AO-1998-005

At about 1123 hours on Sunday 19 April 1998 ZK-HKU, an Aerospatiale AS350D helicopter fitted with an AlliedSignal LTS101 engine, experienced a total loss of engine power while on approach to land at the Skyline Skyrides heliport at Rotorua. The pilot made an autorotational landing onto uneven terrain. No injuries to the helicopter occupants resulted.

The engine involved is in common use in air transport aircraft in New Zealand and overseas. Examination of the engine revealed that excessively worn gas producer turbine rotor shroud sealing rings precipitated internal mechanical failure of the engine, which resulted in a total power loss. The worn sealing rings went undetected as the manufacturer's required engine performance trend monitoring procedures were not being followed.

Safety recommendations were made relating to loose engine B nuts, the provision for securing the B nuts, correct engine performance trend checking procedures, the appropriateness of allowing a person to act as an operator's maintenance controller when also employed by the maintenance service provider, the need for all applicable requirements for engine maintenance to be carried out, and the periodic inspection requirements for the gas producer shroud sealing rings.