The pilot selected the landing gear down during a normal approach to Kununurra airport. Gear extension appeared to stop about midway through the sequence and the gear-down lights did not illuminate. The pilot also reported an acrid burning smell. As the landing gear circuit breakers appeared normal, he attempted to recycle the landing gear. This had no apparent affect. The pilot checked the light bulbs and recycled again before attempting to extend the gear using the manual system. The manual extension handle was jammed, and the gear position remained unchanged.

Following a flypast the pilot was advised that the gear appeared to be down. He decided to continue with a landing, after briefing the passengers on the situation. A landing was made on the grass to one side of the sealed strip. This area was chosen in case the gear was not locked down. As the main wheels touched the ground the pilot felt them collapse. He shut the engines down as the aircraft settled on to its lower fuselage and slid to a stop.

An on-scene inspection determined that the landing gear extension cycle had stopped after 60% travel. Landing loads had torn both main landing gear struts from the mounts in their wheel wells. The nose gear, although not locked down, was held in position by the aircraft's weight and its tail-down attitude. The normal and manual systems were jammed by a failure in the right landing gear actuator. Once the actuator was released the rest of the system worked normally. The gear-motor clutch is designed to slip if the load gets too great. This caused the acrid smell reported by the pilot.

Inspection of the right actuator determined that the crests of the teeth on the extension/retraction screw drive gear had been making contact with the pinion gear body at the base of its teeth (the gears are set at 90 degrees). The additional loads resulting from this contact eventually caused one or more of the teeth to fail, jamming the gears and preventing full landing gear extension.

Damage to the actuator and the right landing gear system prevented an assessment of landing gear rigging. The failure sequence supports the theory that the right gear over-centre lock may not have been operating correctly. This would have placed additional loads on the landing gear actuator during ground operations prior to the accident flight. The loads probably forced one gear against the other leading to contact between the crest of the teeth on one gear and the body of the other.

Any incorrect operation was not evident to the pilot as it was reported that the landing gear appeared to have been operating normally up until the accident.

The pilot reported that he was carrying out touch-and-go landings when the accident occurred. Circuit traffic was heavy with a number of slower Skyfox aircraft. A film shoot was being conducted with three additional aircraft on the duty runway. The pilot said he decided to leave the circuit area. He came back about 10 minutes later to find two Skyfox aircraft still in the circuit also doing touch-and-go landings. He then did three more circuits before another Skyfox gave a taxi call indicating he would be joining the circuits. At that point he decided to make a full stop landing. The pilot said he was doing a wide circuit to avoid the Skyfox aircraft and was higher than normal on base leg. The distraction caused by the traffic, caused him to forget to lower the gear and the aircraft was landed wheels up.

The Airbus A300 aircraft was intercepting the runway 16R localiser for an ILS approach. During the intercept and while the A300 was on final approach in cloud, ATC requested its pilot to slow his aircraft. On the final request, the pilot was informed that his aircraft had a closure rate of 60 kts on a preceding F50 aircraft. When the A300 broke out of cloud at 1,300 ft, its pilot saw that the F50 aircraft was only about two miles ahead. He suggested to ATC that he sidestep his aircraft to approach for runway 16L but the aerodrome controller directed a go-around.

The crew was issued with a runway 27 Dosel 2 standard instrument departure (SID) clearance which was acknowledged correctly. This clearance required that the aircraft maintain a track of 263 degrees after take-off and at 5 NM turn right onto 330 degrees.

After becoming airborne the aircraft initially tracked 263 degrees before turning right at 2 NM. An instruction was then issued by air traffic control to turn right onto 330 degrees and to cancel the SID. There was no loss of separation.

The investigation revealed that the crew inadvertently entered the Dosel 1 SID into the flight management computer and then followed that procedure.  The Dosel 1 SID had the same initial track as the Dosel 2 SID but at 2 NM required a right turn onto 010 degrees.

