Forced/precautionary landing

During cruise the engine experienced a momentary surge with rough running and a decrease in engine speed to 1200 RPM. The pilot stated that he carried out all emergency procedures, but the engine failed to respond and regain power. A forced landing was carried out onto a beach, but during the landing roll the nose wheel entered soft sand and broke off at the fork. One propeller blade and the nose cowls also suffered damaged.

The fuel system was checked and found to be free of contamination, the fuel was of the correct grade with sufficient on board for the flight.

The engine was inspected and then test run successfully with no apparent faults found which may have caused the engine to lose power, although a later inspection found some contamination in the fuel injector distributer valve.

The reason for the engine to lose power could not be positively determined.

At approximately 500 ft after take-off the engine began to run roughly.

The aircraft was immediately positioned for a landing back on to the departure runway. The engine was still developing sufficient power at this point to complete a climbing turn to 800 ft. Approximately mid-down wind, the engine began to run very roughly and then lost all power. In the subsequent forced landing, the aircraft touched down approximately one third of the way along the runway. The pilot was unable to bring the aircraft to a halt in the distance remaining to avoid overrunning the the end of the strip. The aircraft came to rest part way down the sloping sea wall at the end of the runway. All three occupants were able to evacuate the aircraft safely.

Examination of the engine found that the centre electrodes for both spark plugs in the number four cylinder were excessively lead fouled and unable to fire. The porcelain surrounding the electrode on the top spark plug for number two cylinder was also cracked and indications were that this plug was firing intermittently. No other faults were found that could have contributed to to the power loss.

The pilot reported that he established the aircraft on final approach at 60 kt, with full flap selected. He assessed that the aircraft was slightly high on the approach, so he lowered the nose of the aircraft and flew it on to the ground to touch down near the runway threshold. The aircraft bounced and the pilot added some power to cushion the second touchdown. The aircraft then bounced again, more severely than the first bounce, so the pilot elected to go around and applied full power. He stated that the aircraft seemed sluggish and stabilised at about 2 m above the strip, so he retracted the flap to 20 degrees. He then became concerned about the high ground beyond the airstrip and flew towards a gap between trees about 30 m to the right of the strip. He banked the aircraft to avoid a fence and, on seeing more trees ahead, levelled the wings and closed the throttle. The left wingtip dug into the sloping terrain and yawed the aircraft. As the aircraft slowed further, the nose gear was torn off and the right gear bent backwards. The pilot could not recall hearing the stall warning horn operate at any stage during the sequence.

Witnesses reported that, while aircraft belonging to the operator involved in the accident always landed towards the north-west, other operators who used the strip landed towards the south-east when wind conditions dictated, by flying a curved approach to avoid the high ground beyond the end of the strip. The witnesses reported the surface wind as being from the south/south-east when the aircraft flew the approach. The aircraft was described as being close to the runway on base leg and to then fly a steep approach compared with other aircraft they had observed land at the strip. They stated that the aircraft touched down some distance into the strip, up to halfway between the end of the strip and the windsock, and to bounce four or five times before attempting to go around from a position past the windsock.

There was no apparent fault with the aircraft which might have contributed to the accident.

Neither the touch-down or attempted go-around positions could be determined accurately. The performance of the aircraft during the attempted go-around, particularly after the partial flap retraction, indicates that the aircraft probably was operating in ground effect.

Three local considerations were identified which could have contributed to the occurrence:

1. the high ground beyond the south-eastern end of the strip could have created an illusion that the aircraft was low and led the pilot to fly a steeper than normal approach path;
2. the actual wind at the approach end of the strip could have been different to that indicated by the windsock which could have been subjected to local effects caused by the high ground adjacent to the strip; and
3. the pilot was aware that he was operating a charter flight and perceived some pressure to land from the approach, rather than fly another circuit.

The factors considered relevant to this accident were:

1. The pilot's relatively low level of flying experience.
2. The position of the windsock was such that it might not have provided a realistic indication of the surface wind at the south-eastern end of the strip.
3. The terrain under the approach path could have contributed to the pilot experiencing an illusion relating to the aircraft’s approach angle.
4. The pilot perceived pressure to land from the approach.
5. The aircraft was probably high and fast on final approach.
6. The aircraft landed downwind.
7. The pilot made a late decision to go around.

