Helicopter crash off the coast of Newfoundland - 18 aboard, March 2009
Did you try the refresh 'button'? That's what I did....
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S-92 MGB oil level sensor?
From preliminary reading of the report, it is obvious from CVR data that the flight crew believed that there was still oil in the main gearbox.
This was a crucial factor in their deciding not to attempt a controlled ditching, with all its associated risks.
However, we are also left with the impression that there was no direct indicator of the amount of oil in the MGB, just pressure and temperature.
Obviously, if there were NO oil in the MGB, the oil temp reading was meaningless.
Can someone with knowledge of the type confirm whether or not there is an indicator of oil level in the sump of the S-92 MGB?
It would surely be a relatively simple task to design a sensor for oil level.
This was a crucial factor in their deciding not to attempt a controlled ditching, with all its associated risks.
However, we are also left with the impression that there was no direct indicator of the amount of oil in the MGB, just pressure and temperature.
Obviously, if there were NO oil in the MGB, the oil temp reading was meaningless.
Can someone with knowledge of the type confirm whether or not there is an indicator of oil level in the sump of the S-92 MGB?
It would surely be a relatively simple task to design a sensor for oil level.
Maybe I am a complete Dullard....but why not simply require Supplemental Air Devices for all over water flights and prevent folks having to soley rely upon a single breath to escape from a submerged aircraft?
If one smacks the water with some force...gets the breath knocked out of you....as is highly likely...would not having a chance to get some air be worth its weight in Gold?
Again....it sounds like the Government wants to half ass safety requirements!
To repeat my usual rant.....just what is a human life worth?
If one smacks the water with some force...gets the breath knocked out of you....as is highly likely...would not having a chance to get some air be worth its weight in Gold?
Again....it sounds like the Government wants to half ass safety requirements!
To repeat my usual rant.....just what is a human life worth?
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geneman
Level sensors would be very difficult in a helicopter MGB. Flow sensors are easier but more difficult to interpret. After 6 years Sikorsky are introducing these to detect if a pump has failed.
It would be better to introduce an emergency lube system. I had hoped this would be one of the actions Sikorsky were taking.
SASless
It looks like our recent discussion on oil temperature has been validated. Odd TC asked for oil temperature in the FM.
SansA
Yes. It is now clear that the bypass system and the 'extremely remote' loophole were last minute afterthoughts - as some of us here have said - and this explains the delayed EASA certification.
HC
I noticed the social media comments. Some people can at least feel their efforts to shed light on the S-92 MGB and challenge the hype have been recognised.
Level sensors would be very difficult in a helicopter MGB. Flow sensors are easier but more difficult to interpret. After 6 years Sikorsky are introducing these to detect if a pump has failed.
It would be better to introduce an emergency lube system. I had hoped this would be one of the actions Sikorsky were taking.
SASless
It looks like our recent discussion on oil temperature has been validated. Odd TC asked for oil temperature in the FM.
SansA
Yes. It is now clear that the bypass system and the 'extremely remote' loophole were last minute afterthoughts - as some of us here have said - and this explains the delayed EASA certification.
HC
I noticed the social media comments. Some people can at least feel their efforts to shed light on the S-92 MGB and challenge the hype have been recognised.
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Squib said :
"Level sensors would be very difficult in a helicopter MGB... It would be better to introduce an emergency lube system."
Point taken, but an MGB oil level sensor and an emergency lube system are not mutually exclusive.
Tedeco and others make electro-optical fluid sensors that would serve the purpose. While not a trivial task to effectively install these or similar sensors in a slightly-modified MGB, it would surely be possible to do this in a much shorter--and less costly--time frame than designing and deploying either an emergency lube system or a run-dry system.
"Level sensors would be very difficult in a helicopter MGB... It would be better to introduce an emergency lube system."
Point taken, but an MGB oil level sensor and an emergency lube system are not mutually exclusive.
