Sikorsky S-92: Operations
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Good job by the PIC.
I'm assuming this failure mode is covered during FSI.
Just highlights how media-sensitive the S92 is right now, and rightly so.
"Trust the pilots, who trust the engineers, who trust the designers"...a wee bit of trust breakdown in this case. These maintenance "errors" are totally unacceptable, would have been more than a ASB if this had ended up in fatalities, thanks to the PIC's skills this wasn't the case.
What's to prevent this happening again, enhanced awareness is good but procedural auditing etc. is what's really required. This was also an issue with Cougar 491. From the TSB report, under the conclusions section:
Safe flying
Max
I'm assuming this failure mode is covered during FSI.
Just highlights how media-sensitive the S92 is right now, and rightly so.
"Trust the pilots, who trust the engineers, who trust the designers"...a wee bit of trust breakdown in this case. These maintenance "errors" are totally unacceptable, would have been more than a ASB if this had ended up in fatalities, thanks to the PIC's skills this wasn't the case.
What's to prevent this happening again, enhanced awareness is good but procedural auditing etc. is what's really required. This was also an issue with Cougar 491. From the TSB report, under the conclusions section:
Cougar Helicopters did not effectively implement the mandatory maintenance procedures in Aircraft Maintenance Manual (AMM) Revision 13 and, therefore, damaged studs on the filter bowl assembly were not detected or replaced.
Safe flying
Max
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Squib66, you might be right about the AD . I would say Sikorsky reacted to this swiftly to head off the FAA AD, and if issued most operators should all ready be in compliance with the AD if they carried out the ASB.
The pitch change shaft has a 1250 hour replacement schedule, so many of these have been changed out with no issues. The existing Maintenance procedure is clear enough to me. I imagine with this incident will be a revision in the procedure just like the ASB to check for how much thread is showing past the nut to draw attention to be sure is actually in safety.
As 212 man says a dupe ( duplicate inspection) might have helped to catch this to?
The pitch change shaft has a 1250 hour replacement schedule, so many of these have been changed out with no issues. The existing Maintenance procedure is clear enough to me. I imagine with this incident will be a revision in the procedure just like the ASB to check for how much thread is showing past the nut to draw attention to be sure is actually in safety.
As 212 man says a dupe ( duplicate inspection) might have helped to catch this to?
It wasn't missed.
But because it was maintenance error, an order not to discuss it outside the company was issued by the operator under the threat of termination.
But because it was maintenance error, an order not to discuss it outside the company was issued by the operator under the threat of termination.
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an order not to discuss it outside the company was issued by the operator under the threat of termination
This is some of the content from the Sikorsky Safety Advisory (SSA) that came out for operators. I don't think it takes too much reading between the lines to see that there is no need for an AD! Good job by the crew 
It's a pity there is such secrecy by the operator though. Hopefully in due course some of the circumstances surrounding the error will be made public and can be incorporated into Engineering Human Factors courses etc. Similar examples would be the Bond AS332 high speed shaft misassembly (leading to overspeed and shutdown while doing a topping check with the other engine in idle!) a few years ago, and the BMI A320 mag plugs with missing oil seals (leading to total oil loss on both engines.) Both of these incidents feature heavily in human factors courses, and have lead to changes in practices that are designed to prevent re-occurrence.
1. Introduction
An S-92 helicopter operator reported loss of tail rotor control in flight following replacement of the Tail Rotor Pitch Change Shaft. Inspection revealed that the pitch change shaft nut and washer were missing after the flight.
WARNING
When performing maintenance manual SA S92A-AMM-000 Task 64-22-01-900-002, Installation of Tail Rotor Pitch Beam Assembly, make certain that the procedure is performed in its entirety. Failure to follow all steps may lead to loss of the pitch change shaft nut and washer and may lead to loss of tail rotor control.
2. Corrective Action
To preclude loss of tail rotor control after maintenance of the Tail Rotor Pitch Change Shaft or Tail Rotor Pitch Beam Assembly, adhere to procedures in maintenance manual SA S92A-AMM-000 Task 64-22-01-900-002, Installation of Tail Rotor Pitch Beam Assembly.
An S-92 helicopter operator reported loss of tail rotor control in flight following replacement of the Tail Rotor Pitch Change Shaft. Inspection revealed that the pitch change shaft nut and washer were missing after the flight.
WARNING
When performing maintenance manual SA S92A-AMM-000 Task 64-22-01-900-002, Installation of Tail Rotor Pitch Beam Assembly, make certain that the procedure is performed in its entirety. Failure to follow all steps may lead to loss of the pitch change shaft nut and washer and may lead to loss of tail rotor control.
