Collision with terrain

The glider was being test flown after major maintenance had been completed. During lift off the pilot lost control and the aircraft cartwheeled. The pilot received minor injuries, and the glider was substantially damaged.

Investigation found that the ailerons had been connected in the reverse sense. During the maintenance, reassembly, rigging and preflight the glider had passed through four stages of inspection, all of which failed to detect the incorrect rigging of the ailerons.

It was found that 10 types of glider operated in Australia are fitted with common aileron drive gimbals that can be physically fitted to the incorrect side of the aircraft, thereby reversing the sense of the control.

Immediately after the accident the Gliding Federation of Australia issued an Operations Advice Notice advising details of the accident. The notice made the point that crossed controls had occurred before and that an Airworthiness Advice Notice had been issued in 1980 covering the subject. This notice stated, 'this incident emphasises the dangers of complacency; we have come to expect things to operate correctly and therefore assume that if something is working, it is working correctly'.

The Operations Advice Notice made three recommendations relating to the principles of assuring correct sense and the avoidance of external distraction during preflight inspections.

The Gliding Federation also issued an Airworthiness Directive requiring, on the subject gliders, gimbals for the left wing to be painted bright red and for the gimbals for the right wing to be paint bright green. This action is to be performed at the next annual inspection.

At the conclusion of an 8 hour, 500 km flight the visiting foreign glider pilot was forced to outland 1.5 km short of the airfield. The glider suffered extensive damage consistent with having been landed in a stalled condition with a high rate of descent.

The pilot advised that he was in a lethargic state of mind having mentally relaxed once the airfield was in sight. The operator is looking into visiting pilot dehydration, coupled with fatigue, as a factor in this type of accident.

The purpose of the flight was to assess the student prior to his first solo flight. Preflight fuel contents were 95L, and the pre-take off engine run, which included a carburettor heat check, was reported to have been normal.

The instructor pilot reported that two uneventful circuits were completed. On the third circuit, prior to turning onto the base leg, the student applied full carburettor heat and reduced engine power to 1500 RPM. After turning onto the base leg, the approach appeared too high and engine power was further reduced to 1100/1200 RPM. Turning onto the final leg, the aircraft appeared to be undershooting, and the student was prompted to increase power, but there was no response from the engine. The instructor immediately took control, confirmed that carburettor heat was on, the mixture was rich, and changed the fuel tank selection. However, there was no response from the engine, which continued to rotate at 1100/1200 RPM.

By now, the aircraft was well below the required approach path. The instructor made a brief MAYDAY call and tried to manoeuvre the aircraft to land on a cleared area short of the runway, but the landing gear collided with a 2 m high wire fence. The aircraft cartwheeled sideways before coming to rest. Both occupants were able to escape without injury.

Investigation determined that the engine controls were correctly connected and functioned normally. The carburettor hot air box had been squashed in the accident, and the hot air duct was disconnected. It could not be determined if the duct had detached before, or as a result of, the accident. After removing the hot air box, the engine performed normally during a ground test.

The weather conditions at the time were conducive to severe carburettor icing at descent power. It is likely that carburettor icing occurred during the low power descent and precluded the engine accelerating above idle power on the final approach.

The aircraft operator said that the aircraft struck the ground during a turn when the pilot was involved in a crop spraying operation.

The pilot has declined to forward any information.

The pilot said he had landed at the small grass strip a couple of times before. He flew to the area and made inspection runs over the strip at a height of about 100 feet. He then made a landing approach. The aircraft touched down about one quarter of the way in and bounced.

Because there was insufficient landing distance remaining, the pilot applied engine power and selected two stages of flap for a go-around. Lift off was made at 55 knots but the wheels struck a bank at the end of the strip. This impact severely damaged the undercarriage. The pilot turned the aircraft to the left towards a small clear paddock. However, in doing so the left wing struck a small tree and the aircraft cartwheeled.

Significant Factors

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

1 Unsound decision by the pilot to land the aircraft at a strip of minimal dimensions.

2 Misjudged landing approach.

3 The flight was not authorised by a designated responsible person.

4 The operator's procedures did not require the flight to be so authorised.

The pilot reported that he was spraying thistles on the eastern side of Mt Koang. The weather at the time was clear with a moderate easterly breeze blowing. Spray runs were made in a north south direction, starting at the base of the mount and progressing up the slope parallel to a ridge line at the top.

