Sikorsky S-92: From Design to Operations
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I think you had better stop there. It wasn't a double oil pump failure. Just one pump failed.
One of the maintenance staff on my base tells me that there is no indication of a single failure and that is why there is a 50 hour inspection of the oil pump drive. Can you clarify this?
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Dear all, I have been looking through this thread on a regular basis and found the discussion points re the S92 extremely interesting and the technical advisories informative, and thanks to all for that.
With developments recently discussion is bound to move towards one area of interest, this being the transmission and the lubrication system. Though no official finding has been released this area seems to be of particular interest in the so recent tragic event affecting our colleagues and friends in St John’s. This being the case I hope that I can make some general and personal comments regarding what is in my view a critical system and how I had expected design concepts to have ensured continued safe operation, development of emergency procedures that prevented catastrophic failure.
When I started my involvement with off shore commercial helicopters it was the S61, this was before the emergency lube system was installed and the effect of a lubrication failure was hammered home during the technical training, white metal input bearings only work when lubricated, loss of lubrication resulted in the input shaft failure and possible exiting from the GB. Your only decision was down and you hoped that you made it before the transmission failed. When the emergency lube system was installed (lubricating the Input bearings if you had oil) you had a fighting chance of, making a safe landing.
Now we have the new generation of helicopters and a so called safety culture however the basics still apply, oil is needed to lubricate and cool. The illusion that a gearbox will continue and is guaranteed to perform safely for a limited period of time (30 minutes on the AW 139) with no or very low oil pressure is in my view a myth if you look on this as a guarantee to continue on to reach the beach or extend the time frame. The tests are carried out in ideal conditions and may not represent all conditions of system failure or GB condition. It may give a comfort factor though during a decent to a safe altitude and a point when a final decision can be made, low slow and ready or to land. I still remember the definition of “Land Immediately” and the decision responsibility that the commander was expected to take. I also remember the debriefing and questions from individuals who had the benefit of hind sight.
The S92 seems to me to be a great helicopter, lots of really cool electronics plenty of power and lovely flat screen displays, just like the AW 139, but, has the mechanical bit been developed to match. I think not.
That’s it from me;
I am so pleased that I had the opportunity to experience the new technology and progress at the twilight of my time in the industry, but so sad that I am still seeing failure and death from mechanical systems that have plagued me over the past 40 years.
Safe Flying and Blue Skyes.
Outhouse
With developments recently discussion is bound to move towards one area of interest, this being the transmission and the lubrication system. Though no official finding has been released this area seems to be of particular interest in the so recent tragic event affecting our colleagues and friends in St John’s. This being the case I hope that I can make some general and personal comments regarding what is in my view a critical system and how I had expected design concepts to have ensured continued safe operation, development of emergency procedures that prevented catastrophic failure.
When I started my involvement with off shore commercial helicopters it was the S61, this was before the emergency lube system was installed and the effect of a lubrication failure was hammered home during the technical training, white metal input bearings only work when lubricated, loss of lubrication resulted in the input shaft failure and possible exiting from the GB. Your only decision was down and you hoped that you made it before the transmission failed. When the emergency lube system was installed (lubricating the Input bearings if you had oil) you had a fighting chance of, making a safe landing.
Now we have the new generation of helicopters and a so called safety culture however the basics still apply, oil is needed to lubricate and cool. The illusion that a gearbox will continue and is guaranteed to perform safely for a limited period of time (30 minutes on the AW 139) with no or very low oil pressure is in my view a myth if you look on this as a guarantee to continue on to reach the beach or extend the time frame. The tests are carried out in ideal conditions and may not represent all conditions of system failure or GB condition. It may give a comfort factor though during a decent to a safe altitude and a point when a final decision can be made, low slow and ready or to land. I still remember the definition of “Land Immediately” and the decision responsibility that the commander was expected to take. I also remember the debriefing and questions from individuals who had the benefit of hind sight.
The S92 seems to me to be a great helicopter, lots of really cool electronics plenty of power and lovely flat screen displays, just like the AW 139, but, has the mechanical bit been developed to match. I think not.
That’s it from me;
I am so pleased that I had the opportunity to experience the new technology and progress at the twilight of my time in the industry, but so sad that I am still seeing failure and death from mechanical systems that have plagued me over the past 40 years.
