Lack of lubrication certification for helicopter gearboxes
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Like you say, 'less than 10 minutes' seems to be about as precise as we know.
I completely agree that the lack of an emergency lube system is unacceptable.
In my experience it is absolutely drilled into 92 pilots now that MGB oil px below 5 PSI is a land immediately situation - regardless of any other indications.
I completely agree that the lack of an emergency lube system is unacceptable.
In my experience it is absolutely drilled into 92 pilots now that MGB oil px below 5 PSI is a land immediately situation - regardless of any other indications.
It would seem a careful review of the Cougar Accident Report is needed.
For a start....read up about the descent profile that was flown and the time line.
Correlate that with the CVR data that was released.
Then try to fathom what was not released involving the discussion with the Cougar Base....which until released will have to remain subject to conjecture.
Ask yourself why it was not released.....and ponder what might have been said that a lot of people do not want made public.
Anyone care to enlighten us as to what the content and detail of that still private discussion was?
We thrashed this about years ago shortly after the tragedy and later upon release of the Accident Report.
Mis-stating the facts does not serve any good purpose.
As to SA "selling a three Bag System".....who bought it? If it was not the right Kit for the Tasking offshore Newfoundland....then why was the aircraft being operated with it installed?
Prior failures that did not result in Oil Loss....how is that pertinent to an event where Oil was in fact lost?
If the Norwegians, almost five Years later find the ECL re Oil Loss are still "confusing" then who why has that Operator and others not resolved the ambiguity or problems with those Procedures? Don't most Operators write their own Checklists and Procedures....then they must be approved by the Authority they operate under?
The FAA Certification Requirements were met....or so it would appear as the Aircraft was certified and put into and remains in service.
We all can agree those Standards are not as they can and should be....and should be improved and made to improve the safety of the Aircraft and Occupants.
There were design faults with the 92 just as there have been with every aircraft ever built. Sadly, far too often we learn of them in very tragic circumstances.
Pointing the finger in a single direction does not afford much progress in improving the situation. I can see many facets to the MGB designs we see in modern Helicopters but don't see as being "only" the manufacturer's load to carry all by themselves.
It involves everyone in the process to look for problems....in design, manufacturing, testing, certification, and maintenance. It is a long Chain with many Links.....and as we know....one Link fails...the Chain fails.
Just as in the 225 situation with the MGB....we all can accept a proper design should be adequate to prevent two "Extremely Remote" events of aircraft shedding whole Rotor Systems but yet we see the results of exactly two such events in a fairly short time.
For sure....we need to reconsider this "Extremely Remote" concept.
Is it really possible to design a Helicopter that is failure proof?
For a start....read up about the descent profile that was flown and the time line.
Correlate that with the CVR data that was released.
Then try to fathom what was not released involving the discussion with the Cougar Base....which until released will have to remain subject to conjecture.
Ask yourself why it was not released.....and ponder what might have been said that a lot of people do not want made public.
Anyone care to enlighten us as to what the content and detail of that still private discussion was?
We thrashed this about years ago shortly after the tragedy and later upon release of the Accident Report.
Mis-stating the facts does not serve any good purpose.
As to SA "selling a three Bag System".....who bought it? If it was not the right Kit for the Tasking offshore Newfoundland....then why was the aircraft being operated with it installed?
Prior failures that did not result in Oil Loss....how is that pertinent to an event where Oil was in fact lost?
If the Norwegians, almost five Years later find the ECL re Oil Loss are still "confusing" then who why has that Operator and others not resolved the ambiguity or problems with those Procedures? Don't most Operators write their own Checklists and Procedures....then they must be approved by the Authority they operate under?
The FAA Certification Requirements were met....or so it would appear as the Aircraft was certified and put into and remains in service.
We all can agree those Standards are not as they can and should be....and should be improved and made to improve the safety of the Aircraft and Occupants.
There were design faults with the 92 just as there have been with every aircraft ever built. Sadly, far too often we learn of them in very tragic circumstances.
Pointing the finger in a single direction does not afford much progress in improving the situation. I can see many facets to the MGB designs we see in modern Helicopters but don't see as being "only" the manufacturer's load to carry all by themselves.
It involves everyone in the process to look for problems....in design, manufacturing, testing, certification, and maintenance. It is a long Chain with many Links.....and as we know....one Link fails...the Chain fails.
