Safety Topics: Fatigue failures Available to Purchase

Fracture of a tail rotor counterweight bearing journal and a tail rotor spindle, on two different types of helicopter, but both exhibiting fatigue initiation, are described. The first concerns a Bell 214ST which had departed from a platform and some 34 minutes into the flight and at 2,500 feet a severe high frequency vibration was felt and heard. The commander immediately initiated a gentle descent and declared his intention to seek an immediate diversion. Although the vibration was still severe at 80 knots, it had reduced slightly and the helicopter was fully controllable in level flight. When inbound to the diversion platform at a range of one n mile, a low speed (35 knots) handling check was carried out and confirmed that they still had tail rotor control. Although the vibration level had increased slightly, the descent was continued to an uneventful touchdown on the deck. Following disembarkation of the passengers it was noted that, during the shutdown, the amplitude of the vibration increased significantly before ceasing as the rotors stopped.