Circumstances:

The aircraft had been fitted with a tailwheel conversion prior to being imported from the USA. During a touch and go landing, the aircraft was decelerating in the three point attitude through about 20 knots, when the pilot lost control in a violent swing and wing drop to the right, followed by an immediate reversal to the left. The right main gear had separated from the fuselage during the landing roll. The main gear locating bolt and saddle bolts had been fitted incorrectly and were thread bound, allowing the gear leg to place abnormal loads on the saddle. It failed progressively until final overload failure during this particular landing. The aircraft had flown only 13 hours since being placed on the Australian Register. It was imported with the main gear undisturbed. The progressive mode of failure suggests that evidence of impending failure of the saddle should have been apparent for some considerable time.

Significant Factors:

The following factors were considered relevant to the development of the accident:

1. Improper fitment of Tailwheel Conversion Kit by USA maintenance organisation.

2. Overlength bolts holding right main gear were thread bound before the correct clamping tension was achieved.

3. One of the two cast metal saddle sections which locate the gear leg laterally in the fuselage had failed due to fatigue and overload.

4. During the inspection for the issue of a Certificate of Airworthiness, the maintenance organisation did not discover the incorrect installation of the tailwheel kit.

The pilot was tasked to take a passenger to Porphry and bring further passengers back to Kalgoorlie. The flight proceeded normally until shortly after cruise power was selected when the engine began to surge. Attempts by the pilot to rectify the surge were unsuccessful. He turned the aircraft towards Kalgoorlie and, when the oil pressure dropped to zero, the cockpit filled with smoke and the windscreen was smeared with oil, he elected to land on the salt lake almost directly below the aircraft. The landing was uneventful until the nosewheel broke through the lake's crust and the aircraft nosed over and stopped inverted. The loss of oil pressure, the smoke in the cockpit and the oil smear on the windscreen were a result of a hole puntured through the engine crankcase at the base of number 4 cylinder. The conrod of the number 4 piston had suffered a fatigue failure due to a metal embrittlement, brought about by molten material from the number 4 big end bearing coming in contact with the conrod. It is probable that the big end bearing had overheated due to a lack of lubrication, although no evidence was found of a restriction in the oil supply lines. The metallurgical examination concluded that the fatigue failure had developed over a short time and that there was evidence that the number 3 big end bearing had also been overheated due to a lack of lubrication. The pilot chose the site for the forced landing knowing that there was a chance that the surface would be soft. His choice was made after considering that the alternative landing sites were less suitable for a variety of reasons.

The pilot was engaged in a local flight and was practising hovering at various altitudes. With the helicopter heading 320 degrees, the pilot commenced a slow descent from about 15 feet. The wind was 310 degrees at 10 knots gusting to 20 knots. While descending to about three feet, the helicopter began a slow yaw to the right through 30 degrees. The pilot elected to let the yaw continue and carry out a 360 degree pivot turn. After turning through about 100 degrees, the pilot stopped the descent by increasing power and pulling on collective. Coincidentally, the pilot reported that the helicopter then rapidly increased the rate of turn despite the application of full left anti-torque pedal. After about one turn, the pilot said he lost all control and following about another 3-4 turns, the helicopter crashed onto its left side at about 45 degrees angle of bank. During the sequence several mainrotor blade ground strikes occurred. The pilot said that he was also aware of overcontrolling on the cyclic control and pulling on collective at one stage in his efforts to control the helicopter. The investigation could not find any mechanical cause for the loss of control. Both the pilot and passenger reported that at no time did the passenger touch the controls or have his feet near the anti-torque pedals. Studies on helicopter tail rotor vortex rings indicate that these rings can form with a relative wind from 220 to 320 degrees at 10 to 25 knots, with further indications that the worst areas are around 250 and 290 degrees relative. In addition, the conditions suitable for the formation of a vortex ring are most favourable when the tail rotor is moving to the left, as in a right pedal turn. At the point where power was increased, the tail rotor was in a critical position with a relative wind from 250 degrees and strength from the left of between 10 and 20 knots. If the tail rotor was close to a vortex ring state, increased power would, through the torque effect, produce a marked right yaw. Due to the vortex ring, left pedal input would have no effect.

While flying downwind at 30 knots about 50 feet above the ground, the pilot attempted to increase power to accelerate the aircraft. There was no response from the engine, and engine and rotor RPM fell as he applied collective pitch. He attempted to slow the aircraft to land but the heel of the left skid hit the ground and the helicopter rolled on to its side. Examination of the helicopter revealed that a very close tolerance fitting in the linkage between the throttle valve and the mixture control valve caused severe binding. This prevented normal throttle movement.

Following the completion of a flight in the local training area the aircraft was landed on Runway 36 at Roma. At the time the wind was north-westerly at five to eight knots and there was a thunderstorm to the south-west of the field. During the landing roll the wind velocity suddenly increased to about 25 knots. The aircraft swung to the left and ran off the side of the runway. The pilot was unable to regain directional control but shut down the engine before the aircraft ran into a ditch. This accident was not the subject of an on-site investigation.

