Heli ditch North Sea G-REDL: NOT condolences

[nodrama]

EASA AD No: 2009-0087-E

for those of you who want to have a read.

[LastMinute]

Originally Posted by WAH

Originally Posted by AAIB

The investigation has so far revealed that the MGB had suffered from a major failure within the epicyclic module. This is supported by HUMS data; however, this is not yet fully understood.

So HUMS done exactly what it was supposed to be doing in respects to alerting the engineer that there was something abnormal.

I read that part of the AAIB report to mean that the HUMS data from the time of the accident supports their determination that the failure was within the epicyclic module.

The daily inspections were initiated not due to HUMS indications but:

Originally Posted by AAIB

As the result of the discovery of a particle on the main rotor gearbox epicyclic module magnetic chip detector

Furthermore, while the HUMS data were under close monitoring:

Originally Posted by AAIB

No further abnormalities were identified during this period.

I'd say your eagerness to hang the operator and manufacturer HUMS guys out to dry is not warranted by the evidence.

[Mungo5]

BBC NEWS | UK | Scotland | Pilots warn over North Sea safety

"The Air Accidents Investigation Branch's initial report recommended that "additional inspections" be carried out on other Super Puma helicopters to ensure the airworthiness of the gearboxes after the crash on 1 April. The investigation found that the gearbox had suffered a "major failure", which was not yet fully understood, leading the main rotor blades to break off and hit the helicopter."

[mckeg4]

Nervous Offshore Worker

Guys,

Looking for comments from you on the initial recommendations from the AAIB and if you feel they are adequate to ensure non reoccurance pending full report.

I am offshore at the moment and as you can imagine the thought of flying home scares us all at the moment, we have just been informed by management that all MkII Pumas were taken out of service to have these magnetic pick up detectors in the gear box checked and then once ok have been allowed to resume operation, which I believe some are back in service today.

We have also been told that these magnectic detectors will be checked either every 10 hours or on a daily basis which ever comes first for debris and if any are found there will be no continued monitoring period as was the case in last weeks accident but the gearbox will be removed from the helicopter and overhauled, Do you guys know if this is fact or just mear confidence building from our employers???

Should it not be the case that all MkII Pumas are grounded until the full investigation has been carried out and investigation findings are realised??

Also what are the advantages / dis-advantages of checking these probes after every flight, I know that the turn around time would increase but this is a small price to pay for arriving safely.

Any help would be greatly appreciated by a very worried offshore community

Thanks

[heli49]

No, there is no Chip detector for the epicyclic on the L or L2, only a mag plug. However, its all in the same oil system so chips from the epicyclic can still make their way to the chip detector in the sump. It would be interesting to know to what extent the mag plug captures epicyclic chips, thus denying them their rightful place on the sump chip detector.

The 332L2 MGB do have two chip detectors one installed just below the epicyclic and a second one in the sump. Both detectors are connected to HUMS, a chip will be displayed on the HUMS groundstation. Only the sump detector will light a cockpit chip warning.

332L/L1 do only have the sump detector.

[nodrama]

McKeg4

Google search EASA AD No: 2009-0087-E and give it a read. Although written for maintenance personel, you should be able to get the jist of the proceedures that have been put in place.

[Clive J]

Another nervous offshore worker

I think I'm understanding the chip scenarios.

Given the catastrophic failure and earlier comments that cracks may not produce chips why on earth can the recommendation be to continue in a situation where this can happen again?

A chip was produced in REDL's gear box?

No more appeared for 25 hours so extra minitoring stopped, then the gearbox failed.

What is to stop a gearbox failing again? I've not read anything that suggests a nice shower of metal chips will appear in a timely fashion to alert the maintenance guys.

Any load or fatigue data to explain the REDL failure?

What suggests that we have a 'warning system' even live or manual that will predict the failure of another one.

Am I missing something?

What are the pilots of L2's feeling on the 'checks' ?
I generally get in the back if there's someone in the front willing to drive, I'm currrently working on that principle in my head.

Appreciate some more discussion about the failure mode and the likelihood of warning of deterioration.

