Collision with terrain

The pilot stated that he was mustering bulls approximately 5 km west-north-west of Kalmeta homestead. He said he was approximately 40-50 ft high when he hit a wire. He did not see the wire prior to impact. The pilot said that when he realised he had hit a wire he took all necessary action, but lost control of the helicopter, and it fell backwards to the ground. The pilot said that due to the impact and injuries he sustained he did not remember anything further.

The pilot was conducting his first commercial agricultural spraying operation and had been operating on the task for several hours in the afternoon. He was asked by the farmer who owned the property being sprayed, to avoid spraying in the dam on the paddock. Whilst the pilot was attempting to identify the dam, the aircraft's left wing clipped the top of a tree, and the aircraft descended steeply into the ground. The pilot was able to escape from the wreckage, having sustain soft tissue damage, fractures to lower vertebra and both ankles dislocated.

The owner reported that the tail rotor of the helicopter came into contact with a small tree as the pilot was pushing some cattle into a yard. The helicopter then spun out of control to the ground, landing heavily on the left skid before rolling over. The pilot was able exit the helicopter without injury. The owner advised the helicopter was damaged beyond economical repair.

Post flight examination showed that one of the tail rotor blades had separated in flight when it came into contact with the tree.

The pilot reported his aircraft had been hangared since April 1994. He had become seriously ill in November 1994 but, in the past 12 months, he had made a good recovery. He decided that he would go with a friend, who was a qualified pilot, to pick up his aircraft from Roma where it was hangared. The aircraft was flown from Roma to his friend's property.

On the afternoon of the accident, the pilot was using a 220 m runway for take-off, but this distance was well within the performance capability of the aircraft. The friction nut for the throttle control in the aircraft was not functioning correctly, and it was possible for the throttle control to slide back from the full throttle position by about 2.5cm, if the throttle was not held in position manually.

The pilot stated that after becoming airborne in about 70 m he went to apply full flap after building up some speed to clear some low trees at the end of the runway. He said that as he let go of the throttle to apply extra flap, the throttle control slid back with a corresponding reduction in engine power. By the time he realised what had happened and reapplied full throttle, it was evident that the aircraft would not clear trees at the end of the strip. He said he was then left with no alternative but to pull the nose up and 'belly' the aircraft through the trees.

The pilot of the helicopter was conducting a familiarisation flight for the wife of the station owner who had contracted the helicopter. It was late afternoon, with the sun low on the horizon and the fine weather with no cloud or wind. End of daylight was approximately 1745. The homestead, from which the helicopter departed, was located to the west of a swamp. The swamp's water depth was approximately 1 m and the surface was reported as being mirror-flat at the time of the accident. There were two islands located in the swamp and their foliage had a maximum height of approximately 3 m.

The helicopter departed at approximately 1700 and tracked north, climbing to approximately 800 ft AGL before completing a counterclockwise circuit towards the swamp. The pilot decided to make a shallow, northerly approach to the southern island. The island's southern shore was approximately 500 m from the mainland approaching from the south. As the helicopter crossed the mainland-shore on the final approach, the pilot assessed his height as being 20 to 30 ft. 

Late in the approach the pilot decided that a landing on the island was impractical and he commenced a go-around. He stated that he placed the helicopter in an accelerative-attitude and commenced a slight right turn to avoid a bird. The passenger, sitting in the right seat, stated that she thought that the helicopter was at about 10 ft from the surface of the water as the turn commenced. She recalled a spray of water from the front right side just before the helicopter impacted the water. 

The occupants remained secured to their seats and the helicopter remained substantially intact although the canopy bubble imploded, the tail rotor gearbox was flung clear and the main rotor system and fuselage were substantially deformed. The wreckage spread and passenger report indicate that it is likely that the main rotor struck the surface of the water causing the helicopter to cartwheel before coming to rest upright.

After the impact, the occupants released themselves from the wreckage and waded ashore. They reached the shore at approximately 1725.

