Executive summary
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.
Related Recommendations
Reconsiders his decision to continue to approve a person to act as maintenance controller for an operator when that person is also employed by the maintenance service provider contracted to carry out aircraft maintenance for the operator.
Reviews the adequacy of the provision for securing the Pr and Pg accumulator 'B' nuts to their respective fitting in their pressure line, on the LTS101 engine.
Advises all current users of the AlliedSignal (Lycoming) LTS101 engine to inspect and check tighten each 'B' nut that secures the Pr and Pg accumulators to their respective pressure line, inspect and check tighten the 'B' nut that secures the Py line to the over speed governor, and to report to the manufacturer any instances of loose fittings.
Ensure that all of the requirements specified by the manufacturer for LTS101 engine maintenance, including the performance trend monitoring procedures, are being carried out.
Advises all New Zealand operators of the LTS101 engine of the necessity and importance of following the performance trend monitoring procedures specified by the engine manufacturer in order to detect excessive wear of the GP turbine rotor shroud sealing rings.
Reviews the LTS101 engine periodic inspection requirements regarding the GP turbine rotor shroud sealing rings to establish if there is a need for these sealing rings to be replaced or measured as part of the scheduled maintenance.
Advise all New Zealand operators of the AlliedSignal (Lycoming) LTS101 engine to inspect and check tighten each 'B' nut that secures the Pr and Pg accumulators to their respective pressure line, inspect and check tighten the 'B' nut that secures the Py line to the over speed governor, and to report to the CAA any instances of loose fittings.