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EC225 crash near Bergen, Norway April 2016

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EC225 crash near Bergen, Norway April 2016

Old 2nd Jun 2016, 05:51
  #1061 (permalink)  
 
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Originally Posted by OnePerRev View Post
Okay, not good news here at all, but not surprising based on earlier photos we saw.


Next hard part is to determine "Why". Parts break when strength is exceeded by load. designers keep that from happening in theory, supported by testing. But if something breaks, you look at both ends of that basic equation. Was the part weaker than designed or are the loads higher than expected. If the former, due to quality issue, that can usually be contained. If the latter, then heads scratch on entire substantiation, heavy inspections, life limits, etc.
Also note (as stated earlier) the symmetry in fractures - and the number of parts affected. Less likely a quality issue, when affects multiple parts, unless same batch. There may well be a vibratory deflection content that was not anticipated, thus not deigned for. The issue that doomed Norne event was a resonance that AH discounted. They probably are paying attention now...
There is basically Zero chance of a Planetary Gearbox failure that won't result in total destruction, nature of the beast
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Old 2nd Jun 2016, 07:04
  #1062 (permalink)  
 
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Can the engineers tell us if the gearwheel design that integrates a bearing race with the gear teeth is a normal solution to the space limitations within an MRG? Would it not be better to install a standard bearing within the wheel? By standard bearing I mean one that includes both races and the rollers.

G
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Old 2nd Jun 2016, 07:08
  #1063 (permalink)  
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Safety alert issued after metal fatigue found in Norway crash helicopter | World news | The Guardian

Aviation experts investigating the Norway helicopter crash that killed 13 people have found signs of metal fatigue in the gearbox of the downed aircraft. The Accident Investigation Board of Norway (AIBN) is calling on the European Aviation Safety Agency (EASA) to take “immediate action” to ensure other Super Puma H225 helicopters are safe. The board warns that “the current means to detect a failure in advance are not effective”.

Eleven passengers, including oil worker Iain Stuart from Laurencekirk, Aberdeenshire, and two crew members were killed after the aircraft crashed near the city of Bergen on 29 April. Earlier investigations revealed that the helicopter was travelling at 2,000ft when the main rotor head suddenly detached from the body of the helicopter, which then smashed into a tiny island and burst into flames. Investigators said the “sudden catastrophic failure” developed in one to two seconds.

The latest report, published on Wednesday, said metallurgical examinations of parts of the gear workings found “features strongly consistent with fatigue”. The AIBN prelimary report said the findings were of “such significance” that a safety recommendation was required to ensure the continued airworthiness of the main gearbox (MGB) of all helicopters of the same type.

The recommendation states: “It cannot be ruled out that this signifies a possible safety issue that can affect other MGBs of the same type. The nature of the catastrophic failure of the LN-OJF main rotor system indicates that the current means to detect a failure in advance are not effective. The AIBN therefore recommends that EASA take immediate action to ensure the safety of the Airbus Helicopter’s H225 MGB.”........
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Old 2nd Jun 2016, 08:49
  #1064 (permalink)  
 
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This new interim report shows a picture of a second-stage planetry gear. Although it's not mentioned in the text, the caption notes that 3x of the rollers are missing...

How? How do they escape? Or were they never fitted...??
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Old 2nd Jun 2016, 08:58
  #1065 (permalink)  
 
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I think the key statement is this ...

"The nature of the catastrophic failure of the LN-OJF main rotor system indicates that the current means to detect a failure in advance are not effective."

It's important that AH respond to this as quickly as possible so as we can agree on the initial cause. Is this a simple repeat of REDL or did the Airbus scenario occur and the resulting load trigger the secondary fatigue failure of the weakened planetary stage .

What is now undeniable (surely) is that the industry has a real problem with MGBs in mid range shuttles. 3 total loss fatal accidents since 2009 in three types (S92, L2 and 225). This is not just an issue with Pumas there will need to be a major reappraisal of the design of these units to try and get these accident rates down.

Last edited by birmingham; 2nd Jun 2016 at 09:12.
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Old 2nd Jun 2016, 09:20
  #1066 (permalink)  
 
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Originally Posted by birmingham View Post
I think the key statement is this ...

