Sikorsky S-92: From Design to Operations
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Bell 412 incident Dec 2005 off the coast of Brazil
I think my dates are correct but it wuld be easy to check if it is an issue...... anyway the crew had a oil pressure loss in the MGB and headed for the beach at cruise height/speed. They didn't cancel the master caution so didn't see the 'CHIP' warning that came up a short time afterwards. They continued flight until the gearbox gave up and seized at which point they entered autorotation and managed to set it down with an almighty thump in the waters off the Brazilian coast. All survived and one could argue that they did the right thing but IMHO I would have gone for a controlled ditching but, think for one moment, if they had made it to the beach by virtue of being closer then all would hail they made the right choice.
Seems that predictions about how MGBs behave when they run out of oil are not consistent. Maybe the 92 is a 'worst case' - maybe not. If you survive you made the right choice - if not - well - enough said. If the waters are uninviting and your pax have never done HUET training (as in Brazil) your judgement is coloured. If you made the right choice and stuck it in the water , caught a blade on a wave and didn't make it out then ........ well as I said, if you make it out in one piece then by definition you have made the right decision whatever that was.
One problem about carving straight lines in one piece of sky all your life is that the experience of others may pass you by ... and there is much to learn from the way others do it, their mistakes and their successes.
G
Seems that predictions about how MGBs behave when they run out of oil are not consistent. Maybe the 92 is a 'worst case' - maybe not. If you survive you made the right choice - if not - well - enough said. If the waters are uninviting and your pax have never done HUET training (as in Brazil) your judgement is coloured. If you made the right choice and stuck it in the water , caught a blade on a wave and didn't make it out then ........ well as I said, if you make it out in one piece then by definition you have made the right decision whatever that was.
One problem about carving straight lines in one piece of sky all your life is that the experience of others may pass you by ... and there is much to learn from the way others do it, their mistakes and their successes.
G
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DCVC wrote:
What a complete engineering screw up. Why can't the engineers stay focused?
Reason for 2 oil pumps: - Design Objective, to provide redundancy if one oil pump fails by providing maximum oil pressure to the MRGB from the remaining oil pump, to provide fail operational capability.
Problem: -103 oil pump design (with check valves) during single pump failure, provides 17psi, however allows non-scavenged input module to overfill by exceeding capacity of gravity drains.
Solution: - Improve capacity of input module gravity drains to maintain 17 psi with check valves, (oops) remove check valves from oil pump with -104 redesign and accept 5 psi as adequate protection with single pump failure (what happened to our Design Objective?).
Testing Objectives: - Determine by testing, how long the MRGB will survive with 17 psi oil pressure? Determine by testing, how long the MRGB will survive with 5 psi oil pressure?
Did the Cougar flight crew inadvertently provide some of the needed test results?
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 effect 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.
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 effect 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.
Reason for 2 oil pumps: - Design Objective, to provide redundancy if one oil pump fails by providing maximum oil pressure to the MRGB from the remaining oil pump, to provide fail operational capability.
Problem: -103 oil pump design (with check valves) during single pump failure, provides 17psi, however allows non-scavenged input module to overfill by exceeding capacity of gravity drains.
Solution: - Improve capacity of input module gravity drains to maintain 17 psi with check valves, (oops) remove check valves from oil pump with -104 redesign and accept 5 psi as adequate protection with single pump failure (what happened to our Design Objective?).
Testing Objectives: - Determine by testing, how long the MRGB will survive with 17 psi oil pressure? Determine by testing, how long the MRGB will survive with 5 psi oil pressure?
Did the Cougar flight crew inadvertently provide some of the needed test results?
Last edited by Flight Safety; 18th Mar 2009 at 13:41.
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Us Ad2005-12-03
The US2005-12-03 states that loss of MGB oil pressure could cause failure of one or both engine input drives, or planetary gear to sun gear tooth mesh failure, resulting in loss of power to the rotor system.
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Also, does it occur to anyone else (from a design perspective) that bypassing the oil cooler is about the LAST thing you'd want to do, if you loose a MRGB oil pump and the pressure falls to 5 psi (not withstanding a leak in the oil cooler)? At this pressure the oil will be cooked in short order, and without the oil cooler....
