Forced/precautionary landing

The helicopter was being operated on a wildlife survey flight, and while manoeuvring near a crocodile nest the pilot reported an apparent loss of engine power, with a subsequent decay in main rotor RPM. He attempted to regain rotor RPM by opening the throttle fully, applying right anti-torque pedal, increasing forward speed and reducing collective pitch as much as possible but was unable to arrest the descent. When ground impact became inevitable, he levelled the helicopter and applied up collective to cushion the impact, but the resulting heavy landing caused the landing gear skids to collapse and the main rotor blades to strike the ground. The engine was still running and stopped by the pilot.

A brief inspection of the helicopter was made at the accident site, but with some difficulty due to crocodiles in the area. A more detailed inspection was carried out after it was recovered to Darwin. No evidence was found to suggest that it was other than serviceable prior to impact.

The pilot stated that he had departed from Jabiru for the 58km flight with 32 litres of fuel on board the helicopter and was to refuel at a nearby airstrip for the return flight. Inspection revealed that the amount of fuel remaining in the tank at the time of the accident was 65-70 litres, and the helicopter's all up weight was estimated as being just below the allowable maximum.

The pilot later revised his statement to agree that there would have been about 65 litres of fuel on board at the time of the accident and suggested that he may have over-pitched the rotor system when distracted by outside events as he attempted to find a place to land near the crocodile nest.

The pilot reported that the engine lost power shortly after take-off and he landed the aircraft in a ploughed field. During the latter stages of the approach, he saw smoke coming from the engine compartment. The aircraft subsequently burnt out.

Enroute the pilot encountered unforecast fog and low cloud and decided to carry out a precautionary landing. Rain had fallen on the surrounding countryside, causing the pilot to have doubts over the surface condition of paddocks in the area. Hence, an unopened, new section of the Hume highway was selected. Low runs were made over the area to check the surface condition, which appeared suitable. A section about 1200 metres long was selected.

A normal landing was achieved and as the aircraft slowed down it unexpectedly entered a 30 centimetre deep track across the highway surface. The undetected track had been left in the surface to allow vehicles to cross the constructed area. As a result of entering this area the nose and right main gear legs collapsed.

Significant Factors

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

1. The pilot encountered weather conditions precluding further flight in visual conditions and therefore necessitating a precautionary landing.

2. The area selected for the precautionary landing contained a hazard (a 30 centimetre deep track) which the pilot did not see during a precautionary search from the air prior to landing.

The pilot reported that, approaching destination, he had just reduced power to commence descent from 9000 feet when a rattling noise started. The engine then started to vibrate and run roughly and would only deliver partial power. The aircraft entered cloud at approximately 3500 feet and broke out of the cloud base at about 2600 feet.

By this time there was not enough power to maintain level flight, so the pilot elected to land uphill in a paddock. The pilot reported that he was a little high on approach and after touchdown the aircraft ran 150-200 metres before going through two fences and hitting a tree.

The elevation of the accident site was reported as approximately 1000 feet. The pilot said the cloud cover below the aircraft at the time of the engine malfunction was between seven and eight eighths.

Inspection of the engine after the accident revealed a failed connecting rod big end.

Significant Factors

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

1. Failed connecting rod big end in the engine.

2. When the pilot broke out of the cloud base, he was only 1600 feet above the terrain and therefore limited in his choice of areas suitable for a forced landing.

3. Forced landing site not suitable to permit a successful (damage free) forced landing.

The pilot reported that the engine lost power at a height of about 500 ft, shortly after take-off. As he was unable to return to the runway he carried out a forced landing in an open area. During the landing roll the nosewheel entered a ditch and the aircraft overturned. The pilot was able to exit the aircraft without injury.

No defects were found which were likely to have contributed to the loss of power. The engine ran normally during subsequent ground testing.

The owner/pilot advised that he was practising an aerobatic sequence for a future airshow when the engine suddenly suffered a partial power loss. At the time the aircraft was vertical. The pilot pushed over to level flight at about 1000 ft AGL and 80 kts. Then the engine stopped completely. He performed a forced landing in a nearby paddock. The aircraft touched down at approximately 115 kts. During the landing roll the aircraft flipped twice onto its back before coming to rest upright but nose down.

