Loss of control

The pilot said that he loaded the aircraft at the north-western end of the 1,000 m strip oriented south-east/north-west. The strip was partially sheltered from the wind by bordering trees. There was a strong, gusting northerly wind blowing. The pilot assessed that there would be a slight tailwind component for a take-off on runway 12 but believed it was acceptable.

During the initial climb after take-off, the aircraft was subjected to a strong gust of wind which caused it to yaw to the left. It was then struck by another gust. The left wing dropped, and the pilot was unable to regain control before the wing struck the ground. The aircraft cartwheeled onto the right wing and came to rest upright.

An assessment of the weather conditions existing at the time of the accident was made by the Bureau of Meteorology. The wind was from the north at 12 kts with gusts to 19 kts. The temperature was 30 degrees C which meant that the density altitude for the take-off was about 1,800 ft.

The presence of trees which sheltered the strip indicated that turbulence and/or windshear was likely above the tree line. This could have caused the aircraft to lose performance as it climbed above the level of the trees to the extent that it stalled. The height the aircraft was at was probably insufficient to allow recovery before contact with the ground.

It was reported that the aircraft was being used to spread powered fertiliser. There had been light rain prior to the accident flight and the wing surfaces were wet. During loading the wind momentarily lifted the sock, used to fill the hopper, clear of the aircraft and some powder was blown onto the upper surface of the right wing. The rain was not heavy enough to wash the powder off. The aircraft's weight was reported to be at its maximum for take-off. The average wind was a westerly at 8 kts with significant shifts reported as occasional squalls passed through.

The pilot commenced a take-off, with 10 degrees of flap set, towards the west and into wind. The strip slopped down and then up. As the aircraft accelerated the pilot flew the tail off the ground. Shortly afterwards the left wing also lifted, pivoting the aircraft over the right wheel. The pilot introduced left aileron to keep the wings level until he reached take-off speed. The aileron control reached the left stop at the same time as the aircraft became airborne. It continued to roll to the right and began to yaw right. The pilot introduced rudder and then brake in an attempt to stop the roll and yaw. The rudder made little difference, and the brakes were completely ineffective as the wheels were off the ground.

The pilot closed the throttle and, as the aircraft settled back onto the ground in a left-wing-high attitude, it collided with a fence. The aircraft ripped 76 m of fence from the ground before it cartwheeled and overturned.

The aircraft's flight manual contains a caution which indicates that aileron effectiveness is reduced when flaps are used for take-off. The pilot reported that he used flaps as the aircraft was at maximum weight and the strip length was restricted. The aerofoil section of the wings on the AT502 is designed for maximum efficiency. The aircraft manual indicates that any ice must be removed from the wing prior to take-off because of its effect on wing-produced lift. It is probable that the powder-contamination on the right-wing surface adversely affected its aerodynamic characteristics resulting in the roll experienced by the pilot. The pilot's ability to control the roll with aileron was reduced by his use of flap for take-off. The result was a roll and yaw which the pilot was unable to correct before the aircraft collided with the fence. It is possible that a squall-induced wind shift also contributed to the loss of control.

The pilot advised that the weather was fine, water conditions calm, and the river running at 6 - 8kt. The aircraft was launched from the bank and taxied downstream for departure.

The pilot reported that the aircraft's acceleration, and climb onto the step appeared to be normal, but before the aircraft became established on the step it began to porpoise. He attempted to overcome the oscillations by applying forward elevator control pressure which only aggravated the situation. He then tried to find the optimum position on the step by raising and lowering the nose with the elevator control, resulting in him chasing the oscillations.

The aircraft eventually "wheelbarrowed" on its bow, preventing it from accelerating to its safe take-off speed. The pilot persisted with the take off, and while attempting to turn a bend in the river water pressure on the bow damaged the left nose gear door, creating an increase in water drag. This caused the aircraft to water loop to the left, damaging the left sponson and rear fuselage.

The pilot rejected the take off and taxied the aircraft to the shore.

The pilot reported that he commenced the take-off roll on the easterly runway with a quartering crosswind of 5 to 10 kts from the north-east. During the early part of the roll, the aircraft veered to the right before the tail wheel was off the ground. The pilot managed to correct the swing and continued with the take-off. The aircraft swung further right again when the tail wheel was raised. The pilot apparently overcorrected and headed towards the left side of the strip. During this change in direction the left wing lifted, and the right wing struck the ground. The right main gear collapsed during the subsequent slide.

Both occupants evacuated the aircraft from the left side.

The pilot later said that he thought the crosswind swung to a quartering tailwind during the take-off roll.

