What happened
On 22 March 1999, a Sikorsky S76A, registration G-BITR, was conducting a passenger charter flight to an oil and gas platform in the Netherlands sector of the North Sea. Following a routine flight, the co-pilot noticed while supervising a refueling operation that the right-hand tail rotor gearbox fairing was missing from the aircraft. The crew immediately initiated an engine shutdown.
This event followed a similar incident involving another aircraft in the operator's fleet, G-BIBG, which had experienced radio interference and a missing fairing during an approach to Den Helder on 2 February. In that instance, the loss of the fairing had also caused damage to a VHF radio antenna lead.
The investigation
The investigation established that the loss of the fairing was not an isolated event. Following the initial incident in February, the operator's engineering department had issued a global inspection alert. However, the subsequent failure of G-BITR prompted a more intensive investigation into the structural integrity of the fairing attachments.
Subsequent inspections of the operator's fleet revealed that several other Sikary S76A helicopters were suffering from bonding failures between the fairing and the pylon skin. Specifically, six of the operator's aircraft were found to have detached or failing fairings, and two additional aircraft operated by another UK company showed similar defects on the right-hand side of the pylon.
Findings
- The primary cause of the fairing detachment was the failure of the adhesive bonding between the tail rotor gearbox fairing and the pylon side skin.
- The failures were specifically identified on the right-hand fairing, which is located on the same side of the pylon as the tail rotor.
- The detachment of such components posed a significant risk of causing contact damage to the rotating tail rotor blades.