Hi there FS, why don't you ask your FAA representative? They are the one's that have given the world their version of compliance....
Along with so many "non-ICAO" exclusions!
Does anyone out there track ICAO variances filed by the FAA?
I guess the list is pretty long?
Along with so many "non-ICAO" exclusions!
Does anyone out there track ICAO variances filed by the FAA?
I guess the list is pretty long?
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Sorry to enter this extremely interesting technical discussion but I am rather confused. Looking at my Technical Pilots Notes, revision 1.2 I must presume that the content re the operation of the system and the relevant pressures quoted are incorrect. The pressure expected after a single pump failure is quoted as about 45psi. Now its 5psi or 17psi in another post? It seems, what happened to the missing pressure? Did it ever exist?
If two pumps are fitted to allow redundancy, surly one pump should be able to supply a known psi just below the normal operating pressure hold off the low pressure warning bring on an advisory caution at the lower pressure and be identified on the gauge.
The advisory re a double pump failure and the words “safe operation is still possible for a short period of time” seems a little odd.
Any way hope Technical notes have been amended, will continue to view with interest.
outhouse
If two pumps are fitted to allow redundancy, surly one pump should be able to supply a known psi just below the normal operating pressure hold off the low pressure warning bring on an advisory caution at the lower pressure and be identified on the gauge.
The advisory re a double pump failure and the words “safe operation is still possible for a short period of time” seems a little odd.
Any way hope Technical notes have been amended, will continue to view with interest.
outhouse
VL,
Is the UK CAA fully ICAO compliant or do they have variances as well?
Is the UK CAA fully ICAO compliant or do they have variances as well?
Geoffers,
Ex-Colonials if you please.....recall we handed you your hat and coat and showed you the door after a bit of a fuss all those years ago.
Ex-Colonials if you please.....recall we handed you your hat and coat and showed you the door after a bit of a fuss all those years ago.
Is the S-92 Safe for Offshore flying ??
I am shocked and amazed reading through this very interesting thread.
It would seem from from the 'spirit' of the definitions, that the S-92 should never have been certified under the stringent FAR requirements for 30 minutes running time in the event of loss of Transmission lubrication.
What is worse is that despite certification, it became clear over a year ago, that MGB failures were far from a 'remote event' and there would appear to be at least 6 or 7 examples (requiring an immediate landing) in just the short time the aircraft has been operating. It seems the regulating authorities have bowed to commercial pressure to certify this aircraft in the first place (on quite a loop-hole) and furthermore have failed completely to pull the plug when aircraft were being forced to ditch - Thankfully over land.
I am surprised more people (particularly those flying the S-92) aren't asking for it to be grounded for offshore operations, particularly in hostile environments like the North Sea or North Atlantic.
It would seem from from the 'spirit' of the definitions, that the S-92 should never have been certified under the stringent FAR requirements for 30 minutes running time in the event of loss of Transmission lubrication.
What is worse is that despite certification, it became clear over a year ago, that MGB failures were far from a 'remote event' and there would appear to be at least 6 or 7 examples (requiring an immediate landing) in just the short time the aircraft has been operating. It seems the regulating authorities have bowed to commercial pressure to certify this aircraft in the first place (on quite a loop-hole) and furthermore have failed completely to pull the plug when aircraft were being forced to ditch - Thankfully over land.
I am surprised more people (particularly those flying the S-92) aren't asking for it to be grounded for offshore operations, particularly in hostile environments like the North Sea or North Atlantic.
Last edited by Special 25; 19th Mar 2009 at 06:16. Reason: Reduced emotive language
At the risk of repetition, the "extremely remote" refers to total oil loss. Of the events last year, and before, one was an oil loss (of the significance we are talking about - not slight leaks) and that was due to a combination of studs being inappropriately maintained and the choice of material used (since changed.)
Other sections of Part/CS-29 refer to other aspects of MGB reliability, but the one being quoted refers soley to total Oil Loss. I think it has already been established how that section has been dealt with.
Outhouse, that is a mistake in the written material (and hence the simulators) that has been around since the introduction. With no check valve installed (ala -101, -102 and -104) the pressure is about 5-7 psi, with the check valve installed (-103) it is about 17 psi. Both of those pressure are, although within the red range, absolutely sufficient to ensure MGB lubrication. Certainly for long enough to land safely.
