EC225 crash near Bergen, Norway April 2016
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Lynx,
The S61 had at least 3 aircraft chuck a blade back in the late 60s to early 70s. All resulting in a crash, fatally injuring everyone on board. Not the exact failure (rotor head detaching) but same end result. Not sure how familiar you are with aircraft but the S61, prior to the S92 was the Super Pumas main competition. So that happened back then (3 very similar events) and when did we retire the S61? Some 35 years later, as the workhorse of the offshore industry. Most would love to jump back onboard one tomorrow. Mind you, we could not fear monger on Facebook and other forums back then. In fact, the public had to wait until the accident boards revealed the true facts via a live broadcast or new article. Nowadays, the 225 was doomed by the public before the preliminary report was even issued. Thankfully this won't come down to what the public think! The AAIB will complete their investigation and we will carry on from there. Maybe it flies again, maybe not!
Also note, the 3 blade chuckings, were all S61s ... Not a variant of.
Some have said, on here, that the Puma family has run up 9 million hours over all marks.
In that time it has had 3 visualy similar (tho not causal) MRH failures where we can ALL graphically imagine the results.
My questions are;
1 At what point does the statistical likelyhood of this event occuring 3 times stop being chance and become an inherant weakness ?- for whatever reason.
2 Does any other type (same operating area/same hours) have similar record of such a failure?
In that time it has had 3 visualy similar (tho not causal) MRH failures where we can ALL graphically imagine the results.
My questions are;
1 At what point does the statistical likelyhood of this event occuring 3 times stop being chance and become an inherant weakness ?- for whatever reason.
2 Does any other type (same operating area/same hours) have similar record of such a failure?
Also note, the 3 blade chuckings, were all S61s ... Not a variant of.
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5.2 million, sorry .....I,m sure someone can narrow that down.
Whatever ... my point being ...do three visually similar failures point to a design flaw or simply 5.2 million hours?
Does any other aircraft have this track record with 3 failures for the same reason?
S76 blade cuffs?
Gazelle tie bars?
207 jesus nuts?
139/189 tail rotor blades?
s92 filter bowls.
Do any other aircraft type even have this many hours? Whats nearest to the puma?
So many question
Whatever ... my point being ...do three visually similar failures point to a design flaw or simply 5.2 million hours?
Does any other aircraft have this track record with 3 failures for the same reason?
S76 blade cuffs?
Gazelle tie bars?
207 jesus nuts?
139/189 tail rotor blades?
s92 filter bowls.
Do any other aircraft type even have this many hours? Whats nearest to the puma?
So many question
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S61 blade loss
S61 blades being metal had an inherent weakness in the early days as a fatigue crack of the spar under the skin was not detectable easily. Having worked out the weakness following blade losses, a cockpit warning of coming problems was developed involving pressurising the blades and detecting pressure loss due to cracks. There was also a physical tell-tale with tester on the blade root itself.
The result was a solution to an identified problem - that worked. I had several BIM warnings during my 4500 hours on the S61, one was real, the rest spurious electrical problems. In flight actions involved increasing the NR to 102% to increase blade rigidity while finding dry land or a platform to set down on.
I never flew the 225 - after my time( but did 3500 hours approx on the AS332L). I worried more about the NF governing system which caused several total losses but which was never fixed during my time on the beast.
The result was a solution to an identified problem - that worked. I had several BIM warnings during my 4500 hours on the S61, one was real, the rest spurious electrical problems. In flight actions involved increasing the NR to 102% to increase blade rigidity while finding dry land or a platform to set down on.
I never flew the 225 - after my time( but did 3500 hours approx on the AS332L). I worried more about the NF governing system which caused several total losses but which was never fixed during my time on the beast.
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Some observations
There is a limited amount of information released about the onset of the LN-OJF accident, but I have noted some similarities between it and the G-REDL accident, and I want to share my observations. First the source material:
G-REDL Accident Report:
LN-OJF Preliminary report:
LN-OJF Eyewitness statement:
In summary, it seems that two things happened shortly after commencement of the respective catastrophic events:
I propose that one or more MR blades hit the tail-boom and the resulting G-load, however short, triggered the inertia switch. This, in my opinion, is the reason it stopped.
Photoshop illustration of LN-OJF.