"The nature of the catastrophic failure of the LN-OJF main rotor system indicates that the current means to detect a failure in advance are not effective."

It's important that AH respond to this as quickly as possible so as we can agree on the initial cause. Is this a simple repeat of REDL or did the Airbus scenario occur and the resulting load trigger the secondary fatigue failure of the weakened planetary stage .

What is now undeniable (surely) is that the industry has a real problem with MGBs in mid range shuttles. 3 total loss fatal accidents since 2009 in three types (S92, L2 and 225). This is not just an issue with Pumas there will need to be a major reappraisal of the design of these units to try and get these accident rates down.
It's also worth noting that, if the ultimate cause of the accident is in the H225 epicyclic, the AS332L2 uses the same module as the H225 , so they would be similarly affected.
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Old 2nd Jun 2016, 09:32
  #1067 (permalink)  
 
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Yes but the extended TBO several times induces a
higher risk of failure, and leads to a probable connection to the failure incident

Fatigue cracks in a new MRA and MGB is less probable due to the breakdown
statistics of the helicopter type. The breakdown incidents in the past support this.

Also the part of the MRA where the suspension bar fitting is broken,
it coincides with the part of the Outer planetary gear on the epicyclic module
that has a crack that cannot be explained by an other probably cause than a gear failure. If the suspension bar came loose and that ultimately leads to a gearbox failure,
it could be anywhere on the outer planetary gear of the epicyclic module, but it is not.
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Old 2nd Jun 2016, 09:40
  #1068 (permalink)  
 
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Airbus preliminary reaction to the AIBN report:

"We have seen the AIBN report and are reviewing it. In light of this important new finding, we continue to fully support ‎AIBN, EASA, our customers and the ongoing investigation by providing information in full transparency. Safety of the passengers travelling in our helicopters remain our chief priority. We do not wish to comment further as the investigation continues."
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Old 2nd Jun 2016, 09:41
  #1069 (permalink)  
 
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Perhaps AH should revisit its response the their reply to the following REDL safety recommendation (in AAIB annual report 2012)
SAFETY RECOMMENDATION 2011-032
It is recommended that, in addition to the current methods of gearbox condition monitoring on the AS332 L2 and EC225, Eurocopter should introduce further means of identifying in-service gearbox component degradation, such as debris analysis of the main gearbox oil.
Response
Based on FMECA (Failure Mode Effect and Criticity Analysis) and confirmed by the experience, two types of debris can be generated by gearbox deterioration:
3D-particles (volume) or 2D-particles (surface): these types of particles are usually generated by degradation of high-loaded functional surfaces like bearing races or gear tooth (spalling, scale, flaking ...) or by part breakages.
- Wear particles: these types of abrasive particles are usually caused by abnormal high-contact of surfaces (fretting, micro-pitting...) and are generally in suspension in the oil.
A third type of debris can be found in gearboxes is associated with the manufacturing process (swarf...), the assembly process (piece of lockwire, fragment of cotter pin...), or maintenance actions (leading to introduction of foreign objects). All these debris are considered as some 3D or 2D particles.
Because the types of these generated particles are very different, adapted monitoring means must be used in order to monitor each type.
Two monitoring means are presently available to detect such debris:
- Magnetic plugs: these collect the particles and are visually inspected in order to detect 3D or 2D debris, but they can also collect wear particles. An electrical system can be added in order to give an in-service information of particle presence (warning on pilot on instrument panel and/or HUMS system for the maintenance) as soon as the particle(s) collected is (are) able to close the bridge between the two electrical parts of a magnetic plug. All Eurocopter fleet gearboxes are equipped with magnetic plugs (manual or electrical ones) and this is the main monitoring means to detect internal gearbox component degradation (they are also associated to the oil filter cartridge inspection).
- Spectrometric Oil Analysis Program (SOAP): this is used to monitor evolution of the concentration of different metals or else (particle per million) in suspension in the lubricant. It requires following of a dedicated and strict procedure to take periodically a volume of oil in defined conditions (warm and mixed oil taken with specific equipment by qualified personnel with a qualified process) and sending it to qualified laboratory.
SOAP is a monitoring means that is well known to Eurocopter and its principle is described in EC Technical Publications (Standard Practice Manual WC 20.08.02.601 attached). SOAP is considered by Eurocopter as an optional and additional monitoring means. SOAP can be used to monitor the evolution, between two oil replacements, of metallic material concentration or possibly some other material (like mineral) which are in suspension in the oil. SOAP can trigger the requirement of a close monitoring of the main monitoring means (magnetic plugs and filter) if certain dedicated thresholds are exceeded.
This means was introduced in the past during the development of SA 330 (Puma) and at the beginning of AS 332 (Super-Puma) production because the technologies used (bolted assemblies, machining without grinding, etc.) sometimes produced wear particles. This is no longer the case as a result of modern technologies used on the AS332 L2 and EC225 main gear boxes (Electron beam welding instead of bolted assemblies) and manufacturing processes (super finishing, grinding) which generate parts more reliable regarding wear degradation.
Despite the fact that these old technologies could generate some wear particles relevant to SOAP, the experience of Eurocopter demonstrates that this means was not efficient and that, in practice, it had led to many unjustified removals of gear boxes with unnecessarily interference to flight operations and wasted maintenance costs. Against this background, Eurocopter so issued Service Letter 759-00-86 in 1986 25/06/1986.

