type of mgb, reduced time between inspections etc. What you cannot do is to ensure prevention of a recurrence. That can indeed only be ensured when you know why.

I agree that is the basic difficulty here and unless the reason can be established and the problem definitively resolved it will be close to impossible to get this back in the NS O&G sector. Even then the damage may already have been done.

[helicrazi]

I'm amazed people still think there's a chance of its return, the industry has moved on.

[jimf671]

I'm amazed people still think there's a chance of its return, the industry has moved on.

But moved where? Even in an O&G slump we've moved into an era of S-92 accidents. What happens if O&G activity picks up? I am very concerned about unintended consequences of hurried changes in fleet composition.

[helicrazi]

Money talks, supermediums are the future, no need for 2 heavies, S92 is doing the job. Pax numbers reducing, gone are the days of full loads of 19 on every leg. Supermediums are filling the void, 225 has lost its place. If the industry picks up it all seems to be moving ESB or the Atlantic, which shuttling out of shetlands isn't a problem for the supermediums.

[industry insider]

Helicrazi

I think your last 2 points are on the money. Having spent 2 hours reading this report (it needs more study and it's an excellent factual piece of work) I cannot see myself making a recommendation to return the 225 to service to my BOD.

I wonder how similar the 175 MGB architecture is to the 225?

[Fareastdriver]

Onceuponatime. 1981 or thereabouts, the North Sea was going to be infested with Sikorsky S76s. Range and payload-not enough.

[Twist & Shout]

They know what happened so they can definitely mitigate the risk - one type of mgb, reduced time between inspections etc. What you cannot do is to ensure prevention of a recurrence. That can indeed only be ensured when you know why.

I agree that is the basic difficulty here and unless the reason can be established and the problem definitively resolved it will be close to impossible to get this back in the NS O&G sector. Even then the damage may already have been done.

I understand the sentiment, but what if the next rotor to detach is the other brand of gearbox with a TTIS of 35hrs?

They have taken steps they think might mitigate the likelihood of a reoccurrence, but if they don't know why it happened, they can't know if their recommendations will have any mitigating effect whatsoever.

[jimf671]

At 1.16.3.11 there is a description of the pattern of compressive stress in a FAG second stage epicyclic gear from OJF. There is no equivalent information for the SNR gear but a statement appears at the final paragraph of 1.6.8.3 that "differences in the finishing process performed by the suppliers can affect the outer race surface residual stress, with FAG having a significantly higher compressive stress at the race surface". The pattern described in 1.16.3.11 seems quite severe in that it appears to have sudden enough changes to be potentially damaging in this operating environment. It would be interesting to know what the equivalent stress pattern was for the SNR gears and the differences in process characteristics.

I wonder where else these factors occur.

[SASless]

FED,

You are talking 76A's.....and a very long time ago.

Had the S-70 design been thought through and designed for the Civil Market along with the US Military....perhaps it would have been the 70 we were all driving around in.

Actually.....had the 61 been modernized perhaps they would still be flogging around the Oil Patch.

But....we are talking about what could have been.

[G0ULI]

The detail in this report is amazing. The micrographs of the fracture surfaces absolutely stunning. I have never before seen cracks propagating through the grains of a material rather than follow around the grain boundaries. Perhaps of even more significance is that cracks were forming and propagating extensively through the interior material without leaving any significant trace at the surface, apparently due to the compressive carburization hardening process. This certainly has provoked a degree of controversy among the various groups responsible for the investigation as to what initiated the cracking and the speed and method of propagation. The lack of surface damage limited the possibility of spalling metallic chips being generated and detected by devices intended to identify early signs of damage and potential failure of components.

My interpretation of this mode of crack propagation is that the materials used were operating at the absolute limits of their ability to cope with the stresses involved. Once damage started to occur, progressively greater stress was put on the remaining intact structure. A common enough failure mode, but in this case, the cracks were passing through grain structures that were designed to resist cracks.

I can only conclude that the engineering design of the gearbox exceeded the ability of current materials and manufacturing techniques to cope. Simply beefing up the components a little bit will not be enough. Without even more robust materials, cracks will still form and propagate through the metal. It may take longer for a failure to occur, but it will still happen. We appear to have hit the ultimate limits of material science for the time being.

This catastrophic failure mode is a rare event with only three remarkably similar accidents and a couple of near misses recorded. The problem is that there is no reliable current method of detecting impending failure before it occurs. That suggests that the MGB needs to be totally reengineered or the aircraft operated at a much reduced capacity to provide an extra safety margin.

Either way, I can't see it ever being allowed back into North Sea operations again.

[riff_raff]

Very detailed report. Will read all of it when time permits. After a quick scan, one thing that caught my eye was table 5 listing the difference in calculated inner/outer race surface contact stress levels between the FAG and SNR designs. Would expect to see lower design contact stress levels on the inner race than on the outer race, since the loaded sector of the fixed (with respect to load) inner race surface sees more load cycles.

It was also interesting to read the problem began with surface spalling on the outer race. Surface spalling of hertzian contacts usually originates from a subsurface shear failure. This type of subsurface shear failure tends to propagate at a 45deg angle out to the nearest surface from continued rolling contact cycles. Normally, the location of max subsurface shear stress in a hertzian contact, like this planet gear outer bearing race surface, should be well within the carburized case depth.

[birmingham]

I understand the sentiment, but what if the next rotor to detach is the other brand of gearbox with a TTIS of 35hrs?

They have taken steps they think might mitigate the likelihood of a reoccurrence, but if they don't know why it happened, they can't know if their recommendations will have any mitigating effect whatsoever.

I do agree. They can only say it is likely to mitigate the risk to some extent as per EADS and AH's view. No certainty here and as you correctly point out would have no mitigating effect whatsoever if the the accident was caused by a failure mode that remains unidentified. That's the problem.

Also agree with helicrazi when he says (a) the industry has moved on and (b) super mediums are probably the future (oil and gas fields are more automated and require fewer people). Maybe the larger cabs of the future will be mostly military.

As to the H225 Gouli also has a point - more metallurgy needs to be done but it does seem that it may simply be that the design of the gearbox has moved too close to the limits of the materials.. I'm not competent other than to ask the question but it is clear from this excellent report that those who are don't believe they have the answer either

[Mee3]

AH has recently added a "Super Puma Information Centre" section to its website.
It has always been there. Since the Shaft problem.

[Graywhiskers]

Failure is rare. This implies an unusual tolerance stack occurring. Normally the stacks work. On a very rare occasion, an extreme stack is occurring. This is statistical.
This leads to the conclusion that the failure is either due to a) a load sharing problem among the planet gears or b) a vibration problem. Solutions are to improve load sharing if necessary; and reduce vibration by adding damping coatings/rings to the gears. An all new helical planetary (assuming it is spur) would be beneficial. Use damping as an interim solution, and the helical planetary as a long term solution.

[G0ULI]

Current best engineering practice is to design gear mechanisms that mesh in such a way that all parts of the system continually present different wear faces to other components. This ensures that all components wear evenly. Statistically with such a system there will come a time when all the weak spots in the components of such a gearbox will momentarily come into alignment. Similar to all the planets in the solar system lining up on one side of the sun. It happens very rarely, but when it does, that is the time that cracks might be initiated in highly stressed components.

[Tatischeff]

Vibration seems not to be the cause, according to the HUMS data, no abnormal vibration has been detected until 2 seconds before separation.

Fatigue prediction and lifetime calculation are statistics. Taking into account scattering in materials resistance, industry take margins that keep the functionning points far from the real limit.

This kind of tragedy shouldn't happen but it's a nice dream to believe that it's all about design matters. It's a shame that the fractured gear of REDL wasn't recovered (where the crack started)...

Concerning the future of heavies, it still exists and what we know today of O&G will change.

[212man]

1.16.8.3 Oil cooler, has this statement:

....particles of 16NCD13 were found, notably one particle with a surface area of 1.8 mm2 (length 1.8 mm, width 1.3 mm)

Surely that's 2.34 mm2 ?

[CertGuy]

1.16.8.3 Oil cooler, has this statement:



Surely that's 2.34 mm2 ?

Only if it is square.
:)

[212man]

On second thoughts, if it's other than a rectangle it could be correct. Describing a width and length kind of infers a rectangle but a trapezoid could be smaller. It caught my eye because the 330J accident was largely due to misinterpreting the defined maximum surface area of debris. The AMM said 7 square mm and it was read as 7 mm squared - 49 square mm!

[riff_raff]

That statement about finding such a relatively large piece of gear steel debris inside the heat exchanger core seemed odd to me at first, since it would have had to pass thru the oil pump inlet screen to end up there. However, after looking at this image of the oil pump inlet screens (http://i1300.photobucket.com/albums/ag81/kannad405/IMG_20121108_204638.jpg~original)it does seem possible that such a relatively large piece of debris could pass thru due to the coarse mesh size.

One thing that AH might consider is using a finer mesh size for the pump inlet screens. To me, the existing inlet screen mesh seems too coarse. Obviously using a finer mesh size would require increasing the screen area to maintain acceptable flow characteristics. Logically, the size of the screen mesh should be capable of stopping any debris particles that could not pass through the pump without causing unacceptable damage to the steel pump elements. I don't believe it could be demonstrated by analysis that this would be the case with the relatively large piece of gear steel debris found in the heat exchanger.

Would be interesting to see the condition of the oil pump elements, assuming they were recovered.

[S92PAX]

I think you are missing the point completely Riffraff. There shouldn't be debris of this magnitude anyway to warrant any change of filter design. The root cause needs addressing, not the consequences

[birmingham]

Comment in this week's Flight Global ...

"But it seems clear that opportunities were missed. The frankly startling revelation that parts sourced from one of two suppliers have a failure rate three times as high as the alternative is troubling; that no one thought to analyse this data before last year’s Norway crash is almost beyond belief".

Yes, the H225 complies with all the certification requirements, but that begs the difficult question as to whether those standards are still fit for purpose.

[Pittsextra]

Yes, the H225 complies with all the certification requirements, but that begs the difficult question as to whether those standards are still fit for purpose

If you look back at comments to prior incidents/accidents with the type you'll find a number who would seek to put aviation into some special category where normal logic doesn't seem to count.

[Lonewolf_50]

@Pitts: if all you are interested in is providing a wind-up it might be best to avoid hitting the "post" button. (I have more frequently of late overcome the urge to post, which I find is a healthy thing).


It is troubling to me, the idea that of two suppliers for a precision component in a drive train/transmission, one had 3x failure rate (or significantly less reliability) and yet was still retained as a supplier/vendor by the manufacturer. While there may be more to that story, on the face of it someone didn't take reliability as seriously as they ought to have done, or, a batch/lot of material of considerable size was produced and distributed and it took a long time for people to discover and try to remedy that.

[Pittsextra]

Not a wind up. The issue here is fuelled by people, some of whom would be a useful voice within the industry who in the past have shown what one might call ambivalence. As your post goes on to say it is troubling and yet that process can not be a sudden revelation to those embedded in the various organisations. Your attention should be less upon my voice and more upon those whose concern in the recent past extended to selecting a large size of under crackers.

[Concentric]

It is troubling to me, the idea that of two suppliers for a precision component in a drive train/transmission, one had 3x failure rate (or significantly less reliability) and yet was still retained as a supplier/vendor by the manufacturer. While there may be more to that story, on the face of it someone didn't take reliability as seriously as they ought to have done, or, a batch/lot of material of considerable size was produced and distributed and it took a long time for people to discover and try to remedy that.
I think we need to be careful not to conflate spalling with ‘failure’. I am not even sure the term “less reliable” is appropriate either, as Time Since New is not listed against each unit withdrawn, only collective fleet hours fitted with respective bearing types (apart from the Angolan one).

The two catastrophic failures were by fatigue crack propagation beyond the hardened depth. Not all spalling results in deep fatigue cracking, as evidenced by the 20 FAG bearings that have spalled ‘harmlessly’. Remember that 7 SNR bearings have spalled ‘harmlessly’ too. Given the total production numbers of bearings, most of both types would actually appear to have either been still in satisfactory service or have reached design SLL when these statistics were gathered. In that sense the behaviour of all except the REDL and LN-OJF bearings has been ‘reliable’ in that they followed the expected end of life degradation process.

You can look at those same statistics presented in Table 6 a very different way. Look at the total number of units of each type and how many of them DID NOT produce spalling. That would give “reliability” scores of 99.35% and 99.76% for FAG and SNR respectively. Not so clear cut now is it? Remember also the definition of L10 life for bearings (see 1.6.8.2).

You cannot equate that minor difference in reliability simplistically with Hertzian contact stresses of 1800MPa and 1550MPa (86% of 1800MPa) respectively. There is far more to it than that. A lower Hertzian contact pressure (Edit: by widening the path) in a spherical raceway can involve more slippage and, depending on lubrication, generate more surface friction that is more likely to turn a crack inwards.

Further investigation should not only focus on metallurgical differences but the whole tribology of these bearings and their operational conditions.

[Concentric]

Possibly of greater interest than comparing FAG bearing spalling with SNR bearing spalling statistics over the same period, is to compare the information in 1.6.11.4 with that in 1.6.11.5. Excluding the crash items, between 2001-2016, 27 bearings have been removed in service due to spalling or micro-pitting but (according to Airbus) only 2 of those were between 2009 and 2016.

FAG stated (in 1.6.8.3) that there have been no differences to the design or manufacture during the production life of their bearings, yet for the first 8 years 25 bearings (incl. both types) were removed (average 3.125p.a.) and for the next 7 years only 2 were removed (0.286 p.a.), despite any heightened concerns or vigilance there may have been following the REDL crash in 2009. I can’t quite figure that reduction of 91% out.

What, if anything, has changed materially in that time and in particular perhaps in, or shortly before, 2009? Was there any change to lubricants, additives or to internal spray nozzle arrangements?

[riff_raff]

One photo in the report shows an obvious difference in roller face width between the FAG and SNR bearings. But the difference in face width alone may not be responsible for the different hertzian contact stress levels noted. The roller/race osculation ratios can also have a significant effect.

The M50 material used for aircraft bearing rollers/races typically allows a higher material reliability adjustment factor to be used in a conventional rolling element bearing fatigue life analysis than a race using carburized VIM-VAR 9310 gear steel would.

[Concentric]

I agree, the difference in face width is not the only factor. But even the difference in Hertzian contact stress I believe may not be the only driving force behind this failure mechanism. Some bearings in wind turbine applications run up to 3 GPa. Normally fatigue damage is actually stress range raised to the power of 3, or higher depending on the S-N curve assumed for the damage calculation, so such a difference in Hertzian stress would produce even more contrasting results than we are seeing here. That approach would seem to apply more to dry rolling contact.

As I understand it the prevention or delay of damage in rolling/sliding contact is highly dependent on the ability to maintain a thin film of lubricant between the contacting surfaces, most significantly for ball or barrel roller bearings with their element of sliding within the Hertzian contact area. Without changing the bearing design or roller/race osculation ratios, the best way for a manufacturer to improve this would be a change of lubricant or introducing certain additives (some of which can be aggressive). That could significantly prolong surface contact fatigue life and delay the onset of spalling; producing an improvement for both FAG and SNR bearings similar to what we see in the reported statistics post 2009.