Just as in the 225 situation with the MGB....we all can accept a proper design should be adequate to prevent two "Extremely Remote" events of aircraft shedding whole Rotor Systems but yet we see the results of exactly two such events in a fairly short time.
For sure....we need to reconsider this "Extremely Remote" concept.
Is it really possible to design a Helicopter that is failure proof?
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SASless, it's probably not possible to design a helicopter that is failure proof (that's another subject). BUT it is possible to design one with a 30 minute, or more, DRY RUN TIME! They are out there and are flying and have been for decades. 
......and the ones that cannot....what about them?
What about the aircraft with MGB's that are not able to contain a gear failure and afford a safe landing?
How many single point failures do we tolerate that can result in a catastrophic result?
Some of you are banging a drum about run dry and are ignoring another glaring problem right before your eyes.
Why 30 Minutes....why not 60 minutes....120 minutes?
What is magic about 30 minutes?
This gets back to my point about Certification Standards....and the fact they are not made in a vacuum by the various Authorities. Certification testing is not done in a vacuum....thus we should not be having these arguments following some tragedy where we see unforeseen but preventable disasters.....or disasters that go unexplained.
Open your eyes folks....it is not a SA, Leonardo, AH, Bell problem....it is an Industry Problem that affects all of us.
Shall we go back through all the new aircraft from the past few years and remind ourselves of the problems each of them faced after being put into Operation?
The 92 with the Oil Filter and Transmission mounts, the 225 with the Epicycle Module, the 139 Tail Booms, the 109 with its problems, the 205 with its problems, the Chinook....let he who be without Sin here....throw that Stone.
No....there shall never be a fault free aircraft....but we should hope to see them as failure tolerant as possible.
Two good Case Studies can be the 92 and the 225 MGB's if we want.
Why not take a very critical look at each....and see the lessons that can be learned....they take us down separate but similar tracks and lets see where the problems started in each of them.
Each hoped to be State of the Art Machines....and each in its own way is. Each has had problems.
Each started in different Cultures....one American and the other European and they are two very different environments....what role does that play in all of this?
What about the aircraft with MGB's that are not able to contain a gear failure and afford a safe landing?
How many single point failures do we tolerate that can result in a catastrophic result?
Some of you are banging a drum about run dry and are ignoring another glaring problem right before your eyes.
Why 30 Minutes....why not 60 minutes....120 minutes?
What is magic about 30 minutes?
This gets back to my point about Certification Standards....and the fact they are not made in a vacuum by the various Authorities. Certification testing is not done in a vacuum....thus we should not be having these arguments following some tragedy where we see unforeseen but preventable disasters.....or disasters that go unexplained.
Open your eyes folks....it is not a SA, Leonardo, AH, Bell problem....it is an Industry Problem that affects all of us.
Shall we go back through all the new aircraft from the past few years and remind ourselves of the problems each of them faced after being put into Operation?
The 92 with the Oil Filter and Transmission mounts, the 225 with the Epicycle Module, the 139 Tail Booms, the 109 with its problems, the 205 with its problems, the Chinook....let he who be without Sin here....throw that Stone.
No....there shall never be a fault free aircraft....but we should hope to see them as failure tolerant as possible.
Two good Case Studies can be the 92 and the 225 MGB's if we want.
Why not take a very critical look at each....and see the lessons that can be learned....they take us down separate but similar tracks and lets see where the problems started in each of them.
Each hoped to be State of the Art Machines....and each in its own way is. Each has had problems.
Each started in different Cultures....one American and the other European and they are two very different environments....what role does that play in all of this?
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SASless, your very well written argument is accepted. And I agree that typically no new aircraft is without it's problems and the certification process, together with all the other controls, needs to be robust enough to ensure that all potential problems are resolved before the aircraft gains certification. If any issues subsequently come to life after entering service then the certification of that aircraft must surely be reviewed and suspended if necessary.
Then as an operator don't buy it until it's been flying for a few thousand hours (look up the bathtub reliability curve!)
Then as an operator don't buy it until it's been flying for a few thousand hours (look up the bathtub reliability curve!)
