Loss of control

The pilot, with his wife as passenger, was conducting a bore inspection. A search was instigated when the helicopter did not return by night fall. The wreckage was found the next morning. The helicopter had struck the ground in an inverted attitude amongst trees in a dry swamp. There were no witnesses to the accident. The subsequent investigation concluded that control of the helicopter had been lost at a low height and the helicopter had crashed inverted while the rotor was under positive 'g' flight loads, with little rolling motion. No evidence of pre-accident failure of the helicopter or occupant incapacitation was found. Examination of the wreckage and the surrounding area indicated that the helicopter had struck a tree, by settling into its crown, prior to control being lost. No reason for the descent into the tree could be established. It is probable that, following the tree strike the pilot over-reacted with the collective control and was then unable to regain control of the helicopter in the height available.

The pilot reported that the takeoff was being conducted in a crosswind which he estimated was from the left at 10-15 knots. The surface of the 10 metre wide strip was covered in loose gravel. At the beginning of the takeoff roll, the aircraft began to weathercock to the left. The pilot continued, believing that directional control would improve as aircraft speed increased. However, this did not occur and the aircraft ground-looped, striking an embankment at the edge of the strip. The pilot reported that the aircraft was equipped with a small tailwheel which had limited effectiveness on the soft loose surface. Also, the aircraft was a late model Thruster aircraft which had a greater keel surface than earlier models because of its enclosed fuselage. This was the first time the pilot had operated the aircraft in crosswind conditions. The operating manual for the aircraft indicates a demonstrated crosswind capability of 15 knots. This accident was not the subject of a formal on scene investigation.

The pilot had completed one circuit involving a touch and go landing and a go around from the second approach. Following the third approach the aircraft touched down then veered to the left as it commenced the landing roll. The pilot was able to arrest the left swing as the aircraft reached the left side of the runway but a swing to the right then developed and resulted in a ground loop. The left main landing gear collapsed and the left wing impacted the ground. The investigation revealed that the pilot had used an incorrect crosswind control technique and then failed to maintain directional control during the landing roll. There were no pre-existing defects with the aircraft which could have contributed to the accident.

A truck belonging to the pilot's company became bogged on the Normanton - Dunbar road. It was on its way to Rutland with materials needed at the property before the rain closed the road until the end of the Wet Season. A Carpenteria Shire grader was available to move the truck and two others also bogged. Unfortunately the grader had two flat tyres and no spares were available on site. Because of threatening rain the pilot offered to fly the grader driver to his camp to pick up some serviceable tubes. After locating the camp the pilot selected a stretch of road which after an aerial inspection appeared suitable for landing. Towards the end of the landing roll the aircraft veered left slightly under braking forces and the left wing tip struck a dead sapling not seen by the pilot during the aerial inspection.

Circumstances:

The flight was being conducted for the purpose of obtaining aerial photographs of a hospital located about two kilometres from the heliport. Two passengers were carried, one of whom was a photographer occupying the right seat. The weather was fine and mild, with scattered cloud at 2000 feet. The wind was reported to be south south-easterly at about 10-15 knots. The helicopter was seen to make a large right-hand circuit around the hospital at a height generally estimated to be between 600-1000 feet above the ground. It was then observed to commence a second circuit of the hospital. Whilst on a north-westerly heading, it was reported the aircraft either entered a hover, or slowed to a very low forward speed, for a short period. The nose of the helicopter was then observed to begin yawing to the right. The yaw developed into a series of tight spirals, during which the aircraft drifted in a downwind direction, at a relatively low rate of descent. Witnesses reported seeing the main rotor blades slow down during this phase. At about 50-100 feet above the ground, the helicopter was seen to then descend vertically in a steep, nose low attitude, substantially banked to the left, before impacting heavily in the front garden of an unoccupied house. Almost immediately after impact an intense fire broke out, incinerating the occupants of the helicopter before a rescue attempt could be made. The circumstances of the accident were consistent with a loss of tail rotor effectiveness, leading to an uncommanded yaw and loss of control. The aircraft was operating with a high-power setting at maximum all up weight, at a very low forward speed, out of ground effect. It is considered probable that the groundspeed of the aircraft was less than the tailwind component, resulting in a tendency for the aircraft to yaw to the right, into the relative wind. To counteract this tendency, the pilot would have required considerable left pedal to maintain a constant heading. If, as is considered probable, the aircraft yawed rapidly to the right, very little, if any, additional anti-yaw control would have been available from the pedals. In general, the most appropriate course of action available to the pilot, following an uncommanded yaw to the right, would have been to apply full left pedal to counteract the yaw and to apply forward cyclic control to increase airspeed and translational lift. A reduction of collective pitch could also have been used to assist in regaining directional control but may have resulted in an excessive rate of descent.

