North Sea heli ditching: Oct 2012
Pitts, regarding the torque limits, I know its complex but do try to keep up! 70% Q now, because one needs to have a reasonable flight duration between HUMS downloads. Once the MOD 45 airborne alert is in place, no point in limiting torque until after a crack is detected. Hopefully not that often, after all we did manage nearly 100,000 hrs in the company and no cracks at all, so its not as if its going to be cracking every other flight! One needs to keep a sense of scale!
Becoming complacent over MOD 45 alarms; that all is resolved by a reduce to 70% and finish the flight, is just a gamble - I grant you an educated gamble - but a gamble non-the-less.
I take the published data to read that its likely that the helicopter with the highest time shaft ended in the sea after 3845 hours or another after 167 hours.
How does that 100000 hour statistic help anyone now?
Just to confirm - MOD 45 is a specific sensor? I only as because m'arms as a whole is an ATA 45 system.
Of course all this makes perfect sense until you consider that its possible a MOD 45 alarm maybe alerting you to a problem that isn't related to the current issue.
Becoming complacent over MOD 45 alarms; that all is resolved by a reduce to 70% and finish the flight, is just a gamble - I grant you an educated gamble - but a gamble non-the-less.
I take the published data to read that its likely that the helicopter with the highest time shaft ended in the sea after 3845 hours or another after 167 hours.
How does that 100000 hour statistic help anyone now?
Becoming complacent over MOD 45 alarms; that all is resolved by a reduce to 70% and finish the flight, is just a gamble - I grant you an educated gamble - but a gamble non-the-less.
I take the published data to read that its likely that the helicopter with the highest time shaft ended in the sea after 3845 hours or another after 167 hours.
How does that 100000 hour statistic help anyone now?
A gamble - yes of course but so is expecting any helicopter's myriad of rotating bits to stay together for a flight. Certification rules are based on a gamble. If you don't want a gamble, stay in bed. Oh no, then you die of bed sores! Or choose gambling odds that are favourable!
The point about the 100000 hrs is that, although there have been 2 shaft cracks and one with very low hours, there has also been a hell of a lot of other flying with no shaft cracks. You are presuming the shaft cracked because it was "old and tired", maybe it cracked because there was something wrong with the manufacture or utlisation of it (we don't know at this point).
212 - yes the MOD45 is just the particular M'ARMS parameter for the vertical shaft and the one which gives the best warning of cracked shaft. Nothing to do with ATA45!
Last edited by HeliComparator; 22nd Mar 2013 at 15:49.
If the MOD 45 is alerting you to another issue - so what, you didn't have that warning in the cockpit before anyway.
By your logic ignorance is bliss and anything better than ignorance is licence to carry on regardless because "hey you didn't worry before!"
Who said anyone would be complacent about MOD45 alarms?
The change from the current MOD-45 alarm (when its beyond a red threshold) is to check before flight yet and now it might be land as soon as practicable.
Thats an increased risk.
According to EC (and of course we believe everything they say) the false alarm rate for MOD45 is very low - they have looked back at a lot of historic data.
Whilst this isn't all about liability who is going to want to be the one to sign that process off??
A gamble - yes of course but so is expecting any helicopter's myriad of rotating bits to stay together for a flight. Certification rules are based on a gamble. If you don't want a gamble, stay in bed. Oh no, then you die of bed sores! Or choose gambling odds that are favourable!
Its one thing to give it the big one, be a big hero and telling everyone "if you want no risk stay in bed". Its easy to talk about safety (and now we have operators and a manufacturer in PR overdrive) but I suggest it would be a different tune if someone was made personally liable for any future disaster.
Perhaps reflect on the outcome of another North Sea accident and see how this band aid might be viewed...
The point about the 100000 hrs is that, although there have been 2 shaft cracks and one with very low hours, there has also been a hell of a lot of other flying with no shaft cracks. You are presuming the shaft cracked because it was "old and tired", maybe it cracked because there was something wrong with the manufacture or utlisation of it (we don't know at this point).
I don't presume anything. Its a fact that one shaft that failed was very low time and the other was almost certainly the highest time shaft on a 225. Given the time and resources that have been spent so far on this issue I'd say the 100k other hours haven't been relevant in coming to a conclusion.