Significant Factors

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

1. The Dosel 1 and Dosel 2 SIDs had similar sounding names.
2. The crew selected the wrong SID.

Safety Action

There have been a number of occurrences where pilots have mistakenly flown the incorrect SID, with the same name but different numbers. The Bureau of Air Safety Investigation issued interim recommendation, IR950203, to Airservices Australia on 21 September 1995 which stated in part "It is also recommended that the number and naming of departure procedures should be reviewed to ensure that any likelihood of flight crew selecting the wrong procedure is reduced."

The Civil Aviation Safety Authority has advised that the problems associated with the 'Dosel' SID have been recognised and addressed.

Effective from 7 December 1995, the two 'Dosel' SIDs have been combined and renamed into one procedure.

On base leg for runway 26 at Portland the left engine failed without any prior warning. The crew secured the engine, and a successful single engine landing was accomplished.

The engine was removed and transported to the operator's maintenance facility for investigation. During disassembly of the accessory gear drive it was found that the first idler bearing had collapsed. The bearing supported the accessory gear assembly, part number 3103601-6.

When the bearing collapsed the gear moved about the shaft axis and disengaged from the fuel pump spur gear, part number 3102268-2. With the spur gear disengaged, the fuel pump was not able to supply fuel to the engine which shut down without warning, as reported by the crew.

The failed bearing was returned to the manufacturer for investigation, however the factors surrounding the failure have not been advised.

The manufacturer did advise that they have initiated a program to improve the reliability of the first idler bearing by:

- changing from a ball to a roller type bearing,

- changing the idler housing material, and

- improving the retention of the housing thereby improving support and changing the natural frequency.

The program is now at the implementation stage. The operator has determined to retrofit the improved first idler assembly in accordance with the manufacturer's recommendations.

Circumstances

The aircraft was on an approach to land and passing through 120 ft at 70 kts when the engine suddenly stopped. The pilot immediately entered an autorotational descent however, he misjudged the landing flare, and the aircraft landed heavily.

The engine started and ran normally, when it was checked following the accident. Fifteen litres of fuel was recovered from the fuel tank. The aircraft was being operated on unleaded automotive petrol at the time of the accident. A flight manual supplement had been issued which permitted the aircraft to be operated on super grade automotive petrol (commonly referred to in the aviation industry as Mogas) as an alternative to aviation fuel.

The pilot reported that he had been operating at low level in 35-38 degree temperatures for two hours prior to the stoppage. It is suspected that the temperature of the fuel remaining in the tank, which is located next to the engine and exposed to the sunlight, had increased to the point where fuel vaporisation occurred causing fuel starvation and engine stoppage.

Additional safety information

Although not a factor in this accident the reported use of unleaded petrol where only super grade petrol had been approved as an alternative to aviation fuel indicated a possible systemic safety deficiency. It became apparent following discussion with the industry that there is a lack of understanding of the difference between unleaded and super grade petrol and that unleaded petrol could be in widespread use in aircraft.

Super grade petrol is more expensive than unleaded petrol and is becoming the alternative rather than the normal fuel for motor vehicles. There have also been changes in the methods used to supply fuel to pastoral properties which increases the cost of maintaining a secondary stock of super grade fuel. Consequently, many private operators no longer keep a stock of super grade fuel for use in their own or visiting aircraft. These factors have probably led to the use of unleaded petrol as an alternative to aviation fuel. The use of the generic term Mogas to describe automotive fuel may further complicate the issue as it does not differentiate between unleaded or super grade petrol. Although the flight manual supplement indicates that only super grade petrol may be used as an alternative to aviation fuel there is no warning that use of unleaded petrol is not approved.

Both aviation fuel and super grade petrol contain lead which facilitates upper cylinder lubrication including lubrication of the valve guides. Unleaded petrol uses a different process and unless the engine has been designed to operate on unleaded petrol the lubrication that is available may be insufficient to prevent damage to the valves.