Regards, Clive

[Wizzard]

McKeg4

As an L2 driver, I am of course concerned about the recent tragic incident. I am also now relieved that the probable cause of the accident has been established and procedures are in place to monitor the gearbox at an increased level.

There is NO WAY that an operator or manufacturer could issue a statement just to placate the offshore workforce and then not comply: imagine what would happen if there was a further incident!

I will continue to trust my life to the aircraft - if I had any doubts I would not fly. Remember every time you get in the helicopter there's two of us up the front.

The most dangerous part of your trip will continue to be the drive to the airport.


Take care out there.

Wiz

[GJM]

I'm no expert but would that not be 28 and 30

[nodrama]

Presumably a similiar design is also used in the EC155?

I presume you mean the gearbox design? Yes, similar, in the fact that it has two engine inputs and there is an epicyclic gearing arrangement....alot of main g/boxes designs do.

The EC155 is subject to the epicyclic carrier boroscope inspection, same as the 365.

[WAH]

Quote:
Originally Posted by WAH
Quote:
Originally Posted by AAIB
The investigation has so far revealed that the MGB had suffered from a major failure within the epicyclic module. This is supported by HUMS data; however, this is not yet fully understood.

So HUMS done exactly what it was supposed to be doing in respects to alerting the engineer that there was something abnormal.

I read that part of the AAIB report to mean that the HUMS data from the time of the accident supports their determination that the failure was within the epicyclic module.

The daily inspections were initiated not due to HUMS indications but:

Quote:
Originally Posted by AAIB
As the result of the discovery of a particle on the main rotor gearbox epicyclic module magnetic chip detector


Furthermore, while the HUMS data were under close monitoring:

Quote:
Originally Posted by AAIB
No further abnormalities were identified during this period.


I'd say your eagerness to hang the operator and manufacturer HUMS guys out to dry is not warranted by the evidence.

That does not make sense as you are assuming that 1 second the gearbox was fine, and then a second later it comes to a catastrophic collapse without anything causing it. How do you suspect this would have happened? A crack in a gear or a missing tooth will have developed over x amount of time, it does not just appear instantaneous and then cause catastrophic failure. This crack or whatever it was (i do not know) will have been under close monitoring HUMS wise. (Hums on epicyclic was put under close monitoring, that is factual)

You have got it the wrong way round, what would have happened is the aircraft would have landed on the 25th March and the engineer would have downloaded the days flight. An exceedance would have been generated and then reported to BOND HUMS dept. Bond hums dept would then have given advice on what to do or referred it back to EC for their input. The advice given would then have been to carry out frequent mag probe checks along with putting the AC under close monitoring. (This is standard procedure)

Are you suggesting they found chips on the detector out of the blue, i.e during a scheduled maintenance check? They then checked the HUMS to find that it was over threshold and then put it on close monitor? That is back to front, any engineer who is familiar with HUMS will tell you that. Basically HUMS would not go under close monitoring unless there was a reason to do so, i.e it had breached a threshold. You could not possibly close monitor every single component and relevant indicator in the MGB just because there was debris found on the mag pickup probe. It's far too big a job, there are hundreds of different indicators that you could potentially be looking at.

Im not out to hang anyone out to dry, that is unfair as i do not have all the facts, nor have i seen the trend graphs from BOND so it is impossible to make that judgement. I did state however that there are 16 families in grieving and if it does prove that the prior HUMS warnings was pointing to the impending failure then questions are going to need to be asked.

On the other hand, if there were no prior warnings on HUMS in the week or so before the accident then you would have to ask questions as to why and then hope the manufacturer would develop the HUMS system to make sure something like this never happened again.

[mckeg4]

Nervous offshore worker

Wiz,

Thanks for the swift reply and I hope I have not offended any pilots or engineers as that was never the intent, just really jumpy guys out here as I am sure you will be aware of, I am trying to go on the principle that if you guys are happy to drive then we should be as passangers, Further questions have been asked which we wondered may have prevented the failure and that is if the aircraft had the detectors checked when it returned to aberdeen after the first flight in the morning may there have been further build up of debris which would have resulted in the helicopter being taken out of service for a more in depth investigation??? sorry to flood you with what ifs but we wondered if this should be the case in the future for added prevention, again your thoughts would be appreciated

Thanks

[WAH]

I think I'm understanding the chip scenarios.

