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The aircraft was being used for endorsement training of a foreign tourist. It had been operating in the training area east of Jandakot for approximately one hour and was engaged in general handling manoeuvres and aerobatics. Having completed these manoeuvres, the instructor decided to conduct practice forced landing training. During the first approach, from an altitude of 2,500 ft, the instructor reported that the throttle had been opened twice and the engine had responded normally.

The instructor reported that at 200 to 300 ft, with 30 degrees of flap set, he instructed the student to commence a go-around. He reported that the student raised the nose attitude and opened the throttle but the engine did not respond. The student was flying the approach at 65 knots. The stall speed in the finals configuration was approximately 42 knots. The recommended climb speed was 60 knots.

The instructor reported that he checked that the throttle was fully open. He also noticed the airspeed reducing. He took over and attempted to lower the nose attitude to prevent the aircraft stalling but the aircraft did not seem to accelerate. He called to the student to check that the fuel was on.

The instructor reported that he had turned right, then left to avoid a tree and line up on a paddock. He did not assess the rate of descent as being excessive until he tried to flare the aircraft for landing. He did not recall the engine power recovering before impact.

Wreckage evidence indicated that the engine was delivering high power at impact. The wreckage and ground marks also indicated that the aircraft had struck the ground in a flat attitude at relatively low ground-speed. There was sufficient fuel and the fuel selector had been selected to the left tank.

The engine was a Gypsy Major 10, Mk 2, correctly modified for use in the Chipmunk aircraft. During the subsequent engineering examination, the engine was removed and successfully run on a test stand. An examination of the fuel components including the carburettor, fuel pump and filters indicated that there were no pre-existing faults. The engine's original Fairey metal propeller had been replaced by an approved Hoffman wooden propeller. Operators reported that the wooden propeller appeared to have less "flywheel" effect and although the engine could accelerate faster, it would also stop more readily.

Previously reported problems associated with Gypsy Major engine response during go-arounds was pinpointed to worn needle valve seats causing carburettor flooding. A modification was introduced in 1957 to address the fault. The modification was incorporated in the accident engine and the subsequent examination revealed that the valve seat was not worn.

The Gypsy Major engine does not incorporate an accelerator pump and rapid throttle openings have been known to induce a delay due to the fuel/air mixture becoming, momentarily, lean. Whilst this appears to be a known characteristic of the engine, there is no warning in the aircraft's handling notes relating to the consequences of opening the throttle too rapidly.

Evidence indicated that the engine was delivering significant power at impact. The post-accident engine examination and ensuing test run revealed that it was unlikely that a mechanical fault caused the engine to lack power during the go-around. If, however, the throttle was opened too rapidly during the go-around, the engine may have momentarily lost power through a lean cut. The wooden propeller's low inertia associated with the aircraft's low airspeed may have caused the engine to almost stop, further delaying the power response.

By the time the instructor took over, the airspeed had probably reduced rapidly towards the aircraft's stall speed as a result of the drag genrated by the full flap and the pitch attitude. Whilst the manoeuvres conducted by the instructor late in the approach indicated that the aircraft had not stalled, there was probably insufficient airspeed to permit an effective flare before landing. The aircraft may have stalled during the flare, causing it to impact the ground in a near flat attitude at low speed.

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