Tedeco and others make electro-optical fluid sensors that would serve the purpose. While not a trivial task to effectively install these or similar sensors in a slightly-modified MGB, it would surely be possible to do this in a much shorter--and less costly--time frame than designing and deploying either an emergency lube system or a run-dry system.
I'm not sure that I understand the need for a level detector. In this case they had a double indication of zero pressure from two separate sensors. There was talk about "splash lubrication" but its not a piston engine! If you have a large volume of oil sitting in the sump not getting pumped round, how is that any better than having no oil at all? - and so how does a level detector help you?
HC
HC
I think a second obviously different kind of sensor would have encouraged the pilot(s) a little bit more to think about a ditching.
The Report touches a very important point from my point of view, which is partial or perceived systems knowledge and how it can lead to potentially dangerous alternative solution paths to a given problem taken by the pilots. In this case partial systems knowledge led them to apparently assume that only the pump(s) /sensors failed (where there were indeed 2 of them).
In a hostile environment where alternative A (complete loss of Oil) looks grim (ditching with SS4 floats in >SS4 and cold water), it's easy to be tempted to consider any 'better' alternative B (It's only the pumps or the sensors...) if there is any ambiguity...
The only problem I see with level sensors is that they even fail to work reliably in the comparatively benign environment of automotive engines.
I'm afraid they would cause a disoproportionate amount of false alarms thereby reducing their value to close to zero.
The Report touches a very important point from my point of view, which is partial or perceived systems knowledge and how it can lead to potentially dangerous alternative solution paths to a given problem taken by the pilots. In this case partial systems knowledge led them to apparently assume that only the pump(s) /sensors failed (where there were indeed 2 of them).
In a hostile environment where alternative A (complete loss of Oil) looks grim (ditching with SS4 floats in >SS4 and cold water), it's easy to be tempted to consider any 'better' alternative B (It's only the pumps or the sensors...) if there is any ambiguity...
The only problem I see with level sensors is that they even fail to work reliably in the comparatively benign environment of automotive engines.
I'm afraid they would cause a disoproportionate amount of false alarms thereby reducing their value to close to zero.
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HC, add to that no increase in MRGB temperature when the oil cooler bypass switch was finally activated after 77 seconds from the master caution annunciation, something that IMO should have been a memory requirement.
In the PF's defense there was clearly secondary indication missing information from the RFM on land immediately when the master caution alarm was activated i.e. no MRGB lube oil temperature increase should have been stated as a sign of loss of lube oil in the RFM and not just a reference in the PTM.
So did the PF believe that 2 pressure sensors and the temperature sensor all failed at the same time? And if it was a pump failure why did the second pump not deliver pressure albeit churning? So now we have 2 failed pumps, 2 failed pressure sensors, and 1 failed temperature sensor in a A/C with no run-dry time.
Why did the PF not discuss further the key issue regarding the lack of increase in temperature indication with the senior pilot at Cougar dispatch? He had already confirmed that the bypass switch had been activated.
To me the TSB should have went further on this key issue and stated that SAC had not included MRGB temperature indication not increasing with oil cooler bypass switch activated as a key secondary indication of MRGB lube oil loss and failure of the oil cooler bypass switch to prevent further oil loss thus requiring a land immediately condition. Surely the lube oil temperature reading ambient would have been observed during the initial MRGB certification trials during the true run-dry test?
I don't agree with this statement, the PF had incomplete and falsely depicted information, the RFM was flawed and therefore so were the checklists and emergency procedures.
So I blame SAC, FAA and TC for causing so many fatalities. This is what I suspected all along, the TSB just confirmed it for me.
Safe flying
Max
In the PF's defense there was clearly secondary indication missing information from the RFM on land immediately when the master caution alarm was activated i.e. no MRGB lube oil temperature increase should have been stated as a sign of loss of lube oil in the RFM and not just a reference in the PTM.