Given the catastrophic failure and earlier comments that cracks may not produce chips why on earth can the recommendation be to continue in a situation where this can happen again?

A chip was produced in REDL's gear box?

No more appeared for 25 hours so extra minitoring stopped, then the gearbox failed.

What is to stop a gearbox failing again? I've not read anything that suggests a nice shower of metal chips will appear in a timely fashion to alert the maintenance guys.

Any load or fatigue data to explain the REDL failure?

What suggests that we have a 'warning system' even live or manual that will predict the failure of another one.

Am I missing something?

What are the pilots of L2's feeling on the 'checks' ?
I generally get in the back if there's someone in the front willing to drive, I'm currrently working on that principle in my head.

Appreciate some more discussion about the failure mode and the likelihood of warning of deterioration.

Regards, Clive

If it turns out to be a gear crack (Im not saying that it is) then inspection of the mag probes alone will be in my opinion inadequate.

However this coupled with a check of the gearbox HUMS data to see what the epicyclic is doing should put operators minds at ease for releasing these aircraft back to service.

I would not worry about it, this aircraft has an exceptional safety record and the operators would not release an aircraft that was not safe to fly.

As to the bit i highlighted in italic underline in your quote, no this was not the case. the aircraft was still under close monitoring at the time of the accident. The close monitoring refers to the HUMS data, although a daily inspection of the plug would also have been carried out.

I wont repost on this thread again as it may appear like i am trying to incriminate, that really is not what i am getting it. I suppose i'm just thinking out loud so if you choose to agree or disagree with my points then so be it. We will all find out in the end. I've made my point and i'll move on.

Thanks for your time,

WAH

[mckeg4]

Thanks for that much appreciated

[ramen noodles]

HUMS is a tool, not a religeous experience

Ppruners agonize as to how their beloved savior, HUMS, could have failed them. It should go without saying that HUMS is a fine producer of information, tons of it. That information tells many things, and must be related to the health of the system only when all the fault modes are understood. Knowing the modes is the great unknown, and all the HUMS in the world will not foretell failure if all the mode of failure are not yet understood.

Thus, the HUMS, as brilliant as it is, is along for the ride in this latest tragedy, but provides valuable clues to prevent the next one.

HUMS is sort of like a very fine security camera looking out into the dark. It shows everything - it is up to us to figure out what it is telling us.

[JimL]

mckeg4,

It is unlikely that any of us here have enough information to provide you with the assurances that you appear to require. However, we have all seen the AAIB interim report which provides us with some indications about the current thinking. We also have the AD from EASA which, fortunately, has been succinctly summarised in plain words in the Flightglobal report:

Preliminary findings of the inquiry, says EASA, suggest the accident is "connected with a degradation" of the epicyclic module of the main gearbox.

"In the light of this information the detection of any contamination of the main gearbox is of utmost importance as a precautionary measure," it adds.

Operators of AS332L2s need to check the magnetic plug of the main gearbox's epicyclic reduction gear module daily, and ensure that correct maintenance has been applied in case of the discovery of any particle on the plug.

If particles were detected during the previous 200 flight hours without a complete maintenance check, it says, the epicyclic module must be disassembled and inspected.

Companies operating the EC225LP must disassemble and inspect this module each time particles are detected on the magnetic plug, and comply with a similar 200-hour historical check.

It is extremely improbable that the epicyclic module of the MGB can fail without warning - i.e. some debris. Although it appears like a 'one-pony-trick' at this stage, any appearance of particles, in the past (i.e. in the last 200 flight hours), or from now on, will result in a removal and inspection of the epicyclic module (if it wasn't done at the time).

My reading would be that there is an assumption that if that removal and inspection had occurred on the 25th March, the location of the source of the debris might have been established and any crack propagation identified. This is a heavyweight procedure because it would be unlikely, under normal procedures, that such intervention would occur without further confirmation/corroboration.

This is obviously a 'conservative' holding procedure whilst further investigation proceeds. In the interim report, it states:

Investigations are continuing in order to understand completely the accident sequence.