The pilot commenced the last run from the north, flying along the top of the ridge line. Approximately halfway along the ridge line the aircraft hit a wind gust. The pilot was unable to prevent the aircraft from hitting the ridge. The aircraft hit the ground heavily and was destroyed in a post impact fire. The pilot was wearing fire resistant overalls, gloves and a helmet. He received burns to his face which was the only exposed area of skin when the accident occurred.

As the aircraft was about to land at the property strip at night a car positioned at the end of the strip with its headlights shining along the strip.

During the landing the aircraft struck the car with the left main gear and crashed onto the runway with the gear collapsed. The pilot was aware that the car was parked near the end of the strip.

The pilot was ferrying the aircraft to Killara Station for the owner. He had checked the condition of the strip prior to departure and was advised to land on a road near the homestead as the main strip was unserviceable.

The pilot reported that on arrival he made two low approaches to confirm that the road was suitable and then made a third approach for the landing. There was no windsock visible; however, a windmill indicated that the wind was a crosswind from the right. At about 25 ft on final approach the aircraft started to drift away from the centreline of the road. The pilot was unhappy with the approach and decided to go-around. He opened the throttle; however, before the engine could respond the aircraft descended rapidly and landed heavily on the edge of the road. The aircraft ran off the road into trees, the nosewheel dug in and it overturned.

It was reported that there were no unusual atmospheric conditions present at the time of the accident. It is probable that the sudden descent occurred because the pilot inadvertently allowed the airspeed to reduce to the stall speed during the attempted go-around.

FACTUAL INFORMATION

A short local test flight was planned to verify scientific equipment installed in the aircraft before it embarked on an atmospheric research flight.

The take-off was normal from runway 03, and after climbing through 500 ft the pilot reduced the manifold pressure and RPM settings of both engines from take-off to climb power. Sometime after this he turned the auxiliary fuel pump switches from low to off. At 1,500 ft a vibration, which appeared to have originated in the left wing, was noticed by both the pilot and the data systems operator, who also held a private pilot licence endorsed on the aircraft type. They said that the left tip tank seemed to move through 10 - 15 mm, and the equipment pod, mounted on the underside of the left wing moved in the same plane and frequency. The right alternator warning light then illuminated.

Both pilots decided that it would be more prudent to return than continue the flight. The data systems operator suggested that because of the vibration a slow airspeed should be maintained during the descent. The pilot noticed that the airspeed indication was 115 kts, and believed he carried out the descent without any change to the power settings. He notified the control tower of his intention to return, but without advising the actual reason.

Approaching base leg for runway 03 the pilot reported that he selected 10 - 15 degrees of flap, and that the data systems operator extended the landing gear without consulting him. The data systems operator stated that it was after the aircraft had turned onto final approach, he noticed the landing gear selector lever was between the retract and extend positions and moved it to the extend position. He also attracted the pilot's attention to the airspeed, which had dropped to 82 kts, this being only several knots above the stall speed for the aircraft in its present configuration. The pilot advanced both throttles to reduce the high sink rate which had developed due to the slow forward speed, but neither engine appeared to respond. The throttles, pitch levers and mixture controls were then fully advanced, but still without any apparent response from either engine.

The pilot then realised it would be impossible to land the aircraft on the aerodrome, and a forced landing was inevitable. He thought he noticed the data systems operator selecting the flaps up at about this time, although the data systems operator could not recall doing this. As the data systems operator had more flying experience on the aircraft, and also being a glider pilot familiar without landings, the pilot considered him better qualified to carry out the forced landing, so gave him control. The data systems operator then had just enough time to ensure that the wings were level and initiate a flare, which failed to arrest the high rate of descent.

The aircraft impacted the ground heavily on a golf course adjacent to the runway threshold. Both main gear legs failed and separated, the nose gear leg remaining in situ still extended. The aircraft continued along a fairway for 230 m in a direction of 023 degrees, colliding with an automatic sprinkler system control unit, which buried deep into the left-wing root area. The aircraft then struck two small trees. This turned the aircraft to the right before it came to a stop on a heading of 090 degrees. The pilot and data systems operator sustained minor injuries.

The landing gear was found to be extended, with its selector in the corresponding down position, and the flaps retracted with its selector in the up position.