Safe Flying and Blue Skyes.
Outhouse
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There has been now, to the best of my knowledge, 4 failures associated with the 92 MRGB in the last year or so, all resulting in emergency landings. Fortunately 3 were close to land, so successful. I am quite sure all of us operating it have seen and heard of more. To my mind this does not make it an extremely remote possibility. In fact our historical evidence so far, makes this more of a probability than we like to admit. I wonder how many more failures have been prevented maintenance crews. I know of at least one. There are far too many critical points for failure in the MRGB and transmission system, and not enough capability for either accurate indication of the problem or means to deal with it. The oil bypass system works only if the fault is in the oil cooler, and unfortunately that is only one of several possibilities. In fact if the the leak is in the gearbox itself, this will make the problem worse, by accelerating further the rate of loss of oil from the MRGB. However the emergency checklist very clearly states that this is the course of action upon low pressure warning (RED).
More direction is required here, and I suspect modification. I suspect customers are already starting to ask these questions, as are pilots. Whilst I agree a run dry capability is probably a myth, there are ways to better protect ourselves. We must also consider that if this happens again, we need to have the right conditions for a successful ditching. I would suggest that anything over sea-state 5, with the current float system, (sea-state 6 not approved for use yet!!!!!) and at night would not be conducive to a successful ditching. I think there have been enough warnings about the MRGB system already and unfortunately nothing has really been done, so now we have had the first real wake up call, hopefully something positive will come out of this, and we do not lose any more lives. Time for some very real and serious discussion on the way forward with the 92.
More direction is required here, and I suspect modification. I suspect customers are already starting to ask these questions, as are pilots. Whilst I agree a run dry capability is probably a myth, there are ways to better protect ourselves. We must also consider that if this happens again, we need to have the right conditions for a successful ditching. I would suggest that anything over sea-state 5, with the current float system, (sea-state 6 not approved for use yet!!!!!) and at night would not be conducive to a successful ditching. I think there have been enough warnings about the MRGB system already and unfortunately nothing has really been done, so now we have had the first real wake up call, hopefully something positive will come out of this, and we do not lose any more lives. Time for some very real and serious discussion on the way forward with the 92.
To my knowledge, the CH-148 Cyclone is getting an emergency lube system for the MRGB, quite similar to the one on the EC-225. Of course, this means additional weight.Arrakis
VL - drills for low MGB oil pressure where there is either a run-dry capability (however limited) or an emergency lube system where the manufacturers have recognised all the possible failure modes is fine and to be expected on all helicopters.
Drills for low oil pressure on an aircraft that has neither run dry nor ELS seem to fly in the face of 'extremely remote failure' and move more towards 'sh8t can happen, you're on your own but we've put a drill in the RFM so it's not our fault'.
Unfortunately it would appear that Sikorsky have vastly underestimated their clever design and managed, somehow, to get certification of a modern helicopter that has a glaring achilles heel. SK and NL made a huge deal when marketing the S92 of how the new certification made for a super-safe helicopter, especially when compared to older rivals. Are there any other holes in this process waiting to catch people out?
Horror Box - good post, hope someone is listening!
Drills for low oil pressure on an aircraft that has neither run dry nor ELS seem to fly in the face of 'extremely remote failure' and move more towards 'sh8t can happen, you're on your own but we've put a drill in the RFM so it's not our fault'.
Unfortunately it would appear that Sikorsky have vastly underestimated their clever design and managed, somehow, to get certification of a modern helicopter that has a glaring achilles heel. SK and NL made a huge deal when marketing the S92 of how the new certification made for a super-safe helicopter, especially when compared to older rivals. Are there any other holes in this process waiting to catch people out?
Horror Box - good post, hope someone is listening!
Well, whoever told me that one oil pump failed completely and the other one partially, was wrong then I guess...?
BTW what is a partial failure? Anyway, the Norwegian incident you refer to was simply a failure of one pump (or more precisely the vespel spline adapter), which then went into windmill mode producing a pressure of about 5psi. This failure mode now being catered for in the emergency drills (it wasn't when it happened).