The student pilot had completed one previous solo circuit to a full stop. He then backtracked and was taking off for another circuit. He reported that the engine appeared to lose power soon after the aircraft became airborne. He then elected to land the aircraft on the remaining runway. The pilot forgot to lower the flaps, but the aircraft was turned into wind, touching down off the side of the runway. The aircraft was unable to be stopped within the distance remaining and ran through the boundary fence.

The pilot was able to exit the aircraft safely.

The aircraft sustained substantial damage to the nose landing gear, right wing and the tail plane.

Later examination and ground run of the engine was unable to duplicate the power loss described by the pilot.

The instructor reported that the inexperienced student had been authorised to conduct a period of solo circuits. The first two circuits resulted in safe touch and go landings. On the third approach the aircraft was observed to be high and fast. There was almost no landing flare, and the aircraft landed heavily on the nosewheel which collapsed, allowing the propeller to strike the ground.

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.

The pilot was tasked with spreading urea on rice crops.  With about 550 litres of fuel on board he accepted 1150 kg of urea for the first hopper load of the day.  The weather conditions included light and variable wind, less than five knots.  The outside temperature was about 14 degrees Celsius.  He took off to the north from a 700 metre, level, dry, dirt airstrip.  It was his first take-off from this airstrip in this type of turbine powered aircraft.  Prior to the take-off, he was aware that his employer had taken off from the same airstrip with an equivalent load in the same type of aircraft in similar weather conditions in the past.

Well into the take-off roll the pilot assessed that the far bank of an irrigation channel, just beyond the end of the strip, might be a danger so he activated the dump lever.  Very little of the load managed to exit the hopper because solids, like urea, dump very slowly in contrast to liquids.  Soon after the aircraft became airborne the left main landing wheel clipped the one metre high bank.  Beyond the channel was about 600 metres of obstruction free flat paddock.

Suspecting that the landing gear may have suffered damage, the pilot overflew the loader who advised that the left landing gear leg was trailing.  The pilot then elected to fly back to Jerilderie where another slow overfly confirmed the damaged landing gear.  On final he shut down the engine hoping to save it from unnecessary damage.  The aircraft undershot the runway and came to rest in an oat crop about 100 metres short of the threshold.

Had the pilot loaded the aircraft only to 3042 kg, in accordance with the approved flight manual recommended agricultural gross weight for take-off, the hopper would have contained about 150 kg of urea while flying with 550 litres of fuel on board.  This being a highly uneconomical hopper load, the pilot elected to carry 1150 kg because in accordance with the flight manual, operation of the aircraft at a gross weight in excess of the recommended agricultural gross weight for take-off is allowed at the discretion and on the responsibility of the pilot. Subsequent to the accident the pilot's employer again successfully took off from the 700-metre airstrip with 550 litres of fuel on board and 1150 kg of urea in the hopper in similar weather conditions.

The pilot advised that he commenced the take-off from the threshold.  His technique was to progressively increase power to 55 pounds of torque during the initial take-off roll.  Fifty five pounds of torque applies to a reduced take-off power technique favoured by operators in an attempt to save engine wear and tear.  Maximum take-off power is 58.4 pounds of torque which the pilot applied when concerned about the approaching channel bank.

No fault with the aircraft has been found which may have contributed to the accident.  The pilot advised that this aircraft performed as well as others of the same type which he had flown.

The consensus of opinion from other experienced agricultural pilots is that the aircraft was capable of taking off with the 1150 kg.  They believe it possible that the pilot may have applied the reduced take-off power a little too slowly, thereby accelerating too slowly during the initial portion of the take-off roll.  Also, when concerned about the embankment, he may have pulled back on the control column too early and may have inadvertently placed the aircraft nose high in a condition of higher than desirable drag at an airspeed too slow for rotation.  It is also possible that the aircraft encountered a light tailwind during the take-off roll.

Significant Factors

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

1.   The take-off technique applied by the pilot was not optimum for the combined factors of aircraft gross weight, weather conditions, and airstrip length with an obstacle at the end of the strip.