I am no expert but the profile of the crack running deeper into the material ahead of the travel of the rollers looks uncannily similar to that caused by lubricating fluid seepage into a crack with pressurization and possible entrapment effects. There are several recent research papers available here (http://www.sciencedirect.com/science/article/pii/S245232161630405X) and here (https://www.researchgate.net/publication/267583076_Fluid-Crack_Interaction_in_Lubricated_Rolling-Sliding_Contact).

To put it in layman’s terms, this mechanism is similar to hydraulic fracturing (fracking) of highly compressed rock formations in shale gas recovery. Could it also overcome the residual compressive stress in the carburised raceway, even the higher compression on the FAG bearing?

So my big question is – did AH achieve that dramatic improvement in spalling statistics post-2009 by changing the lubricant to one better able to maintain that thin film but potentially also better able to seep into micro-defects and be pressurized behind the crack tip?

By reducing the degradation process of spalling which, at the time of certification was considered to be benign, could AH have removed a crucial indicator and (unwittingly) simultaneously introduced a lethal failure mechanism that leaves no trace?:eek:


I really hope I am wrong.

[G0ULI]

Concentric

This does appear to be a plausible mechanism to explain the crack propagation in the gears. It cannot be the sole reason because a crack has to be initiated by some other event or process first, but once that opening or pit is created it would seem that eventual failure is inevitable. Every compression cycle would be the equivalent of driving an incompressible hydraulic wedge deeper into the material. As the process continues the hardness of the surface layer would assist in driving the crack propagation deeper into the softer underlying material.

[Concentric]

Gouli,

Indeed, the crack has to be initiated somehow and it appears from the report that it was from one of a series of micro-pits 15mm - 16mm from the top face of the bearing, so all of them slightly below the line of maximum Hertzian pressure at 14mm but where sliding contact might begin. That it was not one isolated micro-pit (a rare occurrence in itself) but one of several in a row is, I think, a clue as to how it came to exist. Those other micro-pits should give the metallurgists something to analyse.

[BluSdUp]

Dear All
As we are waiting for the final report , and modification / inspection-cycle or change of manufacturer of certain parts: How many ac are effected ( Norway and UK)
And what have the operators done.
I have followed this thread with great interest , but have little grasp of the local , regional and worldwide consequences for the SuperPuma.

I do compare this with the rudderhardover that B737 did suffer long time ago.
It is do or die, but they found the likely cause and did a good fix!

Anyway, I understand the Norwegian NTSB are mostly respected for not bowing to undue external pressure.

At the end of the day: we can never have main rotors depart without warning like this again. Your part of aviation is inherently more challenging than airliner ops is , never mind the wings going AWOL.

Regards
Cpt B

[S92PAX]

There was a couple of low key press releases by Airbus claiming the 225 will be returning to service soon.
https://www.flightglobal.com/news/articles/h225-helicopter-to-return-to-full-flight-status-soo-438783/

https://www.flightglobal.com/news/articles/uk-caa-sees-no-prospect-of-quick-return-for-grounded-438857/

This survey has appeared on one of the offshore sites.
http://www.airbushelicopterssurvey.com/
I dont think they realise how things have moved on

[atakacs]

I dont think they realise how things have moved on

Not exactly sure to understand what you mean here?

[S92PAX]

I meant the 225 has been replaced and even if was introduced again the strength of feeling against flying in it is too great to overcome.

[terminus mos]

Interesting articles. Regardless of one's individual opinion, the market doesn't really need the H225 at the moment. S-92s took up most of the slack and the Super Mediums are taking slots where they fit which will free up more S-92s to use where a heavy type is definitely required.

[jimf671]

TM is probably right about the current market needs.

Super Puma on the front page of the P&J again today. Plenty of opinions inside from people who know less than nothing about helicopters. Plenty of mistakes as well. (H255?!)

[rotor-rooter]

https://www.energyvoice.com/oilandgas/north-sea/143455/report-super-puma-return-north-sea-skies/

The spokesman said: “Airbus Helicopters has launched an online helicopter users’ survey.

“We are keen to hear directly from these users, mainly pilots and passengers, regarding their thoughts on helicopter features in general and the H225 in particular.

“This broad and valuable feedback is key to helping us address the concerns, priorities and requirements of those who use our helicopters on a daily basis.”

I wonder if they will share the results?

[birmingham]

https://www.energyvoice.com/oilandgas/north-sea/143455/report-super-puma-return-north-sea-skies/



I wonder if they will share the results?

I am sure that if a lot of E&P workers were to reply positively then they would.

More relevant is that the industry in the North Sea changed. Operators/customers increased the use of medium types and many more of these have been introduced. I can see the use of the S92s being reduced and the mediums taking up a bigger share of the market.

What the Bergen crash seems to have been is a catalyst for this change.

AH have a decision to take on their new large helicopter, the mock-up shown in Paris asking as many questions as it answered. This survey is likely to have been issued partly to tell them how closely it can resemble the 225 and still sell, as evolution rather than revolution is always the preferred design approach.

Returning the 225 to the North Sea in any significant quantity has always seemed unrealistic in my opinion - but when you have a lot of history and personal in investment in a product it is very hard to let go.

[jimcarler]

I think a number of the operators are able to claim compensation from Airbus during the time the 225 is grounded - much of this income is then ploughed into medium types, with the remainder kept for other operational costs or, in the rare case given the poor state of the industry, profit. When they are no longer able to make a claim (if/when the 225 is cleared to fly again), they may have to revert back to using it purely for financial reasons. I think there is still a market for them there - the S92 is not without its own problems.

[nowherespecial]

While the oil price is in this current regime, there will be increasing moves away from heavies as for most oil companies, the main driver in all decisions is price. The costs of heavies make them uneconomic in comparison. The H225 is dead in the water commercially unless Airbus can cut their hourly DOC/ PBH dramatically and the leasing companies accept the hit and drop the lease rates dramatically. Even then, it's reputation is still in the toilet.

It goes back to the Air Advisers and C&P people at the oil companies - who is going to sign up their workers to an H225 contract? Answer - no one for the foreseeable future.

IMHO AH would be better off focusing on selling what they have to militaries and spending their time and money creating something else.

[birmingham]

It goes back to the Air Advisers and C&P people at the oil companies - who is going to sign up their workers to an H225 contract? Answer - no one for the foreseeable future.

Agreed - if you don't work in E&P it is easy to miss the commercial point. All the major helicopter people were suffering long before Bergen

CGG a major services company baked by the French state filed for bankruptcy recently, their revenues are only 30% of what they where before the slump. Many other service companies are 50% or less. So the problems go beyond the 225 or helicopters. Since Bergen the North Sea has moved to the S92 and mid-sized types but there have been no significant new orders for new builds announced to meet the gap other than a couple to be used for SAR contracts for Statoil. It has been about redeploying existing machines.

Even if this hadn't happened there would have been a big downturn in demand for helicopters. The timing of the Bergen incident was such that it was probably the final nail in the coffin. The 225 and other Pumas certainly have some sort of future but there are few signs in the O&G market that it will be needed here.

[Mee3]

when you see that AW is dumping 169 at high 6 mil you know wheres the market.

But OEMs somehow come up with the same conclusion that the market will bounce back in foreseeable future. And they are burning cash flow to flood the market when low so they are "prepared for the market comes back".

[birmingham]

when you see that AW is dumping 169 at high 6 mil you know wheres the market.

But OEMs somehow come up with the same conclusion that the market will bounce back in foreseeable future. And they are burning cash flow to flood the market when low so they are "prepared for the market comes back".

The problem this time is fracking and to a certain extent renewables. As soon as the price moves up the US completes more wells. Renewables provide a small but no longer insignificant share - this will increase. Supply will not be an issue for some years,if at all. The N/S will still survive but will be leaner - with smaller operators and a greatly reduced cost base. Statoil will hang on in there; there have even been new discoveries - one very significant. But increasingly it will be the preserve of specialists. - but there will be no return to the status quo of mega platforms and mass transit.

It will be a very different North Sea with different transport needs.

[AlphaZuluRomeo]

I don't think this video from AH, a few months old, has been linked here.
Kinda marketing, but interesting nonetheless.

https://youtube.com/watch?v=KvBLadpVscY

[ethicalconundrum]

Disclaimers: I haven't flown a fling-wing in decades, and when I did it was for the Big Green US team, all we had back then was a chips light, driven by several magnetic sensors in the fluid path. My experience with vibration acoustics is also more than 25 years old, so take that as a caution.

Back when I worked with Solar Turbines and Spectral Dynamics, it was relatively easy to monitor, discover, and trigger on FFT characteristics in a turbine and gearbox. I'm considering the rapid detection and prevention of the catastrophic failure which was found in this accident.

By use of the FFT algorithms in the detector hardware and software, we were able to build a characteristic signature of every turbine and gearbox built and instrumented. In some ways, the signatures are very common, and in other ways they are always slightly different. Think of the concept of a fingerprint and one will get the general idea. In the video above, at the 8:15 time mark you can see a brief image of the vibration signature of some rotating asm(I doubt it's a helicopter gearbox, but hard to say). By use of threading and setting up triggers on both amplitude, frequency, and harmonics I'm inclined to say that discovery and alert of an impending failure once spall 3 or spall 4(almost surely) would be possible.

The amount of vibration noise would be of greatest concern, where specific anomalies could present a trigger warning, which would induce a 'false positive' alarm for potential catastrophic failure. The S/N ratio, and type of detection would require sensors inside the MGB, as I think outer case sensors would not be sufficient to capture the ringing and vibration in an encapsulated gearbox bathed in lubricant. This would require further study.

As I mentioned, my depth of knowledge on this is quite old, but back in the 90s we were able to detect common gear spalling in planetary gearboxes for industrial and non-flight aviation systems, most commonly GPU and remote start mechanisms, as well as fixed generators.

Sensor location: At Spectral Dynamics I was a small part of a team which took great interest in instrumentation for failure discovery. There was clear evidence that the location and orientation of the acoustic/vibration sensors for various gearboxes was critical to gathering useful transient data for the electronics to evaluate. For example, using the main mast as the natural Y axis, and the plane of the planetary/sun gears as the X axis, it would seem that having the piezio-electric sensor aligned with the X axis is most effective. However, there are cases where the sensor alignment has shown better response when the vector moment is some degrees off axis, and aligned slightly to the Y axis(something to do with the materials di-pole moment of inertia? Beyond the scope here).

We only got a small taste of what additional sensors, real time analysis is taking place. Which is sad, because I think that even with this type of very small spall propagation it would be possible to detect using internal sensors in the gearbox, and characterization of the vibration signatures in real time. Of course, each gearbox changes its 'tune' with age and strain, but anomalies are really not very hard to detect, and the spalling taking place in what I've seen in the report, could quite possible have been detected, and a warning issued well before the complete failure. I will respectfully say that I have no idea how long spall 1 proceeded to spalls 2, 3, and 4 but my recall of the instances we had at Solar were that it was many operation hours before the system would self-destruct. Also, before anyone points out, I will point out that our sensors, and all gathering and analysis data was ground mounted, and presents a significant weight in a helicopter where weight is the enemy.

YMMV

[GenuineHoverBug]

As reported elswhere (https://www.pprune.org/rotorheads/607608-turoy-two-years.html) on this Forum, the draft final report was sent for consultation to interested parties on the 9th of February with a deadline for comments on the 10th of April 1018.

A report in the media (https://www.tu.no/artikler/ingen-vil-fly-dem-i-norge-na-skal-de-omstridte-helikoptrene-redde-liv-pa-island-i-stedet/439593) today has a statement from the head of the aviation department at the AIBN that the review of comments has been time-consuming due to the volume of comments and "objections". The review resulted in some changes and an amended draft final report was sent for a second round of consultation to some of the interested parties. The deadline for this second round was on the 13th of June. He also states that the final report should be out before the summer hollidays (which in Norway is about a month earlier than most of Europe.)
The article also for some reason mentions the possibility, according to Annex 13, for a State (formally) to append a dissenting view regarding technical aspects of the Final Report "upon which no agreement could be reached".

[Apate]

I wonder which interested party made the largest volume of comments and objections? The one that has the most to lose if the AIBN publishes what they really think presumably :}

Doesn't Airbus realise that their biggest issue now isn't a technical one, but one of trust? Behaving in such a way to try and protect a dying product will do nothing to repair damaged reputation.

Publishing a "dissenting" appendix by an OEM is a pretty rare occurance IMHO, but was exactly what happened in the accident report for the 1980 Malaysian SA330 Puma fatal crash in Brunei. Which was due to "second stage epicyclic module planetary gear fatigue failure caused loss of the main rotor" :eek: :eek:

I do find the way that Airbus has behaved since the day of the accident to be very disappointing and actually worse than I would have ever imagined. :(

[SASless]

The PR issue notwithstanding....will the Final Report actually determine the cause for the failure of the component(s) that led to the fatal crash?

That is the real issue....with the PR thing merely being collateral damage AH brought upon itself.

I question the wisdom of letting an "interested party" write parts of my Report....after all....don't they have an interest in how the Report turns out that is plainly a challenge to the truth at times?

[Mee3]

It could well be the parties that called the finding before actually finding anything having hard time to back track their claim?

[birmingham]

The PR issue notwithstanding....will the Final Report actually determine the cause for the failure of the component(s) that led to the fatal crash?

That is the real issue....with the PR thing merely being collateral damage AH brought upon itself.


You have hit the nail squarely on the head.

Parties who contributed to the report should be careful to limit any objections to matters that can substantiated by hard facts.

[BluSdUp]

Good Morning.
The Norwegian NTSB has finished the report and it will be published Friday 6 July.
I expect there to be a press conference, and hopefully some in English.
Regards Cpt B

[GenuineHoverBug]

What the AIBN has announced is that there will be a press conference on Thursday the 5th of July at 1330 Norwegian time, in Bergen.
The final report will be made available on the AIBN website then, in English, and a condenced version in Norwegian.

[birmingham]

What the AIBN has announced is that there will be a press conference on Thursday the 5th of July at 1330 Norwegian time, in Bergen.
The final report will be made available on the AIBN website then, in English, and a condenced version in Norwegian.

This will be very interesting - what an incredibly difficult investigation. Hopefully they had enough evidence to get to the bottom of what caused this. That is in everyone's benefit.

[JMACDAS]

It is Brimingham. But this pprune. Where no one is ever satisfied. Watch what follows....

