Having
may in an RFM text serves no useful purpose at all - especially when allied with the notorious sense of optimism shown by most helicopters pilots.
As with all accidents, there were a series of events that led to this catastrophic outcome:
- The gearbox failed its unaided 29.927 'run-dry' test.
- The Subsequent FMECA postulated that the only possible loss of oil would be from the external piping leading to the oil cooler.
- The isolation switch was fitted and the gearbox run without cooling for three hours.
- The aircraft was released to service.
The first question is why was the equivalent safety argument accepted by the FAA - it is not clear that the other Authorities were party to this decision.
Up to this point all could have been well apart from the obfuscation and prevarication that occurred on this (and probably other) forii. Many believed (and were not disabused of the belief) that the gearbox could 'run-dry' for 30 minutes. If you don't believe that was the case look to the spat between HC and Brian Abrahams.
Was this lack of clarity instrumental in the decisions of the crew to turn back and make for land instead of 'landing immediately'? We just don't know but, from discussion on PPRUne, we could imagine others making that same decision
at that stage.
- There was a failure of (titanium) filter studs mid-2008 resulting in a rapid loss of oil.
The problem escalated with the incident at Broome; all of a sudden we had a failure mode that had not been considered in the equivalent safety argument - i.e. a sudden loss of oil from the fracture of the (titanium) oil filter studs. Any hazard analysis conducted
after this incident (which occurred over land) would have concluded that a further occurrence of a (titanium) stud failure would have been reasonably probable. Perhaps this failure was down to incorrect handling or torquing but it was still an extant failure mode within a fleet total hours of less than 150,000 hrs.
Was it considered that this (new) failure mode was 'extremely remote' and that the probability of it occurring again within a year or 1,250hrs was zero (or close to it)? Well it must have been because that was the essence of the letter to operators issued by SAC in January. If the S92 had had a 30 minute run-dry capability, this could have been a reasonable (stop gap) policy to keep the fleet in the air - without it (and in hindsight) it was not.
We are not solely concerned with the apparent lack of compliance with 29.927 (but the questions will be asked "was the FMECA rigorous enough"), or the use of titanium in the filter studs.
We are concerned that there was insufficient information provided to the pilots; worse, that they were led to believe that the aircraft was in compliance.
Perhaps we ought to be most concerned that, having had a near catastrophy, a further risk assessment (FMECA) had not been carried out which considered the probability of further filter stud failures and the likely consequences for an aircraft which spends most of its life over the open seas.