The pilot later reported that he was unaware of the difficulties associated with visually judging height over calm water. Lacking a radio altimeter, the final approach starting altitude and shallow angle was inappropriate in the prevailing conditions. It is likely that, when the pilot selected the accelerative-attitude and commenced the right turn, the helicopter descended slightly causing the main rotor to strike the surface of the water. The smooth water surface, failing light and low foliage height probably caused the pilot to underestimate the helicopter's height above the water and not perceive a slight descent during the go-around.

The floatplane took-off from a coastal lake in strong gusting winds associated with passing squalls. As the aircraft approached the coast, and flew over the beach at low altitude, it descended until the left float struck the top of a wave. The aircraft nosed over into the ocean and began to sink. The pilot and passenger managed to evacuate the semi submerged aircraft without injury.

The pilot subsequently reported that, after taking off toward the south into the strong wind, he had to turn left at low altitude to avoid a small hill adjacent to the shore. The aircraft had then probably encountered windshear on the downwind side of the hill, which resulted in the unintended loss of altitude and subsequent contact with the water.

The aircraft was involved in a cotton spraying operation. The pilot reported that on the tenth take-off the aircraft failed to accelerate to normal climb speed, only reaching a height of about 15 ft. He dumped the load but was unable to prevent the aircraft descending into the cotton crop. Although the aircraft was substantially damaged the pilot was uninjured.

The engine subsequently performed normally during a test run. The pilot reported that he remembered strong 'willy willy' activity in the area immediately after the accident. He concluded it was likely that the take-off performance of the aircraft had been adversely affected by a wind gust at liftoff.

FACTUAL INFORMATION

The AS350 helicopter was engaged in a controlled burn of a logging coupe. A drip torch was slung underneath the helicopter. It dripped ignited napalm gel on command to initiate burning on the ground. The drip torch weighed 250 kg when fully loaded with napalm.

The pilot advised that while at 50 kts and 200 ft over cleared ground, the helicopter suffered a hydraulic failure. It banked violently to the right and the hydraulic warning light began to flash but the loud warning horn never activated. He turned the hydraulics off using the switch on the collective lever and regained level flight. The helicopter then banked to the right but not as severely. He tried to electrically release the drip torch from the cargo hook but it failed to detach. He then tried the mechanical release but the load still failed to detach. At the request of the pilot, the crewman on board also tried to mechanically release the drip-torch, but still the load would not release. For four minutes, the pilot flew the helicopter back to the airstrip under control, hydraulics off, with the hope of releasing the sling load and performing a run-on landing. He flew one circuit without being able to release the sling load. Then at about 40 kts and 200 ft AGL, the helicopter banked sharply left, pitched nose down, yawed left and entered a left spiral from which the pilot could not recover before ground contact. A crewman watching from the ground said that the helicopter banked smartly to the left and nosed down almost vertical to the ground with the drip torch swinging wildly underneath. Finally the helicopter landed on top of the drip torch. The main rotor and the tail rotor blades impacted the ground but the helicopter did not roll over.

After the accident it was discovered that the main rotors had struck the tail boom and the tail rotor drive shaft was severed. It has not been determined whether the drive shaft was severed in flight during an unusual manoeuvre or when the helicopter landed on top of the drip torch.

The load-ring attaching the drip torch cable to the cargo hook was oval in shape. The client provided the load-ring as part of the drip torch equipment. The ring had been manufactured to suit a slightly different type of cargo hook which may also be fitted to an AS350. Prior to being used operationally, inflight trials had been conducted with the load-ring to ensure it was not prone to dynamic roll out from the hook. The ring was in good condition and had been in service successfully for a considerable time. After the accident it was discovered that it was possible for the load ring to lodge itself partially around the cargo hook housing under negative "G" conditions. Once lodged around the housing, the rim of the only weld on the ring could snag on the housing. In this condition, neither the electrical nor the mechanical release system could detach the snagged load-ring.

