Shortly after an apparently normal take-off, engine power was lost and the pilot was committed to a landing straight ahead. Initial touchdown was in a flooded rice paddy, and the aircraft then struck a levy bank and ran through a fence, coming to rest inverted in an adjoining dry paddock. Investigation revealed that one cylinder head had become detached from the engine and had removed a section of the inlet manifold. The cylinder head had failed as a result of fatigue cracking which had commenced at the edge of an exhaust valve insert.

Circumstances:

The aircraft was approaching to land into a 15-knot wind, with a slight crosswind component from the left. At about 60 feet above ground, the wind suddenly dropped completely, probably due to terrain and buildings. As the pilot yawed the nose of the aircraft to the right to line up with the strip the right wing stalled. The aircraft entered an incipient spin and impacted the ground nose first, approximately 100 metres to the right of the strip.

The pilot had been carrying out a series of joy flights at a rural field day. Refuelling was taking place from 200 litre drums, which had been placed in the shade of a large tree. On the second occasion that fuel was required, the pilot hover taxied to the drums, which were rolled out of the way on completion of the refuelling. As the pilot started to hover taxy again, the helicopter suddenly rose higher than anticipated and the main rotor struck the overhanging branches of the tree. One rotor blade de-laminated, severe vibration occurred, and the helicopter struck the ground heavily. With the helicopter hover taxying two feet above the ground, there was only three feet of clearance between the rotor blades and the tree branches. The reason the helicopter rose sharply and struck the branches was not determined, but may have been the result of a wind gust.

The pilot reported that while he was hovering the helicopter at about 25 feet agl, the engine suddenly lost power. He placed the helicopter in an autorotation but maintained the throttle setting that had been set while the aircraft was hovering. Just as the skids were about to contact the bushes, the engine momentarily regained power. The helicopter impacted the ground on its right hand side and fire broke out. Both the occupants escaped from the helicopter before it was destroyed by fire. An examination of the engine revealed that both valves in one cylinder had been striking the top of the piston, and the inlet valve was badly chipped. It was likely that when the inlet valve failed, a flashback occurred in the induction system, resulting in a complete loss of engine power. The engine regained power momentarily when the mixture build-up again reached a combustible level. Had the pilot closed the throttle when the engine initially failed, the sudden power surge should not have affected his ability to control the autorotation.

The aircraft was cruising at an altitude of about 300 feet above ground level when the pilot heard a loud bang, then felt a severe vibration. The engine continued to operate for about two to three seconds before stopping. Because of the unsuitable terrain over which the aircraft was flying, the pilot was forced to land into trees and the aircraft rolled on its side. An inspection of the engine found that the number 3 connecting rod had failed. The failure was initiated by galling between the big end bearing and the connecting rod, inducing a fatigue failure of the connecting rod. Specialist opinion indicates that the engine was improperly rebuilt following a bulk strip some 200 hours earlier, in that excessive clearance was permitted between the crankshaft and big end bearing.

Fog had forced the pilot to abandon an earlier attempt to reach a property to conduct spraying operations. After a delay of about one hour, the pilot departed for a second attempt. He later reported that during descent through a hole in the lifting fog, the right spray boom became detached. He decided to return to the DEPARTURE aerodrome, but as the aircraft was clearing some mist, it collided with the top of a gum tree. The pilot shut down the engine because of severe vibrations and carried out a forced landing on a ridge. It was considered that the pilot had not checked that the quick-disconnect fitting on the spray boom was securely fastened during the pre-flight inspection. He had been distracted by the displaced boom and had not seen the tree until it was too late to take avoiding action.

While enroute to the treatment area the pilot noted a loss of engine power. After the load of superphosphate was dumped, he realised he would be unable to return to the DEPARTURE strip and selected a track as the most suitable landing area. During the landing roll the aircraft ran over a hump which caused it to slew off the track into the surrounding bush. Engine examination revealed that the fuel injector system was out of adjustment, producing a lean mixture at high power settings. The resulting high combustion temperatures produced abnormal engine wear and led to spark plug failure.

Cattle were being mustered from open country with the helicopter operating at 15 to 20 feet agl in wind gusting to 25 kt. At the completion of one downwind run the trainee flared instead of turning into wind. The main rotor blades overpitched and the helicopter struck the ground heavily, tail down, before the instructor could recover control of the situation.

The pilot was making an approach to land at his private strip. Wind conditions were gusty and the aircraft was observed to be making a lower approach than was usual. In the vicinity of the boundary fence a substantial increase in engine noise was noted, and the aircraft was seen to be climbing steeply. After reaching a height of about 100 feet the aircraft rolled, descended steeply and struck the ground in an inverted attitude. The reason for the pilot making a lower than normal approach profile was not established. It was determined that the right wing of the aircraft had become entangled with the boundary fence. In an attempt to regain control the pilot had probably instinctively applied large corrective inputs. The fence wire then broke but the aircraft was in an airspeed and attitude configuration such that the pilot was unable to prevent a stall and consequent total loss of control.

The aircraft had previously suffered from aileron flutter and a new set of wings had been constructed and installed. Although the problem of flutter had been removed the aircraft then flew slightly right wing low. A trim tab was fitted and the subject flight undertaken to check its setting. Initial engine running and flight after take-off were normal until the aircraft was on the downwind leg of the circuit. The engine speed was heard to reduce and the aircraft settled into a glide descent. The left wing struck a tree and the aircraft landed heavily on its left wheel and wing tip. The wing separated at its root and the aircraft bounced, landing again on its left side 25 metres further on. Specialist examination of the aircraft indicated that the fuel primer bulb in the engine fuel line had a valve installed incorrectly. Under certain orientation conditions the valve could prevent an adequate fuel flow for continued engine operation. The fuel system layout was such that the position of the primer bulb could vary after handling between flights. As the engine was either stopped or running at idle power at the time of ground impact, the fuel flow is believed to have been restricted, causing engine fuel starvation. No other engine or airframe defects were found. Calculations showed that flutter would not have occurred in the re-designed ailerons and no evidence of flutter was found in the wreckage. When faced with a forced landing in moderately treed terrain, the pilot had misjudged his distance from a tree and was unable to regain control of the aircraft in the height available.