The crew reported hearing/feeling a thump during flap retraction after takeoff. As all cockpit indications were normal the noise was interpreted as a bird strike and the flight proceeded uneventfully. A post flight inspection revealed damage to the the right hand inboard leading edge device (including a section of flap missing) and impact damage to the leading edge of the right horizontal stabilizer. The aircraft's last major servicing was conducted overseas by an overseas organization on 13 December 1988. The servicing was inspected by company engineers. Some time later a loss of drive to a section of leading edge flaps occurred. The drive unit output shaft had disconnected at the drive coupling there was no evidence of three coupling retaining screws having been fitted. This fault was rectified and the aircraft was later inspected by a different overseas organization at a different location. In the message requesting the inspection the company had asked for all leading edge flaps to be inspected assuming that all leading edge devices would be checked. However the devices between the fuselage and the inboard engines are known as "krueger flaps" and were not inspected by the overseas organization. Analysis of the damage to the starboard krueger flaps indicated that the following sequence occurred. During taxi for departure when the flaps were extended to setting one all leading edge devices extended automatically. At this time the torque tube between the hinges on the inboard krueger flap panel became disconnected at its outboard end. This disconnection allowed the inboard hinge of this panel to travel over-centre during takeoff. This hinge then remained fully extended for the duration of the flight. On flap retraction after takeoff the outer two krueger flap panels retracted normally together with the outboard hinge of the inboard panel. At some time during this retraction the inboard panel may have cracked and drive was lost in the area of the torque tube between the gearbox and the inboard end of the centre krueger flap panel. This torque tube showed no obvious damage and is believed to have become disconnected at one end. The movement of the inboard panel resulted in a section breaking off and striking the starboard horizontal stabiliser.

The pilot departed the treatment area as darkness fell, to fly the 15 kilometres to Ayr aerodrome. His loader/driver had left the agricultural strip earlier after the last load of urea fertilizer had been loaded into the hopper of the aircraft. He had directions from the pilot to deploy kerosene lights on one side of runway 11 at Ayr for a night landing. Immediately before the accident, the aircraft was seen to orbit a farmhouse three kilometres north-west of the threshold of runway 11. It was flying low with the spray lights ON, in a very intense thunderstorm. Heavy rain was falling at the time. The farmer saw the aircraft lights disappear to the south and at the same time the electricity supply was cut. Convinced that the aircraft had crashed, he drove to the area where he had seen it disappear. When he arrived at a crossroads, he saw downed powerlines and the pilot, whom he recognised, standing among them. The pilot was in shock and incoherent. The aircraft had struck 11,000 Volt powerlines at a major junction of the electricity grid. It had cartwheeled and came to rest, upright, in tall sugar cane, 100 metres from the intersection. The pilot holds a Class Four and a Five Instrument Rating which entitle him to fly at night in Visual Meteorological Conditions (VMC). However, the aircraft was certified for Visual Flight Rules (VFR) only. Weather at destination was such that VMC was not met and flight by visual reference was not possible. The pilot had decided to return to Ayr so that spray gear could be fitted to the aircraft in preparation for work on the following day.

Circumstances:

Following a period a local familiarisation flying, the landing was selected down, pre-landing checks were completed and a green down-and-locked indication obtained. The aircraft subsequently landed on the lower fuselage, main landing gear doors, flaps, and propeller tips. During the investigation, a retraction test and partial disassembly of the landing gear mechanism confirmed that the extension cycle had terminated prematurely. This termination was caused by interference with the down limit and indicator microswitches mounting plate by the up-limit actuating screw. Movement and activation of these switches terminated the gear down travel and presented a false gear down-and-locked indication. Only the main landing gear doors extended before the cycle stopped.

Significant Factors:

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

1. Failure of the landing gear to extend after a "down" selection - due to mechanical interference of the down limit switch.

2. Failure of the landing gear indicator to indicate an unsafe gear situation - due to mechanical interference of the down indicator switch. This accident was not the subject of an on-scene investigation.

The pilot was attempting to land on a 500 metre one-way agricultural strip affected by a gusting downwind component of about 10 knots. The strip was bordered by tall trees and had an uphill gradient of about 5 percent in the landing direction. The strip surface was covered by short wet grass. On short final approach the pilot realised the downwind component was excessive for the strip length available but was unable to go around due to tall trees. He landed the aircraft but was forced to initiate a ground loop to avoid overruning the strip end.

The aircraft was carrying out a night flight to a strip lit by portable fluorescent lights. These lights were spaced 190 metres apart along the length of the strip. During the approach the left main gear struck rising ground, which formed the end of the built-up strip surface, approximately 29 metres short of the threshold. The left main gear drag brace failed and the oleo leg was bent, however, the gear did not collapse and the landing was completed without further incident.