Subsequently an engineer discovered that the crankshaft thrust bearing had seized. The pilot and the engineer believe that, during aerobatic manoeuvres, the oil pickup pipe had been exposed and sucked air, thereby starving the thrust bearing of oil.

This particular aircraft has a more powerful engine installed than the standard Pitts. The additional horsepower enables very high-performance aerobatics.

The owner/pilot, his engineer, the manufacturer and the CAA are involved in achieving an improved oil supply to the thrust bearing before the engine is returned to service.

Significant Factors

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

1. The crankshaft thrust bearing was inadequately lubricated during aerobatic manoeuvres.

2. The crankshaft thrust bearing seized and stopped the engine.

3. During the landing roll, the aircraft encountered an undulation and overturned.

On arrival at Moorabbin the pilot asked a staff member the fuel state of the aircraft. The staff member said he thought it was full but for the pilot to check. The pilot said he checked the tanks visually during his pre-flight inspection and believed they were full. He could not recall what the fuel quantity gauges were indicating. Engine runup prior to departure was normal. The fuel selector was selected to the BOTH position and was left at that position for the entire flight.

The purpose of the flight was for the pilot to practise intercepts on the Cowes navigation aids. There was a safety pilot in the right seat whose task was to watch for traffic and to "keep an eye" on the pilot. The safety pilot was not familiar with the aircraft type. After completing the Airwork and while preparing to return to Moorabbin, the engine gave a short miss. At this time, the pilot said they were about five miles to the east of Phillip Island airstrip at an altitude of 3500 feet.

Shortly afterwards the engine missed again. This missing then occurred at more frequent intervals. The pilot therefore decided to make a precautionary landing at Phillip Island. At this time, the aircraft was still at 3500 feet and in a high wide base position for the 220 degree strip, which he decided to use. The pilot said he checked the magnetos, turned the electric fuel pump on, checked the mixture was rich and checked the fuel selector was in the BOTH position. He did not move the selector.

Because the aircraft was high, the throttle was selected to the idle position and landing gear and full flap were extended. Some S turns were made on final approach to lose altitude, but the aircraft still arrived over the strip far too high. At the upwind end of the strip the pilot pushed the throttle forward hoping there would be power available for a go around but there was no response from the engine. He then pulled the aircraft up into a left turn, to avoid going into the sea, and crash landed in sand dunes to the east of the airstrip.

The investigation revealed that there was approximately 40 litres of fuel in the left tank but the right tank was probably empty.  The right-wing tank fuel lines had been severed in the accident so fuel could have escaped from these lines after the accident. However, when refuelling records were checked against known fuel usage, 40 litres was about what should have been remaining and that much was drained from the left tank. The tank filler necks on this aircraft are fitted with anti-syphon (flapper) valves which have to be depressed to visually check tank contents. The pilot did not depress those valves during his pre-flight inspection.

After the wreckage was recovered. the entire fuel system was inspected, and no faults were found. The engine was removed and placed in a test rig where it ran faultlessly through its entire power range. In the Emergency Procedures section of the Pilot's Operating Handbook, for the Engine Failure in Flight checklist, item 5 of the checklist says, "Fuel Selector - FULLEST TANK (check other two positions)". In the Air start checklist, item 2 of the checklist says, "Fuel Selector - FULLER TANK". This item is followed by a note which says "To minimise restart time, select the fuller tank. Do not use the BOTH position".

Although the pilot was not attempting an air start, he did leave the selector in the BOTH position. A study of the fuel system suggests that if one tank is empty and the other contains fuel, then it is possible that the engine will be supplied with a "fuel air cocktail" through the fuel selector if the selector is in the BOTH position. Tests done on another Rockwell 114 confirmed that this was probably the cause of the engine malfunction.

Significant Factors

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

1. The pilot was unaware of the fuel state of the aircraft prior to departure from Moorabbin.
2. When the engine started to miss, the pilot did not take appropriate corrective action.
3. The precautionary landing approach was badly misjudged.
4. When the pilot attempted to go around from the misjudged approach, engine power was not available.
5. The pilot then had no option but to land the aircraft on unsuitable terrain.