[BluSdUp]

I would like to ask a rather strange question, if you all do not mind!
In the Helicopter world in general and Offshore , in particular: Do You think the Norwegian AIBN have the resources, technical expertise , operational expertise and the independence from politics and manufacturers to cover this case!
I think they do, but we may have this sorted before the report.
Keeping in mind there is two sides at 180 degree opposite view. Unions in the north-sea hates it , Airbus loves it.
Regards
Cpt B

[birmingham]

I would like to ask a rather strange question, if you all do not mind!
In the Helicopter world in general and Offshore , in particular: Do You think the Norwegian AIBN have the resources, technical expertise , operational expertise and the independence from politics and manufacturers to cover this case!
I think they do, but we may have this sorted before the report.
Keeping in mind there is two sides at 180 degree opposite view. Unions in the north-sea hates it , Airbus loves it.
Regards
Cpt B

The fact that the unions don't like it is not a problem for the AIBN. That and the flat market for offshore heavies is all part of the realpoletik of the business.
The AIBN do have the resources, and they can call upon other agencies/laboratories when needed. I do however think AH's response to this and some of their public statements have been quite extraordinary. Who is right and who is wrong can only be determined by an evidence based, impartial report which hopefully we will see soon. My bigger worry is whether AIBN have been able to get to the bottom of this and establish definitive cause ie why not what happened. No matter how good the agency, in the real world, this is not always possible.

[SASless]

Worse Case Scenario.....the actual root cause of the failure(s) cannot be determined with specificity.....then what?

Do we not have approval from several Authorities for the 225 to continue in service?

How does that work....a known fatal problem and no known determination of cause...yet an Authority approves the aircraft to be flown?

[BluSdUp]

SASless and Birmingham
Thanks
The main thing is we do not want to see another helicopter fall utterly helpless like that!
We have all lost great pilots, but most of them at least could fight for survival on the way down,,,,,.

Lets hope we have something concrete from the report.
Regards
Cpt B

[Mee3]

love how sas can pretend to impartial and then take a cheeky slap at EC.

[SASless]

Catch up Old Man....it is AH now.

The question posed is straight forward and if you care to check it....the slam would be on the Authorities that would allow the aircraft to be put back in service AFTER no cause was determined. (One must read the post carefully as it dealt with a hypothetical situation.)

I believe the gentlemen doth protest too much.

[RVDT]

BSU,

I would like to ask a rather strange question, if you all do not mind!
In the Helicopter world in general and Offshore , in particular: Do You think the Norwegian AIBN have the resources, technical expertise , operational expertise and the independence from politics and manufacturers to cover this case!
I think they do, but we may have this sorted before the report.
Keeping in mind there is two sides at 180 degree opposite view. Unions in the north-sea hates it , Airbus loves it.
Regards
Cpt B

Accident Investigation from the State of Manufacture will be heavily involved and in this case the French BEA - Bureau d'Enquêtes et d'Analyses pour la Sécurité de l'Aviation Civile

[birmingham]

Catch up Old Man....it is AH now.

The question posed is straight forward and if you care to check it....the slam would be on the Authorities that would allow the aircraft to be put back in service AFTER no cause was determined. (One must read the post carefully as it dealt with a hypothetical situation.)

I believe the gentlemen doth protest too much.

Well that has already happened hasn't it? The A/C was cleared well before the final report but the AIBN and AAIB held back permission to resume flying for some time after it was granted by the Europeans/Americans etc.. The A/C remains approved with operational restrictions.

There have been a number of troubling dissenting statements; from the initial "suspension bar" theory, through to apparent comments that have been reported to have been added to the, as yet unpublished, final report. If we still don't have a cause and we still don't have a consensus we don't really have a long term solution do we? To move this forward requires the publication and review of the AIBN's final report which we are told will be with us next week.

From the outside looking in it certainly seems to have been a very difficult exercise logistically, scientifically, emotionally and politically.

[212man]

The AIBN and AAIB don’t give ‘permission’ for anything - it’s the national aviation authorities and EASA that do that.

[SASless]

The question still stands...if no definitive cause identified....thus allowing for a reliable method to prevent yet another catastrophic failure of the Rotor System as seen in the Norway crash....should the Authorities withdraw their approval of the aircraft to be flown?

It does not matter the Make, Model, Type, or Mark .... airplane or helicopter.....where should the line be drawn to ensure safety in these situations?

Should it be a mad game of Russian Roulette where you pays your money and takes your chances or should the Bar be set a bit higher than that?

[birmingham]

The press conference and report (https://www.aibn.no/About-us/News-archive/The-Helicopter-Accident-near-Turoy-Invitation-to-press-conference-in-connection-with-the-publication-of-the-final-report-5-July-2018) are out tomorrow. Hopefully some definitive news ...

[birmingham]

Report is published 1330 Norway time tomorrow. Hopefully it will be able to shed some much needed light on the cause.
link to AIBN (https://www.aibn.no/About-us/News-archive/The-Helicopter-Accident-near-Turoy-Invitation-to-press-conference-in-connection-with-the-publication-of-the-final-report-5-July-2018)

[birmingham]

Report out tomorrow

https://www.aibn.no/About-us/News-archive/The-Helicopter-Accident-near-Turoy-Invitation-to-press-conference-in-connection-with-the-publication-of-the-final-report-5-July-2018

[GenuineHoverBug]

The final report (https://www.aibn.no/Aviation/Published-reports/2018-04) has been published.

12 Safety recommendations: 9 to EASA, 1 to The Commission, 1 to ICAO and 1 to Airbus.

An Appendix I from Airbus Helicopters is included:
"... Airbus Helicopters agrees with the overall analysis and conclusions set out in the Report in relation to the root cause of the accident as well as the AIBN's proposed Safety Recommendations. The comments presented below focus on certain aspects of the Report which, in the interests of aviation safety, Airbus Helicopters consider important to be noted."

[birmingham]

"The Accident Investigation Board Norway recommends that Airbus Helicopters revise the type design to improve the robustness, reliability and safety of the main gearbox in AS 332 L2 and EC 225 LP."

[airsound]

Very interesting. For laypeople, I strongly recommend the 4mins 34secs video which you can download from the end of the list of downloadable appendices - or from the end of the 'downloads' column on the right.

airsound

[SASless]

What the Certification Authorities and AH (....and other designers) do now shall be very interesting.

The Report points out some issues that affect the Industry as a whole.

AH has some “splaining” to do about the success rate of second stage components making it to Design Life.

[jimcarler]

This is what AH is saying https://www.airbus.com/helicopters/info-centre/ln-ojf-accident-investigation-status.html

[jimf671]

What the Certification Authorities and AH (....and other designers) do now shall be very interesting.

The Report points out some issues that affect the Industry as a whole.

AH has some “splaining” to do about the success rate of second stage components making it to Design Life.

PLM, Product Lifecycle Management, is the favoured design regime of modern times. This, or some other term with a more aviation flavour may start to be heard more widely and taken more seriously if this report gets the attention it deserves.

And yes, implications for the industry as a whole, especially since this is the most examined helicopter type in history so we don't know what we don't know yet in respect of other types.

[AnFI]

And yes, implications for the industry as a whole, especially since this is the most examined helicopter type in history so we don't know what we don't know yet in respect of other types.

err ...
exactly, what we do know is that COMPLEXITY has a cost (not knowing what you don't know being one of them).
It is part of the price paid to buy engine redundancy.
That cost should be accounted for, you cant take the credit for the upside of engine redundancy without taking responsibility for the downside.

[Twist & Shout]

err ...
exactly, what we do know is that COMPLEXITY has a cost (not knowing what you don't know being one of them).
It is part of the price paid to buy engine redundancy.
That cost should be accounted for, you cant take the credit for the upside of engine redundancy without taking responsibility for the downside.

We will take that into account everytime a combining gearbox fails catastrophically. Irrelevant in this case, but even you know that. I hope.

[birmingham]

AH has some “splaining” to do about the success rate of second stage components making it to Design Life.


The tables around page 25 of the report go into some detail and as you would expect the situation is somewhat more nuanced. After REDL for example Heli One adopted a policy of replacing on first overhaul. They also most usually fitted the NTN-SNR variant which proved more resilient. Nevertheless, only 10% of both types combined made it to operational life.

What would be interesting is if any of our helicopter maintenance colleagues could take a look at the tables and tell us if the level of damage from in service operations is very different from other types?.

[Geoffersincornwall]

You can call me a cynic but in my experience, large organisations, whether public or private, have the necessary power-base to ensure that their version of events prevails and that the external dermis of such organisations is so Teflon-like that they will contrive to escape censure. We have already seen, I believe, their influence on the certification process that has seen national aviation authorities apparently bullied into accepting an analysis of the events that is in line with one of Europes largest and most powerful industrial entities wishes, not the truth. WTHIH !!!

G

[HeliComparator]

Seems like a very good report. I note that AH and EASA both come in for some stick for being obstructive in taking months to release relevant documents, and in AH's case not allowing the documents out of the factory due to their commercial sensitivity. Seems sad that once again commercial interest/secrecy/bureaucracy is put ahead of safety. AH also get some stick for smoke screening with their suspension bar theory. And how often have we heard about unreliable parts just being binned and replaced, without the cause of their unreliability being explored? (answer: often!).

[212man]

AH also get some stick for smoke screening with their suspension bar theory

Where do you see that? I looked and can only see reference to it be one of the options to be looked at and the quickly ruled out as they shown to be correctly mounted at the time of the break up.

[EESDL]

Not investigating why so many items failed to reach their design life will be gratefully accepted by the negligent lawyers.
i note ERA have already settled - agreeing to hold no one to blame....

[birmingham]

Not investigating why so many items failed to reach their design life will be gratefully accepted by the negligent lawyers.
i note ERA have already settled - agreeing to hold no one to blame....

The type is clearly still persona non grate in the North Sea. The unions still regard the unresolved issues too significant to rehabilitate the type.

Unite the Union: recent report shows Super Pumas should be banned from North Sea - Original 106 (http://www.originalfm.com/unite-the-union-recent-report-shows-super-pumas-should-be-banned-from-north-sea/)

[BluSdUp]

So!
Were does it go from here? The once so super Puma!
Are the new regime good enough for all N-CAAs and a bit like the 737-rudderhardover that got solved!
Or should the bird be grounded.
According to some here in Norway it must never fly again.
Any toughts
Regards
Cpt B

[jimjim1]

Every helicopter has components that must not fail in flight if disaster is to be avoided. It would appear that minimising these would be a desirable design goal.

It seems that it might not be essential to include pretty much the entire gearbox in the list of these critical components. Clearly any gearbox failure is likely to result in a loss of drive and a subsequent autorotation, however there seems no essential need to combine the gearbox with the support of the main rotor as seems to be commonly done.

The two EC225 crashes may have had a better outcome if these functions were separated.

I am fairly sure for example the the Robinson R22 separates the reduction gearbox (belts:-) from the rotor support structure.

It may of course be more challenging to arrange a 3,000HP helicopter that way as opposed to the 100HP Robinson but I don't see that it would be impossible or even impractical.

[Evil Twin]

Every helicopter has components that must not fail in flight if disaster is to be avoided. It would appear that minimising these would be a desirable design goal.

It seems that it might not be essential to include pretty much the entire gearbox in the list of these critical components. Clearly any gearbox failure is likely to result in a loss of drive and a subsequent autorotation, however there seems no essential need to combine the gearbox with the support of the main rotor as seems to be commonly done.

The two EC225 crashes may have had a better outcome if these functions were separated.

I am fairly sure for example the the Robinson R22 separates the reduction gearbox (belts:-) from the rotor support structure.

It may of course be more challenging to arrange a 3,000HP helicopter that way as opposed to the 100HP Robinson but I don't see that it would be impossible or even impractical.

Only one crash was a 225, the other a 332L2.:ok:

[SASless]

Yes we know....but there are some amazing similarities between the two types and the cause and result of the crashes would you not agree?

[aheoe26104]

The S76 MGB emergency procedure flows into monitoring for increase in vibration, torque and noise level.. I wonder if this failure has caused a rethink and if the design differences in gearboxes would change the result in a catastrophic failure of a sun gear? Over the years the loss of oil and dry run time on a gearbox have been topical but again, if any of those cracks exist and you have to contend with a run dry situation, (now things are really becoming very hypothetical..) then how would those sun gears or any other component with subsurface cracks respond?
The comment below has just started me thinking..
"Following that, given that it might not be possible to assess the fatigue reliability of internal gearbox components, it recommends EASA require a fail-safe main gearbox, in which no failure of an internal component leads to a catastrophic failure." (https://www.verticalmag.com/news/norway-h225-crash-report-recommends-changes-to-super-puma-type-design/)

[riff_raff]

I have some experience with epicyclic gear drive design. And when I looked at a cross section drawing of this gearbox, one thing that seemed questionable to me was the rim section thickness of the 2nd stage planet gears. The radial section thickness at the face width center appears to be less than 1x the gear tooth whole depth. I recall being given a stern lecture by a very experienced gearbox designer about making sure to provide plenty of rim section thickness with planet gear configurations like this. The alternating 2/rev tension/compression stress cycles at the bearing race surface resulting from "bending" of the rim will be more of a problem than you would think. There is a great illustration on page 8 of appendix H that shows how the planet gear rim deforms under load

It is also important to apply a suitable analysis factor to account for unequal load distribution between the planet gears. For this particular arrangement of eight planet gears with good accuracy mounted on fixed carrier pins, AGMA recommends using an analysis load factor of 1.3. Unfortunately, the analysis report produced by Romax Technology in appendix H (https://www.aibn.no/Aviation/Published-reports/2018-04?iid=24468&pid=SHT-Report-Attachments.Native-InnerFile-File&attach=1) assumes equal load sharing between all eight planet gears, which would be much lower loading than industry recommendations.

[bigglesbutler]

I have some experience with epicyclic gear drive design. And when I looked at a cross section drawing of this gearbox, one thing that seemed questionable to me was the rim section thickness of the 2nd stage planet gears. The radial section thickness at the face width center appears to be less than 1x the gear tooth whole depth. I recall being given a stern lecture by a very experienced gearbox designer about making sure to provide plenty of rim section thickness with planet gear configurations like this. The alternating 2/rev tension/compression stress cycles at the bearing race surface resulting from "bending" of the rim will be more of a problem than you would think. There is a great illustration on page 8 of appendix H that shows how the planet gear rim deforms under load

It is also important to apply a suitable analysis factor to account for unequal load distribution between the planet gears. For this particular arrangement of eight planet gears with good accuracy mounted on fixed carrier pins, AGMA recommends using an analysis load factor of 1.3. Unfortunately, the analysis report produced by Romax Technology in appendix H (https://www.aibn.no/Aviation/Published-reports/2018-04?iid=24468&pid=SHT-Report-Attachments.Native-InnerFile-File&attach=1) assumes equal load sharing between all eight planet gears, which would be much lower loading than industry recommendations.
So for a layman would the required redesign be a new gearbox or could they redesign the inside whilst not increasing the gearbox outside dimensions too much?

[Geoffersincornwall]

As so often the case in helicopter design, the 'weight engineers' have it over the others. I remember a video conference held by Shell Aircraft at LHR with the engineering guys at Sikorsky following a number of issues caused by components with a lack of tolerance to any kind of minor abuse (dent, scratch knock). The chairman invited the Sikorsky Chief Engineer to take a flight bag containing 30kg of metal and "put it back in the airframe". When you trim the margins to 1 x the critical load factor I guess you are the very definition of someone pushing their luck - actually YOUR luck. BTW there was only a chuckle from the three engineers in the US.