Significant Factors:

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

1. High gross weight combined with high required power.

2. Flight below translational speed, out of ground effect.

3. Tailwind component.

4. Uncommanded yaw due to loss of tail rotor effectiveness.

5. Following a loss of control, the pilot encountered conditions beyond his level of experience.

Near the end of the landing roll the left wing rose and the aircraft lifted off the strip, then settled back onto the ground on the right mainwheel. The brakes were still applied and the aircraft turned sharply to the right and the right wing struck the ground. The aircraft rolled over and came to rest inverted. The pilot had assessed the crosswind component affecting the main property strip as being close to the maximum for the aircraft type. He had therefore decided to use an adjacent area, which was aligned into wind, but because of the position of buildings at the end of the area a go-around was not possible. It is possible that mechanical turbulence from the buildings effected the aircraft during the landing roll. The approach was conducted at a higher airspeed than that recommended in the P charts, and heavy braking was applied on touchdown before the tailwheel had contacted the ground.

The pilot reported that he was flying straight and level at 200 feet above ground level(AGL) and about 55 knots when the aircraft sideslipped to the left and nosed over. The nose continued to drop to the almost vertical position and the speed built up to 60 knots. At about 100 feet AGL, the pilot attempted to pull out of the dive but the aircraft did not respond and struck the ground in the almost vertical nose down attitude. Eyewitnesses reported that the aircraft was in the circuit area when they saw a wing drop and the nose of the aircraft fall sharply. The AUF Safety Officer reported that the flying surfaces of the aircraft were undamaged and he suspected that a stall/spin DEPARTURE was experienced by the pilot. In addition to cuts and bruises, the pilot suffered compound fractures to both legs and his right arm. This accident was not the subject of a formal on scene investigation.

When the pilot arrived at the destination, the wind was swinging from south to south-west and gusting from 15 to 35 knots. Runway 23 was unserviceable, and the pilot later advised that there were no suitable grass areas for an into-wind landing. An approach was made to runway 26, but during the landing roll the aircraft was affected by a strong wind gust. The pilot was unable to maintain directional control, and the aircraft groundlooped, collapsing the right maingear. The pilot was relatively inexperienced on tailwheel type aircraft. He had elected to make a landing approach after being informed that the present wind was from 190 to 230 degrees at 18 knots. This would have resulted in a crosswind component of between 9 and 15 knots, while the maximum allowable for the aircraft type was 12 knots. More favourable landing conditions existed at other aerodromes in the area. The pilot had apparently not considered the possibility of strong wind gusts as he made the approach.

After a dual check the pilot's instructor briefed the pilot to carry out two circuits, each with a full stop landing. Following the first circuit and landing, the pilot applied power to commence the take-off without bringing the aircraft to a stop. The aircraft veered sharply to the left, became airborne momentarily, before settling back onto the ground outside the flight strip. Flaps were selected fully down and the aircraft continued under full power across a storm water drain for another 38 metres before coming to rest. This was the pilot's second solo exercise. Following the loss of directional control it appears that the pilot became confused and did not apply the correct control inputs to bring the aircraft to a stop.

The pilot had been spreading in the general area of the strip for most of the afternoon. When he commenced operations to the south of the strip an area of sink was experienced on approach to the selected paddock. To allow for this, a reduced weight was uplifted on following flights, and a further six loads were spread successfully. However, as he commenced the turn to line up for the first spreading run with a new load, strong sink and turbulence were encountered. Realising that the aircraft would not clear a line of trees, the pilot continued the turn to the left but the angle of bank suddenly increased and the nose pitched down. The pilot dumped the load and applied right rudder but the aircraft struck the ground heavily. No defect with the aircraft was subsequently discovered which may have contributed to the development of the accident. It was likely that the aircraft was affected by a strong wind gust, which generated a substantial downdraft. The aircraft stalled during the pilot's efforts to avoid the trees, and there was insufficient height available in which a recovery could be effected. It was possible that had the pilot dumped the load before the aircraft stalled, the aircraft may have had sufficient performance to counteract the downdraft.