What is particularly interesting is AP2 cycled off/on 5 times in the cruise at 3000' before the rapid descent, and AP1 cycled off/on twice over the same period. Both times AP1 went off AP2 also went off. That has to be an action of the crew, because whilst an AP can switch itself off for whatever reason (e.g. electrical interruption), the only way it can come on again is by pilot action. And both AP switching themselves off at the same time is impossible to believe.
AP2 is powered off the essential bus, as are the stick trims. Interruption of essential bus power the collective stick trim system no longer holds the collective in the set position and it will probably lower slightly. This is consistent with observation of the FP reporting to the Captain. Passenger reporting burning smell on the previous sector could also be indicative of an electrical problem. Spinning EHSI might also be indicative of an electrical problem (the report didn't mention whether both were spinning, I would be surprised if both EHSI were doing the same thing). The spinning compass makes no sense. The standby magnetic compass is completely removed from the electrical systems, it just aligns itself with the earths magnetic field and the aircraft pivots around the compass fixed in space. If the compass was spinning, it is the aircraft spinning around the compass. It is impossible to believe the aircraft was spinning.
Also the Captain report of the aircraft not responding to lateral cyclic movement is impossible to believe, unless the control itself couldn't move which would be indicative of a mechanical jam forward of the mixing unit, or a lateral cyclic damper jam. If the control moves but the aircraft fails to respond, a control tube has come undone and it would be impossible to land the aircraft.
Without the full set of FDR data this one will take quite a bit of thinking to sort out what was real, and what might have been confused.
I am wrecking my brains contemplating why a crew might switch an AP off/on 7 times during the course of a flight. Reason being. An AP that keeps turning itself off is telling you that it doesn't want to be turned back on again, so leave it off. Or, if there is an AFCS malfunction of some sort, if turning an AP off/on once doesn't solve the problem, turning it off/on another 2+ times isn't likely to result in a different outcome.
It is an onerous responsibility on a pilot to decide to land a $10 million helicopter on the ocean with 11 people on board, particularly for a Captain with only 306 hours PIC time. Very lucky that the sea state was calm.
Last edited by gulliBell; 19th Mar 2016 at 11:20.