G

[Fareastdriver]

Epicyclical automatic transmissions installed in automobiles are built up and then inserted into the gearbox. This means that the orbital gear is separate from the gearbox case. The 225 problem is that this gear is integral with the gearbox case so any damage affects the main rotor support structure. A complete redesign where the reduction gearing is separate from, with sufficient room for debris to be ineffective, might be the answer.

You are still going to lose the drive to the main rotor but at least you will have still have some form of control in autorotation as long as you do not shut down the engines.

The gearbox will be bulkier and a bit heavier but it should still be able to fit within the doghouse.

[Geoffersincornwall]

I believe the MD902 has a design that separates the rotor support from the main gearbox such that the rotor loads are transmitted to the airframe directly and not through the transmission.
G

[SASless]

We have had similar discussions in the past about the difference in MGB design philosophy between the European and American methods.

There is a difference.

The major difference is the “Load Bearing” and damage resistance post internal failure.

Perhaps a qualified Design Engineer could provide us an accurate summary of the differences between the S-92 and 225 gearbox designs?

[birmingham]

Only one crash was a 225, the other a 332L2.:ok:

True but relevant only to the extent that these are the two models that share the eight planet gear design that has resulted in the two accidents.
Both the lower power/weight 332L2 and later H225 designs have suffered near identical failures resulting in major loss of life.

The flaw remains in both types.

As the AIBN put it ...


"The protective measures in the RTS likely reduce the product’s exposure to unsafe
conditions leading to another catastrophic event."

but ...

"The following issues are currently not fully resolved:
- Data, analyses and tests do not conclusively prove that the planet gears still in
service will not have the potential to develop subsurface and possible
undetectable fatigue cracks from a surface damage."

All depends on the degree of risk that individual customers/operators/travellers are prepared to accept

[aheoe26104]

Where do you see that? I looked and can only see reference to it be one of the options to be looked at and the quickly ruled out as they shown to be correctly mounted at the time of the break up.
Page 143 of the report..
"2.8.6.2 Despite the intentions of the G-REDL test program and the safety measures introduced to improve the chip detection system, the AIBN finds that the actions undertaken by Airbus Helicopters following the G-REDL accident could have been more effective with regards to a possible scenario with limited spalling, assessing the effectiveness of the detection system and reviewing the MGB design features. The AIBN also finds that the oversight of Airbus Helicopters by EASA could have been more effective with regards to implementation of the safety recommendations and the follow-up on the information from the G-REDL accident report. In summary, Airbus Helicopters and EASA did not successfully manage to realise the safety potential from the G-REDL accident report."

and

"2.13.1.3 The AIBN understands EASA’s obligation to follow its procedures as a public administrative body. However, the AIBN had to wait for two to six months before receiving some of the documents from EASA and consequently this influenced the progress of the investigation."

further

"2.14.1.2 Further, it is essential for the AIBN to assess the safety actions already taken following this accident in order to issue relevant safety recommendations. In addition, this investigation has been affected by the grounding of the AS 332 L2 and the EC 225 LP helicopters and the subsequent effort by Airbus Helicopters and the regulators concerning the return to service (RTS) (see Appendix F). During this process, important information related to the return to service was delayed or not disclosed to the AIBN."

and

"2.14.2.3 On 7 October 2016, EASA lifted the flight prohibition based on the RTS actions put in place by Airbus Helicopters. According to EASA, the mandated RTS actions ensured airworthiness was restored at an acceptable level of safety in accordance with Part 21 and EASA procedures. Furthermore, the CARI was developed to make further improvements (see Appendix F to the report).
2.14.2.4 The investigation was ongoing with important aspects still open. The AIBN understands EASA’s role and Airbus Helicopters’ position, but would have expected a more precautionary approach at the time, since the accident involved a critical part in which failure has led to two catastrophic events. The national bans on flying in Norway and UK imposed by the CAAs remained in place."



In this section and paragraphs of the report it becomes pretty clear that more should have been done by both Airbus and EASA.

[aheoe26104]

https://cimg0.ibsrv.net/gimg/www.gmforum.com-vbulletin/1450x339/new_gearbox_d0e77651f72694f1593607056ed1cf0c538cb02a.jpg

This can go anywhere including finally killing the Puma (of all models..)

[HeliComparator]

Where do you see that? I looked and can only see reference to it be one of the options to be looked at and the quickly ruled out as they shown to be correctly mounted at the time of the break up.
para 2.11.3.1
Page 149-150.

well perhaps “stick” is an exaggeration, but reading between the lines the smokescreen was noted!

[ericferret]

The comments on weight saving made me smile. The AW169 has dozens and dozens of titanium screws holding on various panels.
Every time an engineer rounds one out it is going to cost about 30 dollars a steel equivalent is less than dollar.
Seems to be a new AW profit centre AW 139 winglet screws are even worse for price.
AW must have shares in a screw factory.
The number of screws holding purely trim panels is past a joke, try getting access in the baggage bay to the avionics.

[twisted wrench]

ericferret: The S92 is the same majority of the panels are held on by Titanium screws.

[Hot_LZ]

Place all of those titanium screws in a bag and weigh them and then do the same with their steel counterparts and see what the weight difference is....

LZ

[industry insider]

From Helihub (Source ERA)

The following statement, issued by Era Group to the US Securities & Exchange Commission (original here (https://www.sec.gov/Archives/edgar/data/1525221/000152522118000082/a732018era8-ksettlement.htm)), states that Airbus has agreed a $42 Million payout to Era relating to the operators purchase of eleven H225s.

“On July 3, 2018, Era Group Inc. (the “Company”) and Era Helicopters, LLC (together with the Company “Era”), entered into a litigation settlement agreement (the “Settlement Agreement”) with Airbus Helicopters, Inc. and Airbus Helicopters, S.A.S. (together “Airbus”) in the matter of Era Group Inc., and Era Helicopter, LLC v. Airbus Helicopters, Inc., and Airbus Helicopters, S.A.S (the “Action”). The Settlement Agreement settles all claims made by Era against Airbus related to Airbus’ marketing and sale, and Era’s purchase, of eleven H225 model helicopters. Pursuant to the Settlement Agreement, Airbus has agreed to pay Era $42.0 million in cash and provide Era with certain trade account credits that may be used by Era for up to five years. Era has agreed to release Airbus from any and all liabilities, claims, counterclaims, demands, complaints, costs, losses and expenses relating to the Action and to dismiss the Action with prejudice without any party admitting fault.”

Looks like the value that Airbus is prepared to pay for each now useless offshore H225 is about $3.8m (approx 15c - 20c on the $ purchase price for fleet buyers) I expect that this will set the benchmark for other compensation claims from owners of 225s wanting out.

After the AIBN report which is fairly damning, its hard to see how flying the 225 with passengers can be justified. It will be interesting to see if those 225s which have remained in service with the Airbus reduced gearbox overhaul life and FFMP continue in service or are quietly withdrawn.

[birmingham]

From Helihub (Source ERA)

The following statement, issued by Era Group to the US Securities & Exchange Commission (original here (https://www.sec.gov/Archives/edgar/data/1525221/000152522118000082/a732018era8-ksettlement.htm)), states that Airbus has agreed a $42 Million payout to Era relating to the operators purchase of eleven H225s.

“On July 3, 2018, Era Group Inc. (the “Company”) and Era Helicopters, LLC (together with the Company “Era”), entered into a litigation settlement agreement (the “Settlement Agreement”) with Airbus Helicopters, Inc. and Airbus Helicopters, S.A.S. (together “Airbus”) in the matter of Era Group Inc., and Era Helicopter, LLC v. Airbus Helicopters, Inc., and Airbus Helicopters, S.A.S (the “Action”). The Settlement Agreement settles all claims made by Era against Airbus related to Airbus’ marketing and sale, and Era’s purchase, of eleven H225 model helicopters. Pursuant to the Settlement Agreement, Airbus has agreed to pay Era $42.0 million in cash and provide Era with certain trade account credits that may be used by Era for up to five years. Era has agreed to release Airbus from any and all liabilities, claims, counterclaims, demands, complaints, costs, losses and expenses relating to the Action and to dismiss the Action with prejudice without any party admitting fault.”

Looks like the value that Airbus is prepared to pay for each now useless offshore H225 is about $3.8m (approx 15c - 20c on the $ purchase price for fleet buyers) I expect that this will set the benchmark for other compensation claims from owners of 225s wanting out.

After the AIBN report which is fairly damning, its hard to see how flying the 225 with passengers can be justified. It will be interesting to see if those 225s which have remained in service with the Airbus reduced gearbox overhaul life and FFMP continue in service or are quietly withdrawn.

It will - the current market conditions must make a complete redesign out of the question - especially given that even the successor airframe has been pushed into the long grass. They still have military/parapublic customers for other Puma types. So I would imagine that they are digesting the report - whose conclusions they have accepted, and are making up their minds how far they can go. If withdrawing the fleet is cheaper than implementing the recommendations then what would you do?

[DOUBLE BOGEY]

An awful lot of outstanding technology lost due to one critical defect. For those of you who have never flown a 225 this will be lost on you.

[industry insider]

An awful lot of outstanding technology lost due to one critical defect. For those of you who have never flown a 225 this will be lost on you.

Only the envelope protection and autopilot DB.

The rest of it was not so special. The fuel system was from 1960s, the engines were old and smokey, the rotor system was nothing really new with no icing clearance etc. All in all, the 175 made it look very old.

[HeliComparator]

Only the envelope protection and autopilot DB.

The rest of it was not so special. The fuel system was from 1960s, the engines were old and smokey, the rotor system was nothing really new with no icing clearance etc. All in all, the 175 made it look very old.

Well no, the rotor system was a big improvement over the L2, very smooth at high speed and high weight. The EFIS is still the best IMO - simple but effective. By comparison, that on the S92 and the AW189 look like the scribbling of a child, far too much information, not at all calm, logical and inuitive as the 225 is. The engines became less smokey after a mod to the oil breather system. Rotor de icing was available, just not needed our side of the N Sea.

The 175 May or not be a good helicopter, too soon to know if it has a fatal flaw. And I didn’t like it not having a centre screen, bad HMI because it means that when something goes wrong you have to use one of the screens for system info, which means the PF and PM do not have the same info. How can you be an effective PM if your screens aren’t showing the same as PF?

But unfortunately a helicopter is only as good as its weakest link.

[SASless]

When the “weak link” is Rotor Head retention.....that pretty much kills the deal.....and everyone aboard when that minor flaw occurs.

[Fareastdriver]

The only reason that the 225 was smoother than the 332 predecessors was that they put five blades on it. In the early days of the 330 there were concerns over the vibration level. They were at the point of cutting metal for a five bladed head when somebody came up with the idea of the barbeque plate to isolate the rotor vibrations for the fuselage.

From that point on all Pumas from the 330 B to the 332L2 were condemned.

[HeliComparator]

When the “weak link” is Rotor Head retention.....that pretty much kills the deal.....and everyone aboard when that minor flaw occurs.
If that’s your idea of a minor flaw I would hate to see one of your major flaws!

Although it has to be said that most of the time, the rotor head didn’t fall off. But from an airworthiness point of view it does seem to be a dead duck. Of course we have had a few “pilot error” fatal accidents and near misses on other types that couldn’t have happened on the 225. So the 225 trades a fundamental flaw in helicopters - the pilots! - with another fundamental flaw - the rotor head falling off. From a pilots’ point of view I can see why they wouldn’t like it since most pilots think that a pilot-error fatal accident could never happen to THEM, only to others. But for the passengers, a dispassionate calculation would probably show that the 225 was safer than many other types.

[Pablo332]

After the improvements how many 225s are flying civilians?

[Twist & Shout]

After the improvements how many 225s are flying civilians?

What improvements?
I’m only aware of smoke, mirrors and increased monitoring.

[cyclic]

HC, I know you have been out of the game a while but why do you need to monitor the systems on a 175? The hierarchy is such that you never look at the ‘systems’ unless there is a reason to. The master list concept made the 175 a whole lot better than the 225. As for the mechanicals, as you say, only time will tell but it does seem a great deal less frantic than the 225. AH are being extremely cautious with the gearbox. I do hope it is a success in the long run as it is the most quiet, smooth and fast rotary machine I have ever flown. Take it to a FL and it is like a plank wing....apart from the orange suit, underwater breathing apparatus and life jacket...and the constant awareness that it is all about to go wrong...

[Pablo332]

What improvements?
I’m only aware of smoke, mirrors and increased monitoring.

Should have posted ‘improvements’ in italics my apology.

Anyone flying people who have a choice in a 225?

[Mars]

The following article from 'Helihub' appears to capture reservations held by a number on PPRune.

"The Final Report is also worrying. The following are the key features that cause most concern:

There is no way of assuring detection of possible failure of the MGB sufficiently in advance of total failure. There was no spalling detected during the growth in cracks in the planet gears and thus little or no probability of detecting cracks growing before a complete fracture (section 2.4.2.6), the investigation discovering that the oil cooler acted as a particle trap preventing 44% of the debris from reaching the oil filter including the largest particles (section 2.5.7). Airbus have improved the capture of particles in the oil by introducing a new full flow magnetic plug increasing the capture rate from 12% to 50% and strengthened inspection criteria and equipment allowing a more detailed analysis of these particles.
Airbus Helicopters and the European Aviation Safety Agency (EASA) did not realise the safety potential from the G-REDL accident report (section 2.8.6.2). The G-REDL report was described as a “turning point with respect to the continued airworthiness of the AS 332 L2 and the EC 225 LP helicopters”, the UK’s Air Accident Investigation Branch (‘AAIB’) making safety recommendations clearly relevant to the LN-OJF accident which were not followed through by EASA or Airbus (section 2.1.1.3). In particular, the Final Report of the AIBN (section 3.2.9) found that:

“Less than 10 % of the second stage planet gears ever reached their intended operational time before being rejected during overhaul inspections or non-scheduled MGB removals due to signs of degradation.
Airbus Helicopters did not perform systematic examination and analyses of unserviceable and rejected second stage planet gears in order to understand the full nature of any damage and its effect on continued airworthiness.
Airbus Helicopters did not section and inspect any of the second stage planet gears that were scrapped during overhaul. Therefore, it remains uncertain whether any of these gears had subsurface cracks similar to observations made on LN-OJF.
The differences between the two planet gear bearing designs had not been previously assessed through in-service statistics and calculations.”

EASA and Airbus acted precipitately when EASA removed the flight prohibition on the H225 on 7 October 2016, with the investigation ongoing and important aspects still open: “The AIBN understands EASA’s role and Airbus Helicopters’ position, but would have expected a more precautionary approach at the time, since the accident involved a critical part in which failure has led to two catastrophic events” (section 2.14.2.4).
The following issues are currently not fully resolved (section 3.2.11):

Data, analyses and tests do not conclusively prove that the planet gears still in service will not have the potential to develop subsurface and possible undetectable fatigue cracks from a surface damage;
The capability to detect and interpret metal particles of few mm2 in the MGB oil system to prevent critical failure;
Why the cracks in the outer race grew subsurface into the gear bulk material and finally resulted in a fatigue fracture while creating limited spalling.


Airbus do state that they have reduced these risks by replacing planet gears equipped with the type present on LN-OJF to the alternative manufacturer, while at the same time reducing the life limit.

