AS350 / AS355 Tail Rotor heads-up
The aircraft in question is an AS355F1, but since the tail rotor system is identical on all AS350s andAS355s I suggest the lessons from my little episode apply across these types. After engine shut-down, during the rotor run-down, I decided for some trivial reason to play with the pedals: a bit left, a bit right, less than an inch either way. Then I noticed something peculiar: every time I applied any amount of right pedal I would hear some sound from the tail section which in retrospect I would describe as a soft grinding or rubbing sound. The sound would not change in either pitch or volume while applying more or less right pedal, and would immediately stop with neutral or left pedal.
It turned out to be the bearing in the tail rotor pitch change spider (sometimes referred to as the tail rotor swashplate) in the process of self-destruction. The engineer saw an angular difference developing between the rotating and stationary parts as I moved the pedals back and forth. On removal the bearing felt very “gritty” and rough as the races were rotated. The engineer reckoned on another 1-2 hours (!) before complete destruction and possibly seizure. The bearing was about 1100 hours into its 1200-hour life.
The grinding sound was so soft that if I’d kept a little right pedal in during the whole run-down I’m convinced I wouldn’t have noticed anything. Same, of course, for neutral or left pedal. So from now on I shall be gently “walking the pedals” during every rotor run-down; I strongly suggest other AS350/AS355 drivers do the same.