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EC225 crash near Bergen, Norway April 2016

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EC225 crash near Bergen, Norway April 2016

Old 28th Jun 2016, 21:56
  #1401 (permalink)  
 
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That was it for the planetary gears of the H 225 / ASs 332 L2 Super Puma and AS 532 U2 Cougar.

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

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

And if after G-REDL nothing had been changed due to the safety recommandations by AHF, they are sucide canditates in present stressed (offshore) markets.
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Old 28th Jun 2016, 22:00
  #1402 (permalink)  
 
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From the last report:

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

This puts Airbus' earlier statements in a very weird light...
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Old 28th Jun 2016, 22:10
  #1403 (permalink)  
 
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Norwegian article with several statements from Halvorsen from ABIN:
Havarikommisjonen: Dette forårsaket helikopterulykken - Bergens Tidende

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

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

"- Det betyr at vi mener dette var en feil som var umulig å detektere med vanlige vedlikeholdsrutiner, sier Halvorsen."
Translation: "This means that we are of the opinion that this was a fault that was impossible to detect using ordinary maintenance routines, says Halvorsen"
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Old 28th Jun 2016, 22:20
  #1404 (permalink)  
 
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There is a new version of the AIBN preliminary report published today.
Investigation of helicopter accident at Turøy near Bergen in Hordaland county, Norway | aibn

Arrakis
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Old 28th Jun 2016, 22:30
  #1405 (permalink)  
 
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Red face

Seems quite clear...

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

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

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

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

What initiated the fracture has not yet been determined.



Over to you Airbus.... seems those 225 ashtrays are going to be sat on the ground for some considerable time..
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Old 28th Jun 2016, 22:31
  #1406 (permalink)  
 
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Echoes of G-BJVX
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Old 28th Jun 2016, 22:42
  #1407 (permalink)  
 
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"June 28, 2016

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



Norway-Statement - Airbus Helicopters


Too bad for them that their very strange statement from May 27th is still on the same page:
"Out of these seven scenarios, only one – the failure of the attachment of a suspension bar – can be assessed as probable by Airbus Helicopters, based on the information available to date."
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Old 28th Jun 2016, 23:00
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@Tatischeff: By looking on http://isambardkingdom.com/wp-conten...Gear-Box-1.jpg I see three axles / drive shafts and a virtual rotor mast discontinuous (fr. discontinue), meaning four machine elements one upon the other,
  • don’t see any continuous (fr. continue) rotor mast,
  • don’t see it’s axial and radial bearing at bottom / sump of MRGB,
  • don’t see its upper bearing in the conical housing,
  • and see only a bevel gear and two epicyclic modules,
  • which are worst ‘axial and radial bearings' to prevent disalignment..
By this your questions and your non-neophytedisalignment’ (= tous les côtés sur la ligne entre deux points) will find an answer by technical and constructively facts.
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Old 28th Jun 2016, 23:27
  #1409 (permalink)  
 
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Is there any information out there about the nature of the road accident? Was the transmission in a container? Was there external damage to the case components? Was the truck destroyed? I would think it would have to be a significant accident to initiate a fracture of internal gearbox components. Is it correct that the inspection and repair by AH prior to the installation in January was the inspection required due to the road accident? Why was the transmission being transported at that time (with continued time on it)? How extensive were their repairs and more importantly, what did they inspect (how deep did that go)? If that is the case then 260 hours elapsed between the road accident and the failure. I have no doubt that anything can happen during shipping. I've seen fork lift holes in blade boxes, engine cans that have rolled over and been severely dented and seen the gyro we were waiting for AOG fall off the top of a stack of boxes the delivery person was carrying. His comment was "If you think that was bad, you should come to our warehouse sometime". If it turns out that there is any correlation, it makes a viable argument to what we sometimes see as OEMs being overly cautious when they say "you have to overhaul that component as if it were a sudden stoppage/hard landing incident" even when we know it wasn't that bad. I think any OEM is out on a limb if they are willing to comply with the minimum they think is necessary for an incident scenario that may be unusual or uncommon. Of course, I have no idea if that was the case. Just another part of this nasty puzzle.
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Old 28th Jun 2016, 23:44
  #1410 (permalink)  
 
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Some of what has been said by AIBN representatives about the road accident as far as I have seen is:

-The gearbox received some unkind treatment and had to be repaired.
-The accident happened in Australia in last year.
-The gearbox was transported on a small lorry, which had an accident and the gearbox fell/came off the lorry.
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Old 28th Jun 2016, 23:49
  #1411 (permalink)  
 
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lowfat "the accident most likely was a result of a fatigue fracture in one of the eight second stage planet gears."

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

anyone in authority got a maths o level?
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Old 29th Jun 2016, 00:17
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I don´t understand this statement:

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

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

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

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

What about the chip detectors?

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


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

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

I am disappointed in AIBN, a very weak preliminary report
with vague statements.
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Old 29th Jun 2016, 00:23
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"Why is the gearbox modified, inspected and repaired by Airbus at 1080 hours?"

