Originally Posted by
DOUBLE BOGEY
I hesitate to say this, but if it is a TR Drive/Low power Hard over, he seems to take a long time to react. Many rotations under near hover power before the descent takes place.
Have you personally experienced this particular failure, or practiced it in a simulator? Thirty years ago I was a QHI involved in a full motion helicopter simulator project for the UK military and was part of a team (of two) tasked to expand the then current teaching on tail rotor malfunctions, which was woefully inadequate. We did some practical test flying (hours costed by MOD on behalf of Boscombe Down) and developed a syllabus. We then began teaching both "ab initio" and experienced squadron pilots alike. I saw many highly experienced pilots fail to arrest the yaw rate in time, despite being pre-briefed and pre-warned that the T/R was about to malfunction. Bear in mind that this was in a simulator lesson doing
nothing but tail rotor malfunctions.
Given that it takes a second or two to diagnose the failure in the real case, the pilot probably did as well as anyone could have in the circumstances. Note the slight pause in the yaw rate - it's likely that full opposite pedal was applied in an attempt to stop the yaw, probably a pilot response.Then once the tail rotor blades produced no more effective thrust, round it went again at an increased rate of yaw. Once a rapid fuselage spin develops, response to cyclic inputs may not be what is normally expected and that effective rotor rpm is reduced.
Other things that could cause a sudden yaw are a gust of wind, an autopilot/SAS malfunction, or an inadvertent foot touching a yaw pedal. Dumping the lever and chopping the engines would be an inappropriate immediate response.
This unfortunate pilot probably experienced a T/R drive failure at the most critical stage of flight imaginable. I say "probably" because AAIB haven't yet released initial findings and I am quite possibly wrong; obviously I'm only an amateur compared to some experts here.