Strict checks advised for helicopters

Press, 27 April 1984, Page 21

Strict checks advised for helicopters

PA Wellington Air accident investigators have suggested tougher airworthiness checks for some helicopter engines. This follows an incident where serious corrosion caused the sudden engine failure and crash of a helicopter in a steep gully south-east of Tokoroa. A pilot, aged 29, escaped serious injury in the earlymorning crash, but his Fairchild Hiller helicopter was wrecked. A report prepared by the Office of Air Accidents Investigation said the helicopter had barely taken off when the pilot heard “two tingling sounds” and then a loud bang from the vicinity of the engine. The engine lost all power and the helicopter de-

scended rapidly into a steep gully where it crashed on rough terrain. Engineers checking the wreckage of the helicopter found that engine compressor wheels had been torn from the rotor. A close inspection of the compressor rotor showed evidence of corrosion. It was considered that the compressor failure had resulted from corrosion leading to fatigue failure. In the operating manual for the Allison 250-ClB engine used in the helicopter, owners were warned that corrosion and erosion would cause damage to the compressor blades which could result in engine failure. A series of cleaning instructions, including a call for a daily water rinse if

the helicopter was used in a salt water area, was suggested. The helicopter which crashed had been used in conditions not considered to be “primarily a salt air environment.” It was recommended to the Director of Civil Aviation that when aircraft powered by Allison 250 C-18 and C-20 engines were imported, consideration be given to checking the compressor blades for corrosion before an airworthiness certificate was issued. The inspection should be made when the engines had a history of low use or long periods of storage, the report said.