TL;DR: I note some similarities in initial aircraft behaviour as well as hypothesize that the reason for the CVFDR seizing recordings only seconds into the catastrophic events for both G-REDL and LN-OJF, is due to MR blade strikes on the tail-boom and thereby triggering the CVFDR's inertia switch.
G-REDL Accident Report:
Directly after the loss of MGB oil pressure, the helicopter deviated from its cruise conditions. With only four seconds of flight data (before CVFDR recording seized), analysis of the helicopter response was limited. During these four seconds, the helicopter initially rolled left to -11.3° before rolling right to 9.1° within two seconds. Magnetic heading increased by 30 degrees.
The recorded flight data was provided to the manufacturer who ran a simulation to analyze the consistency between flight control inputs and the helicopter response during the final seconds of operation. The results indicated that, two seconds after the MGB oil low pressure warning, the helicopter was no longer responding normally to flight control inputs.
Recorded fault messages downloaded from the SMDs revealed that, at approximately the same time as the final radio transmission (20s after MGB oil low pressure warning), data from both the Heading Sensor Units (HSU) and the radio altimeter was lost to all four SMDs concurrently. The radio altimeter is located in the tail section of the helicopter on the shelf above the CVFDR, and the HSUs further aft.
Damage to the tail boom of the helicopter confirmed that it had separated from the fuselage prior to the impact with the sea. It had suffered from multiple main rotor blade strikes on the boom and at the base of the fin. Damage to the tail rotor drive shaft was consistent with the shaft rotating when it was struck by the main rotor blades.
The recorded flight data was provided to the manufacturer who ran a simulation to analyze the consistency between flight control inputs and the helicopter response during the final seconds of operation. The results indicated that, two seconds after the MGB oil low pressure warning, the helicopter was no longer responding normally to flight control inputs.
Recorded fault messages downloaded from the SMDs revealed that, at approximately the same time as the final radio transmission (20s after MGB oil low pressure warning), data from both the Heading Sensor Units (HSU) and the radio altimeter was lost to all four SMDs concurrently. The radio altimeter is located in the tail section of the helicopter on the shelf above the CVFDR, and the HSUs further aft.
Damage to the tail boom of the helicopter confirmed that it had separated from the fuselage prior to the impact with the sea. It had suffered from multiple main rotor blade strikes on the boom and at the base of the fin. Damage to the tail rotor drive shaft was consistent with the shaft rotating when it was struck by the main rotor blades.
The recordings on the CVFDR showed that everything appeared to be normal until a sudden catastrophic failure developed in 1-2 seconds. The CVFDR recordings ended abruptly at the same time. A spectral analysis of the CVR data has been carried out. There was no obvious indication of an abnormality before the sudden detachment of the rotor head.
I was looking at the helicopter as it was flying normally. Then after a few seconds it started veering back and forth quite substantially followed by 3-4 quite loud bangs where we then clearly see parts coming off of the helicopter. A few seconds after that there is one additional bang after which the helicopter goes straight down and the rotor has come off.
1. Both aircraft apparently veered back and forth initially.
I will not attempt to try and explain the exact reason for the "veering" in either accident, but I found it interesting enough to remark the similarity.2. The CVFDR on both aircraft seized recording after 2-4 seconds.
As for the CVFDR stopping so prematurely in both cases, consider the following:- In the G-REDL case it has already been documented that the MR blades struck the tail-boom multiple times, and that it eventually seperated prior to impact with the sea.
See photoshop illustration of G-REDL.- In the LN-OJF case I believe that the MR blades struck the tail-boom as well. I base this belief on my observations of the wreckage images and videos released publicly. From watching the chilling video of the falling rotor hub frame by frame, I'd argue that one can see several blades damaged (some severely) before hitting the ground. The approximate pattern of damage can then be confirmed by looking at the images of it on the ground. Damage to the tail-boom itself can be seen in several different images, as well as in this video where it is being hoisted out of the water.
So what does this have to do with the CVFDR stopping abruptly? Well, while I cannot say for sure which CVFDR was installed in G-REDL, the one installed in LN-OJF have been pictured in press releases. It is a combined CVR and FDR from Honeywell, see manual here. The location where it is normally installed in the helicopter (L1, L2 & 225) is the forward port side of the tail/cargo-hold wall as far as I understand it (see final image). To avoid overwriting the latest data after a crash, the CVFDR will stop recording if:1. It receives no power
The CVFDRs in the puma fleet should AFAIK be connected "direct battery", meaning it is among the very last of the essential electrical consumers that should lose power after failure of the generators.2. Its immersion switch is triggered
It was not immersed in water at the time it seized recording.3. Its inertia switch is triggered (6g)
I propose that one or more MR blades hit the tail-boom and the resulting G-load, however short, triggered the inertia switch. This, in my opinion, is the reason it stopped.
