Flight control systems involving a Robinson R44, VH-JFK, Southport Aerodrome, Queensland, on 29 January 1997

Sequence of Events

Following an extended period of hovering practice and a circuit, the student remarked that the lateral trim was heavy. The instructor flew another circuit. He noticed that increasing left cyclic control pressure was required to prevent the helicopter from rolling right. At about 150 ft AGL a loud metallic "springing" noise was heard and a reaction felt through the controls and airframe. The cyclic pressures returned to normal. The helicopter was landed safely and closed down.

An after-flight inspection found that the lateral trim springs had parted, and right cyclic control was restricted to about 50% of the normal control authority.

Safety Action

Following this incident, the Civil Aviation Safety Authority was notified and made two submissions for the manufacturer to take urgent action. The manufacturer had been aware of a potential problem involving undue wear on a shaft in the trim assembly which could cause binding. A service letter, SL-13, which called for an inspection at each 100-hour inspection and annually was issued prior to this incident. Service Bulletin, SB-19, which called for a mandatory inspection of the trim shaft to determine the minimum diameter of the shaft was issued on 16 April 1997. Time of compliance was within the next 50 flight hours or by 31 May 1997, whichever came first.