The helicopter was being ground run after two of the three rotor blades had been refitted. The aircraft apparently experienced ground resonance and the main rotor struck the ground. The aircraft rolled over and came to rest against a tree. The sole male occupant was admitted to hospital.

Enquiries revealed the person operating the helicopter did not hold a pilots or engineers licence. The helicopter had apparently been purchased on behalf of another person with the intention of shipping it out of the country.

Since the person who was running the helicopter was released from hospital he has been pursued by the CASA for questioning but has disappeared.

Ground running of helicopters must be performed by a licenced helicopter pilot, and if the helicopter is tied down, may be performed by a licenced engineer.

The pilot requested taxi clearance for departure from runway 11, but as this runway was not available due to maintenance being carried out on the arrestor cable, he was instructed by air traffic control to taxi for runway 18 and advised of a 9-knot crosswind component.

During take-off the pilot lost directional control, and the aircraft ground looped to the left, collapsing the right landing gear leg. The aircraft came to a stop at the intersection of runways 36/18 and 29/11.

The flight was planned from Maroochydore to Griffith with a refuelling stop at Nyngan. On arrival at Nyngan the refuelling agent could not be contacted so the pilot diverted to Dubbo to refuel. Prior to departure from Dubbo, the pilot estimated that he would arrive at Griffith at last light. He was not night VFR rated. The aircraft ultimately arrived at Griffith at about last light. Conditions were dark and runway lights were required for landing. The pilot made several circuits of the aerodrome while he attempted to turn on the pilot activated aerodrome lighting (PAL) system.

The pilot reported that he made two attempts to turn on the PAL but without success. He then made an attempt to land without the aid of runway lighting. After touchdown he realised he had landed well beyond the threshold and would not be able to stop by the end of the runway. He applied power and attempted to go around but the aircraft stalled and hit the ground in a left wing low attitude after which it cartwheeled to a stop. Although the aircraft was substantially damaged and there was still a significant amount of fuel in the tanks, there was no post impact fire.

During a practice touch and go landing, the aircraft ballooned during the flare. The pilot applied some power to prevent a subsequent heavy touchdown/bounce and persisted with the landing attempt. She said that she was then distracted by the proximity of a runway strip marker on the left side of the aircraft. The pilot lost directional control of the aircraft, and a ground loop ensued.

FACTUAL INFORMATION

Sequence of events

The pilot was conducting a visual flight rules scenic flight. These flights were done on a regular basis by the operator and the pilot had flown the DH-82 type on many of these. Commonly, the route flown was from Jandakot to the Fremantle area, north to about Mullaloo Point, then Observation City, Perth City and back to Jandakot. The pilot occupied the rear cockpit seat and the passenger the front cockpit seat. Shortly after passing the Fremantle Golf Course, at an altitude of 1,000 ft, the engine misfired and commenced to vibrate badly. The pilot transmitted a Mayday call to the Perth Radar Advisory Service (RAS). At this stage, the indicated altitude was 900 feet.

The pilot told the RAS controller that he had a partial power failure and said he was going to put the aircraft down in an area near Leeuwin Barracks, on the bank of the Swan River. The pilot was aware of the general details and location of the selected area. He tracked for a left base, while losing altitude, intending to land towards the west. The aircraft was halfway through the turn onto final, at a height of about 300 feet and with everything proceeding as planned, when the pilot suddenly saw a set of high-voltage power lines across his track. A large transmission-line tower for these lines was also now directly in front of him.

The pilot decided to complete a 270-300 degree right turn over the water to avoid the tower and pass under the wires and still land in the selected area. It was a tight, gliding turn and when passing through a heading of about east, at a height of about 150 feet, the aircraft stalled and started to spiral right. The pilot applied left rudder but was unable to prevent the aircraft from diving into the river at a steep angle. After impact, the aircraft floated vertically with the tail out of the water and both cockpits under water. The pilot found himself out of his cockpit swimming on the surface, but the passenger was still in the front cockpit.

Shortly afterwards, assistance arrived, and the passenger was released from his seat by a water-police diver. Both pilot and passenger were then conveyed to hospital.

Wreckage examination

Inspection of the engine showed that the number one connecting rod had failed. Approximately half the rod, including the big end attachment to the crankshaft, was missing. Inspection of the remaining fracture surfaces showed that the fracture was caused by fatigue crack growth. The crack had propagated along the centre of the connecting rod 'I' beam from the region of the connecting rod/crankshaft bearing housing. The reason for the initiation of the fatigue cracking could not be determined, due to the absence of pieces crucial to the investigation. The other three connecting rods were inspected but no cracks were found in any of these. The investigation was unable to trace the history of the failed connecting rod.