The investigation revealed that the strip had been lengthened but the operator had not been notified of the change. The available portable lights had been evenly spaced along the length of the strip. However, due to insufficient lights being available, the spacing between them exceeded double the prescribed spacing and the threshold was inadequately marked. The pilot was not aware of the length and spacing anomalies. Consequently, because of these anomalies, he was presented with a false perspective of the angle of approach and misjudged the approach.

The pilot reported that he was hovering the helicopter at about 200 feet above ground level. The wind was blowing from 90 degrees left of the helicopter's heading at about 15 knots, with some higher gusts. As he moved the cyclic pitch control to accelerate the helicopter forward, a greater than normal sink rate developed. The pilot increased power to compensate but there appeared to be no response and he heard the low rotor rpm warning horn sound. The pilot then fully lowered the collective pitch control and applied full throttle. He expected the engine rpm to recover quickly but the horn continued to sound. He saw the engine/rotor rpm gauge indicating 85-90 percent. At this stage, he was forced to manoeuvre the helicopter, using all available power, around terrain and trees. A short time later, he again fully lowered the collective pitch control in an effort to regain engine /rotor RPM, however, the horn continued to sound. Because of approaching trees, which he knew the aircraft could not clear, the pilot was forced to land in a less than ideal area. The main rotor blades struck a small tree, and the helicopter touched down firmly on the left skid, causing damage to the engine frame. No fault was found with the helicopter which might have contributed to the accident. It is possible, however, for there to have been some transient fault, the evidence of which was lost lost during recovery of the helicopter by vehicle over very rough terrain. The other possible cause for the loss of rpm is that the main rotor blades were overpitched when the pilot first reacted to the excessive sink. There were a number of other aspects of the helicopter's operation which were likely to have affected the outcome of the occurrence. The helicopter was operating at high all-up-weight, near the boundary of the flight envelope for hover out of ground effect. This meant that there was little excess power available to counter the loss of lift when the helicopter was accelerated forward. By not operating the helicopter into wind, the pilot was increasing the time and power required to achieve translational lift. The manoeuvre the pilot was forced to make to avoid terrain and trees (using all available power) would have negated any rpm recovery that had been achieved from the initial lowering of the collective pitch control. In summary, while there is doubt whether there was an initial power loss, a number of factors were present which would have rendered an effective recovery difficult, if not impossible, from the ensuing situation.

The pilot had flown the aircraft from his base to the property strip earlier in the morning. The aircraft was loaded with 375 kilograms of a pelletised material called "Grassland" for spreading. The performance of the aircraft up to this time had been normal. The pilot reported that the initial part of the takeoff run appeared normal. However, as the aircraft approached the end of the strip, he became aware that the airspeed was about 10 knots below the desired speed. The aircraft became airborne, struck some small trees, and continued to lose performance before coming to rest about one kilometre from the end of the strip. Examination of the aircraft determined that the engine compression was low and that one cylinder was cracked. No positive reason for a sudden reduction in performance on this takeoff was found. The pilot reported that he had not thought about dumping the load as he was busy flying the aircraft and trying to maintain control. The product was expensive and the pilot's actions indicated that he might have been concerned about the commercial implications of dumping the load.

The pilot reported that after he had hand started the engine, the aircraft rolled forward and the nosegear struck a concrete culvert.

Circumstances:

The aircraft was observed to take off normally and climb to about 200 feet above ground level. Shortly after passing beyond the end of the strip, an apparent change in aircraft engine noise was heard by witnesses. The aircraft was then seen in a steep nose-down, inverted attitude. It remained in this attitude until ground impact. On site examination showed that the aircraft had struck the ground in an inverted nose-down attitude of 35 degrees. No fault was found in the aircraft or its systems which might have contributed to the accident. The engine was operating at impact. Witnesses reported that the pilot had complained of chest pains both on the morning of the accident and the previous evening. The postmortem report on the pilot indicated that, if other causes of the accident were excluded, there was sufficient chronic heart disease present for sudden heart failure or sudden death to have been likely events.

Significant Factors:

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

1. The pilot probably became incapacitated during flight, causing control of the aircraft to be lost.

The pilot had experienced a smooth flight and after checking the wind direction positioned the aircraft on the downwind leg for a normal circuit. He reported that after reducing speed he lowered one stage of flap and then selected the landing gear down. He believed that he also checked the gear indicator on final approach and saw three green lights. The speed on final was reported as about 80 kts with a power setting of 16 inches and full flap. After round out power was reduced to idle and the pilot then sensed that the aircraft was settling further than usual. When the propeller began striking the runway the pilot pulled back sharply on the control column and applied full power. The aircraft failed to respond as expected and the pilot turned to the left away from the strip. Shortly afterwards the aircraft mushed into the ground. Ground witnesses reported that the aircraft made an approach with the gear up and that the gear began to extend when the pilot pulled up in his attempt to go around. The aircraft gear was fully or partially extended on impact and the main legs were torn off. The aircraft came to rest some 300 metres from the centreline of the runway. Initial on-site inspection could not find any reason for the failure of the gear to extend and showed that the gear warning horn was operable.