Last edited by espresso drinker; 3rd Aug 2017 at 06:15. Reason: typo
needs to be robust enough to ensure that all potential problems are resolved before the aircraft gains certification
About to enter downwind at home base following an offshore flight in a 212, when a high freq manifested itself, lasted about ten seconds, and terminated with a bang. Everything normal in the cockpit, and normal landing and shutdown followed. Big puddle of oil underneath on the pad coming from the hell hole. Oil in transmission sight glass zilch. Rotor brake disc was found lying on the deck and the bevel gear had dropped into the trans and flung about taking chunks out of gear wheels various. Ultimate cause I don't know, but I'm not about to suggest it signified a great problem for the 212 type. Stuff happens, though I'm mutchly glad it didn't happen offshore and having to ditch in mega seas in the middle of winter.
One of our pilots landed a 205 on fixed floats in the ocean to pick up the survivors from the above Wessex. Aircraft was returning home at low altitude and slow speed with a high freq, when it suddenly rolled inverted and crashed. Two pilots survived, crewman and pax perished. Cause? Gearbox spat a wheel out through the case, which in turn removed one of the jacks. Only ever flew the H-34 version, but once again I'm not about to suggest the aircraft had a history of main G/B issues. Stuff happens.
The Bell MGB design use a long shaft that affords the ability of the Gear Box to provide a Load Path that works to transfer loading when gears begin to break apart. I am curious about the basic differences between the new designs as compared to the older designs in that regard.
I wonder what the statistics are on MGB failures in Legacy Aircraft are as compared to "new" design Gearboxes.....particularly in Catastrophic failures that result in the loss of the aircraft and its occupants.
I wonder what the statistics are on MGB failures in Legacy Aircraft are as compared to "new" design Gearboxes.....particularly in Catastrophic failures that result in the loss of the aircraft and its occupants.
@SASless: the Seahawk/Blackhawk/S-70 main rotor shaft goes all the way through the transmission "box" from the bottom (where the Jesus nut is) out through the top to the head, though the shaft extension is what connects it to the hub. I am pretty sure the S-92 is the same since the gbx (and much else) were S-70/Blackhawk derivative. There are a variety of things that can go badly.
Well over a decade ago a carrier assembly had a serious failure inside a Blackhawk box, which was a major factor in the Navy, the Army (and IIRC the Air Force) getting together with Sikorsky and agreeing on an improvement/redesign of the carrier assembly. So far so good.
Gearboxes are hard things to get right, to be sure. (I think the guys at Sikorsky are reliving that reality again as they work their way through the details on the CH-53K).
Well over a decade ago a carrier assembly had a serious failure inside a Blackhawk box, which was a major factor in the Navy, the Army (and IIRC the Air Force) getting together with Sikorsky and agreeing on an improvement/redesign of the carrier assembly. So far so good.
Gearboxes are hard things to get right, to be sure. (I think the guys at Sikorsky are reliving that reality again as they work their way through the details on the CH-53K).
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Your point is excellent. The purpose of qualification testing, including the run-dry test procedure, is to validate all analysis used to certify the design. There is a specific type of certification analysis performed called Failure Mode, Effects and Criticality Analysis (FMECA) that is intended to ensure no credible failure mode will produce a catastrophic event. The FMECA evaluates every component and system from design thru manufacturing and throughout its service life. Of course, the analysis does not consider unforeseen conditions, as you noted above.
The 1982 CH-47 crash in Mannheim is a perfect example of how an unanticipated event involving the lube system of a main rotor gearbox resulted in a catastrophic failure. What makes this case even more unusual is that it was caused by loss of flow at a single oil jet, while the rest of the gearbox lube system continued to function normally. The crew had no idea what was causing the problem, and the final catastrophic structural failure occurred just a couple minutes after the crew became aware of a problem. The picture below shows the rear main gearbox separated from the airframe.
It is quite possible that the aircraft had been flying with the blocked oil jet for a substantial number of hours. Unfortunately, this particular loss-of-lube failure mode was never considered in the FMEA. So no steps were taken to prevent it from happening, or even alert the crew it was occurring so they could take appropriate action.
After it was determined that the root cause of this loss-of-lube failure was the small oil jet orifice becoming obstructed by walnut shell debris trapped inside the gearbox housing oil galleries from grit blast cleaning during an overhaul, the overhaul procedures were modified and the design of oil jets were revised. It is now standard industry gearbox design practice to include a "last chance" filter screen on every lube oil jet to prevent debris from obstructing the small diameter metering orifice holes.
riff_raff, I remember doing a US Army accident course in '71 and mention was made of an engine oil leak in the Chinook which travelled up the gearbox drive tunnel and acted as a blow torch on the gearbox, with the same results as your photo. How do you go about predicting an event such as that? An unenviable job attempting to dot all the i's and cross all the t's of what can occur.