Photoshop illustration of LN-OJF.
TL;DR: I note some similarities in initial aircraft behaviour as well as hypothesize that the reason for the CVFDR seizing recordings only seconds into the catastrophic events for both G-REDL and LN-OJF, is due to MR blade strikes on the tail-boom and thereby triggering the CVFDR's inertia switch.
Last edited by Magjam; 29th May 2016 at 16:40. Reason: Illustrations
Now you're just twisting my words, I didn't say that they have to present the final report, I said that as I understand it they won't until they are convinced they have figured out the true cause. If that can't be done, I guess the final report will either never be presented or that it will say so. In either case my point was simply that I don't see how you can claim that they have to come up with the cause "soon". What dictates this is the investigation and what they can figure out, not the calender.
Why are you so desperately panicked to insist on one cause despite not even the Investigators being sure about the cause at this point in time. Did you think about talking to your psychiatrist about this?
A little bit of speculation is fine but what is all this crap with you Amateur accident investigators all about? And any one who doesn't follow your amateurish reasoning blindly will be madly attacked by you.
Is it asking too much to wait with the final verdict until someone KNOWLEDGEABLE has come up with some real evidence (not Armchair evidence)?
(Taking this one of your posts randomly I could have chosen any other one.
Here's hoping your not a Professional Pilot (Or professional anything else for that matter)). Rant over!
Super Puma fleet hours are 5.2 million.
4m on the L (580 a/c)
730k on the L2 (90 a/c)
546k on 225 (268 a/c)
Plus a few on the H215.
4m on the L (580 a/c)
730k on the L2 (90 a/c)
546k on 225 (268 a/c)
Plus a few on the H215.
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Is it possible to determine where the front suspension bar was positioned in relation to the gap in the fractured ring gear ?
Would be interesting if they were closely aligned . . . . just an idea.
Would be interesting if they were closely aligned . . . . just an idea.
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Tylermonkey, look at 3D computer image on the next page of where you found that picture in the updated preliminary report. (The one with the pieced together conical housing.)
The breach in the ring is at the 4-5 O'clock position, with the forward suspension bar being at 12 O'clock.
Coincidentally(?), the breach was reported to be in the 5 O'clock position on G-REDL's ring as well..
The breach in the ring is at the 4-5 O'clock position, with the forward suspension bar being at 12 O'clock.
Coincidentally(?), the breach was reported to be in the 5 O'clock position on G-REDL's ring as well..
A breach in the circumference of the bevel gear support plate at the approximate 5 o’clock position, matched the location of the vertical split in the epicyclic ring gear.
those gears and bearings show distress over time. Not a few seconds. More like several or many minutes.
Sun gear teeth rounded, wear, not sudden fracture.
Already discussed the bearing race of the fractured planet.
LN-OMG showed gearbox capable of pulling out the support plate rather than break apart at conical housing.
Suspension bar theory was likely included by aibn to satisfy AH. While all is preliminary at this point, probably nobody technical in investigation really thinks it's the strut. Only scenario is that lack of strut support put abnormal high loads onto conical housing. Over time the housings develop fatigue fracture and begin to deflect. Misalignment then cause gear and bearing distress. Gearbox gives up the ghost and then.... Problems with that chain of events is you won't get gearing distress until housing fracture. And loads sufficient for that would be evident at support plate as well.
Perhaps more likely it starts with epicyclic.
Did AH fix the earlier problem or just improve the possibility of detection?
Sun gear teeth rounded, wear, not sudden fracture.
Already discussed the bearing race of the fractured planet.
LN-OMG showed gearbox capable of pulling out the support plate rather than break apart at conical housing.
Suspension bar theory was likely included by aibn to satisfy AH. While all is preliminary at this point, probably nobody technical in investigation really thinks it's the strut. Only scenario is that lack of strut support put abnormal high loads onto conical housing. Over time the housings develop fatigue fracture and begin to deflect. Misalignment then cause gear and bearing distress. Gearbox gives up the ghost and then.... Problems with that chain of events is you won't get gearing distress until housing fracture. And loads sufficient for that would be evident at support plate as well.