I'm trying to keep my posts on this subject as factual as possible in an attempt to correct errors and misconceptions, without getting into the debate about what's right and wrong. If others chose to do so, then at least try to get your facts correct before launching off into emotional diatribes that do none of us a favour. I have as much of a vested interest as the next man - I'm about to climb into a 92 this morning!
Other sections of Part/CS-29 refer to other aspects of MGB reliability, but the one being quoted refers soley to total Oil Loss. I think it has already been established how that section has been dealt with.
The pressure expected after a single pump failure is quoted as about 45psi. Now its 5psi or 17psi in another post
I'm trying to keep my posts on this subject as factual as possible in an attempt to correct errors and misconceptions, without getting into the debate about what's right and wrong. If others chose to do so, then at least try to get your facts correct before launching off into emotional diatribes that do none of us a favour. I have as much of a vested interest as the next man - I'm about to climb into a 92 this morning!
Last edited by 212man; 19th Mar 2009 at 06:24.
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Do we know what dash number pump was installed in the Cougar accident a/c?
No disrespect 212man, but until I knew the answer to that question, I would not be climbing into the 92.
No disrespect 212man, but until I knew the answer to that question, I would not be climbing into the 92.
ASB 92-63-013 required removal of the check valve within 30 days of it's issue (29th September 2008) so I would say all S-92s have the -104 pumps.
I cannot emphasise enough that pump failure is not in itself a scenario that will result in gearbox failure, unless it is in some form of mechanical break up. In that regard the aircraft is no different from any other type - you can't protect against that.
Total oil loss is a different subject entirely.
I cannot emphasise enough that pump failure is not in itself a scenario that will result in gearbox failure, unless it is in some form of mechanical break up. In that regard the aircraft is no different from any other type - you can't protect against that.
Total oil loss is a different subject entirely.
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I cannot emphasise enough that pump failure is not in itself a scenario that will result in gearbox failure
I will say again, the prudent thing to do would be ground all S92's until there is a definitive cause. What would be the result of that? A few guys will have to ride to work in boats for a few weeks. The other scenario is just not justified in my opinion.
I am sorry, but until this investigation is complete you have no way of knowing that
I would be far more interested or concerned in mechansims that might result in oil loss, such as cracked pipes etc, than pump issues.
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Ok, if you are only referring to past known single pump failures, you have a point. But that is why I will stand by this statement:
This could be an entirely, as yet unknown, new problem. Why take that chance?
Have you seen the latest grounding of ALL the 206 fleet? This because of a faulty flight control bearing discovered in a newly manufactured aircraft. However, erring on the side of safety, they have grounded the entire series.
the prudent thing to do would be ground all S92's until there is a definitive cause.
Have you seen the latest grounding of ALL the 206 fleet? This because of a faulty flight control bearing discovered in a newly manufactured aircraft. However, erring on the side of safety, they have grounded the entire series.
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Apologies to anyone if I've stepped on toes and whose patience may have been tested, particularly in making the Mods earn their salary 
, but it was to seek the truth ie to what standard the box was certified.
HC #1270
At post #62 (20 December 2002) Nick posted a Sikorsky press release "Sikorsky S-92 Awarded FAA Type Certification" which has in part,
So it would seem to me that the box was originally certified to the 30 minute standard, else why would some one of Nicks standing post otherwise. I'm sure he would have had something to say if it was mere hyperbole inserted by marketing as suggested by some. Secondly, I doubt a corporation of Sikorskys stature would put into print something which they know to be false, litigation being what it is. Obviously the original certification would seem to have been overtaken by events. That the box may be having trouble in the field at the moment is but one of the many hiccups that an aircraft can go through in the maturing process.
HC #363
Interesting last para HC.
HC, with respect to earlier comments (now deleted, regarding actions based on sources of information other than contained in the RFM) what I was alluding to is much better said by Nick in his post #964. I've highlighted what I think are the thought provoking elements.
Of course the trick is to know when to be smart and when to be a slave, for the Monday morning quarterbackers will have you for lunch.
The official report into this most unfortunate accident will make for interesting reading, will be lessons aplenty for all I'm sure.