“Two catastrophic events and the service experience of few second stage planet gears reaching their operating time limit, may suggest that the operational loading environment, on both AS 332 L2 and EC 225 LP, is close to the limit of endurance for the design” (section 2.14.4.1).

In response to the Final Report, Gilles Bruniaux, Head of Aviation Safety issued a statement on the Airbus website (https://www.airbus.com/helicopters/info-centre/ln-ojf-accident-investigation-status.html) which includes the following quote:

“the available degree of scientific and technical knowledge meant it was neither foreseeable nor foreseen that a crack in a plant gear could propagate in a sub-layer, and as a result generate very low levels of detectable particles…With knowledge gained from this investigation, Airbus Helicopters has introduced a series of safety measures on the H225. Some of the technology that has been developed is ground-breaking for the helicopter industry. Airbus Helicopters will continue to pursue innovations and improve safety standards through a proactive approach that sees us challenge internally everything we do. Work on a number of potential improvements to the H225 are in progress, and I remain optimistic that this concerted and complex work will yield new advances.”"

[Toomanyflthrs]

Greetings from the GOM. Food for thought, though I’ve not read nor heard anyone linking the two Puma characteristics:

1) Makila engines compressor stall regularly. (Normal for all gas turbines, according to Eurocopter/Airbus). After personally experiencing it in the 225 I can testify it is moderately violent and affects the entire drive train and airframe.

2) Components within the gearbox have a history of failing.

Any thoughts on the shock of multiple compressor stalls on MGB components?

[jimf671]

... ... But for the passengers, a dispassionate calculation would probably show that the 225 was safer than many other types.

That is where I stand, HC. There is no current sign of there being a search for intelligent life in the UK North Sea, so the subject doesn't really come up. However, if I were getting on a helicopter at Dyce or Scatsta tomorrow then I would happily get on the world's most examined rotorcraft, which is the 225. The numbers tell me that is the correct approach.

I still fly in 92s for other purposes. It's a great aircraft and along with the 225 has given us a huge step forward in large rotorcraft safety during the last 14 years but I remain a little suspicious of it. Quite a few ifs and buts in its engineering history though nothing compared to many older types of course. These subjects are so distorted by people happily ignoring hundreds of deaths that have occurred across the history of the helicopter.

[SASless]

These subjects are so distorted by people happily ignoring hundreds of deaths that have occurred across the history of the helicopter.

More a cautious concern about possible future deaths I would suggest.

It is hard to reckon with the findings of the AAIB Report quoted by Mars.

A loss of two Rotor Heads in fairly short succession....does give grounds for pause don't you think?

Before you challenge the above, consider I would be saying the same thing no matter the Type.

Every "new" aircraft will have unforeseen issues no matter how good its designers think they are....the 92 and 225 are alike in that.

The difference being the 225 issues have not been completely sorted to the satisfaction of the AAIB as I read it.

Are they not supposed to be the Subject Matter Experts when it comes to analyzing these kinds of things?

[GrayHorizonsHeli]

my eyes hurt Mars....thanks for the RED text :ooh:

[Jimmy.]

Greetings from the GOM. Food for thought, though I’ve not read nor heard anyone linking the two Puma characteristics:

1) Makila engines compressor stall regularly. (Normal for all gas turbines, according to Eurocopter/Airbus). After personally experiencing it in the 225 I can testify it is moderately violent and affects the entire drive train and airframe.

2) Components within the gearbox have a history of failing.

Any thoughts on the shock of multiple compressor stalls on MGB components?


I don't have the technical background needed to support or refuse your idea, but it can be verified, considering all compressor stalls shoul be recorded by the M'MARMS and reported as well.

[Geoffersincornwall]

I'm retired now so I can look back on a 50-year career in aviation and contemplate what I have learnt about human nature in that time. The saga of the AH and EASA 'shortcomings' in this sad tale has served to underline the fact that justice is inversely proportional to the size/power/money available to the transgressor. If you are lucky enough to have access to any of those 'assets' then 'getting-out-from-under' is a mere formality. The only good thing I have to say about such villainy is that it helps to provide a good plot-line for my next book. Look out for the crooked engineering manager in the next crime thriller at www.geoffnewman.co.uk

[SASless]

Will the Engineering Manager be named Jethro and be Cornish with a sense of humor?

[HeliComparator]

HC, I know you have been out of the game a while but why do you need to monitor the systems on a 175? The hierarchy is such that you never look at the ‘systems’ unless there is a reason to. The master list concept made the 175 a whole lot better than the 225. As for the mechanicals, as you say, only time will tell but it does seem a great deal less frantic than the 225. AH are being extremely cautious with the gearbox. I do hope it is a success in the long run as it is the most quiet, smooth and fast rotary machine I have ever flown. Take it to a FL and it is like a plank wing....apart from the orange suit, underwater breathing apparatus and life jacket...and the constant awareness that it is all about to go wrong...

I’m a bit slow to come back to,you, but I don’t think you read my post properly. I said “when things go wrong”. I totally get the absence of need to monitor systems when everything is working fine, which is hopefully 99.9% of the time, and so PM can monitor with the same info that PF has. But in that rare crisis situation where something is going wrong, just when the pressure is suddenly on the PM can no longer monitor the PF optimally because one of his screens is used to display systems info. So just when workload and stress are at maxima, the PM’s effectiveness is degraded.

[Geoffersincornwall]

SAS - Just remember that the train to Plymouth from Penzance doesn't stop at Camborne on Tuesdays.

As to which of the OEM hierarchy should be painted the 'villain' we need a story-line that creates uncertainty and multiple possible transgressors.

Remember the golden rule of The Peter Principle' (people are promoted to their own level of incompetence) - all employees are required to be 'TEAM PLAYERS' which, when translated into corpoarte reality means that YOU play the game but THEY (management) ram the bat up your a****e.

[SASless]

HC....Having a PM looking over your shoulder is nice....not necessary.

The PM can relieve the PF of some of that stress by analyzing and troubleshooting and offering up a plan of action while the PF.....flies the aircraft....right?

We did all this Single Pilot long before "Screens" and automation were heard of and it worked.

Do you reckon Pilots...PM or PF are less capable today because of the very Technological advances and changes in Training/Cockpit Procedures?

Are they really becoming "Children of the Magenta"?

[S92PAX]

That is where I stand, HC. There is no current sign of there being a search for intelligent life in the UK North Sea, so the subject doesn't really come up. However, if I were getting on a helicopter at Dyce or Scatsta tomorrow then I would happily get on the world's most examined rotorcraft, which is the 225. The numbers tell me that is the correct approach..
Could you explain this please in case I have misunderstood your meaning?

[cyclic]

True HC but having done plenty of emergencies in the sim, it has never been an issue. You can display so much more on the PFD that the PM is really at no disadvantage when it comes to monitoring the PF. The systems are a great deal simpler than the 225 as well, so time spent diagnosing is much reduced and it does a lot more for you. If you thought the 225 was smooth then the 175 is like wafting along on a magic carpet! You don’t go deaf after a double either...

[HeliComparator]

HC....Having a PM looking over your shoulder is nice....not necessary.

The PM can relieve the PF of some of that stress by analyzing and troubleshooting and offering up a plan of action while the PF.....flies the aircraft....right?

We did all this Single Pilot long before "Screens" and automation were heard of and it worked.

Do you reckon Pilots...PM or PF are less capable today because of the very Technological advances and changes in Training/Cockpit Procedures?

Are they really becoming "Children of the Magenta"?

I appreciate that you are one of those Single Pilots (never married?) who always flew perfectly and never had any self-induced near misses or accidents. But unfortunately that does not apply to all Single Pilots. There was plenty of crashery - it's just that you have blotted that bit out! And let's remember that most of your Single Pilot flying was VFR. It's a bit easier when you can see what you are doing!

Anyway the point of multi-crew is to improve safety. Most people think it does, although I realise that not all do. Single Pilot can be fairly safe. Multi pilot can be safer. It's just a matter of degree. However the benefits of multipilot only occur if the crew operate together well (I think someone once said it was called CRM) and the chap not in charge is empowered to make interventions. Also, during critical phases of flight, it helps if the other chap can see the same "picture" as the pilot - it's hard to monitor someone if you can't see what they can see. Therefore if you are going to design a new helicopter to be as safe as can be (and bearing in mind that the humans are probably the least reliable bit) why not maximise the crew's ability to work together by giving them the same information - even and especially when things are going up the creek?

PM and PF are not becoming less capable these days, it's just that the skill set is changing. Less importance is now placed on the captains ability to shout orders and ensure everyone knows he is the boss, less importance on the copilot doing a good impression of a quivering subservient wreck, and more importance on working together to ensure a good outcome. Scary, isn't it!

[HeliComparator]

True HC but having done plenty of emergencies in the sim, it has never been an issue. You can display so much more on the PFD that the PM is really at no disadvantage when it comes to monitoring the PF. The systems are a great deal simpler than the 225 as well, so time spent diagnosing is much reduced and it does a lot more for you. If you thought the 225 was smooth then the 175 is like wafting along on a magic carpet! You don’t go deaf after a double either...

Yes I had a jolly in a 175 a few years ago so I know it is nice to fly! But that was the point when I noticed the screens weren't optimal. Obviously one can cope with only 4 screens, but I still maintain 5 would have better. Surely you can see that if you are used to 2 screens displaying flight info, and suddenly in an emergency you are down to 1 whilst the other chap still has 2, you are worse off than if you had the extra one because you not only have an abnormal screen setup to display the flight (instrument approach etc) but you also now have the stress of an emergency to deal with?

[SASless]

HC,

Nice Rant....but you have some facts out of whack.

I am familiar with single pilot IFR in several kinds of aircraft....fixed and rotary.

Yes lots of VFR/VMC but enough VFR/IMC and IFR/IMC to know of what I speak.

I don't suppose in your modern world....one can lean over towards the other pilots side and monitor events on his side of the cab....or is that not allowed these days?

When you were instructing....did you demonstrate maneuvers using your instruments or the Student's?

During an Instrument Approach....what critical information is not displayed on the on the Non-Handling Pilot's side that cannot be seen on all of the other sources?

Are you, as usual, trying to make a Mountain here?

I would be far more concerned about hidden screens....that layered as malfunctions occur and you have to work your way down through the stack because the system does not present the most critical failure ahead of all of the others.

The lack of a Screen surely has nothing to do with CRM.....or do you wish to explain how you took that road off the Roundabout?

[cyclic]

HC, as the first UK operator of the type we are still learning but my experience during some fairly involved LOFT scenarios doesn’t show that using 4 screens instead of 5 is a disadvantage. We will have to agree to disagree! Still a brilliant machine which is even safer to fly in terms of the flight envelope protections than the 225.

[Flying Bull]

I don't suppose in your modern world....one can lean over towards the other pilots side and monitor events on his side of the cab....or is that not allowed these days?

When you were instructing....did you demonstrate maneuvers using your instruments or the Student's?

During an Instrument Approach....what critical information is not displayed on the on the Non-Handling Pilot's side that cannot be seen on all of the other sources?



modern manufaktur allow switching the CoPilot Multi Function Displays without leaning through the cockpit, they add a switch in the center console

https://cimg2.ibsrv.net/gimg/www.gmforum.com-vbulletin/900x406/03d6ab5d_2412_4ef9_a092_c0e226e55e78_f99da7029b70dc64cdf716d bdeb2170040ea62f9.jpeg


FND - Flight Nav Display,
VMD - Vehicle Management Display

;-)

[SASless]

FB,

Tis HC that is lamenting the loss of a screen while handling Malfunctions/Emergencies.

I am asking if it is impossible to garner necessary information by means of looking at the other pilots screens or back up instruments?

Merely asking why HC perceives it to be such a problem!

[megan]

I would be far more concerned about hidden screens....that layered as malfunctions occur and you have to work your way down through the stack because the system does not present the most critical failure ahead of all of the others A prime contributor to an industrial accident in our company that caused deaths and injuries, and left the community without gas for two weeks. Besides, I like to be able to see trends, I don't wish to be informed when the software decides a pressure or temperature has exceeded some preset limit, I want to see it rising or falling from its normal setting, I know regular scanning of such mundane items is not much taught.

[Flying Bull]

Hi SASless, hi Megan,

some words in advance.
Pilots still use Brain 1.0 which was updated last ????

The job of the pilot is to aviate, navigate, communicate and when all this is done he wants to monitor trends with an occasional glance on the instruments?

The computer can do this much better - and it shows a misunderstanding of the systems, when someone thinks, you only get a warning, when a red line is reached
The computer records several times a second the values, compares them in relation to ambient conditions (pressure/temperature).
It does it regardless who is flying in the morning, in the afternoon or the night and therefore can detect trends much earlier than a pilot.
Depending on the rules it it also possible to compare values with other aircraft from the same operator or even worldwide for that model.

The idea behind that is to reduce pilot workload so he can do, what he is there for, flying the bird, looking out, talking to airtraffic and so on.
But it also requires a fullout understanding, what to find where, if needed.
There can be a problem with pilots with an old mindset (the ones, which have an mobile phone but no smartphone i.e.)
You need to „play“ with the system and the pages, to stay current, where to find and/or alter what you want/need.
The most important information you get with either one or at least two button presses.
Reconfiguration, altering times and so on takes a few more steps.
If one only uses the daily operation screens he might have trouble finding the right ones, when the stress level is higher.
The modern pilot has to adopt, change from a manual worker to a system manager.
But to manage the system, one has to understand how it works and there are some shortcomings with some pilots, not willing to go through a manual which is three times as thick as the old ones ....
If you open minded, you will see how much assistance you can get and if you use it, you can sit back and let bird do the work, relaxed enjoying the ride...

[PlasticCabDriver]

A prime contributor to an industrial accident in our company that caused deaths and injuries, and left the community without gas for two weeks. Besides, I like to be able to see trends, I don't wish to be informed when the software decides a pressure or temperature has exceeded some preset limit, I want to see it rising or falling from its normal setting, I know regular scanning of such mundane items is not much taught.

The 175 does this for you. ENG TREND/HYD TREND etc etc, there really is no need to have a set of gauges up for you to monitor. As FB said above, it will do it better than you ever will. And if it loses the ability to monitor the trends, it will tell you that too!

[SASless]

Several folks seem to have no problem with the design, function, and handiness of the current systems in use.

HC, on the other hand, does seem to have an issue with at least one system.

Which view is the most correct?

Are all of you on the same page but saying it differently?

The way to answer my questions is to discuss HC's statement of concern.....as he is the one that raised the issue and I am just considering what he is saying.

I suggest one perspective is he is comparing the 225 Displays to the 175's and is suggesting the 175 was a step backwards.

How does the 225 and 175 differ and is the "newer" system less Pilot friendly?

[trescothic]

HC....Having a PM looking over your shoulder is nice....not necessary.

The PM can relieve the PF of some of that stress by analyzing and troubleshooting and offering up a plan of action while the PF.....flies the aircraft....right?

We did all this Single Pilot long before "Screens" and automation were heard of and it worked.

Do you reckon Pilots...PM or PF are less capable today because of the very Technological advances and changes in Training/Cockpit Procedures?