Perhaps more likely it starts with epicyclic.
Did AH fix the earlier problem or just improve the possibility of detection?
Looking at the G-REDL description of roll and yaw, although accidental control surface inputs will also be part of the picture, the motions appear consistent with gyroscopic forces occurring when a downward force is applied at the rear followed by the opposite.
I expect that this is indicative of the supporting structure coming apart piece by piece. We know that the root cause in G-REDL is in the epicyclic but still these forces are consistent with the suspension bar arrangement progressively failing. I conclude that whatever the root cause in a rotor detachment accident there is going to be a confusion of evidence as the forces on the rotorhead rip things apart.
I expect that this is indicative of the supporting structure coming apart piece by piece. We know that the root cause in G-REDL is in the epicyclic but still these forces are consistent with the suspension bar arrangement progressively failing. I conclude that whatever the root cause in a rotor detachment accident there is going to be a confusion of evidence as the forces on the rotorhead rip things apart.
That's why it's so critical to get all the parts. Investigators evaluate for clues on sequence and time relationship.
Conical housing fracture surfaces may be inconclusive on fatigue evidence due to corrosion from seawater.
Strut should be straight forward. Impact, fatigue, overload, should be preserved enough.
Lab evaluation of gears and bearings will take time but they would already know about heat generated and wear modes. Even if they see fatigue they will still need to find out why. The missing carrier may hold clues about the puzzle.
If AH farmed out the gearbox design as suggested then they may not even have the expertise themselves.
That makes the fast interpretation all the more questionable.
Conical housing fracture surfaces may be inconclusive on fatigue evidence due to corrosion from seawater.
Strut should be straight forward. Impact, fatigue, overload, should be preserved enough.
Lab evaluation of gears and bearings will take time but they would already know about heat generated and wear modes. Even if they see fatigue they will still need to find out why. The missing carrier may hold clues about the puzzle.
If AH farmed out the gearbox design as suggested then they may not even have the expertise themselves.
That makes the fast interpretation all the more questionable.
AIBN could have clearly stated what they found and what was still missing in their initial version of the preliminary report. Instead of beating around the bush with some vague hints and suggestions.
Overall I don't see any new major findings in the revised preliminary that they couldn't have already put in the initial version, or am I missing something?
Looking at just the reports, some internet discussions and magazine articles, it seems like they let external pressure influence their work a little too much, reacting rather than acting. But I must admit that's a bit far-fetched without having way more insight into the process. Although I'm still startled by the fact that they let the journalists wander around the wreckage.
Overall I don't see any new major findings in the revised preliminary that they couldn't have already put in the initial version, or am I missing something?
Looking at just the reports, some internet discussions and magazine articles, it seems like they let external pressure influence their work a little too much, reacting rather than acting. But I must admit that's a bit far-fetched without having way more insight into the process. Although I'm still startled by the fact that they let the journalists wander around the wreckage.
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I must say I am still, about a month in, struggling to make sense of all this.
AH came out 48 hours after the accident and effectively said this was not an epicyclic incident.
AH have the most experience with this machine. They know that a full investigation is ongoing which will, if it is in anyway possible, get to the bottom of this and publish a report. Following that report they know litigation will be inevitable.
So surely they must have access to the engineering equivalent of a smoking gun.
But, one month in nothing of that nature has been made public. There may well be solid reasons for this. But, even if that is the case the AIBN clearly think that the "doors they need to close" consist of more than tidying-up the evidence ahead of a final report.
The regulator reviews the advice of the manufacturer and AIBN and decides if a suspension can be relaxed. There is clearly a difference of opinion rather than emphasis between the manufacturer and the investigator.
The latest statement made by AH is carefully worded to say suspension failure is the only probable scenario but don't say why. That is understandable for legal reasons.
So what we can't know from the public statements is whether
(a) AIBN believe, given the 3 recent gear related accidents, epicyclic failure must be explicitly ruled out as the primary cause. That in order to do that 100% they need supporting mechanical and if possible metalurgical evidence from parts as yet unfound
or
(b) this is rather more than a door closing exercise and they don't buy the suspension strut theory.