I'm with Geoffers when it comes to Engine Fire drills. Some other aircraft RFMs seems to favour the:
fire main/fire reserve..;
still have indications (even if they are false)...;
land immediately drill.
Now if that isn't driven by the lawyers I don't know what is.
Personally I think the "check for signs of fire first" action is sensible. But if you guys want to ditch a serviceable aircraft instead because the manufacturer is covering it's behind then please go ahead....
Geoffers...the argument for standing in the witness stand is one for the company management to face, not the line pilot if he follows company SOPs. I know you are a training professional and have the background to accept that. If not, perhaps you can point to a case where a line pilot followed SOPs but was still deemed negligent?
Outwest, I didn't say the crew were notified that only one pump had failed, just that it was a fact after the event. I think that no pumps = no pressure so it is probably pretty obvious once it does happen.
As I said in a previous post, the S92 compliance with the "run dry" capability requirements of JAR/FAR 29 is a sham. I'm obviously not defending that, in fact it is crap, my last few postings are just trying to balance out the hysterical postings of others.
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"Extremely Remote Failure Conditions are those having an Average Probability Per Flight Hour of the order of 1x 10-7 or less, but greater than of the order of 1 x 10-9."
So.....if 50 aircraft do a thousand hours per year....then one aircraft every twenty years will succumb to a MGB failure....along with the occupants?
So then if we consider the Brunei, Norway, and now Cougar events......errr...ahhhh....uhhhh...".Holy Jeepers Batman!"
Am I getting all confused here?
So then if we consider the Brunei, Norway, and now Cougar events......errr...ahhhh....uhhhh...".Holy Jeepers Batman!"
Am I getting all confused here?
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So.....if 50 aircraft do a thousand hours per year....then one aircraft every twenty years will succumb to a MGB failure....along with the occupants?
So then if we consider the Brunei, Norway, and now Cougar events......errr...ahhhh....uhhhh...".Holy Jeepers Batman!"
Am I getting all confused here?
So then if we consider the Brunei, Norway, and now Cougar events......errr...ahhhh....uhhhh...".Holy Jeepers Batman!"
Am I getting all confused here?
I guess that makes the situation far worse than even I thought!
I am beginning to think I might wish to divest myself of that UTX stock I am holding in anticipation of Sikorsky buying Bell from Textron. (Helicopter pilots are always on to a real get rich quick deal!)
I am beginning to think I might wish to divest myself of that UTX stock I am holding in anticipation of Sikorsky buying Bell from Textron. (Helicopter pilots are always on to a real get rich quick deal!)
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Outwest, I didn't say the crew were notified that only one pump had failed, just that it was a fact after the event.
I was only asking if there is anyway the crew would know if one pump has failed (caution light, lower than normal pressure, etc) or if there is a scenario where, sometime between hour 1 and 50 of the pump drive inspection, a pump fails and the a/c departs with only one pump operating without the crew knowing it.
Not trying to stir anything or point fingers, just trying to understand the system.
Rotorfix
Only one pump failed (actually its drive failed) but, there being no check valves, it created a leak back to the sump so that the other pump could only muster about 5 psi or so into the gearbox, below the threshold for "land immediately" in the RFM at the time. In other words, there were 2 pumps but the failure of only one of them would bring the heli down. Good design!
HC
Only one pump failed (actually its drive failed) but, there being no check valves, it created a leak back to the sump so that the other pump could only muster about 5 psi or so into the gearbox, below the threshold for "land immediately" in the RFM at the time. In other words, there were 2 pumps but the failure of only one of them would bring the heli down. Good design!
HC
Is it to much of simplyfing things to relate the MGB problems that have come up(oil pump failure, oil leaking and more) to the M/R vibrations and the roughness of this four blade rotorhead. Is this rotor not just giving this box real tough time??? More than Sikorsky thought, planned it would.
There has been rumor about a 92 B model with one more blade attach to its head, maybe to solve this problems??
Maybe I’m wrong and this is just then bad individual parts that are failing…
I don’t think anyone flying this thing will accept this ONE in TEN mil flight hours for “remote failure”blablabla
Remember Murphy!
Why don’t they just put in this emergency lube system from the Mil variant even if it costs some payload??