What is actually quite frightening with the EC225 are the other elements of these ditchings and the associated failures, then in the next breath everyone is supposed to be totally cool with EC pushing the limit with a variety of band aids.
Last edited by Pittsextra; 22nd Mar 2013 at 17:47.
HC,
So let me get this straight....you seem to have no great concern about flying with a cracked shaft in the 225 Gear Box.....would comfortably reduce MCP, and continue on to the nearest dry landing spot....all the while happily trusting EC's statement to you that the Power Reduction would stop any crack from getting worse.
How do you know the shaft is not broken and merely beginning to crack?
With the Shaft fully severed....any concerns the Warning you see in the Cockpit might be grossly understating the problem?
We don't care about False Warnings or Warnings that accurately report the beginning of a Crack....but how do we decide if the Shaft has FAILED?
So let me get this straight....you seem to have no great concern about flying with a cracked shaft in the 225 Gear Box.....would comfortably reduce MCP, and continue on to the nearest dry landing spot....all the while happily trusting EC's statement to you that the Power Reduction would stop any crack from getting worse.
How do you know the shaft is not broken and merely beginning to crack?
With the Shaft fully severed....any concerns the Warning you see in the Cockpit might be grossly understating the problem?
We don't care about False Warnings or Warnings that accurately report the beginning of a Crack....but how do we decide if the Shaft has FAILED?
Last edited by SASless; 22nd Mar 2013 at 17:06.
....but how do we decide if the Shaft has FAILED?
SASless, if I understand how this shaft works, your indication of failure looks to be the oil pressure dropping (possibly as a follow on to the "hey, it's cracking" indication) and that followed by chip detectors going off as bits of metal start to float about in the lubricating fluid?
There's probably more to it than that, but those are secondaries that make intuitive sense.
I may also have misunderstood your question.
SASless, if I understand how this shaft works, your indication of failure looks to be the oil pressure dropping (possibly as a follow on to the "hey, it's cracking" indication) and that followed by chip detectors going off as bits of metal start to float about in the lubricating fluid?
There's probably more to it than that, but those are secondaries that make intuitive sense.
I may also have misunderstood your question.
Lonewolf - yes quite and REDL accident report shows what can follow chip detection warnings and oil pressure alarms.
If you start getting comfortable over looking alarms at some point you'll get bitten.
Currently HUMS is an early alert to something not being well. That is a good thing.
Having a mental state that starts getting comfortable or it no longer matters and you can fly on waiting for chip detection warnings and a low oil pressure alarm is madness.
If you start getting comfortable over looking alarms at some point you'll get bitten.
Currently HUMS is an early alert to something not being well. That is a good thing.
Having a mental state that starts getting comfortable or it no longer matters and you can fly on waiting for chip detection warnings and a low oil pressure alarm is madness.
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Eurocopter identifies cause of bevel shaft crack in ec225 ditchings
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When the vertical shaft starts to crack, the MOD45 pickup will detect it after a defined length of propagation. Reducing the detection threshold to indicate earlier in the propagation a is reasonable. Once the threshold is reached there could be an indication in the cockpit.
At this stage everything is working inside the gearbox normally.
It makes sense to now reduce power, which EC have data to indicate, dramatically slows the propagation, and LAND AS SOON AS POSSIBLE. Which means land at the nearest suitable site, rig, platform or airport etc.
If the shaft fails (Are you listening SAS), the crew immediatley get 4 independent indications of total MGB oil px failure.
As an interim solution I would work this all day long.
PITTS - ditching a helicopter successfully requires optimum performance of a minimum number of safety systems.
helicopters carry a myriad of systems to ensure the minimum number provide an optimum result. For EG the CPI has 5 backups in one form or another.
In both recent cases the outcome was optimum but not just because of EC225 provision, but decades of careful analysis following many ditchings worldwide. We seem to learn something from every single one. Especially how all the gear, crew, pax and the environment interact on each other. We are lucky in EASA land that our Authorities make sure that manufacturers and operators continue to apply what we learn.
It is for these reasons that reading your drivel on this post and others, childishly trashing many countless professionals in EC, the Operators and the Authorities literally boils my piss!!
DB
At this stage everything is working inside the gearbox normally.
It makes sense to now reduce power, which EC have data to indicate, dramatically slows the propagation, and LAND AS SOON AS POSSIBLE. Which means land at the nearest suitable site, rig, platform or airport etc.
