Bye bye tail rotor.
- By Kiba
- The Bear Pit
- 17 Replies
My bet is on tail rotor gearbox (most likely) or driveshaft failure.
The video shows that the tail rotor changed speed substantially at the same time the yaw started. Normally, main rotor and tail rotor are coupled via a power tap on the main rotor gearbox, a rigid driveshaft inside and along the length of the tail boom and a 90 degree gearbox at the end of the tail boom. Which means that the tail rotor cannot change rpm independently from the main rotor unless there is a failure in the drive train.
A failure in the pitch control of the tail rotor would also have resulted in a yaw but would NOT have caused a sudden change in tail rotor rpm.
Disclosure: I work for a helicopter manufacturer but have not stayed at a Holiday Express recently.
Based on the video it sure appears to initially be a failed or disconnected pitch change link that is swung outwards by centripetal force, followed by tail blade pitch asymmetry as at that point one blade is still connected and controlled as normal while the other will take a neutral aerodynamic position, and then the vibrations and forces from that thrust imbalance caused a tail gearbox failure including separating it from the airframe. In one of the videos you can see the gearbox detach and get flung towards the person taking the video and then landing in the parking lot.
And as an added bonus we get to see the results of mast bumping captured on fairly clear video.
Again... the video is pretty damning, but I'll wait until the initial incident report comes out, hopefully with pictures of the tail rotor components.