It also has to be noted that SOAP is not adapted to detect 3D or 2D particles because such particles are not in suspension in the oil. So SOAP is not adapted to detect spalling.
In addition, the magnetic plugs are able to detect incipient spalling at a level where, even if the whole volume of particles generated was in suspension in the oil, the concentration would not be detectable by SOAP taking in account the important oil volume in a main gear box.
Eurocopter considers that magnetic plugs and/or chip detectors are the most efficient means to detect gearbox internal failure modes, and that they are sufficient to ensure the flight safety so that further means of identifying in-service gearbox component degradation, such as debris analysis of the main gearbox oil, are not necessary. Here, it is relevant to note that the particle detection capability of the sump and epicyclic plugs has been enhanced by the removal of the ring of magnets from the lower area of the epicyclic module.
Status - Rejected

It seems EC/AH got hung up on SOAP and MCDs rather than looking at other methods of monitoring.
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Old 2nd Jun 2016, 09:51
  #1070 (permalink)  
 
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What other methods of monitoring would you suggest?
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Old 2nd Jun 2016, 09:53
  #1071 (permalink)  
 
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Can anyone confirm that Airbus Technical Agreement on extended TBO on MGB

says that only 90% of max cruise speed can be used?

According to flight logs available, it is evident that the aircraft did not
fly at 90% of max cruise speed at the time of the breakdown incident,
nor did it do that at a date before the claimed MGB change.

Is there any flight logs available that claims the downtime of LN-OJF
during the claimed MGB and MRA change?
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Old 2nd Jun 2016, 09:58
  #1072 (permalink)  
 
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Originally Posted by turboshafts View Post
Yes but the extended TBO several times induces a
higher risk of failure, and leads to a probable connection to the failure incident

Fatigue cracks in a new MRA and MGB is less probable due to the breakdown
statistics of the helicopter type. The breakdown incidents in the past support this.

Also the part of the MRA where the suspension bar fitting is broken,
it coincides with the part of the Outer planetary gear on the epicyclic module
that has a crack that cannot be explained by an other probably cause than a gear failure. If the suspension bar came loose and that ultimately leads to a gearbox failure,
it could be anywhere on the outer planetary gear of the epicyclic module, but it is not.
...Abolutely, as an engineer it is impossible to argue against what you say. If it were 2009 I think this would be an entirely sensible approach.

The problem is that it is 2016 the only way we could continue as normal is to persuade the passengers that reducing the TBO would be enough to ensure their safety.

5 gear related accidents, 3 total loss fatalities worldwide in E&P since 2009, 4 of them on the same range of A/C.

Plus we have this from the AIBN...

"The nature of the catastrophic failure of the LN-OJF main rotor system indicates that the current means to detect a failure in advance are not effective."

a. Clearly we couldn't give them an absolute guarantee of no failures nor should we.
b. They won't be listening this time.

What will come out of this will be some form of industry wide initiative so that future aircraft have more reliable gearboxes.