2. Corrective Action
To preclude loss of tail rotor control after maintenance of the Tail Rotor Pitch Change Shaft or Tail Rotor Pitch Beam Assembly, adhere to procedures in maintenance manual SA S92A-AMM-000 Task 64-22-01-900-002, Installation of Tail Rotor Pitch Beam Assembly.
Last edited by 212man; 20th Feb 2011 at 03:21.
Both of these incidents feature heavily in human factors courses, and have lead to changes in practices that are designed to prevent re-occurrence.
So what is not working?
Is it the fault of the designers who after making helos for many years still can't fool-proof critical systems from poor engineering practices?
Is it the fault of the documentation?
Is the the fault of the engineers who are not trained properly?
Is it the fault of the time-pressures brought by the management to get the engineering done asap?
Is it a fault of the operators for not paying decent wages to attract quality engineers?
Is it the fault of the aircrew who should be diligent and thorough on their walkrounds?
I suspect, like all incidents, there is a mixture of more than one fault (the old swiss cheese analogy) but whatever the reason, all the corporate knowledge, the 'lessons learned', the extra training in human factors and all the other mitigation measures have failed in this case - only the skill of the pilot stopped this being a fatal accident.
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I agree with all who think the crew did an excellent job of making a safe landing out of an engineering failure.
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Is that really true? If so its a scandle and would be a sign that Air Log becoming Bristow USA was just a cynical and lzay rebranding not a sign of achieving high, uniform standards. I do hope however that the Bristow CEO discusses this in his keynote speech at CHC's safety conference next month which has the conference theme of Corporate Responsibility vs. Personal Accountability: Two sides of the same Coin.
chw
I think you will find the nut was missing after the flight not before, so not detectable on a walk around. The large nut is screwed onto the pitch change shaft and forces a splined ring to engage with shallow splines in the shaft. The nut is torqued to 183-202 ft-lbs (the variation allows the holes for the secondary locking screws to align). I believe that a possible assembly effor is to have the splines misaligned.
twisted wrench
Maybe it is but Sikorsky issued a massive change last week to the procedure for the tail rotor pitch beam assembly, TREV 64-10.
I've just been shown a copy and it has 20 changes and many new illustrations designed "to ensure proper component alignment".
Industry insider
because it was maintenance error, an order not to discuss it outside the company was issued by the operator under the threat of termination.
chw
I think you will find the nut was missing after the flight not before, so not detectable on a walk around. The large nut is screwed onto the pitch change shaft and forces a splined ring to engage with shallow splines in the shaft. The nut is torqued to 183-202 ft-lbs (the variation allows the holes for the secondary locking screws to align). I believe that a possible assembly effor is to have the splines misaligned.
twisted wrench
The existing Maintenance procedure is clear enough to me.
I've just been shown a copy and it has 20 changes and many new illustrations designed "to ensure proper component alignment".
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BMI A320 mag plugs with missing oil seals (leading to total oil loss on both engines.) Both of these incidents feature heavily in human factors courses, and have lead to changes in practices that are designed to prevent re-occurrence.
On May 5, 1983, Eastern Air Lines Flight 855, a L-1011 registration N334EA, while flying from Miami to Nassau, shut down the #2 engine due to low oil pressure and began a return to Miami. Both of the remaining engines later failed. Without power, flight 855 descended from 13,000 to 4,000 feet (1,200 m) before the #2 engine was restarted and the aircraft landed in Miami without injuries. Incorrect engine maintenance had led to the loss of oil on all 3 engines. (seals not put on the mag plugs)
Lessons get lost and it's why the safety people will never be without a job, and accident investigators unfortunately.
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back to years a go
squib66
My apology to the flight crew regarding the walk around remark earlier (I know better)
fantastic job landing the truck !
What I should have said is, we should may be go back to have the flight crew do a pre flight/daily inspection of the Rotor craft by climbing on to the airframe look under the cowlings etc and examining the parts on which worked has been carried out.
Years a go we use to have the crews do they're own daily inspections on the large offshore helicopters but than every one wanted to be like the airlines and the flight crews where more or less told to stay out of the hangar. In the long run this may disconnect the flight crew from the flying machine.
My apology to the flight crew regarding the walk around remark earlier (I know better)
fantastic job landing the truck !What I should have said is, we should may be go back to have the flight crew do a pre flight/daily inspection of the Rotor craft by climbing on to the airframe look under the cowlings etc and examining the parts on which worked has been carried out.
Years a go we use to have the crews do they're own daily inspections on the large offshore helicopters but than every one wanted to be like the airlines and the flight crews where more or less told to stay out of the hangar. In the long run this may disconnect the flight crew from the flying machine.