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

"
The AIBN is aware that the gearbox was involved in a road accident in 2015. The gearbox was inspected, repaired and released for flight by the manufacturer before it was installed in LN-OJF in January 2016."
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Old 29th Jun 2016, 00:24
  #1414 (permalink)  
 
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@AnFI: AS 332 L1 has 9 plantetary gears and obviously that's the 'less sensitive' construction.

Math? Perhaps Planetengetriebe & ZAR5 Planetengetriebe & http://www.hexagon.de/zip/zar5_d32.zip
will be a first help.

Last edited by AW009; 29th Jun 2016 at 00:36.
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Old 29th Jun 2016, 09:05
  #1415 (permalink)  
 
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Two points on the latest AIBN report ...

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

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

Last edited by birmingham; 29th Jun 2016 at 09:17.
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Old 29th Jun 2016, 09:32
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Originally Posted by buzz66 View Post
Can't be a Sus Bar failure because the Gearbox split in 2 parts.
Sus Bar or Pin failure would see the Barby Plate and whole gearbox leave the scene. Almost has to be major Gear failure internal to the Gbox.
I bet my bottom dollar they are the bits they want to still find.
... looks like you might be correct
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Old 29th Jun 2016, 09:48
  #1417 (permalink)  
 
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By looking on Isambard's Lad | The sun shines out of the Engineers I see three axles / drive shafts and a virtual rotor mast discontinuous (fr. discontinue), meaning four machine elements one upon the other,
- don’t see any continuous (fr. continue) rotor mast,
- don’t see it’s axial and radial bearing at bottom / sump of MRGB,
- don’t see its upper bearing in the conical housing,
- and see only a bevel gear and two epicyclic modules,
- which are worst ‘axial and radial bearings' to prevent disalignment..
AW009, thank you for explaining you view, but I'm a little disappointed by its support (a very simplified block diagram).

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

I don't think that hyperstatism ever did well with the wear resistance ...
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Old 29th Jun 2016, 10:04
  #1418 (permalink)  
 
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Originally Posted by turboshafts View Post
I don´t understand this statement:

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

From the G-REDL report, it is quite clear that there was abnormal HUMS readouts in the days before the accident.´
But it was not known how to interpret the data,
that showed increased vibrations. According to Eurocopter the debris should be determining the Health of the gearbox and not the HUMS readouts.
I think it's pretty clear. You must see this sentence in context of the previous:
Originally Posted by AIBN
AIBN believes that a sub-surface crack has propagated without creating a significant amount of magnetic debris from spalling. Also, the HUMS appears unable to identify symptoms of such degradation in the epicyclic module.
They are saying that there were no warning signs before the accident neither from the chip detectors or HUMS for LN-OJF. They see this as a "certification flaw" as the certification was based on the premise that a fatigue crack would produce a warning from at least one of these systems.

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

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

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

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

When it comes to the chip detectors, they say this:
Originally Posted by AIBN
No findings indicate any malfunctions to the magnetic debris detection system on LN-OJF, or fail to follow procedures for visual inspection and checks before flight. Neither are there any records of magnetic debris findings from inspections made since the gearbox was installed on LN-OJF in January 2016.
That seems pretty clear to me.

Originally Posted by turboshafts View Post
I already read that Visual inspection of gears are done at 2000 hours. up to that spalling can occur, that is not dangerous to the gearbox operation.
This is not what I read in the report. Quite the opposite, they say that the design philosophy assume that a spalling will not develop into a fracture because of the material properties, but that this accident indicates that this assumption is wrong:
Originally Posted by AIBN
An essential design philosophy regarding a possible failure inside the epicyclic module has been that propagation of a crack would be suppressed by the compressive surface stress. Thus a crack in the surface area should grow outboard and create spalling that would produce magnetic debris, which will be detected on the magnetic plugs (chip detectors). The optional HUMS1 is an additional means for detecting developing degradation.
Originally Posted by turboshafts View Post
"The main gearbox (MGB) was received from Airbus Helicopters after modification, inspection and repair before it was installed in LN-OJF 15 January 2016. At the time of installation, the MGB had accumulated 1 080 hrs since new"

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

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

Originally Posted by turboshafts View Post
I am disappointed in AIBN, a very weak preliminary report
with vague statements.
Not as I read it. I think it's perfectly clear in the areas being addressed. That all remote, unlikely connections aren't included is to be expected as it is preliminary and the investigation is still ongoing.
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Old 29th Jun 2016, 10:15
  #1419 (permalink)  
 
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Originally Posted by birmingham View Post
Two points on the latest AIBN report ...

(1) I may be naive but these latest updates from AIBN have rather shocked me. Not because of what they reveal but in respect to the original AH statement about the suspension assembly. I genuinely believed that to put that out with all its inevitable effects AH must have had access to the engineering equivalent of a smoking gun. If AH have made a genuine mistake they should explain why and clarify why they made those remarks on their website. Some folks at CHC must have been through hell because of it.
As I have stated before, I don't give much for any statement or report by any commercial organization. The reason is that the actual truth is so far down on their list of priorities. I doubt it was a "mistake", it was a gamble, probably a relatively desperat gamble, and it failed.
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Old 29th Jun 2016, 11:58
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Now that the focus is squarely on the planet gears, investigators will doubtless be looking into all aspects of their design, manufacture, assembly and operation.

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

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