The pilot noticed what sounded like a slight misfiring noise coming from the engine after start up, however, all other indications, including a magneto check, were normal. The pilot flew the aircraft to a one metre hover, carried out a power and handling check, which was normal, and entered translational flight for a DEPARTURE from the heli-pad. Shortly after entering translational flight the aircraft began to descend. The pilot opened the throttle and raised the collective lever, however, this did not correct the descent. The pilot observed that both engine and rotor rpm were decreasing. At this point the aircraft was approaching a one metre high post and wire fence and the pilot assessed that the aircraft would clear the fence and touchdown in the open area on the other side of the fence. Both skids collided with the top of the fence causing the pilot to lose control of the helicopter which fell to the ground on the far side of the fence. A post accident engineering inspection disclosed that the movement of the exhaust valve in the No. 2 cylinder was restricted by a build up of carbon deposits. The top end of the engine had been overhauled, in Canada, 442 hours prior to the accident. It is likely that the sticking exhaust valve caused the loss of power reported by the pilot. Sticking valves is a known problem with the engine model fitted to the accident aircraft and the manufacturer, the Civil Aviation Authority and the operator had already taken action to correct it.

The pilot reported that he had moved the landing gear to the down position and obtained the green light indicating that the gear was down and locked. During the landing roll, with a crosswind from the left, the right main gear leg collapsed. The landing gear operating system had been stiff during circuits in the previous week. Maintenance inspection determined that the overcentre link on the right gear mechanism was binding. During extension of the gear the push rod apparently bent and the gear struts did not go over centre. The pilot was not aware of this as there is only one light to indicate gear down and this did not indicate the exact position of the gear legs. This accident was not the subject of an on-site investigation.

The aircraft was engaged in a passenger charter operation from Moree to Tenterfield. After landing at Tenterfield, when the aircraft turned off the strip, the left main landing gear broke away and the aircraft settled on the left wing. Prior to the previous takeoff, whilst the aircraft was taxiing at Moree, the landing gear aural warning had sounded momentarily. The pilot and an engineer inspected the landing gear down lock system but no fault was found. The aircraft then operated normally to Tenterfield until the aircraft turned off the strip. Subsequent investigation of the landing gear showed that the forward trunnion pin had became disengaged from the trunnion and the rear pin had migrated some distance aft and finally failed in overload. Movement of the trunnion pins was the direct result of incorrect assembly procedure.

At the start of the take-off run, one propeller blade separated from the hub. The resulting propeller imbalance caused damage to the engine and airframe. The fracture was caused by the growth of a fatigue crack from the second blade retention thread. No material abnormalities or stress concentrators contributed to fatigue initiation. It was estimated that fatigue growth had occurred over a period of approximately 2100 take-off/landing cycles. The Civil Aviation Authority subsequently amended the Airworthiness Directives relating to this type of McCauley propeller, when fitted to agricultural aircraft. These amendments include a reduction in hours between overhauls, and more detailed inspections of the threaded section of the blades.

Circumstances:

The aircraft had been delayed in servicing and repair and had only been released six weeks prior to the accident. This delay had caused the operator/pilot to fall behind in his commitments and, according to some witnesses, caused him to worry about the situation. On the day of the accident, the pilot had just completed spraying a 243 hectare paddock and had landed to reload. After take-off for the new task, the pilot was seen to make an aerial inspection of the paddock before entering the first swath run. At the end of this run, the aircraft collided with a Single Wire Earth Return (SWER) powerline and crashed. It was later shown that the aircraft was in a bank to the right of about 18 degrees. The SWER line ran across one end of the paddock at an angle and on the crop side of a windmill just inside the fence which bordered the road. The line contacted the right main gear and outboard spray boom attachment struts on the right wing. The wire broke after impact, but the aircraft hit the ground heavily on the right main gear. The gear detached from the aircraft, the propeller struck the ground and the aircraft slewed around as it came to rest after some 27 metres of ground travel. The front half of the aircraft was destroyed by fire which broke out almost immediately the aircraft stopped. Two main hypothesis were proposed. One was that the pilot was distracted from a less than demanding task by business worries. The other was that the pilot had perceived that the SWER line was on the right of the windmill and outside the fence and therefore did not present an obstacle to his procedure turn. Neither hypothesis could be substantiated. An additional concern was the fact that the pilot had died from impact injuries in an accident that, prima facie, was survivable. Concern focused on whether the pilot had secured his harness properly and/or whether the inertia reel had failed. Detailed engineering inspection of the inertia reel by the Bureau and the manufacturer could not positively determine the mode of operation of the inertia reel. However, the postmortem report showed that the nature of injuries to the pilot, while sufficient to cause death prior to the fire, were such as to indicate that the inertia reel had probably not failed.

Significant Factors:

The following factor was considered relevant to the development of the accident:

The pilot did not see the powerline in time to avoid a collision.