The aircraft was being used for a pipeline survey, involving a number of landings and take-offs, prior to the accident. As the aircraft approached Red Hill, a survey check point, the pilot noticed that the fuel gauge indicated that the equivalent of 170 l of fuel remained. He elected to proceed to Paraburdoo, 116 NM away, to refuel. The pilot calculated that the trip would take 77 minutes, and he would arrive at Paraburdoo with approximately 40 l of fuel remaining (the minimum operational requirement).

About 20 minutes after leaving Red Hill the pilot noted that the fuel gauge still indicated 170 l. It remained at this reading for a further 10 minutes before beginning to oscillate and fall rapidly. The pilot reassessed the readings and determined that he still had sufficient fuel for the flight.

Approximately 5 km north-west of Paraburdoo, as the aircraft was descending through 3500 ft, the turbine temperature and engine RPM began to fluctuate. The pilot assumed an engine malfunction and entered an autorotational descent rather than risk a more significant problem during a normal approach.

When 500 ft above the ground the pilot observed that the area he had selected for landing was unsuitable. He adjusted his approach to land at a more suitable site however, it was further away. During the extended glide, to the new site, the pilot allowed the rotor RPM to decrease (the low RPM warning sounded during the approach) and in the ensuring heavy landing a main rotor blade struck and damaged the tail boom. The engine continued to run at idle during the approach and was shut down by the pilot after landing.

A post-accident inspection found that the fuel gauge indicated the fuel tank contained the equivalent of 19 l of fuel.

Draining the tank retrieved around 15 l of a fuel/water mixture (confirmed by laboratory testing) from the aircraft. Additional fuel/water was found when the fuel contents sender units were removed for testing. Tests on the fuel contents sender units indicated that it was possible for the gauge to stick between readings of 114 and 190 l.

Calculations indicate that the helicopter left Port Sampson with an endurance of 220 minutes and that it had been operating for about 206 minutes at the time of the engine malfunction. The low fuel pressure lights did not illuminate during the accident sequence indicating that the fuel inlet remained covered at all times. Background information indicates that the turbine engine fitted to the Bell 206 helicopter is tolerant of water held in suspension in the fuel however, ingestion of a fuel/water mixture where the percentage of water has increased as a result of its settling out of the fuel into the bottom of the tank, may cause fluctuations similar to those reported by the pilot.

The most likely reason for the engine malfunction was that the low fuel state raised the percentage of water in the fuel/water mixture to a point where it began to effect engine performance.

Evidence indicates the pilot did not carry out water disclosing check at Port Sampson prior to departure. Had he done so he may have determined that water was present and taken action to correct the situation before it led to an emergency landing.

The low RPM state prevented the pilot from arresting the descent sufficiently to prevent a heavy landing.

The pilot did not complete a flight plan or a fuel log for or during the flight. Consequently, he had to rely solely on the fuel gauge indications which, in this case, may have been incorrect.

The helicopter was conducting a scenic flight at Kings Canyon when the engine began to run rough and lose power. The pilot lowered the collective pitch lever, opened the throttle and turned towards lower terrain. The engine would not deliver sufficient power to sustain level flight, so the pilot commenced an approach to an adjacent helipad. During the landing the tail stinger and tail rotor struck the ground.

An examination of the engine revealed a spark plug malfunction and an intermittently sticking exhaust valve in the number 4 cylinder, and the pushrod ball end in the number 1 cylinder was also found to be loose, preventing the exhaust valve from fully opening.

The power loss from these engine faults, combined with the high-density altitude and weight of the helicopter at the time of the occurrence left the pilot with little option than to make a low powered, semi-autorotational landing as soon as possible.

The pilot reported that the aircraft was on descent when the engine lost power. He attempted to maintain altitude but was unable to do so.

The pilot sighted what appeared to be a gravel strip of sufficient length in the middle of the mud flats he was overflying, and he decided to fly an approach for a landing on that strip.

On late final approach, the pilot observed some powerlines crossing the end of the strip. He manoeuvred to avoid the powerlines but was unable to line the aircraft up properly, again, with the strip before the touchdown. The aircraft ran off the side of the strip and the horizontal stabiliser collided with an earth bank.

The reason for the power loss was not determined.