Everything old becomes new again, in a way. The P-47 in WWII European theatre were having an inordinate number of engine failures. Cause was sand from the casting process not being successfully cleaned out.
small oil jet orifice becoming obstructed by walnut shell debris trapped inside the gearbox housing oil galleries from grit blast cleaning during an overhaul, the overhaul procedures were modified and the design of oil jets were revised. It is now standard industry gearbox design practice to include a "last chance" filter screen on every lube oil jet to prevent debris from obstructing the small diameter metering orifice holes
Candy Bar Wrappers were being found in Chinook Transmission Sumps....Boeing discovered the boxes in for overhaul were stored next to an employee break area and the wrappers were being thrown into them instead of Trash Cans.
Once the Transmission halves were moved away from the Break Area....the problem was solved.
Then there was the Bell Short Shaft on the Huey....that could be installed wrong way around.
Lots of Murphy issues have cropped up over the years.
Once the Transmission halves were moved away from the Break Area....the problem was solved.
Then there was the Bell Short Shaft on the Huey....that could be installed wrong way around.
Lots of Murphy issues have cropped up over the years.
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The US DoD does a good job of documenting "lessons learned" from every accident, and they make the reports readily available, so there is no excuse for anyone making the same mistake again. One very important factor in preventing problems is an engineering staff with lots of relevant experience. But there was a long period where relatively few new rotorcraft gearboxes were designed in the US, so much of the collective experience was lost.
The Russians build some very impressive gearboxes for their large helicopters.
Is there anything different about their design approach that could be usefully exploited by others?
Is there anything different about their design approach that could be usefully exploited by others?
Within a page or two...you get a very quick answer to your question.
I did not read further as it is early and I am just getting into my first Cup of Coffee!
https://ntrs.nasa.gov/archive/nasa/c...9910005833.pdf
I did not read further as it is early and I am just getting into my first Cup of Coffee!
https://ntrs.nasa.gov/archive/nasa/c...9910005833.pdf
Within a page or two...you get a very quick answer to your question.
I did not read further as it is early and I am just getting into my first Cup of Coffee!
https://ntrs.nasa.gov/archive/nasa/c...9910005833.pdf
I did not read further as it is early and I am just getting into my first Cup of Coffee!
https://ntrs.nasa.gov/archive/nasa/c...9910005833.pdf
It suggests that Russian helicopters don't much use planetary gear arrangements in their transmissions.
Why not is a question that requires a level of knowledge and expertise that only an industry professional could muster, if they are willing to offer it.
Prompted by SAS's last post I got to thinking about what gearboxes internals involve. Hats off to the engineers/designers/manufacturers. Shakespeare in "As You Like It" wrote "And thereby hangs a tale", in the case of gearboxes, thereby hangs a tail - yours and mine.
https://www.geartechnology.com/issue...x/Involute.pdf
https://ntrs.nasa.gov/archive/nasa/c...9860005142.pdf
http://www.dtic.mil/dtic/tr/fulltext/u2/a257727.pdf
http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADP000703
https://www.geartechnology.com/issue...x/Involute.pdf
https://ntrs.nasa.gov/archive/nasa/c...9860005142.pdf
http://www.dtic.mil/dtic/tr/fulltext/u2/a257727.pdf
http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADP000703
Megan, when flying Sea Sprites and Seahawks, the three things I always worried about were the blades, the head, and the main transmission. (The tail you can survive if it goes ... though a tail failure did kill a guy I know ... )
Some things, if they break, mean that you are dead.
I won't say that's why I drink, but I will say it's a contributor to the overall libation.
Some things, if they break, mean that you are dead.
I won't say that's why I drink, but I will say it's a contributor to the overall libation.
There were times when flying single pilot over wide expanses of saltwater in good weather with not much to do but "think"....I sometimes pondered the notion of what would it be like to shuck a Blade.
What really had me wondering was what Clock Angle the Blade would depart... and would you be able to see it disappearing from view as it went!
What really had me wondering was what Clock Angle the Blade would depart... and would you be able to see it disappearing from view as it went!