Are they really becoming "Children of the Magenta"?

What has this to do with the subject matter of this thread?

[SASless]

Yes I had a jolly in a 175 a few years ago so I know it is nice to fly! But that was the point when I noticed the screens weren't optimal. Obviously one can cope with only 4 screens, but I still maintain 5 would have better. Surely you can see that if you are used to 2 screens displaying flight info, and suddenly in an emergency you are down to 1 whilst the other chap still has 2, you are worse off than if you had the extra one because you not only have an abnormal screen setup to display the flight (instrument approach etc) but you also now have the stress of an emergency to deal with?


The Thread has drifted from the 225 crash....as often happens.

[megan]

Many thanks FB and PCD for the insight provided. Did fly glass in my latter years, some aspects of which I liked, indeed loved, some I didn't.

[HeliComparator]

The 175 does this for you. ENG TREND/HYD TREND etc etc, there really is no need to have a set of gauges up for you to monitor. As FB said above, it will do it better than you ever will. And if it loses the ability to monitor the trends, it will tell you that too!
I am reasonably well aware of the philosophy of the 175 design, including the absence of need to routinely look at the system gauges. A great concept, especially as when in the Sim I could set a system gauge to slowly creep into the red over many minutes and virtually no-one would notice until the warning light came on!

My only point is that when there IS an emergency, let's say a transmission oil issue, one would then I think want to monitor the gauge and thus a screen is lost from its normal function (providing PM with the same info as PF). So 99.999% of the time the concept is fine. For that 0.001% of the time when the crew are maxxed out with both an emergency and say an instrument approach, a 5th screen would have been better.

[HeliComparator]

What has this to do with the subject matter of this thread?

I'm not sure there is any more to be said directly on the thread subject matter. (if there is, please do so and we will all shut up!). But actually what is behind this thread drift is pointing out that other factors in helicopter design can be just as relevant to overall safety as one fatal flaw that is nevertheless extremely unlikely to manifest itself. Good HMI and an autopilot that does its best to prevent the pilots flying into the sea may result in fewer fatal accidents than eliminating a type that has a one in a million flight hours (or whatever) chance of losing its rotor head. Of course the 175 does have very good HMI and autopilot, my point was only that I wish it could have been slightly better (for 2 pilot IFR use) by having a 5th screen. Its mechanical reliability and possible presence of a fatal flaw does of course remain to be seen, as with all new types.

[HeliComparator]

Several folks seem to have no problem with the design, function, and handiness of the current systems in use.

HC, on the other hand, does seem to have an issue with at least one system.

Which view is the most correct?

Are all of you on the same page but saying it differently?

The way to answer my questions is to discuss HC's statement of concern.....as he is the one that raised the issue and I am just considering what he is saying.

I suggest one perspective is he is comparing the 225 Displays to the 175's and is suggesting the 175 was a step backwards.

How does the 225 and 175 differ and is the "newer" system less Pilot friendly?

I don't have an issue really, it is just that with the 225 when there was an engine or systems malfunction, the pilot's main screens and thus ability of PM to monitor PF, was unaffected. Not so with the 175. On the other hand the concept in the 175 of there being no need to monitor the systems routinely - they are not routinely displayed - is a good one. In particular that not only does the pilot get a warning when a systems limit is exceeded, he also gets a warning if the trend is for a systems limit to be exceeded in the future, eg a slowly decreasing oil pressure, slowly increasing temperature etc that has yet to breach a limit. As has been said, it does a far better job of monitoring the Ts and Ps than most pilots do!

We are back to the fundamental design concept difference between the French and the US - the former believe all pilots are stupid and best to give them as little information as possible so as to reduce the opportunities for messing up, the latter believe in telling the pilots absolutely everything possible and leaving them to sort it out (after all, they are all descended from Chuck Yeager). I am inclined to go along with the former philosophy!

Obviously the decision to not have a 5th screen was a cost-based one. There is plenty of room for it and when I raised my point with AH originally, it was implied that it would be an option in the future (don't know if that ever transpired). The 175 HMI is great, especially when compared to the competition from Italy and US, my point is only that it could so easily have been even better and that it wasn't I think is partly down to AH's lack of appreciation of the N Sea 2 pilot IFR role. The guys at the factory are more aligned with single pilot VFR.

[Pablo332]

Any 225s still flying?

[Apate]

Any 225s still flying?

Yes. Next question?

[GenuineHoverBug]

Today it has been 3 months since the final report was published, including the 12 safety recommendations.

According to Regulation 996/2010 Article 18.1 "The addressee of a safety recommendation shall acknowledge receipt of the transmittal letter and inform the safety investigation authority which issued the recommendation within 90 days of the receipt of that letter, of the actions taken or under consideration, and where appropriate, of the time necessary for their completion and where no action is taken, the reasons therefor."

Hopefully that potentially interesting information will be available too all soon.

[GenuineHoverBug]

Follow-up of safety recommendations
Here are the replies to the 12 AIBN Safety recommendations that appear to have been received so far:

Safety recommendation SL No. 2018/01T
The failure mode, i.e. crack formation subsurface with limited spalling initiated from a surface damage, observed in the LN-OJF accident is currently not fully understood. The investigation has shown that the combination of material properties, surface treatment, design, operational loading environment and debris gave rise to a failure mode that was not previously anticipated or assessed.

The Accident Investigation Board Norway recommends that the European Aviation Safety Agency (EASA) commission research into crack development in high-loaded case-hardened bearings in aircraft applications. An aim of the research should be the prediction of the reduction in service-life and fatigue strength as a consequence of small surface damage such as micro-pits, wearmarks and roughness.

Reply from EASA
The Agency intends to commission a research project, the scope of which will include identification of rotor drive system critical parts and associated damage mechanisms, identification of significant design, operational and environmental parameters, identification and characterization of significant threats and recommendation of design standards to ensure flaw tolerant structural integrity. The research project is listed as RES.008 (Rotorcraft main gear box (MGB) design to guarantee integrity of critical parts and system architecture to prevent separation of the main rotor following any MGB failure) in the draft European Plan for Aviation Safety 2019-2023, which is currently undergoing consultation with the Agency's advisory bodies.

EASA status – Open

Safety recommendation SL No. 2018/02T
The MGB, which was later installed in LN-OJF, fell off a truck during transport. It was inspected, repaired and released for flight by Airbus Helicopters without detailed analysis of the potential effects on the critical characteristics of the MGB. The current regulatory framework for large rotorcraft does not make connections between the Instructions for Continued Airworthiness (ICA) and requirements for critical parts subject to an unusual event.

The Accident Investigation Board Norway recommends that the European Aviation Safety Agency (EASA) assess the need to amend the regulatory requirements with regard to procedures or Instructions for Continued Airworthiness (ICA) for critical parts on helicopters to maintain the design integrity after being subjected to any unusual event.

Reply from EASA
EASA will conduct a Preliminary Impact Assessment (PIA) in order to assess the need to amend the certification specifications for large rotorcraft (CS-29) with regard ·to procedures or instructions for continued airworthiness for critical parts on helicopters to maintain the design integrity after being subjected to any unusual event. Once the PIA is mature, stakeholders will be consulted. Consultation is expected to take place In 02Q2019.

Depending on the outcome of the PIA, EASA will include an appropriate task in the European Plan for Aviation Safety.

EASA status – Open

Safety recommendation SL No. 2018/03T
Rolling contact fatigue as observed in the LN-OJF accident was not considered during type certification, neither is it directly addressed in the current certification specifications.

The Accident Investigation Board Norway recommends that European Aviation Safety Agency (EASA) amend the Acceptable Means of Compliance (AMC) to the Certification Specifications for Large Rotorcraft (CS-29) in order to highlight the importance of different modes of component structural degradation and how these can affect crack initiation and propagation and hence fatigue life.

Reply from EASA
EASA will conduct a preliminary impact assessment (PIA) to assess the need to amend the Acceptable Means of Compliance (AMC) to the Certification Specifications for Large Rotorcraft (CS-29) in order to highlight the importance of different modes of component structural degradation and how these can affect crack init iation and propagation and hence fatigue life. The aim of such AMC could be to add specific reference to modes of component structural degradation related to rolling contact fatigue and how these can affect crack initiation and propagation and, hence, fatigue life. Once the PIA is mature, stakeholders will be consulted. Consultation is expected to take place in 02Q2019.

Depending on the outcome of the PIA, EASA will include an appropriate task in the European Plan for Aviation Safety.

In the meantime, EASA is already raising the issue during certification projects via a dedicated Certification Review Item (CRI) providing Interpretative Material to better assess the effect of rolling contact fatigue.

EASA status – Open

Safety recommendation SL No. 2018/04T
The chip detection system fitted to LN-OJF did not produce any warnings of the impending planet gear catastrophic failure, and the potential of detection was limited. The Certification Specifications for Large Rotorcraft (CS-29) do not specify the chip detection system’s functionality and performance.

The Accident Investigation Board Norway recommends that the European Aviation Safety Agency (EASA) revise the Certification Specifications for Large Rotorcraft (CS-29) to introduce requirements for MGB chip detection system performance.

Reply from EASA
EASA has recognised the need to improve certification specifications in CS-27 (small rotorcraft) and CS-29 (large rotorcraft) relating to Main Gear Box (MGB) chip detectors.

The current CS 27 /29.130S(a)(23) and CS 27 /29.1337(e) require chip detectors to provide a warning to the flight crew when particles of a sufficient size (or accumulation) are detected and are intended to allow the flight crew to check the correct operation of the relevant elements ' of the drive system.

EASA has conducted a Preliminary Impact Assessment (PIA) on the possible actions to improve the likelihood of detecting chips or particles in gearbox oil. The outcome of the PIA was the inclusion of a dedicated Rulemaking Task (RMT) 0725 in the draft European Plan for Aviation Safety (EPAS) 2019-2023 which is currently undergoing consultation with the Agency's advisory bodies.

The planned RMT.0725 will consider an amendment of the current certification specifications and their associated acceptable means of compliance for demonstrating that the chip detectors perform their intended function.

EASA status – Open

Safety recommendation SL No. 2018/05T
The LN-OJF accident was a result of a fatigue fracture in one of the eight second stage planet gears in the epicyclic module of the MGB, a critical part in which cracks developed subsurface to a catastrophic failure without being detected. It might not be possible to assess the fatigue reliability of internal MGB components, or design a warning system that works with sufficient efficiency and warning time, thus the MGB should be designed fail-safe.

The Accident Investigation Board Norway recommends that the European Aviation Safety Agency (EASA) develop MGB certification specifications for large rotorcraft to introduce a design requirement that no failure of internal MGB components should lead to a catastrophic failure.

Reply from EASA
The Agency understands that the objective of this Safety Recommendation is that future rotor drive system design requirements will ensure that "no failure of internal MGB components should lead to a catastrophic failure." However, such designs would be so radically different from existing transmission systems that their feasibility needs to be assessed.

EASA considers that the number of potentially catastrophic failure modes should be minimised. Accordingly, any component, the failure of which has a potentially catastrophic failure effect, should not be acceptable if the failure hazard severity can be mitigated to a reduced level and where such measures are considered to be technically feasible and economically justifiable.

It is clear that design choices regarding rotor drive system architecture and individual gearbox design will influence the number of potentially critical parts.

In order to better understand the significance of these design choices, research is planned within the scope of project RES.008 (Rotorcraft main gear box (MGB) design to guarantee integrity of critical parts and system architecture to prevent separation of the main rotor following any MGB failure) in the draft European Plan for Aviation Safety (EPAS) 2019-2023, which is currently under consultation with stakeholders.

EASA status – Open

Safety recommendation SL No. 2018/06T
The investigation into the accident to LN-OJF has revealed that the tests performed during the design and certification of the Airbus Helicopters EC 225 LP were in accordance with applicable regulations. However, with regard to the risks associated with offshore operations, there is a less stringent continued operational reliability test requirement for large rotorcraft compared with the Extended Operations and All Weather Operations regime for fixed wing aircraft.

The Accident Investigation Board Norway recommends that the European Aviation Safety Agency (EASA) develop regulations for engine and helicopter operational reliability systems, which could be applied to helicopters which carry out offshore and similar operations to improve safety outcomes.

Reply from EASA
EASA previously evaluated the suitability of the concept proposed in this safety recommendation, i.e. applying the ETOPS principles to helicopters conducting offshore operations, following the receipt of a safety recommendation from the CAA UK. At the end of 2015, EASA concluded that rulemaking was not deemed justified, owing to the differences in term of designs and operating conditions between helicopters and aeroplanes flying ETOPS.

EASA will re-evaluate its conclusion in the light of this safety recommendation. Depending on the results of the review of the concept, a preliminary impact assessment (PIA) may be prepared if deemed appropriate; the PIA would then review possible actions, including rulemaking, and a consultation of stakeholders would be performed.

EASA status – Open

Safety recommendation SL No. 2018/07T
The investigation into the accident to LN-OJF has found that only a few second stage planet gears in Airbus Helicopters EC 225 LP and AS 332 L2 ever reached their intended operational time before being rejected during overhaul inspections or non-scheduled MGB removals. The parts rejected against predefined maintenance criteria were not routinely examined and analysed by Airbus Helicopters.

The Accident Investigation Board Norway recommends that European Aviation Safety Agency (EASA) make sure that helicopter manufacturers review their Continuing Airworthiness Programme to ensure that critical components, which are found to be beyond serviceable limits, are examined so that the full nature of any damage and its effect on continued airworthiness is understood, either resulting in changes to the maintenance programme, or design as necessary, or driving a mitigation plan to prevent or minimise such damage in the future.

Reply from EASA
EASA will consider amending the Acceptable Means of Compliance (AMC) and Guidance Material (GM) to point 21.A.3A of Annex I (Part-21) to Commission Regulation (EU) No 748/2012, in order to clarify the obligations of Type Certificate Holders to ensure compliance with the requirement of "collecting, investigating and analysing reports of and information related to failures, malfunctions, defects or other occurrences which cause or might cause adverse effects on the continuing airworthiness of the product( ... )".

This will be performed within the frame of rulemaking task RMT.0031 dealing with the regular update of AMC/GM to Part-21. The next NPA is planned to be published 02Q2019.

EASA status – Open

Safety recommendation SL No. 2018/08T
The investigation into the accident to LN-OJF has found that only a few second stage planet gears in Airbus Helicopters EC 225 LP and AS 332 L2 ever reached their intended operational time limit before being rejected during overhaul inspections or non-scheduled MGB removals.

The Accident Investigation Board Norway recommends that the European Aviation Safety Agency (EASA) review and improve the existing provisions and procedures applicable to critical parts on helicopters in order to ensure design assumptions are correct throughout its service life.

Reply from EASA
EASA issued Certification Memorandum (CM) CM-S-007 in 2015. The purpose of this CM was to supplement the existing guidance for compliance with CS 27 /29.602 (Critical Parts), detailing the need for post certification actions to verify the continued integrity of Critical Parts.

These actions should ensure that critical parts are controlled throughout their service life in order to maintain the critical characteristics on which certification is based. In addition, the effectiveness of any associated design, maintenance and monitoring provisions, which either help ensure the continued integrity or provide advance indication of impending failure of critical parts, should be assessed.