Or is it expense versus life here once again??
But to be fair, does anyone of you here remember how many accidents there have been on large helicopter through the years where there was total MGB failure???
There has been rumor about a 92 B model with one more blade attach to its head, maybe to solve this problems??
Maybe I’m wrong and this is just then bad individual parts that are failing…
I don’t think anyone flying this thing will accept this ONE in TEN mil flight hours for “remote failure”blablabla
Remember Murphy!
Why don’t they just put in this emergency lube system from the Mil variant even if it costs some payload??
Or is it expense versus life here once again??
But to be fair, does anyone of you here remember how many accidents there have been on large helicopter through the years where there was total MGB failure???
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I note with the continuing discussion that there are at least two different problems. One was transmission cases that cracked with a subsequent loss of oil and the other was the oil pumps and the vespel splines.
The transmission itself is just that, a bunch of gears that spin around and get oil sprayed on them with the oil going to an external oil cooler. That's a pretty common concept. This really seems more of a manufacturing problem than a design flaw. Making cases and pumps and splines that last should fix the problems.
A few years back, there were a couple of main rotor masts in the 76 that were found to be cracked, one almost half way round. Turned out to be a bad manufacturing batch. Kind of like the any MGB, the mast is what NASA would call a "criticality one" component.
Let's hope we find out quickly what happened and get it corrected.
The transmission itself is just that, a bunch of gears that spin around and get oil sprayed on them with the oil going to an external oil cooler. That's a pretty common concept. This really seems more of a manufacturing problem than a design flaw. Making cases and pumps and splines that last should fix the problems.
A few years back, there were a couple of main rotor masts in the 76 that were found to be cracked, one almost half way round. Turned out to be a bad manufacturing batch. Kind of like the any MGB, the mast is what NASA would call a "criticality one" component.
Let's hope we find out quickly what happened and get it corrected.
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The S-92 MGB lubrication system uses two pumps operating in parallel providing pressure, but operating independantly to scavenge their respective input modules. Normally, the operating pressure is around 55-56 psi.
The Norsk machine (referred to here) had a vespel spline adapter failure, which allowed the remaining pump to reverse flow the oil through the windmilling failed pump, in preference to the more restrictive pressure line - like a short circuit, it took the path of least resistance. The pressure dropped to somewhere around 5 psi or slightly less, which was, at that time, a LAND IMMEDIATELY drill. The crew were lucky that a platform was sufficiently close that they were able to land there instead.
That aircraft had the -101 pump. An initial fix was the -102 pump with improved finishing on the splines and an inspection requirement.
The -103 pump was then introduced which had a check valve thereby isolating the two pumps. In the event of a single pump failure, the remaining pump would produce around 17 psi.
However, an aircraft then had a pump failure (associated with the vespel spline adapter) and the efcet of not scavenging the input module became apparent through an action known as churning, whereby kinetic heating of the oil took place within the gears. The crew landed onshore.
An earlier event had also taken place where churning had manifested itself (212man's event?) but that was not associated with a pump failure.
A revised emergency procedure was introduced to address this phenomenon, whereby the engine of the affected module is throttled back to reduce the heating effect. the check valves were also removed from the -103 pumps to create the -104 pump. This was to stop the input modules being filled with oil so rapidly - which was overcoming the ability to scavenge by gravity drain. The remaining pressure of 5 psi is still sufficient to lubricate the MGB adequately.
None of the above events have anything to do with the "extremely remote" reference - that is solely referring to total loss of oil.
On aircraft did experience a total oil loss, following an oil filter mount cracking. There were maintenance issues involved, as well as choice of manufacturing material for the studs (titanium vs steel.) Both those issue have been addressed.
There have been cracked MGB casings around the oil galleries. the cracks have been small and the leaks very slight - certainly nothing that would lead to total loss in flight. Again fixes are on there way.
I hope the above cures some of the misconceptions and hysteria that seems to be abounding on this thread. It is all in the public domain and a little research and effort is better than the "someone once told me", "yeah, but I thought this happened" and "I'll pull a whole bunch of totally unrelated events and lump them with another statistic to prove a point" type comments we see above, by some.
If anything I have said is incorrect, then feel feel to correct me - as my name implies, it is not necessarily a type I have direct experience of.