Last edited by birmingham; 2nd Jun 2016 at 10:08.
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Old 2nd Jun 2016, 10:39
  #1073 (permalink)  
 
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Originally Posted by birmingham View Post
...Abolutely, as an engineer it is impossible to argue against what you say. If it were 2009 I think this would be an entirely sensible approach.

The problem is that it is 2016 the only way we could continue as normal is to persuade the passengers that reducing the TBO would be enough to ensure their safety.

5 gear related accidents, 3 total loss fatalities worldwide in E&P since 2009, 4 of them on the same range of A/C.

Plus we have this from the AIBN...

"The nature of the catastrophic failure of the LN-OJF main rotor system indicates that the current means to detect a failure in advance are not effective."

a. Clearly we couldn't give them an absolute guarantee of no failures nor should we.
b. They won't be listening this time.

What will come out of this will be some form of industry wide initiative so that future aircraft have more reliable gearboxes.
I agree, but it depends if the outcome is
due to fatigue of use and improper overhaul/maintenance
how can you ever monitor that better?
you can only minimize the risk by decreasing TBO.

If that was new parts that leads to catastrophic failure
after less than 1 month operation time, the
issue is the qualification testing and certification at the manufacturer.

both have up until now proven insufficient as we have the bevel gear incident as well.

But even for the bevel gear incident it was introduced on all types of
Aircrafts of the type, decreased TBO, decontamination of oil
and cleaning of the part. Still CAAN approves 2 times in less than a month
extended TBO. I think that is also a main mistake.

Last edited by turboshafts; 2nd Jun 2016 at 11:01.
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Old 2nd Jun 2016, 11:44
  #1074 (permalink)  
 
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Originally Posted by turboshafts View Post
... Still CAAN approves 2 times in less than a month extended TBO. I think that is also a main mistake.
I'm confused - was the gearbox that ruptured the same gearbox that had a 2 times TBO extension? If not then this is a completely irelevant point. Nope, pretty sure I'm not confused!
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Old 2nd Jun 2016, 12:00
  #1075 (permalink)  
 
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Originally Posted by HeliComparator View Post
I'm confused - was the gearbox that ruptured the same gearbox that had a 2 times TBO extension? If not then this is a completely irelevant point. Nope, pretty sure I'm not confused!
What do you mean?

It is highly unclear if gearbox is changed or not

Media reported it was changed. Was it?

Fatigue cracks in a 1 month old gearbox?

I guess we will know when the final AIBN report is released.

Until then, if you are interested in understanding the root cause
of the breakdown incident, to me its not irrelevant.
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Old 2nd Jun 2016, 12:16
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Epi

Quite often a replacement puma family mgb comes in its box without the epicyclic or accessory modules.Depending on the removed mgb epi's remaining tbo, that removed epi might be fitted to the new/overhauled mgb.
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Old 2nd Jun 2016, 12:40
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@ HeliComparator referring to http://www.pprune.org/rotorheads/578298-ec225-crash-near-bergen-norway-54.html#post9396103 :
Enrichment
/ irradiating of critical MRGB gears by low radioactivity and inflight measuring of the trend (grade, guantity) of abrasion under given conditons in oil flow by means of semiconductor detector(s).

Last edited by AW009; 2nd Jun 2016 at 16:30. Reason: my poor english
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Old 2nd Jun 2016, 12:41
  #1078 (permalink)  
 
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Originally Posted by BTC8183 View Post
Quite often a replacement puma family mgb comes in its box without the epicyclic or accessory modules.Depending on the removed mgb epi's remaining tbo, that removed epi might be fitted to the new/overhauled mgb.
Does it mean that contaminated oil from the old epi
can also come in and deteriorate in an new MGB if not
clean/flushed out sufficiently? or are there separate lubrication circuits?
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Old 2nd Jun 2016, 12:43
  #1079 (permalink)  
 
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Also,

Main gearbox
Main rotor assembly

Is the epicyclic module separate or included in one of those two units,
when they are changed?
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Old 2nd Jun 2016, 13:15
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Originally Posted by turboshafts View Post
Until then, if you are interested in understanding the root cause
of the breakdown incident, to me its not irrelevant.
To me, if the point relates to equipment that was not installed on the helicopter at the time of the crash, it is totally irrelevant. What we in UK call a red herring. But if you just want to dig up dirt then perhaps it is relevant.
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