EASA will conduct a Preliminary Impact Assessment (PIA) in order to assess the potential safety benefit and economic: impact of a number of changes to improve the Guidance Material applicable to CS 29.602.

Consideration will also be made to include the provisions of CM-S-007 within the Acceptable Means of Compliance of CS-29 'Book 2'.

Consultation is expected to take place in 02Q2020.

EASA status – Open

Safety recommendation SL No. 2018/09T
The investigation into the accident to LN-OJF has demonstrated that a critical structural component could fail totally without any pre-detection by the existing monitoring means.

The Accident Investigation Board Norway recommends that the European Aviation Safety Agency (EASA) research methods for improving the detection of component degradation in helicopter epicyclic planet gear bearings.

Reply from EASA
The Agency intends to commission a research project into rotorcraft gearbox health monitoring. The purpose of this research will be to investigate the use of new technologies, including both hardware and methods of analysis, to improve prognostic health monitoring capability for tilt rotor, helicopter and hybrid aircraft gearbox failures.

The scope of this research will include health monitoring of epicyclic gearbox components. This project is listed as RES.011 (Helicopter, tilt rotor and hybrid aircraft Gearbox health monitoring - ln-situ failure detection ) in the draft European Plan for Aviation Safety 2019-2023 which is currently undergoing consultation with the Agency's advisory bodies.

EASA status – Open

Safety recommendation SL No. 2018/10T
During the investigation into the accident to LN-OJF, considerable time and resources by the AIBN has been drawn to request, wait for release acceptance and review of design and certification documents.

The Accident Investigation Board Norway recommends that the European Commission (DG MOVE) in collaboration with European Aviation Safety Agency (EASA) evaluates the means for ensuring that investigation authorities have effectively free access to any relevant information or records held by the owner, the certificate holder of the type design, the responsible maintenance organisation, the training organisation, the operator or the manufacturer of the aircraft, the authorities responsible for civil aviation, EASA, ANSPs and airport operators.

No reply appears to have been received

Safety recommendation SL No. 2018/11T
During the investigation into the accident to LN-OJF, considerable time and resources by the AIBN has been drawn to request, wait for release acceptance and review of design and certification documents. ICAO Annex 13 Chapter 5.12 does not refer explicitly to the protection of sensitive proprietary information regarding design and certification.

The Accident Investigation Board Norway recommends that the International Civil Aviation Organisation (ICAO) evaluates the means for ensuring that investigation authorities have effectively free access to any relevant information or records held by the owner, the certificate holder of the type design, the responsible maintenance organisation, the training organisation, the operator or the manufacturer of the aircraft, the authorities responsible for civil aviation, certification authorities, ANSPs and airport operators.

Reply from ICAO:
Amendment 16 to Annex 13 — Aircraft Accident and Incident Investigation, upgrades Recommendation 5.4.3 to a Standard and will become applicable on 8 November 2018. Standard 5.4.3 reads that “A State shall ensure that any investigations conducted under the provisions of this Annex have unrestricted access to all evidential material without delay.” And Standard 5.6 states that “The investigator-in—charge shall have unhampered access to the wreckage and all relevant material, including flight recorders and ATS records, and shall have unrestricted control over it to ensure that a detailed examination can be made without delay by authorized personnel participating in the investigation.”

Annex 13, 5.18 provides for the participation of accredited representatives appointed by the various States taking part in an investigation. Accredited representatives are entitled to appoint advisers who, in turn, would be able to obtain relevant information stemming from the aircraft manufacturer, type certification holder, operator, maintenance organizations and other information necessary for the investigation.

It is therefore believed that Annex 13 provisions, together With associated guidance material, provide the means to ensure that accident investigation authorities have timely access to relevant information and pertinent records necessary for the investigation.

Safety recommendation SL No. 2018/12T
The LN-OJF accident was a result of a fatigue fracture in one of the eight second stage planet gears in the epicyclic module of the MGB, a critical part in which cracks developed subsurface to a catastrophic failure without being detected. With the knowledge from this investigation, all effort should lead to a robust design in which a single load path should demonstrate compliance to CS 29.601(a), 29.602 and 29.571 without compromising its structural integrity and not only by depending on detection systems or maintenance checks.

The Accident Investigation Board Norway recommends that Airbus Helicopters revise the type design to improve the robustness, reliability and safety of the main gearbox in AS 332 L2 and EC 225 LP.

Reply from Airbus Helicopters:
Airbus is currently defining, together with authorities, the perimeter of a future set of evolutions in order to improve the robustness, the reliability and safety of the main gearbox in AS332 L2 and EC225 LP.

The associated roadmap will be presented beginning of 2019.

[rotor-rooter]

https://www.flightglobal.com/news/articles/airbus-helicopters-finds-root-cause-of-turoy-h225-cr-460792/

An interesting development, although the impact on the 225 market may take some time to understand.

[Variable Load]

Airbus are declining to disclose the root failure mode. What a bizarre way to try and regain customer confidence in the aircraft. :ugh:

[barbados sky]

5 years ago today, RIP.

https://www.energyvoice.com/oilandgas/north-sea/318499/five-years-norway-helicopter-crash/?utm_source=Sailthru&utm_medium=email&utm_campaign=Energy%20Voice%20-%20Daily%20Newsletter%202021-04-29&utm_term=Energy%20Voice%20-%20Newsletter

[industry insider]

Article here:Workers dubbed the Super Puma helicopter model, once dominant in the sector, the “flying coffin” after the crash off the island of Turoy in 2016.

It was the last straw for the sector, which had endured a spate of crashes since 2009, claiming 33 lives, with the Super Puma, which has not been in service in the North Sea for the last five years.

Jake Molloy, regional organiser of the RMT union, said: “For a lot of the guys it would instil terror to get into that particular model of aircraft and I think a lot of guys breathe easy at the thought that we’re not using them.

“I recall it, like I’ve recalled so many down the years, with deep despair that life can so tragically be lost. It really is an event that I wouldn’t want anyone to experience. I’ve lost good friends and colleagues through the years in events like this.

“It sits in the forefront of your mind all the time. Even sitting in the garden, as I am now, seeing them flying overhead, those thoughts come back to you. They never go away.”
© AIBNhttps://wpcluster.dctdigital.com/energyvoice/wp-content/uploads/sites/4/2018/11/The-main-rotor.-Photo-AIBN-1024x768.jpg (https://wpcluster.dctdigital.com/energyvoice/wp-content/uploads/sites/4/2018/11/The-main-rotor.-Photo-AIBN.jpg)
https://wpcluster.dctdigital.com/energyvoice/wp-content/uploads/sites/4/2018/10/1F56E5F3-36D4-4B5A-96AF-168566B97D63.jpg-1024x517.jpg (https://wpcluster.dctdigital.com/energyvoice/wp-content/uploads/sites/4/2018/10/1F56E5F3-36D4-4B5A-96AF-168566B97D63.jpg.jpg)
https://wpcluster.dctdigital.com/energyvoice/wp-content/uploads/sites/4/2021/04/A49746D2-4D4B-431E-A35B-16FC62AEFC94-847x564.jpg (https://wpcluster.dctdigital.com/energyvoice/wp-content/uploads/sites/4/2021/04/A49746D2-4D4B-431E-A35B-16FC62AEFC94.jpg)1/3 – The main rotor detached from the helicopter.On April 29, 2016, a CHC-operated Super Puma went down while carrying oil workers from the Gullfaks B platform to Bergen Airport.

Iain Stuart, 41, from Laurencekirk, was among those killed in the crash off Turoy in Norway, taking place after the main rotor detached from the helicopter.

In the last seconds of its journey the chopper fell 2,000 feet (https://www.energyvoice.com/oilandgas/north-sea/176042/airbus-says-norway-copter-crash-not-preventable-despite-similarities-with-fatal-peterhead-accident/), with witnesses describing an “explosion in the sky”.
The rotor broke off due to a “fatigue fracture” in a “second stage planet gear” in the main rotor gearbox.

Investigators later said it was probable (https://www.energyvoice.com/Users/allister.thomas/Downloads/2018-04%20LN-OJF%20Summary%20report.pdf) that the failure was caused by tiny pieces of debris wearing away at the component. The system installed for detecting the particles was “inadequate”, they added.
AirbusManufacturer Airbus said it has always expressed “deep regret for the accident off Turoy” and in recent times has reached settlements with families of the victims, “while fully appreciating that such arrangements cannot possibly atone for the loss of their loved ones”.

A spokesman said: “All of us were shocked and saddened by this event and we continue to extend our sincere and profound sympathies to the families of the bereaved.”

Despite the Super Puma crashes, though, many pilots still back the aircraft, which Airbus continues to sell widely in industries such as law enforcement and search and rescue.

Mr Molloy, of RMT, said, for whatever reason, the North Sea appears to have been its “Achilles heel”.

Along with Norwegian colleagues, trade unions in the UK plan to maintain a position that the Super Puma cannot fly again in the industry.

“I think you’d find a considerable pushback from the offshore workforce for that ever to be suggested in any case,” he said.

“Certainly this generation won’t be climbing into a Super Puma anytime soon.”

The victims were Iain Stuart, 41, Behnam Ahmadi, 54, Arild Fossedal, 43, Ole Magnar Kvamme, 60, Odd Geir Turøy, 54, Otto Mikal Vasstveit, 54, Kjetil Wathne, 51, Michele Vimercati, 44, Tommas Helland, 50, Espen Samuelsen, 35, Lyder Martin Telle, 57, and Olav Bastiansen, 57 and Silje Ye Rim Veivåg Krogsæther, 32.

[etudiant]

It seems surprising that after 5 years there has not been a test to destruction of the gear box design involved.
Afaik, we have a plausible failure sequence, but no firm take away conclusions that would allow future designers to avoid a similar disater.
Can anyone shed light on the state of play in this area?

[Twist & Shout]

It seems surprising that after 5 years there has not been a test to destruction of the gear box design involved.
Afaik, we have a plausible failure sequence, but no firm take away conclusions that would allow future designers to avoid a similar disater.
Can anyone shed light on the state of play in this area?

“Plausible” “No firm conclusions” “Similar disasters”
You have pretty well summed it up.

It’s likely, in any operation where the people on board, IE pilots/pax, have any say, that an EC225 won’t be used.

[RVDT]

It seems surprising that after 5 years there has not been a test to destruction of the gear box design involved.
AFAIK, we have a plausible failure sequence, but no firm take away conclusions that would allow future designers to avoid a similar disater.
Can anyone shed light on the state of play in this area?

Read post #1916 "between the lines". Each first paragraph sums it up and is a "hole in the cheese".

You can test the gearbox to destruction but that would be pointless unless you had some idea as to what you would do to initiate it.

This is a seriously deep rabbit hole!!

[HeliComparator]

“Plausible” “No firm conclusions” “Similar disasters”
You have pretty well summed it up.

It’s likely, in any operation where the people on board, IE pilots/pax, have any say, that an EC225 won’t be used.

And yet look at that recent report about the S92 in Canada. Ok they missed the sea by 13’ but it was very close. And not the first time. The 225 may have a quickly-detachable rotor head but the autopilot made the aircraft much safer in the face of loss of SA/pilot incompetence. But as ever, unfortunately humans don’t evaluate risk logically or rationally.

[helicrazi]

And yet look at that recent report about the S92 in Canada. Ok they missed the sea by 13’ but it was very close. And not the first time. The 225 may have a quickly-detachable rotor head but the autopilot made the aircraft much safer in the face of loss of SA/pilot incompetence. But as ever, unfortunately humans don’t evaluate risk logically or rationally.

It's been a long while since I strapped into a 225, but I dont think this is entirely accurate. The 225 flown without any upper modes would still get you into trouble. The hidden protections would only help with at least 1 upper mode engaged. So in this instance (I dont think the 92 had any upper modes engaged) then the outcome may have been the same. (Assuming the 225 gearbox could take the ramp up in torque that the 92 took)

Look at G-REDU, that flew itself straight in... no upper modes...

[PPI Zulu]

And yet look at that recent report about the S92 in Canada. Ok they missed the sea by 13’ but it was very close. And not the first time. The 225 may have a quickly-detachable rotor head but the autopilot made the aircraft much safer in the face of loss of SA/pilot incompetence. But as ever, unfortunately humans don’t evaluate risk logically or rationally.

Can you link to that report?

[helicrazi]

Can you link to that report?

S92 Report (https://www.tsb.gc.ca/eng/rapports-reports/aviation/2019/A19A0055/A19A0055.html)

[PPI Zulu]

S92 Report (https://www.tsb.gc.ca/eng/rapports-reports/aviation/2019/A19A0055/A19A0055.html)
:ok: Ten Characters.

[Twist & Shout]

And yet look at that recent report about the S92 in Canada. Ok they missed the sea by 13’ but it was very close. And not the first time. The 225 may have a quickly-detachable rotor head but the autopilot made the aircraft much safer in the face of loss of SA/pilot incompetence. But as ever, unfortunately humans don’t evaluate risk logically or rationally.

I agree about the risk evaluation not necessarily being logical.
The thing that resonates with me is: If the rotor head departs, no matter what, no matter how good or lucky you are as a pilot, you have a few seconds of terrifying life left.
Most of us believe, rightly or wrongly, that catastrophic incompetence can be avoided, or even recovered from, as in the S92 near miss referenced.

[HeliComparator]

I agree about the risk evaluation not necessarily being logical.
The thing that resonates with me is: If the rotor head departs, no matter what, no matter how good or lucky you are as a pilot, you have a few seconds of terrifying life left.
Most of us believe, rightly or wrongly, that catastrophic incompetence can be avoided, or even recovered from, as in the S92 near miss referenced.
Yes I get that. Every pilot thinks it (a major piloting cockup) couldn’t possibly happen to me because I’m not that stupid. But I can’t see how that translates onto the passengers. Whether they crash and burn due to pilot error, or due to system design/manufacture error, surely doesn’t matter to them.

[HeliComparator]

It's been a long while since I strapped into a 225, but I dont think this is entirely accurate. The 225 flown without any upper modes would still get you into trouble. The hidden protections would only help with at least 1 upper mode engaged. So in this instance (I dont think the 92 had any upper modes engaged) then the outcome may have been the same. (Assuming the 225 gearbox could take the ramp up in torque that the 92 took)

Look at G-REDU, that flew itself straight in... no upper modes...

you are correct on a simplistic level. But the point is that the 225’s upper modes are so capable that they tend to get used eg on a visual segment post-MAP, and any sensible operator encourages or mandates it. The S92s upper modes can’t be used at low IAS and anyway are quite soggy, so it’s back to the human and fallible pilot by necessity.

Of course since I left the N Sea in 2013 things have moved on to the 175 and 189, which probably have good autopilots (well the 175 certainly does) but then again, have the fatal design flaws on those new aircraft manifested themselves yet? Who knows!

[helicrazi]

you are correct on a simplistic level. But the point is that the 225’s upper modes are so capable that they tend to get used eg on a visual segment post-MAP, and any sensible operator encourages or mandates it. The S92s upper modes can’t be used at low IAS and anyway are quite soggy, so it’s back to the human and fallible pilot by necessity.