At 0948:32, there was continued reading of the procedure, stating that the temperature should increase following activation of the bypass. Shortly thereafter, the PNF mentioned that the oil pressure should stabilize or fluctuate in the range of 5 psi to 25 psi and that the temperature would slowly increase into the red zone. At this point, the PF pointed out that the MGB oil temperature did not increase following the activation of the bypass switch as indicated in the RFM. The PF then reiterated that he believed their indications were related to a sensor malfunction. The pilots did not discuss the fact that the oil temperature was not behaving as expected with the bypass activated.
A radio discussion began with one of the senior company pilots that had proceeded to the Cougar dispatch centre to see if the crew of CHI91 required any additional assistance. During that communication exchange, the PF indicated that he suspected they had experienced a pump failure. This assessment was based on the fact that while the oil pressure indicator was at zero, the oil temperature indication had not increased and was still indicating normal operating temperatures. It was also indicated that they were headed directly for the closest landfall, in the event that the situation would deteriorate. The pilot in the Cougar dispatch centre acknowledged the information and added that the temperature would increase if the MGB oil bypass switch was selected. The PF acknowledged. The pilot in the Cougar dispatch centre then suggested that they review the emergency descent and ditching checklist to ensure that they would be ready for that eventuality.
The pilots misdiagnosed the emergency due to a lack of understanding of the MGB oil system and an over-reliance on prevalent expectations that a loss of oil would result in an increase in oil temperature. This led the pilots to incorrectly rely on MGB oil temperature as a secondary indication of an impending MGB failure.
The captain's fixation on reaching shore combined with the first officer's non-assertiveness prevented concerns about CHI91's flight profile from being incorporated into the captain's decision-making process. These breakdowns in crew resource management contributed to the selection of an unsafe flight profile
So I blame SAC, FAA and TC for causing so many fatalities. This is what I suspected all along, the TSB just confirmed it for me.
Safe flying
Max
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TSB Report
And again as with the S76 Tail Rotor control failure ( saving weight with leave the centering quadrant out) and the 214 ST crash ( the pilot switched of one inverter the standby inverter was not synchronised needed a few extra wires) root cause of the accident is not addressed . Root cause, design engineering failure !
I vote for six steel bolts and move on to the next problem that may occur, what els is lurking to take the (or any) machine down.
I vote for six steel bolts and move on to the next problem that may occur, what els is lurking to take the (or any) machine down.
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I'm not sure that I understand the need for a level detector. In this case they had a double indication of zero pressure from two separate sensors. There was talk about "splash lubrication" but its not a piston engine! If you have a large volume of oil sitting in the sump not getting pumped round, how is that any better than having no oil at all? - and so how does a level detector help you?
In the first (205) the cause was a split "O" ring seal, and of course have no idea how long it took before the simultaneous red light and zero oil pressure. Flew on for approx 15 minutes.
The second occasion (212) the rotor brake drive fractured leaving the disc lying on the cabin roof and dropping the bevel gear and shaft into the guts of the MGB, where it bounced around tearing up gear wheels but continuing to run OK. It took approx 6 minutes for the MGB to empty itself.
I ask, would it not be nice know what was happening to the level? May go a long way towards your decision making, rather than waiting for caution lights and pressure indications. Finding yourself suddenly with zero pressure (say) in the cruise at 9,000 is going to eat up lot of that 11 minutes (as demonstrated) getting to the ground/water.
Buys you time.
Our fixed wing brothers/sister have level indicators on many of their aircraft, so it ain't rocket science.
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So I blame SAC, FAA and TC for causing so many fatalities.
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Our fixed wing brothers/sister have level indicators on many of their aircraft, so it ain't rocket science.
Last edited by Outwest; 11th Feb 2011 at 06:22.
Probably more useful and practical than an oil level sensor is the solution some other types have, whereby the two pumps take their feed from different levels within the sump. When the higher one loses its supply it generates a caution and when the lower one loses it supply it generates a warning. This gives a sequence that points directly to oil loss.
... the solution some other types have, whereby the two pumps take their feed from different levels within the sump.
HC
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The problem with a gauge is that most crews don't fly along looking at the gauge all the time, therefore a departure from normal is only noticed once it brings on a caution light.
