Forced/precautionary landing

It was reported that the pilot and passenger were conducting a stock survey at 200 ft above ground level when there was a loud noise and severe vibration from the area of the engine. The pilot immediately entered an autorotation descent and turned the helicopter into wind. A check indicated that no power was available from the engine. The terrain was rocky and covered in trees, so the pilot attempted to cushion the landing as much as possible. On touchdown one skid collided with a large rock causing the helicopter to roll over onto its side. It caught fire immediately and the passenger, who was the first to exit the wreck, assisted the pilot to escape. The helicopter, including the emergency locator beacon, was destroyed by fire.

The operator maintained its own search and rescue watch on its aircraft, and a search was commenced as soon as the aircraft was reported as overdue. The pilot and passenger were found the following day by search aircraft attracted by a signal fire lit by them.

Post accident inspection indicated that the engine problem was caused by the failure of a big-end bolt in the conrod of the no.1 cylinder which allowed the conrod to come loose and punch a hole in the crankcase. The engine had been overhauled by the manufacturer 300 hours (operating time in service) prior to the accident. The fire was probably started by oil that had leaked from the hole in the crankcase onto the exhaust system.

The pilot reported that soon after take-off at a height of 150 to 200ft the engine spluttered and then stopped. The aircraft was landed on the remaining runway. The left main landing gear was torn off and the right wing was damaged during the landing. The cause of the engine stoppage was apparently caused by fuel flow interruption, however extensive post flight examination could find no fault with the engine or fuel system.

The pilot reported that shortly after departure from Jandakot the engine lost power and then stopped altogether. He attempted to carry out a forced landing in a grassed paddock, but the aircraft was damaged in the process.

An inspection of the aircraft's fuel system disclosed that the fuel filter, lines and carburettor were contaminated by a significant amount of rust-coloured water. However, no water was evident in fuel obtained from the drain points on either the main or auxiliary fuel tanks. The pilot reported that he had drained a significant amount of water from the main fuel tank prior to departure.

The main fuel tank was constructed of corrugated metal. The longitudinal corrugations were not connected to each other, and most were not connected to the single drain-sump. Water had collected in the corrugations, and some was still evident after the accident. The drain-sump was not located on the lowest part of the tank and undrainable water could accumulate in the tank, aft of the sump, with the aircraft in the ground attitude.

An experienced Tiger Moth engineer reported that inadequate fuel tank drain systems was a known problem, and an Airworthiness Directive (AD) had been issued which required that fuel-drain points, fitted to some aircraft types (including the Tiger Moth), be designed so that water could not be conveyed to the engine in any normal attitude for the aircraft. These drain points were usually fitted to the lowest point on the tank. That is, along the rear edge. The AD was withdrawn when a number of requirements, covered by several ADs, were incorporated into Civil Aviation Orders Part 100. Transfer of the fuel-drain requirements to the CAOs was incomplete because, whilst similar fuel-drain requirements exist for aircraft constructed in accordance with the amateur-built category of aircraft there is no longer any requirement to retrofit similar systems to existing aircraft, such as the Tiger Moth.

Two Tiger Moth fuel tank modifications, designed to meet the requirements of the AD before it was withdrawn, were available to overcome the lack of drainage found in this tank. Both incorporated drain points along the rear edge. Neither of these modifications had been incorporated in VH-HPH's fuel tank. It is probable that in-flight aircraft movement allowed some of the water that had collected in the corrugations, and at the rear of the tank, to make its way into the fuel system and cause the engine stoppage.

An inspection of the ground marks at the accident site indicated that the aircraft touched down whilst it was still in a sideslip to the left. Touchdown was followed by a partial ground-loop as the aircraft tipped up onto its nose and left upper wing. The aircraft was approaching a fence on touchdown. It is possible that the pilot used the sideslip manoeuvre in an attempt to lose height quickly and touchdown earlier but did not stop the sideslip in time for the landing.

An inspection of the lower left wing during the post-accident investigation disclosed that one spar had fractured some time prior to the accident. It was also evident that reconstruction of the wing, also carried out some time prior to the accident, was not in accordance with the manufacturer's specifications.

The pilot had recently passed his General Flying Progress Test (GFPT), and on the day of the accident had completed a dual check on VH-PXB. He had subsequently made three local passenger carrying flights. During the fourth flight the pilot stated that, as the aircraft approached Archerfield circuit area, and shortly after he had changed the fuel selector from the right tank to the left tank, the engine lost power. The pilot decided to conduct an emergency landing on a road. During the landing roll, the left wing struck a signpost.

Both fuel tanks were drained after the accident and the left fuel tank yielded 18.5 litres and the right fuel tank 9 litres. The published unusable quantity for each tank is 1 litre. This implies that adequate fuel was available for continued engine operation. However, the pilot reported that the flying conditions were turbulent at about the time he changed tanks, and it is possible that air may have entered the fuel system while the right tank was selected. The engine was ground run after the aircraft had been recovered and functioned normally.

The reason for the loss of engine power was not determined.

The aircraft was taking off from a bush strip. The pilot said that the take-off run took about 600 m of the 800 m available. However, the aircraft failed to climb away so the pilot rejected the take-off at a late stage. The aircraft was landed beyond the end of the strip, amongst saplings and trees.

The pilot attributed the lack of performance to a partial power loss, although he had not heard a change in engine note, nor had he noticed any abnormal engine indications. During subsequent testing of the engine, full power was able to be achieved. Two other pilots later stated that the strip surface was affected by soft sand, and only had a usable length of about 500 m. The aircraft performance charts indicated that a take-off roll of approximately 600 m was required under the prevailing conditions.

It is considered likely that the pilot attempted to fly the aircraft off the ground prematurely. As a result, the aircraft climb performance was adversely affected by induced drag.

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 pilot, who still had an area restriction annotated on his pilot's licence, planned to ferry the aircraft to Kalgoorlie where he was going to pick up another pilot for the remainder of the flight to Melbourne. Prior to departure from Jandakot he checked the fuel tanks were full. On taxy out, with the left tank selected, the pilot observed fuel venting from the right-wing tank. As a take-off clearance had already been given, he elected to continue with the flight.

Whilst cruising at 2,500 ft the engine lost power. The pilot attempted to correct the situation by changing magneto settings, but this failed to work. He then concentrated on completing a safe forced landing. As the aircraft touched down in a farm paddock two sheep ran towards the aircraft and collided with the landing gear. The pilot lost directional control, and the landing gear collapsed.

The aircraft operations manual indicates that the right-wing fuel tank must be selected for take-off and until the contents reduce to one quarter full. If this is not done it is possible for the excess fuel, which is normally returned to the right tank, to be vented overboard; thus, reducing the range. The pilot had the left tank selected for take-off and he observed fuel venting from the right wing. it is probable that the aircraft ran out of fuel because the pilot did not operate in accordance with the operations manual instructions. The pilot had limited experience on the aircraft type and was not aware of the fuel management requirements.

During a ferry flight the aircraft's engine began to run rough, then stopped about 20 seconds later.

The pilot made a successful forced landing into scrub-covered terrain in an inaccessible area of a national park, with the aircraft suffering only minor damage.

An examination of the engine revealed the cam ring had fractured.

During cruise the aircraft suffered an engine failure with oil covering the windscreen. The pilot carried out a successful landing onto a beach 40 km west of Milingimbi.

Later as the tide filled the aircraft, which was undamaged, became immersed in salt water.

An inspection of the engine indicated that the number six cylinder gudgeon pin had failed allowing the connecting rod to separate from the piston. As the engine continued to rotate the loose connecting rod struck and holed the crankcase.