Originally Posted by
Thrust Augmentation
Is it not a bit early to be pointing the finger at the lift fan - for all we know this operated as expected, but the engine did not?
Simple observation. The aeroplane bounces and is in a stable hover when suddenly it pitches violently nose-down, rotating about the rear nozzle. The engine is clearly still producing thrust and the rear nozzle stays at the same height (not rising or descending) until other factors intervene. This is extremely unlikely to be a reaction controls issue. The sudden removal of support from the lift fan is the explanation which fits the observed dynamics. Whether this is due to a transmission failure (clutch, shaft, gearing etc) or some misadventure in the control shuttering is something the investigation will discover. There was no sign of mechanical distress from the fan prior to or during the pitch-down - no thrown debris etc, so it's unlikely to be mechanical break-up in the fan itself. The high pitch
rate would (in my view) tend to point to the transmission failure because I don't think even full uncommanded shuttering could achieve that sort of response.
The inability to shut down the engine is possibly a separate, and more concerning, issue. AIUI in the hover the F35B only has digital throttle due to the need to maintain synchronisation between nozzle and fan thrust - there is no "manual fuel control" option. This would tend it suggest the software was still commanding thrust even after we assume the pilot had closed the throttle, right up until the ejection sequence cut the fuel. Why this happened needs to be understood as quickly as possible as it has other ramifications[IMHO].
PDR