If the shaft fails (Are you listening SAS), the crew immediatley get 4 independent indications of total MGB oil px failure.
As an interim solution I would work this all day long.
PITTS - ditching a helicopter successfully requires optimum performance of a minimum number of safety systems.
NS
In both recent cases the outcome was optimum but not just because of EC225 provision, but decades of careful analysis following many ditchings worldwide. We seem to learn something from every single one. Especially how all the gear, crew, pax and the environment interact on each other. We are lucky in EASA land that our Authorities make sure that manufacturers and operators continue to apply what we learn.
It is for these reasons that reading your drivel on this post and others, childishly trashing many countless professionals in EC, the Operators and the Authorities literally boils my piss!!
DB
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With regard to "the Pitts":
I post this because from the moment you appeared you have been agressive, arogant and downright rude. You have no real idea, from your own admission, of what you are talking about other than regurgitating reports and seem to think you know it all because you can fly.
Si
P.S. I would get back in a 225 tomorrow if they gave me one, because I trust our engineers to know what they tell me, our trainers to know what they teach me and my own judgement on the aircraft.
I post this because from the moment you appeared you have been agressive, arogant and downright rude. You have no real idea, from your own admission, of what you are talking about other than regurgitating reports and seem to think you know it all because you can fly.
Si
P.S. I would get back in a 225 tomorrow if they gave me one, because I trust our engineers to know what they tell me, our trainers to know what they teach me and my own judgement on the aircraft.
Last edited by bigglesbutler; 22nd Mar 2013 at 19:51.
So in summary DB are you saying the only trigger for the MOD45 alarm is this current problem?
It's all very good boiling your piss over criticism of the 225 etc but all you've done is talk around the issue. On top of slagging me off over not wanting a mate passenger in a helicopter with what are clearly serious issues until they are properly fixed. What's wrong with that?
It's all very good boiling your piss over criticism of the 225 etc but all you've done is talk around the issue. On top of slagging me off over not wanting a mate passenger in a helicopter with what are clearly serious issues until they are properly fixed. What's wrong with that?
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The article doesn't say what the cause (s) are. Residual stress and corrosion.
Last edited by terminus mos; 22nd Mar 2013 at 22:54.
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SASless, if I understand how this shaft works, your indication of failure looks to be the oil pressure dropping (possibly as a follow on to the "hey, it's cracking" indication) and that followed by chip detectors going off as bits of metal start to float about in the lubricating fluid?
Not really, broken shaft leads to zero oilpressure, hence no fluid circulation, hence no chip detection.
Not really, broken shaft leads to zero oilpressure, hence no fluid circulation, hence no chip detection.
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....but how do we decide if the Shaft has FAILED?
SASless, if I understand how this shaft works, your indication of failure looks to be the oil pressure dropping (possibly as a follow on to the "hey, it's cracking" indication) and that followed by chip detectors going off as bits of metal start to float about in the lubricating fluid?
SASless, if I understand how this shaft works, your indication of failure looks to be the oil pressure dropping (possibly as a follow on to the "hey, it's cracking" indication) and that followed by chip detectors going off as bits of metal start to float about in the lubricating fluid?
The trick is to detect fractures before they have propagated sufficiently to cause a failure, and there are currently techniques available to do this with rotating components. However, these crack detection techniques require dedicated instrumentation and monitoring systems. In other words, the gearbox has to be designed to look for such an event.
The image below shows an example of how such a system might work. It uses a pair of radial displacement probes (probably something like a proximity sensor) and an angular encoder to monitor radial shaft deflection vs. angular shaft position. This technique will detect a transverse shaft fracture (like the one that occurred in the EC225 bevel shaft) much earlier than a lube oil chip detector will, since there is not much debris generated until the fracture has propagated substantially. However, even the technique shown will not readily detect a transverse fracture until it begins to "breathe". This means that the fracture must be significant enough to alter the structural stiffness characteristics of the shaft.
Regards,
riff_raff
Rif_raff:
Thanks, that was very enlightening.
Thanks, that was very enlightening.
Rid-raff, surely the same thing is achieved with currently installed HUMS sensors? In either case, detection will only occur once the shaft starts to "breathe" as you put it. However your system introduces additional components inside the box, which could possibly have some impact on gearbox integrity, whereas HUMS is a purely non-invasive technique - ie nothing extra inside the gearbox.