Thank you all for your PMs - you know who you are and I'll not reply individually.
, but it was to seek the truth ie to what standard the box was certified.HC #1270
Nick Lappos never said that the S92 had 30mins dry running time
Breaking new ground for medium-weight helicopters, the S-92 provides unprecedented levels of safety and reliability. It is the only aircraft in its class certified to the latest specifications for flaw tolerance, bird strike capability and turbine burst protection. In addition to its civil helicopter capabilities, the rotor system and dynamic components are designed to meet the UH-60 BLACK HAWK ballistic tolerance requirements and all gearboxes are capable of running 30 minutes after loss of oil. Corrosion protection meets or exceeds current maritime standards.
HC #363
Its my understanding that the S92 does not have true 30 min dry running capability. In order to meet the certification requirements it relies on retaining some oil in the sump by shutting off the external pipework. This fudge clearly only works if
a) the leak is from something other than the main gearbox and
b) the pump(s) are still running.
If there are no pumps working, dry running time is unknown but less than 30 minutes.
In this case it seems that the pumps had not stopped working altogether, as apparently there was still about one tenth of normal pressure showing on the gauge, and with the destination platform being so close they got away with it. With the drive to both pumps presumably slipping, I doubt it would have been long before the wear caused the pumps to stop altogether.
It will be interesting to see whether the perceived certification fudge that allowed the S92 to enter service without true 30 minute dry running time will come back to haunt SKy sooner than we thought!
a) the leak is from something other than the main gearbox and
b) the pump(s) are still running.
If there are no pumps working, dry running time is unknown but less than 30 minutes.
In this case it seems that the pumps had not stopped working altogether, as apparently there was still about one tenth of normal pressure showing on the gauge, and with the destination platform being so close they got away with it. With the drive to both pumps presumably slipping, I doubt it would have been long before the wear caused the pumps to stop altogether.
It will be interesting to see whether the perceived certification fudge that allowed the S92 to enter service without true 30 minute dry running time will come back to haunt SKy sooner than we thought!
HC, with respect to earlier comments (now deleted, regarding actions based on sources of information other than contained in the RFM) what I was alluding to is much better said by Nick in his post #964. I've highlighted what I think are the thought provoking elements.
I wrote the S76 checklist, and in the intro paragraph to Chapter 3 gave the pilot the latitude to be more than a sweaty flight-manual reader. The difference between airmanship/wisdom and memorizing flight manuals is the difference between pilots and stick wigglers, IMHO. If the flight manual words say "XXX" and you think you must do it, then do so. However, if the PIC decides to actually try some airmanship, in many cases it would be welcomed.
The ease of saying and preaching (in the ease of a Sunday at the keyboard criticizing your fellow pilot) blind obedience to the flight manual, "land immediately" is often confounded by the actual conditions, and by the fact that the aircraft is still flying nicely, even if a few lights are on. I am reminded of the American Airlines DC10 Chicago engine drop-off accident: In simulator trials afterward, the crews that obeyed the checklist and slowed to Vy (while they were climbing at over 2000 fpm before the slow-down) all died like dogs, those that flew wisely like airmen landed successfully.
I do not know what happened with this specific aircraft, at all, but I am lead to believe from 212man's posts that it did not lose all or most of its oil, rather, it might be that it had an oil leak. Any pilot who ditches a load of passengers with an oil leak (even if he memorized the flight manual in that case) might deserve to be ppruned to death, afterwards.
212man, any comments?
A second illustration of what I mean:
The Air Florida National Airport icing crash occurred because the crew obeyed and believed the EPR gages in spite of the fact that they had no climb and were about to hit the ground. They were gloriously slaved to the checklist and the flight manual, and their slavish unairmanship doomed their passengers. Had they simply pushed the throttles up, they would have climbed. The difference between thinking and memorization might be a problem in some cultures (frankly, I am about to get into PPRuNe trouble here) the typical European attitude that the lords of the flight manual and the CAA know more than mere vassels. This religeous following of every word is more likely to lead to airmanship problems than the attitude that these pubs are guidelines for smart people to follow, but not slave themselves to.