Ground slash marks, and damage to all propeller blades indicated that the engines were operating at impact. The right propeller had all blades bent back, one blade severely bent, with lesser bending on the other two, indicating that each blade had contacted the ground before the engine stopped. Two of the blades also had forward bending tendencies, but marks on the blades indicated they had been buried in the ground when stationary, and this bending occurred as a result of the aircraft turning at the end of the ground run. All blades on the left propeller were bent back in a gradual curve, the bending again corresponding with each blade contacting the ground before the engine stopped.

Witnesses who observed the aircraft on its final approach reported hearing engine noise. Black smoke was also noticed coming from the right engine, and several backfiring sounds were heard.

After the accident, when the pilot was securing the cockpit and turning off electric power, switches, and fuel, he noticed that an auxiliary fuel pump switch was in the high position. He could not recall this pump being turned on at any time during the flight. An inspection revealed that the right engine exhaust pipes had deposits of soot, but none at the outlet or along the underside of the nacelle. There was no soot in the left engine exhaust pipes.

All fuel filters were found to be clear of contamination, there were no obstructions in the fuel lines from the tanks to engines, and normal quantities of fuel were found at the engines in the fuel control units and distributor valves. Laboratory testing found no problems with the fuel.

No faults were found with the ignition systems which may have caused both engines to fail.

All external pods and probes were correctly attached, and no damage or defects could be found which may have contributed to the reported inflight vibration.

Both engines were inspected and no defects found which could have affected their operation. They were then installed in an engine test stand and ran normally at all power settings, responding correctly to all throttle movements.

The aircraft had been operated in the private category. The flight manual states that pilots required to operate the aircraft must be trained and approved to fly this particular aircraft when configured for atmospheric research with external pods, pylons and probes fitted. The pilot had undergone several hours of familiarisation training 12 months previously but had not flown the aircraft since. The operator did not conduct recency checks or give continuation training for pilots.

ANALYSIS

An inspection of the aircraft and its ancillary pods, pylons and probes failed to find any looseness, faults or any other airframe problems which may have caused the inflight vibration. It is possible that slight turbulence may have produced the effect. Illumination of the right alternator light was not considered as having contributed to the accident.

Both engines were found to be serviceable and capable of delivering full power. The propeller slash marks in the ground and damage suffered by the propeller blades before the engines stopped indicated that they were developing power at impact.

It is possible that the right auxiliary fuel pump was accidentally turned on as the pilot turned the pump switches from low to off during the climb. This would have produced a rich mixture in the right engine with associated rough running and vibration. It would also account for the deposits of soot in the right engine exhaust pipes, and the smoke seen by the witness.

While returning to the aerodrome the pilot stated that he did not adjust the engine power settings for the descent to circuit height. Due to possible task saturation, he probably reduced the power without realising it, otherwise, with its engines operating normally, the aircraft would have accelerated. During this time however, the airspeed deteriorated from 115 kts to 82 kts.

The pilot selected 15 degrees of flap on base leg, and then after turning final was warned of the slow airspeed by the data systems operator, who had extended the landing gear, causing more drag. The aircraft would have been near its stall speed, with a subsequent high rate of descent. This would have been exacerbated if the data systems operator had raised the flaps, which he could not recall doing.

When the pilot opened the throttles, he may have gained the impression that the engines were not developing power as the aircraft would have continued its rapid descent. With all the unusual activity going on it is possible that the pilot failed to register an increase in engine noise. The application of power probably prevented a stall developing, with subsequent loss of control.

There was no evidence found to indicate that both engines had suffered failures simultaneously and were not capable of responding to throttle movement.

SIGNIFICANT FACTORS

1. A possible rich mixture on the right engine may have caused an inflight vibration.
2. The pilot and data systems operator became worried about a vibration, and did not monitor the aircraft's progress adequately.
3. The pilot was not current on the aircraft and allowed the airspeed to deteriorate with the aircraft developing a high rate of descent.

The aircraft was engaged on agricultural operations in hilly country when it encountered a sink conditions.

Although the pilot applied full power and take-off flap, he was unable to prevent the aircraft from descending into trees tops on a ridgeline. The pilot dumped the load, but the aircraft continued to descend and impact the ground.

The pilot had not been aware of any sink indications during previous spray runs.