Cougar ulykken

Jeg kan uten videre si at rapporten er veldig trist lesning. Sikorsky får massiv kritikk, sertifiserende myndigheter likeså, treningen til flygerne har vært mangelfull, flygerne må ta noe av skylden fordi de lette etter unnskyldninger for ikke å følge "Land Immediately" prosedyren. Når de mistet halerotordrive, så var utførelsen av prosedyren helt håpløs, antakelig på grunn av mangelfull trening. Sammendrag følger under. Jeg kommer nok en gang inn på vibrasjonsnivået i maskinen som jeg opplevde som voldsomme. Dette må slite på hele maskineriet. Jeg savner en diskusjon om dette i rapporten. Sikorsky ville levere en maskin med 5 MRB`s dersom de fikk SAR-X kontrakten med USA. Dette fikk Flyoperativt Forum bekreftet direkte fra Jack Donahue i Sikorsky for flere år siden. Denne ble imidlertid kansellert. Vi pekte i den forbindelse på vibrasjonsnivået.

Findings as to Causes and Contributing Factors


1. Galling on a titanium attachment stud holding the filter bowl assembly to the main gearbox (MGB) prevented the correct preload from being applied during installation. This condition was exacerbated by the number of oil filter replacements and the re-use of the original nuts.
2. Titanium alloy oil filter bowl mounting studs had been used successfully in previous Sikorsky helicopter designs; in the S-92A, however, the number of unexpected oil filter changes resulted in excessive galling.

3. Reduced preload led to an increase of the cyclic load experienced by one of the titanium MGB oil filter bowl assembly attachment studs during operation of CHI91, and to fatigue cracking of the stud, which then developed in a second stud due to increased loading resulting from the initial stud failure. The two studs broke in cruise flight resulting in a sudden loss of oil in the MGB.
4. Following the Australian occurrence, Sikorsky and the Federal Aviation Administration (FAA) relied on new maintenance procedures to mitigate the risk of failure of damaged mounting studs on the MGB filter bowl assembly and did not require their immediate replacement.

5. 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.

6. Ten minutes after the red MGB OIL PRES warning, the loss of lubricant caused a catastrophic failure of the tail take-off pinion, which resulted in the loss of drive to the tail rotor shafts.

7. The S-92A rotorcraft flight manual (RFM) MGB oil system failure procedure was ambiguous and lacked clearly defined symptoms of either a massive loss of MGB oil or a single MGB oil pump failure. This ambiguity contributed to the flight crew's misdiagnosis that a faulty oil pump or sensor was the source of the problem.

8. The pilots misdiagnosed the emergency due to a lack of understanding of the MGB oil system and an over-reliance on prevalent expectations that a loss of oil would result in an increase in oil temperature. This led the pilots to incorrectly rely on MGB oil temperature as a secondary indication of an impending MGB failure.

9. By the time that the crew of CHI91 had established that MGB oil pressure of less than 5 psi warranted a "land immediately" condition, the captain had dismissed ditching in the absence of other compelling indications such as unusual noises or vibrations.

10. The captain's decision to carry out pilot flying (PF) duties, as well as several pilot not flying (PNF) duties, resulted in excessive workload levels that delayed checklist completion and prevented the captain from recognizing critical cues available to him.

11. The pilots had been taught during initial and recurrent S-92A simulator training that a gearbox failure would be gradual and always preceded by noise and vibration. This likely contributed to the captain's decision to continue towards CYYT.

12. Rather than continuing with the descent and ditching as per the RFM, the helicopter was levelled off at 800 feet asl, using a higher power setting and airspeed than required. This likely accelerated the loss of drive to the tail rotor and significantly reduced the probability of a successful, controlled ditching.

13. The captain's fixation on reaching shore combined with the first officer's non-assertiveness prevented concerns about CHI91's flight profile from being incorporated into the captain's decision-making process. The lack of recent, modern, crew resource management (CRM) training likely contributed to the communication and decision-making breakdowns which led to the selection of an unsafe flight profile.

14. The throttles were shut off prior to lowering the collective, in response to the loss of tail rotor thrust. This caused significant main rotor rpm droop.

15. The pilots experienced difficulties controlling the helicopter following the engine shut-down, placing the helicopter in a downwind autorotative descent with main rotor rpm and airspeed well below prescribed RFM limits. This led to an excessive rate of descent from which the pilots could not recover prior to impact.

16. The severity of the impact likely rendered some passengers unconscious. The other occupants seated in the helicopter likely remained conscious for a short period of time, but became incapacitated due to the impact and cold water shock, and lost their breath hold ability before they could escape the rapidly sinking helicopter.

S-92A fikk det amerikanske Collier Trophy i 2002.....