The ease of saying and preaching (in the ease of a Sunday at the keyboard criticizing your fellow pilot) blind obedience to the flight manual, "land immediately" is often confounded by the actual conditions, and by the fact that the aircraft is still flying nicely, even if a few lights are on. I am reminded of the American Airlines DC10 Chicago engine drop-off accident: In simulator trials afterward, the crews that obeyed the checklist and slowed to Vy (while they were climbing at over 2000 fpm before the slow-down) all died like dogs, those that flew wisely like airmen landed successfully.
I do not know what happened with this specific aircraft, at all, but I am lead to believe from 212man's posts that it did not lose all or most of its oil, rather, it might be that it had an oil leak. Any pilot who ditches a load of passengers with an oil leak (even if he memorized the flight manual in that case) might deserve to be ppruned to death, afterwards.
212man, any comments?
A second illustration of what I mean:
The Air Florida National Airport icing crash occurred because the crew obeyed and believed the EPR gages in spite of the fact that they had no climb and were about to hit the ground. They were gloriously slaved to the checklist and the flight manual, and their slavish unairmanship doomed their passengers. Had they simply pushed the throttles up, they would have climbed. The difference between thinking and memorization might be a problem in some cultures (frankly, I am about to get into PPRuNe trouble here) the typical European attitude that the lords of the flight manual and the CAA know more than mere vassels. This religeous following of every word is more likely to lead to airmanship problems than the attitude that these pubs are guidelines for smart people to follow, but not slave themselves to.
The official report into this most unfortunate accident will make for interesting reading, will be lessons aplenty for all I'm sure.
Thank you all for your PMs - you know who you are and I'll not reply individually.
Of course the trick is to know when to be smart and when to be a slave, for the Monday morning quarterbackers will have you for lunch
blind obedience to the flight manual, "land immediately" is often confounded by the actual conditions, and by the fact that the aircraft is still flying nicely, even if a few lights are on
Remember, "it is better to be on the ground (or maybe in a dinghy) wishing you were flying, than to be flying and wishing you were on the ground!" I'm sure plenty of posters can attest to that - I know I sure as hell can!
PS. The references to what crews did in a DC-10 simulator are also biased, I believe, because clearly the successful crews applied what knowledge they had about the accident in question. Prior to that, the outcomes would likely have been similar. The Air Florida accident is a different case, of course - any crew that doesn't firewall the throttles when presenetd with what they had, deserves the outcome
. Sadly their pax did not!
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to ditch or not to ditch
212
In 1997 (ish) an S76B model driven by one RS was faced with a fire warning that would not extinguish after both bottles had been discharged. The RFM said 'ditch'. He chose not to and landed safely on a nearby platform. What would the outcome have been had he chosen to ditch in a rough sea and a large number of pax on board?
I made the comment at the time that if a pilot arrives at the correct decision by disobeying the RFM then something needs to be done to rectify the situation. What happened - NOTHING CHANGED. Everyone involved in regulation and operation was too scared of the lawyers to change the checklist to one that read -
If the FW Light illuminates, select idle and check for signs of fire.
Our 139 RFM invites you to Land As Soon As Practical following a Hyd System Failiure but we follow the Good Chopper Pilots Guide* and recommend Land As Soon As Possible. You just don't know what's going on back there.
*An unpublished document based on years of PPruners contribution to a fullsome debate on the many aspects of safety that concern us.
G
In 1997 (ish) an S76B model driven by one RS was faced with a fire warning that would not extinguish after both bottles had been discharged. The RFM said 'ditch'. He chose not to and landed safely on a nearby platform. What would the outcome have been had he chosen to ditch in a rough sea and a large number of pax on board?
I made the comment at the time that if a pilot arrives at the correct decision by disobeying the RFM then something needs to be done to rectify the situation. What happened - NOTHING CHANGED. Everyone involved in regulation and operation was too scared of the lawyers to change the checklist to one that read -
If the FW Light illuminates, select idle and check for signs of fire.
Our 139 RFM invites you to Land As Soon As Practical following a Hyd System Failiure but we follow the Good Chopper Pilots Guide* and recommend Land As Soon As Possible. You just don't know what's going on back there.
*An unpublished document based on years of PPruners contribution to a fullsome debate on the many aspects of safety that concern us.
G
Last edited by Geoffersincornwall; 19th Mar 2009 at 13:12.