The cable between the load-ring and the drip torch was not long enough to enable the pilot to land beside the drip torch with its cable still attached to the cargo hook. The existing cable length had proven to be successful during normal operations; its length minimised the potential pendulum effect of the load. If the helicopter pilot had been able to hover safely, hydraulics on, and rest the load on the ground, a crewman could have stood under the helicopter, de-snagged the load ring from the housing, and manually released the load.

With various combinations of helicopter cargo hooks and sling gear equipment, problems in not being able to release a slung load, or inadvertent load release, have been rare. Dimensions for the primary attachment ring to the cargo hook are contained in the AS350 flight manual supplement for the cargo hook. The load ring in use in this accident was larger than the dimensions described in the supplement.

Subsequent inspection of the hydraulic pump, its drive belt, the hydraulic servos, accumulators, and flight controls, found no significant fault with the mechanical aspects of the hydraulic system. No hydraulic fluid leaks were found. No fault was found with the hydraulic solenoid and switches. However several wires were found to be broken, mostly as a result of the damage sustained during the landing. The wire which controlled the hydraulic warning horn was found to be corroded and broken; this broken wire de-activated the warning horn. A wire to the hydraulic on/off solenoid was found to be broken but it could not be determined whether or not this wire was broken before the accident.

The company chief pilot had previously checked out the pilot and found him to be competent coping with hydraulic emergencies; this included successful hovering of the AS350 with hydraulics off. Weather was not a contributing factor in the accident. The helicopter was within its centre of gravity and weight limits.

ANALYSIS

The load ring was larger than allowed by the flight manual supplement. The way that the load-ring caught on the cargo hook housing was most unusual. Momentary negative "G" must have occurred in flight to have lifted the load ring high enough to snag.

Despite a thorough examination of relevant components no definite cause of the hydraulic failure has been ascertained. The problems encountered in flight by the pilot might have resulted from a wiring problem causing an uncommanded intermittent on/off situation with the hydraulics. The pilot may have experienced heavy, non servo assisted controls suddenly followed by servo assisted light control forces. This could partially account for the unusual inflight attitudes experienced by the pilot. The drip torch swinging wildly underneath the helicopter probably exacerbated the pilot's ability to control the helicopter.

SAFETY ACTION

The operator advised that load rings have since been replaced to prevent snagging. The operator has adopted a system of colour-coding load rings and cargo hooks to ensure that wrong size rings are not used on the variety of cargo hooks fitted to different helicopters owned by the company.

The provider of the drip torch has removed the oval load-rings from service and is working closely with the helicopter operator to ensure that sling equipment is compatible with the cargo hook fitted to helicopters used in controlled burning.

The student was approaching first solo standard, having completed some four hours of incident free circuits prior to a dual session of take-offs and landings. During the first take-off from runway 11C, just prior to rotation speed, the student applied full back stick and 'froze' on the controls. The instructor was unable to regain control before the Tomahawk lifted off and stalled at a height of about 30 ft. The aircraft struck the runway under full power, incurring substantial damage. Both the student and instructor were uninjured

The pilot was carrying out spraying operations and had already spread two hopper loads of spray medium onto a cotton crop. Weather conditions were fine with clear skies and light winds from the north-north-east. The hopper was again filled, and two swathe runs were completed. The pilot reported that on the third swathe run, he left the pull-up manoeuvre to clear trees too late, and the aircraft's propeller collided with branches.

The aircraft initially gained about 100 ft following the collision, however, it then commenced to lose height. The pilot quickly realised that the impact had caused damage resulting in a loss of power and/or thrust. In an attempt to improve the aircraft's climb performance, he selected the dump valve to the fully open position and jettisoned the remaining hopper contents. This action failed to arrest the sink rate of the aircraft and it subsequently stalled into trees and collided with the ground. Whilst the pilot escaped with minor bruising, the aircraft was consumed by fire.