The Norsk machine (referred to here) had a vespel spline adapter failure, which allowed the remaining pump to reverse flow the oil through the windmilling failed pump, in preference to the more restrictive pressure line - like a short circuit, it took the path of least resistance. The pressure dropped to somewhere around 5 psi or slightly less, which was, at that time, a LAND IMMEDIATELY drill. The crew were lucky that a platform was sufficiently close that they were able to land there instead.
That aircraft had the -101 pump. An initial fix was the -102 pump with improved finishing on the splines and an inspection requirement.
The -103 pump was then introduced which had a check valve thereby isolating the two pumps. In the event of a single pump failure, the remaining pump would produce around 17 psi.
However, an aircraft then had a pump failure (associated with the vespel spline adapter) and the efcet of not scavenging the input module became apparent through an action known as churning, whereby kinetic heating of the oil took place within the gears. The crew landed onshore.
An earlier event had also taken place where churning had manifested itself (212man's event?) but that was not associated with a pump failure.
A revised emergency procedure was introduced to address this phenomenon, whereby the engine of the affected module is throttled back to reduce the heating effect. the check valves were also removed from the -103 pumps to create the -104 pump. This was to stop the input modules being filled with oil so rapidly - which was overcoming the ability to scavenge by gravity drain. The remaining pressure of 5 psi is still sufficient to lubricate the MGB adequately.
None of the above events have anything to do with the "extremely remote" reference - that is solely referring to total loss of oil.
On aircraft did experience a total oil loss, following an oil filter mount cracking. There were maintenance issues involved, as well as choice of manufacturing material for the studs (titanium vs steel.) Both those issue have been addressed.
There have been cracked MGB casings around the oil galleries. the cracks have been small and the leaks very slight - certainly nothing that would lead to total loss in flight. Again fixes are on there way.
I hope the above cures some of the misconceptions and hysteria that seems to be abounding on this thread. It is all in the public domain and a little research and effort is better than the "someone once told me", "yeah, but I thought this happened" and "I'll pull a whole bunch of totally unrelated events and lump them with another statistic to prove a point" type comments we see above, by some.
If anything I have said is incorrect, then feel feel to correct me - as my name implies, it is not necessarily a type I have direct experience of.
If anything I have said is incorrect, then feel feel to correct me - as my name implies, it is not necessarily a type I have direct experience of.
Outwest, my understanding is that a single pump failure will manifest itself as a lower oil pressure.
Sikorsky are currently working on a modification that would give the crew a more obvious indication of pump failure. The modification is a result of the vespel spline problems, etc previously covered.
Does any other aircraft out there have a MGB oil pump fail warning system? Not trying to make any particular point here, just curious......
Cheers
VL
Sikorsky are currently working on a modification that would give the crew a more obvious indication of pump failure. The modification is a result of the vespel spline problems, etc previously covered.
Does any other aircraft out there have a MGB oil pump fail warning system? Not trying to make any particular point here, just curious......
Cheers
VL
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Does any other aircraft out there have a MGB oil pump fail warning system?
If the oil pressure drops below 8 psi, whether due to a pump failure or loss of oil, the ELS automatically kicks in and you get a XMSN PRESS caution light as well as a green light on the ELS.
Sometime the old ways are better.
Outwest, my understanding is that a single pump failure will manifest itself as a lower oil pressure.
Sikorsky are currently working on a modification that would give the crew a more obvious indication of pump failure. The modification is a result of the vespel spline problems, etc previously covered.
Sikorsky are currently working on a modification that would give the crew a more obvious indication of pump failure. The modification is a result of the vespel spline problems, etc previously covered.
There is a probability of a new caution being displayed on the EICAS saying MGB PUMP FAIL 1/2 (or words to that effect.)
I'm reluctant to say too much, for various reasons that will be obvious to some here, and will leave that to others who seem equally in touch. What I will say, however, is that there are a number of representatives from the operators' technical pilot community who are actively engaged with the Sikorsky design and Flight Test representatives, on a bi-annual basis, and you can be assured that all of the above topics and many more are discussed vigorously and robustly, with the best of intentions, and a mutual desire to see positive outcomes, on both sides.