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CHW:
Hard to say if this would have helped or not having Pilots still do a more detailed walk around.
Would mean for this particular instance the maintenance stand would be needed to get close enough to the tail rotor to actually inspect it and possibly see it was not assembled correctly.
Was not normal in my past experience when pilots were doing a more
in-depth walk around to put a ladder or stand in place to check the tail rotors.
Hard to say if this would have helped or not having Pilots still do a more detailed walk around.
Would mean for this particular instance the maintenance stand would be needed to get close enough to the tail rotor to actually inspect it and possibly see it was not assembled correctly.
Was not normal in my past experience when pilots were doing a more
in-depth walk around to put a ladder or stand in place to check the tail rotors.
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Thanks to 212man for posting this on the Cougar accident thread
Federal Register | Special Conditions: Sikorsky Aircraft Corporation Model S-92A Helicopter; Installation of a Search and Rescue (SAR) Automatic Flight Control System (AFCS)
Choice cuts
Intro
But now, 3.5 years later
So what features are not already in service with the UK Coast Guard?
Looking at the features of the AFCS I can't see anything that is not seen on other SAR helicopters.
A sinister turn considering the MGB oil test failure just before certification of the S-92
Federal Register | Special Conditions: Sikorsky Aircraft Corporation Model S-92A Helicopter; Installation of a Search and Rescue (SAR) Automatic Flight Control System (AFCS)
Choice cuts
Intro
On July 30, 2007, Sikorsky applied for a change to Type Certificate (TC) No. R00024BO to install an optional SAR AFCS in the model S-92A helicopter.
These special conditions were recently developed due to the intended function of the S-92A SAR AFCS not being completely defined until late in the certification program
Looking at the features of the AFCS I can't see anything that is not seen on other SAR helicopters.
The SAR system is composed of a navigation computer with SAR modes, an AFCS that provides coupled SAR functions, hoist operator control, a hover speed reference system, and two radio altimeters. The AFCS coupled SAR functions include
(a) Hover hold at selected height above the surface.
(b) Ground speed hold.
(c) Transition down and hover to a waypoint under guidance from the navigation computer.
(d) SAR pattern, transition down, and hover near a target over which the helicopter has flown.
(e) Transition up, climb, and capture a cruise height.
(f) Capture and track SAR search patterns generated by the navigation computer.
(g) Monitor the preselected hover height with automatic increase in collective if the aircraft height drops below the safe minimum height.
(a) Hover hold at selected height above the surface.
(b) Ground speed hold.
(c) Transition down and hover to a waypoint under guidance from the navigation computer.
(d) SAR pattern, transition down, and hover near a target over which the helicopter has flown.
(e) Transition up, climb, and capture a cruise height.
(f) Capture and track SAR search patterns generated by the navigation computer.
(g) Monitor the preselected hover height with automatic increase in collective if the aircraft height drops below the safe minimum height.
Normally, in adopting special conditions, the FAA provides notice and an opportunity for comment before issuing the final special conditions. However, because the delivery date of the Sikorsky model S-92A helicopter is imminent, we find that it is impracticable to provide prior notice because a delay would be contrary to the public interest. The FAA therefore finds that good cause exists for making these special conditions effective upon issuance.
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I'm assuming that the FAA has had a review of this occurrence:
http://www.aaib.gov.uk/cms_resources...RC%2002-11.pdf
Still other gremlins to be worked out IMO before this type is really good enough for SAR.
Safe flying
Max
http://www.aaib.gov.uk/cms_resources...RC%2002-11.pdf
Still other gremlins to be worked out IMO before this type is really good enough for SAR.
Safe flying
Max
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Its odd that Cougar claim (p2 below in a brochure that pre-dates there accident) to have 4-axis autopilot already.
IIRC, at the public inquiry after their accident it was said that the system was not certified and TC were waiting on the FAA.
http://www.cougar.ca/media/images/br...cougar-sar.pdf
Perhaps the urgency in Canada in delivering what was claimed to be in place is what is driving this.
Sikorsky seem to be well behind the competition though. The FAA Special Condition for similar capability on the EC225 went out for comment in November 2008!
IIRC, at the public inquiry after their accident it was said that the system was not certified and TC were waiting on the FAA.
http://www.cougar.ca/media/images/br...cougar-sar.pdf
Perhaps the urgency in Canada in delivering what was claimed to be in place is what is driving this.
Sikorsky seem to be well behind the competition though. The FAA Special Condition for similar capability on the EC225 went out for comment in November 2008!