Each shoulder harness was attached to a transverse cable which in turn was attached, via a bracket at each end, to the aircraft structure. One of the attachment brackets for the rear seat shoulder harness had failed, with the bolt pulling out of (tearing) the bracket. The rear seat lap strap also failed. This probably happened because the seat moved during the impact sequence and the strap was cut by the metal edge of the seat. Even with the failures the rear seat harness absorbed considerable impact energy before failing although, the pilot did receive some facial injuries. One of the front seat shoulder harness attachment brackets, which was attached by three bolts, sustained a partial failure when two of the bolt heads separated. The harness however, remained intact.

The aircraft was equipped with leading edge slats on the upper wing. These devices have the facility to be locked closed. When unlocked, they open up when the aircraft approaches stalling speed. The slats have the effect of slightly reducing the stall speed and also provide a warning to the pilot that the aircraft is close to the stall. The flight manual for the aircraft included a statement that slat extension provides acceptable visual warning of approaching stall.

There were two placards in the cockpit that stated that the slats were unserviceable and not to be operated. Also, the operator's handling notes for the type included instructions that the slats were not to be used for take-off or landing. The slats were locked closed.

Weather data

The surface wind at Jandakot on departure was from the south-west at about 12 knots.

Forced Landing Options

The power loss occurred over a built-up area. There were very few forced landing areas available within gliding range. The Fremantle Golf Course, which was behind the aircraft when the engine malfunction occurred, was probably one option. Another was the area, near Leeuwin Barracks selected by the pilot. This latter area was aligned approximately east-west and had a set of high-tension power lines across the eastern end, aligned approximately north-south. The pilot was not previously aware of the power lines. The power lines and associated tower were not particularly obvious when looking down on them from above, and the restricted visibility from the rear cockpit of the DH-82A was another inhibiting factor.

ANALYSIS

The major reason for the accident was the engine malfunction which forced the pilot to attempt an emergency landing in a built-up area. The location of the engine malfunction meant that the pilot's options were limited. His choices were the golf course, which by then was behind the aircraft and out of sight, or the Leeuwin Barracks area.

To use the golf course the pilot had to execute a 180-degree turn. To reach the Leeuwin Barracks area the pilot only had to make a right turn of about 90 degrees. As a result, he opted for the site near the Leeuwin Barracks.

The pilot was satisfied all was going well until late in the approach when he suddenly saw the power lines and tower. This late sighting caused him to rapidly change his plans and attempt to avoid them. The aircraft was in a poor position, at a height of about 300 feet, for the pilot to attempt a large turn. However, this appeared his only option. During this attempted turn through 270-300 degrees, the pilot allowed the airspeed to reduce to stalling speed and he lost control of the aircraft. There was insufficient altitude to recover control before impact.

The fact that the slats were unserviceable and locked closed possibly deprived the pilot of an important stall warning indication. Had they been available and unlocked, they may have assisted in preventing the loss of control.

SIGNIFICANT FACTORS

The following factors were considered relevant to the accident:

1. Fatigue cracking of the engine's number one connecting rod caused it to fail. The factors which led to the fatigue crack could not be determined.
2. The failure of the connecting rod caused significant vibration and loss of power. These led to a forced landing.
3. There was a lack of suitable landing areas.
4. The pilot did not detect a power line and its associated tower until very late in the approach.
5. The pilot's attempt to avoid the power line led to a significant loss of airspeed.
6. The loss of airspeed led to a stall followed by loss of control at a height that was too low to effect recovery before impact.
7. The unserviceable slats may have been a factor in the pilot's failure to recognise the impending stall in time to prevent loss of control.

After landing on runway 34R in light rain, the aircraft vacated to the right, via taxiway 'T', continuing to decelerate, with the flaps still in the landing configuration. As the aircraft turned left onto taxiway 'J', the aircraft ran off the paved surface to the right of the taxiway and became bogged in soft wet ground. The crew reported they felt minor slipping during the turn but were unable to regain directional control by braking action or the application of reverse thrust. The wind was reported as 050/10-15 and there were patches of standing water on the taxiway. A subsequent engineering investigation found no fault with the aircraft or its steering system.

The taxiways were constructed with a slight camber, designed to assist water runoff. Photographic evidence indicated that the aircraft had commenced the left turn whilst on the right side of the centreline. A replay of the recorded surface movement radar indicated that the aircraft entered the turn faster than preceding aircraft, at about the maximum design speed for the taxiway.

It is considered likely that the north-easterly wind, acting upon the vertical surfaces of the aircraft, reduced the steering effectiveness of the nose gear in the slippery wet conditions as the aircraft turned from a northerly to a westerly heading on the right side of the cambered taxiway. Corrective action by the crew could not prevent the aircraft leaving pavement.