Of course since I left the N Sea in 2013 things have moved on to the 175 and 189, which probably have good autopilots (well the 175 certainly does) but then again, have the fatal design flaws on those new aircraft manifested themselves yet? Who knows!

They can be used at low air speeds on a 92 and are used at low airspeeds, in a DVE the rad alt can be left engaged until committal to give protection. Granted it's not as good as the 225, but they can be used. Simplistic about sums it and me up :E

Anyway, thread drift etc...

[industry insider]

have good autopilots (well the 175 certainly does)

But not such a good gearbox with double the removals and 50% of Mil 8 TBOs.

[Twist & Shout]

.......things have moved on to the 175 and 189, which probably have good autopilots (well the 175 certainly does) but then again, have the fatal design flaws on those new aircraft manifested themselves yet? Who knows!

I’d personally describe the 189 AFCS (and FMS) as “disappointing”. Not as good as the 139, and a different league to the 225. I’m hoping for some improvements with subsequent “Phases”.

As an Aircraft as a whole - I really like it (AW189). Hoping for no undiscovered “fatal design flaws”.

[etudiant]

But not such a good gearbox with double the removals and 50% of Mil 8 TBOs.

That is pretty disappointing. Is there a broader trend, that the more recent helicopters are less durable?
I keep thinking that SpaceX appears to have transformed launch economics by focusing on robustness rather than peak performance.
Is a similar shift in philosophy potentially possible in the helicopter market?

[Twist & Shout]

That is pretty disappointing. Is there a broader trend, that the more recent helicopters are less durable?
I keep thinking that SpaceX appears to have transformed launch economics by focusing on robustness rather than peak performance.
Is a similar shift in philosophy potentially possible in the helicopter market?

Traditionally, components like Gearboxes seemed to be over engineered, then lifed conservatively.
For safety: Obviously.

Then with fleet information gleaned over time from inspections and testing of “time EX” gearboxes (for example), TBO’s could often (usually) be extended.
For reduced operating costs: Obviously.

Anecdotally, increased competition and greed now mean pushing everything to it’s limit*. For the brochure. Then, when a few fail, reducing the TBO is the easy, and potentially profitable way out, for the manufacturer.

EC225’s had a MTOW of 11200Kg*. What did the Puma start out at 8350Kg? (Or less? - I never flew a non “Super” Puma.)

[Fareastdriver]

When I started flying Puma in 1971 the MAW was 6,400 kgs. and the gearbox life was 900 hrs. Around 1973 the AUW was increased to 6,700 kgs and at the same time they initiated the CAAP Programme. (Component advanced ageing programme)

The was a programme to fly selected aircraft; two RAF and four French Army, one hundred hours a month each with the gearboxes stripped every two hundred hours so as to extend the fleet's life to 1800hrs.

This was successful so the Puma entered the civilian market. I flew the 'J' model with plastic blades up to 7.400 kgs.

[finalchecksplease]

EC225’s had a MTOW of 11500Kg*.

The EC225 MTOW was 11000 Kg or 11200 Kg with external load.

[Fareastdriver]

As I mentioned in a previous post: Too much new wine in old bottles.

I had a chance to convert to them late in my working life but being one of HC's 'Old Dinosaurs' I didn't like the way it was operated so I backed out and stayed on the 332L1.

[JoeCool88]

As we all know it was the same crack in a second stage planet gear on G-REDL on 01.04.2009 and LN-OJF on 29.04.2016, which caused the MR to separate. After all the measures taken, like reduction of the MGB TBO to roughly one third of the initial TBO, installation of another mag plug, flight ban on one type of planet gear etc etc, the 225 could be considered as safe for flight (again), imho. Especially the more frequent scheduled MGB removals drive the costs per flight hours, but who cares.
However, after thousands of engineer hours and millions of Euros for the regarding technical investigation, the reason why a crack (twice) could propagate inside the gear rim, undetected by e. g. HUMS and the classical methods like mag plug and filter, remains still unknown. Strange, isn't it?

[rotor-rooter]

As we all know it was the same crack in a second stage planet gear on G-REDL on 01.04.2009 and LN-OJF on 29.04.2016, which caused the MR to separate. After all the measures taken, like reduction of the MGB TBO to roughly one third of the initial TBO, installation of another mag plug, flight ban on one type of planet gear etc etc, the 225 could be considered as safe for flight (again), imho. Especially the more frequent scheduled MGB removals drive the costs per flight hours, but who cares.
However, after thousands of engineer hours and millions of Euros for the regarding technical investigation, the reason why a crack (twice) could propagate inside the gear rim, undetected by e. g. HUMS and the classical methods like mag plug and filter, remains still unknown. Strange, isn't it?

There is quite a bit more to this story. Airbus announced in September 2019 that they had determined the root cause, but as far as I am aware, has still never released any of this information into the public domain. There may be many reasons for not releasing this information, but none of them bode well for Airbus, as secrecy in the realm of accident investigation is a dangerous path to tread and may result in the unintended consequence of challenging their overall credibility.

AIRBUS HELICOPTERS FINDS ROOT CAUSE OF THE TUROY H225 CRASH | OGPNetwork (http://ogpnetwork.com/airbus-helicopters-finds-root-cause-of-the-turoy-h225-crash/)

OGP NETWORK OIL GAS & POWER LATEST NEWS (http://ogpnetwork.com/) AIRBUS HELICOPTERS FINDS ROOT CAUSE OF THE TUROY H225 CRASHBy
OGP Network (http://ogpnetwork.com/author/ogpnetwork/)
-
September 13, 2019 On April 29, 2016, one H225 Super Puma helicopter operated by CHC Helicopter, en route from Gulfaks B to Bergen, went down close to the small island of Turoy, west of Bergen, Norway. All 13 occupants of the heavy-twin, two pilots and eleven oilfield staff died within the accident after the primary rotor separated from the plane at 2,000ft. The lack of the primary rotor in flight is essentially the most dramatic accident that may occur to a helicopter. There are not any phrases to explain it.

The UK journal Flight Global reported that Airbus Helicopters has recognized the basis explanation for the primary gearbox (MGB) failure behind the deadly 2016 crash of an H225 in Norway. In its last report in July 2018, Norwegian investigators decided second-stage planet gear within the MGB’s epicyclic module had failed as a result of sub-surface cracking and fracture of a bearing race. However, they have been unable to say what had triggered the occasion.

“The investigation has proven that the mix of fabric properties, floor remedy, design, operational loading surroundings and particles gave rise to a failure mode which was not beforehand anticipated or assessed,” the report says.

But the airframer has continued its personal evaluation of the occasion, says H225 programme director Michel Macia, resulting in identification of the basis trigger and a profitable replication of the failure in testing. That work has been externally validated, he says. Findings from that effort have been subsequently shared with Norway’s SHT accident investigation physique, regulators together with the European Union Aviation Safety Agency, and different producers, says Macia.

“Everyone now is aware of that the basis trigger is known and has been reproduced,” says Macia. Although he declines to element the failure, he says the security obstacles put in place to allow the H225 to return to service take care of the underlying difficulty. These measures embrace a heightened inspection regime, shorter life limits on elements and – considerably – the exclusion of one of many two totally different bearing designs used on the helicopter.

The H225 and the associated AS332 L2 have been grounded for 4 months following the crash, and though each at the moment are cleared for service, they’ve but to be introduced again to operation within the North Sea area for offshore transport. While that’s largely as a result of overcapacity within the sector, there stays vital opposition from the oil and fuel workforce to the H225.

But Airbus Helicopters chief government Bruno Even nonetheless believes the rotorcraft could make a comeback within the North Sea and says the plane wants time to realize acceptance.
“We are doing all that we’re capable of do, however ultimately, it’s the buyer who has to determine.”
The UK Civil Aviation Authority says its place on the H225 has not modified and it has but to obtain an software from an operator to renew H225 passenger flights within the nation.
(Source: Flight Global – Image: Aibn/Super Puma rotor on Turoy Island)

[JoeCool88]

Last year I was in a meeting with M. Macia and his key engineers regarding this issue. What I've understood is that, in Airbus opinion, each cracking of the planet gear (which is coincidentally the outer race of its bearing) starts unavoidably with producing a particle from this outer race. Secondly the crack has a certain progressing time. For the particle they now have a third Full Flow Magnetic Plug with a catch rate of more than 90%. And for the growing of the crack in the rim they have the safety barrier to remove the planet gear every 1000 h (SLL). After all I still have doubts if really each crack will start with a particle. And even if, the particle easily could get lost inside the mgb housing before reaching one of the mag plugs. I'm not convinced of anything until an technically understandable reason for the failure is pinpointed.

[jimf671]

Has anyone considered the resulting stresses from combining the bearing and gear components? When one designs a gear one is principally concerned about the tooth bending stress and the contact stress on the flanks of the teeth. I have never designed anything similar to a high speed rolling element bearing but I would think it would be mainly about contact stress but in a different format to the intermittent contact stress on a gear tooth flank.

So if two components are mounted together with a bearing inside a gear there is extra material (and thus weight) and many of the stress influences are isolated within each individual component. If one forms a bearing race as part of the gear, there is less material and fewer stresses are isolated because there is no helpful component boundary. There is a cycle of bending nearer the outside of the component caused by two or more gear engagements and a cycle of contact stresses nearer the inside of the component caused by contact with the rolling elements. The component has surface heat treatment so that material properties on the surfaces of the component are stronger and more brittle and the core remains less strong and more ductile. Everyone hopes that the core ductility of their surface hardened component will deal with the more quirky stresses and development testing should prove it. However, in my head I can visualise the combination of stresses having an effect like peeling up an old piece of lino.

[JoeCool88]

According to Airbus all the different stresses were taken into consideration. Due to the hardened surface of the bearing races and teeth,16NCD13 layer after a nitrid process, and the "weaker" material inside the rim (M50), stress usually peels of the hardened surface. Resulting in flakes, splinters etc. on the mag plug. Which gives an early warning of the degradation. What was new in the G-REDL and LN-OJF case is that only a very limited such surface particle production - if any at all - took place during all the hours where the crack has grown inside. After a lot of time spent trying to understand what happened, my last idea was resonance frequency. In the MGB you have a lot of shafts, gears etc. turning with different speeds, inducing frequencies into the system. What if, in addition to the mentioned stress, the planet gears are exited with a frequency closed to their natural frequency? In combination with a micro pitting in the bearing race, as starting point, this could explain the crack growth inside the rim. Consequently a slightly different rotor speed could lead to a different planet gear behavior. According to this theory a crack would not grow even if initiated by a pitting, if the MR Rpm is e. g. 263 instead of 266 or vice versa.

[jimf671]

Resonance is an interesting one. One could have different aircraft seeing different levels of risk based on random variations through acceptable tolerance in avionics settings, engine set-up, gear machining, and so on, plus the variations in load cycles across the fleet. Surely someone has visited these ideas?

[JoeCool88]

All what's said is correct. However, for the gears and bearing materials currently used by the industry (and not only Airbus) it is sheer impossible to improve the products in a way that no spalling or micro pitting will occur anymore. The two main micro pitting drivers are corrosion and the overrun of particles. You couldn't use stainless steel in bearings because it tends to brittle. And you could micro filter the oil as much as you like, you'll never reach 100 % purity, respectively could avoid that particles are overrun in the bearings. Bearing spalling accures since decades on all gearboxes of all manufacturers. What was new is that two planet gears cracked through, most probably initiated by the micro pitting just discussed. So the question is why the planet gears on other h/c models, using the same materials, do not tend to crack through under the same conditions? The only answer which makes sense is that it must be, however, the design. So Airbus had only two options to bring the 225 back in service. Option one would have been a complete new design of the epicyclic, Millions of Euros spent into a product with an unpredictable future. Combined with the admission that the existing design was faulty. Option two was staying with the design, reducing the service life and installing a third mag plug. It's obvious why they have choosen option two.

[Fareastdriver]

I think the 225 is out of the medium civil helicopter market for other reasons now: The design looks dated, its too narrow with just three seats in a row, you cannot stand up in it and it's reputation leaves much to be desired.
I flew Pumas and Super Pumas from 1971 to 2008.I have retired and so should the basic design.

[Arnie Madsen]

According to Airbus all the different stresses were taken into consideration. Due to the hardened surface of the bearing races and teeth,16NCD13 layer after a nitrid process, and the "weaker" material inside the rim (M50), stress usually peels of the hardened surface. Resulting in flakes, splinters etc. on the mag plug. Which gives an early warning of the degradation. What was new in the G-REDL and LN-OJF case is that only a very limited such surface particle production - if any at all - took place during all the hours where the crack has grown inside. After a lot of time spent trying to understand what happened, my last idea was resonance frequency. In the MGB you have a lot of shafts, gears etc. turning with different speeds, inducing frequencies into the system. What if, in addition to the mentioned stress, the planet gears are exited with a frequency closed to their natural frequency? In combination with a micro pitting in the bearing race, as starting point, this could explain the crack growth inside the rim. Consequently a slightly different rotor speed could lead to a different planet gear behavior. According to this theory a crack would not grow even if initiated by a pitting, if the MR Rpm is e. g. 263 instead of 266 or vice versa.

Hi Joe .... my comment is about ... "how the crack grows undetected"

I followed this investigation closely (read everything) back in the day ..... a small surface crack may not progress on its own unless there was a flaw in the original metal (rare in this case) ...... the problem is the rolling bearing is compressing oil at a very high pressure that causes hydraulic fracturing into the crack which causes it to keep growing over time.

Same physics that can split a granite rock when a drop of water seeps into a crack and freezes and expands.

[Twist & Shout]

I think the 225 is out of the medium civil helicopter market for other reasons now: The design looks dated, its too narrow with just three seats in a row, you cannot stand up in it and it's reputation leaves much to be desired.
I flew Pumas and Super Pumas from 1971 to 2008.I have retired and so should the basic design.

Also, the DOC’s are probably comparatively high these days. Only made worse by the reduced TBO on the MRGB

[jimf671]

I think the 225 is out of the medium civil helicopter market for other reasons now: The design looks dated, its too narrow with just three seats in a row, you cannot stand up in it and it's reputation leaves much to be desired.
I flew Pumas and Super Pumas from 1971 to 2008.I have retired and so should the basic design.

One the other hand, it is the best ride out there. Always my favourite way home. Smoother than all the rest, with those big escape windows, jettisonable big doors, good run-dry spec, good flotation spec. If you know of a large rotorcraft that has done 12 years of intensive CAT without a fatality, please let me know.

[Twist & Shout]

....good run-dry spec..

PMSL
That’s classic!!!

Thanks - I needed a good laugh.

”Arrrgh, somethings happening - we have some red lights. Do we need to spray Glycol into the MRGB to stop it melting? Can’t really tell - might be a sensor. Spray it in!!? Ok.”
“Did it work? Can’t really tell. Want to wait and see if we get vibrations and/or grinding sounds? No - run the ditching check list.”

Reminds me of the classic “Explosive bolts” scene on “Dr Strangelove” (Peter Sellers 1964)
”Explosive bolts. Negative function”