It then goes on to say:

The investigation has so far revealed that the MGB had suffered from a major failure within the epicyclic module. This is supported by HUMS data; however, this is not yet fully understood. The examination of the MGB is continuing in conjunction with detailed analysis of the HUMS and other recorded information.

Earlier in the interim report, the AAIB told us:

The HUMS data for the day’s operation, including the accident flight, has also been recovered.

The HUMS data leading up to this flight, and that which was recorded during the flight, can now be examined (in the light of the accident) to see if there is any evidence of the proximity of the failure. This is quite unlike the way that HUMS data is usually analysed because it is being done in hindsight (we all appear to be quite good at that).

Notwithstanding the comments by Sultan a few posts back, about past analyses of seeded faults of the epicyclic module, my guess would be that some signature will be found - along with a timeline. There are also other tools that could be used in this analysis; in an earlier post, HC informed you of a trial that had been taking place on historic data using software that was not looking for events (which are difficult to find using just threshold data). This software, which has been developed by GE and tested on Bristow data from the warehouse, finds 'clusters' in 'n-dimensional space' - i.e. clusters of data points that would not have raised an alert but which form unusual patterns. It would be amazing if the 'normal tools' and the 'neural net tools' between them cannot spot some precursor pattern.

There are no guarantees here but the best brains in the industry will be working day and night to establish a methodology to prevent this happening again.

Finally, the AD is very conservative - EASA, EC would have risk assessed this to ensure that it contains the situation. The last thing they need is to have another occurrence.

Jim

[SASless]

Helicopter flying by its very nature entails risk as does any kind of flying.

Technology and engineering knowledge has progressed over the years and made great improvements in the safety of helicopter flying.

Passengers should remember pilots are not suicidal by nature and engineers are not serial killers.

If we are willing to fly the machine and share the risk with you then you should be comforted by that fact. You may rest assured most pilots will the first to refuse to fly a suspect machine either a particular machine or a type of machine as one has to be alive to spend the big bucks.

There will be an improvement in the system as a direct result of this tragedy and thus we should be more confidant than before.

If you are a member of the "White Knuckle Club".....lean back, relax, and get a good grip on the armrest....and try to enjoy the flight!

[LastMinute]

Originally Posted by ivor the driver

what an epicyclic gearing system looks like...

I'm no mechanical engineer so I'm a bit confused by that diagram. How do you get the sun and planet gears rotating in the same direction? And how do you get shafts 28 and 30 rotating in opposite directions?

[Edit: OK - I've looked at the patent explaining the diagram, and I think I just about understand it now...]

I do know that the L2 drive train isn't quite like that. The two engine drive shafts don't drive the epicyclic ring directly; rather, they combine (through their freewheel units) to drive the tail rotor drive shaft, and that connects through bevel gears to the central shaft of a two-stage epicyclic train (whose output is the main rotor shaft).

A picture would say a thousand words, of course, and I've got the diagram from the RFM, but I'm not sure whether it's permissible/appropriate to post that, and besides I've got nowhere handy to host it.

Originally Posted by WAH

Are you suggesting they found chips on the detector out of the blue, i.e during a scheduled maintenance check? They then checked the HUMS to find that it was over threshold and then put it on close monitor?

What I am suggesting is that the AAIB report makes no mention of the HUMS exceedances you assert were already known about, and that it does suggest that the discovery of the particle on the magnetic plug was the first event that led to the increased checks.

I am not saying you're wrong, I'm just questioning the inferences that you have made from the information that is available.

[mckeg4]

Nervous offshore worker

Guys,

I want to thank you all for taking the time out to explain in great detail what this means to us, we all know that you are very professional in your job and thank you for the countless trips that you have achieved to take us to and from work safely, its just when something so terrible happens like this we can all put ourselves in the same helpless situation and it dosent bear thinking about, we all know that helicopter travel entails risk but knowing what you guys think means alot to us. Thanks again and I hope you have a pleasent weekend

Greig

[T4 Risen]

Another thing to bear in mind guys, if you work offshore, you only have to do the trip every couple of weeks, us Pilots do it more or less evey day we go to work. We would not do it if every time we flew we were wondering if something like what has happened was going to happen.......

T4