At last a reply from Bell reference the "bounce incident". Names/ser numbers have been withdrawn for sensitivity reasons.
See what you lot reckon:
Firstly please accept my apologies for the long delay in answering your request regarding:
Flight Safety Occurrence Report fsor\Shawbury – RAF\60(R) Sqn\Griffin\##\#####2.
Bell Helicopter has reviewed the incident report of s/n #####7 regarding the abnormality your Griffin crew experienced and could not construe any plausible aircraft system fault that could duplicate the characteristic and duration of the vibration described.
Bell Helicopter considers the most likely catalyst for this short term vibration may have been from an external source.
It is possible that the rotor wash caused something to be picked up into the tail rotor which would create a momentary large span wise imbalance and generate a similar vibration to what was reported by your crew. Unfortunately without any physical evidence this cannot be proven.
Any debris caught up in the rotor would likely shed after a short duration eliminating the vibration which may have been in coincidence with the autopilots being selected ON.
During flight testing Bell Helicopter has observed that when the tail rotor is in a significant out of balanced span wise condition a vertical/fore/aft airframe (hop) vibration is felt at the pilot station.
It also should be noted that the AFCS was not designed to nor has any influence on dampening of vertical airframe vibrations.
Although I am confident that any of the following would have been mentioned in your very detailed report:
· By chance was there any video monitoring the helipad area at the time of this occurrence?
· After the incident was there any evidence of possible contact on either rotor system in particular the tail rotor blade and tail rotor hub?
· After the incident was there any evidence of FOD in the area where it occurred? (FOD can be thrown/ blown long distances).
If Bell Helicopter can provide any assistance with this or other items please do not hesitate to contact us again.
Regards,
It does not, for me, answer the questions posed to Bell in fact it leaves me none the wiser.