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HC-
First, let me admit that the only detailed knowledge I have of the EC225 MGB design in particular is that I have gleaned from the public domain. However, I am an engineer by trade with a fair amount of rotorcraft drivetrain design experience.
As for your question regarding the impact on MGB "integrity" resulting from adding non-contacting instrumentation such as shaft radial displacement probes or shaft angular position sensors, there would be no real impact on "integrity". These sensors are solid state devices, and are thus extremely reliable and rugged. However, I believe even the best current MGB HUMS typically only employ sensors for chip detection and vibration monitoring with regards to detecting structural failure of rotating components such as gears, bearings or shafts. And there is nothing similar to the approach I showed currently in widespread use.
The outputs of turboshaft engines commonly include a "torquemeter" that measures the speed and torque transmitted through the output shaft. The torquemeter often consists of a pair of angular position sensors (such as Hall effect devices) and trigger wheels at opposite ends of the output shaft, which measure the torsional deflection of the output shaft under load. The engine HUMS records the accumulated shaft rotations and torque moment applied during each such event.
Lastly, even the most basic MGB HUMS utilize instrumentation that would be considered "invasive". There are chip detectors in the lube oil return circuit, there are pressure and temp sensors in the lube oil pressure circuit, there is a differential pressure sensor in the lube oil filter housing, there is a level sensor in the lube oil reservoir, etc.
Regards,
riff_raff
First, let me admit that the only detailed knowledge I have of the EC225 MGB design in particular is that I have gleaned from the public domain. However, I am an engineer by trade with a fair amount of rotorcraft drivetrain design experience.
As for your question regarding the impact on MGB "integrity" resulting from adding non-contacting instrumentation such as shaft radial displacement probes or shaft angular position sensors, there would be no real impact on "integrity". These sensors are solid state devices, and are thus extremely reliable and rugged. However, I believe even the best current MGB HUMS typically only employ sensors for chip detection and vibration monitoring with regards to detecting structural failure of rotating components such as gears, bearings or shafts. And there is nothing similar to the approach I showed currently in widespread use.
The outputs of turboshaft engines commonly include a "torquemeter" that measures the speed and torque transmitted through the output shaft. The torquemeter often consists of a pair of angular position sensors (such as Hall effect devices) and trigger wheels at opposite ends of the output shaft, which measure the torsional deflection of the output shaft under load. The engine HUMS records the accumulated shaft rotations and torque moment applied during each such event.
Lastly, even the most basic MGB HUMS utilize instrumentation that would be considered "invasive". There are chip detectors in the lube oil return circuit, there are pressure and temp sensors in the lube oil pressure circuit, there is a differential pressure sensor in the lube oil filter housing, there is a level sensor in the lube oil reservoir, etc.
Regards,
riff_raff
The outputs of turboshaft engines commonly include a "torquemeter" that measures the speed and torque transmitted through the output shaft. The torquemeter often consists of a pair of angular position sensors (such as Hall effect devices) and trigger wheels at opposite ends of the output shaft, which measure the torsional deflection of the output shaft under load. The engine HUMS records the accumulated shaft rotations and torque moment applied during each such event
R-R, however on the EC / AS aircraft, the sensors you refer to for oil temp, pressure and chip are already there as part of the basic certification requirements. HUMS just piggy-backs onto them. The only extra sensors for HUMS are all mounted external to the gearbox.
With your scheme, for each shaft you need at least a pair of sensors in quadrature, probably more for multi-bearing shafts. Whereas for external vibe sensors, one can share a number of shaft/gears/bearings and/or more than 1 sensor can look at the same element to give corroboration. With the amazing "power" of signal averaging, current hums technology is pretty good at detecting the sort of shaft breathing you are referring to. Sorry but I remain unconvinced that proximity/position sensing is a better way to do it.
With your scheme, for each shaft you need at least a pair of sensors in quadrature, probably more for multi-bearing shafts. Whereas for external vibe sensors, one can share a number of shaft/gears/bearings and/or more than 1 sensor can look at the same element to give corroboration. With the amazing "power" of signal averaging, current hums technology is pretty good at detecting the sort of shaft breathing you are referring to. Sorry but I remain unconvinced that proximity/position sensing is a better way to do it.