So I am back to square one. Surely AH would not be releasing these statements unless they can stand them up.
AH came out 48 hours after the accident and effectively said this was not an epicyclic incident.
AH have the most experience with this machine. They know that a full investigation is ongoing which will, if it is in anyway possible, get to the bottom of this and publish a report. Following that report they know litigation will be inevitable.
So surely they must have access to the engineering equivalent of a smoking gun.
But, one month in nothing of that nature has been made public. There may well be solid reasons for this. But, even if that is the case the AIBN clearly think that the "doors they need to close" consist of more than tidying-up the evidence ahead of a final report.
The regulator reviews the advice of the manufacturer and AIBN and decides if a suspension can be relaxed. There is clearly a difference of opinion rather than emphasis between the manufacturer and the investigator.
The latest statement made by AH is carefully worded to say suspension failure is the only probable scenario but don't say why. That is understandable for legal reasons.
So what we can't know from the public statements is whether
(a) AIBN believe, given the 3 recent gear related accidents, epicyclic failure must be explicitly ruled out as the primary cause. That in order to do that 100% they need supporting mechanical and if possible metalurgical evidence from parts as yet unfound
or
(b) this is rather more than a door closing exercise and they don't buy the suspension strut theory.
So I am back to square one. Surely AH would not be releasing these statements unless they can stand them up.
Last edited by birmingham; 30th May 2016 at 10:17.
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I believe with the ring gear as shown in http://www.pprune.org/rotorheads/578...ml#post9392368 the game for AH / H225 in offshore ops (at minimum) is over. It is only a question of time till the final report will presented by AIBN.
A minimum chance might be given, if AH and AVIO would work 24/7/365 on completely new solutions, but those also must be evaluated and certified and this takes time. A stopgap solution I don’t see on the horizon due to the already ordered grounding of Super Puma.
This is meaning the remaining operators have to work with alternate HC-Types. To switch back to AH / Super Puma after approx. one year or more might therefore be a very theoretical question.
To quote former Chairman Gorbachev: "Those who are late will be punished by life itself".
A minimum chance might be given, if AH and AVIO would work 24/7/365 on completely new solutions, but those also must be evaluated and certified and this takes time. A stopgap solution I don’t see on the horizon due to the already ordered grounding of Super Puma.
This is meaning the remaining operators have to work with alternate HC-Types. To switch back to AH / Super Puma after approx. one year or more might therefore be a very theoretical question.
To quote former Chairman Gorbachev: "Those who are late will be punished by life itself".
Last edited by AW009; 30th May 2016 at 14:29. Reason: formatting
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I believe with the ring gear as shown in http://www.pprune.org/rotorheads/578...ml#post9392368 the game for AH / H225 in offshore ops (at minimum) is over. It is only a question of time till the final report is presented by AIBN.
A minimum chance might be given, if AH and AVIO would work 24/7/365 on completely new solutions, but those also will be evaluated and certified and this takes time. A stopgap solution I don’t see on the horizon due to the already ordered grounding of Super Puma.
This is meaning the remaining operators have to work with alternate HC-Types. To switch back to AH / Super Puma after approx. one year or more might therefore be a very theoretical question.
To quote former Chairman Gorbachev: "Those who are late will be punished by life itself".
A minimum chance might be given, if AH and AVIO would work 24/7/365 on completely new solutions, but those also will be evaluated and certified and this takes time. A stopgap solution I don’t see on the horizon due to the already ordered grounding of Super Puma.
This is meaning the remaining operators have to work with alternate HC-Types. To switch back to AH / Super Puma after approx. one year or more might therefore be a very theoretical question.
To quote former Chairman Gorbachev: "Those who are late will be punished by life itself".
If you are correct and frankly (given the current financial situation) even if you are not, what you predict may well come to pass.
However, for AH the situation could be much worse than that.
AH are part of EADS and the last episode halved the groups net cash position. The CEO (who knows a very great deal about the Puma) is looking at this strategically and you can bet Toulouse is looking over his shoulder.
We have more than enough 92s to cope and the AW189, H175 and soon Bell 525 are new if slightly smaller options for operators. So a re-engineered Puma may be a total non starter.
So maybe AH will bite the bullet and go for an entirely new machine but as the FT said last time; by the time AH have a really new airframe, the market may have gone.
Last edited by birmingham; 30th May 2016 at 11:13.