The pilot was carrying out a fence inspection at 500 feet above ground level when the engine power reduced to idle. He changed the fuel tank selector to the fullest tank but there was no response from the engine. The pilot then closed and opened the throttle lever a number of times. This resulted in an increase to 1000 revolutions per minute, but power again returned to idle when he stopped moving the throttle. As the aircraft was losing altitude the pilot discontinued his trouble shooting activities and attempted a forced landing in heavily timbered terrain. The aircraft struck a number of trees during the landing.

The only fault found during an inspection of the wreckage was a fuel tank vent line containing a wasps nest. Testing of the line indicated that the nest could move causing either a partial or full blockage. The vent outlet was covered with a piece of gauze to prevent this type of occurrence. The fuel tanks were fitted with vented fuel caps.

The reason for the loss of power was not determined.

Enroute from Curtain Springs to Alice Springs, while flying low and slow to observe cattle, the pilot heard a loud noise followed by an immediate increase in engine RPM and decrease in rotor RPM. An autorotational approach and landing was carried out into the rough hilly terrain, but the helicopter landed heavily and rolled over.

A subsequent investigation revealed that the clutch assembly upper bearing had failed allowing the engine drive to disconnect from the rotor system.

The bearing was a commercial bearing, not a genuine Robinson bearing, although the manufacturer's instructions clearly state that only genuine bearings, having the correct internal clearances, must be installed. A specialist report indicated that the failure was due to brinelling of the bearing races, possibly caused by the bearing being dropped or damaged during assembly of the clutch. There was also evidence that the bearing had not been sufficiently lubricated which would have decreased its time to failure.

Although the accident was survivable, severe spinal and lower back injuries were suffered by both occupants. It was reported that the space below the seats contained a number of hard items including a hand fuel pump. The flight manual for this type of helicopter, and placards placed near the under-seat compartments caution against placing hard objects in them as they could cause injury to occupants if the seats crush while absorbing energy during a heavy landing.

SAFETY ACTION

As a result of the investigation, the Civil Aviation Authority issued Airworthiness Directive AD/R-22/39, which requires an inspection of the upper clutch actuator bearing of all R22 helicopters to ensure only approved parts are fitted.

The crew were carrying out a goat eradication program at the time of the accident. The aircraft was transiting from the hover to forward flight, at approximately 50 feet above ground level, when the engine suddenly stopped.

The pilot immediately entered autorotation and attempted to cushion the landing by increasing the collective pitch. The aircraft touched down heavily, tail first, before colliding with trees.

An inspection of the aircraft failed to disclose any reason for the sudden engine stoppage.

Weather conditions were conducive to the formation of carburettor ice however, the pilot had carburettor heat selected at the time of the accident.

The reason for the sudden stoppage could not be determined.

About 10 minutes after departing Bankstown for a local flight, the pilot noticed a reduction in engine RPM. Believing the throttle friction had become loose, he increased the throttle setting and tightened the friction. Soon after, the RPM again decreased so the pilot commenced to turn back towards the airport. During the turn the engine oil pressure indication decreased to zero. The pilot advised the tower of the problem, and of his intention to land on an abandoned airstrip. The engine was shut down after it began to vibrate, and the pilot informed the tower that a forced landing would be carried out in a field. During the subsequent landing the nosewheel entered a drain and the aircraft overturned.

Investigation later revealed that a connecting rod bolt had failed, resulting in a loss of oil pressure and subsequent engine failure.

After departing Tyabb, the aircraft was climbed to 2000 feet for the short flight to Penfield. Shortly after levelling at 2000 feet the engine suffered a major power loss. The pilot performed basic emergency checks, but these did not result in a resumption of engine power. An area was selected for a forced landing but on short final approach the pilot had to veer to avoid a man walking his dog. The aircraft touched down heavily, sustaining substantial damage.

After the accident the engine was successfully run in an engine test stand. No faults were found that could have explained the reason for the engine failure. Weather conditions were conducive to the formation of serious carburettor icing at any power setting and there were indications that this could have been the cause of the power loss. Factors The reason why the engine failed was not determined but the most probable cause was carburettor ice.

On the flight from Flinders Island an electrical failure occurred. The pilot continued to Latrobe Valley and made a landing approach behind another aircraft. On final approach, for runway 21, the aircraft was too low, and the pilot advanced the throttle to correct for this. The engine missed then fired again. The pilot checked the carburettor heat setting and found that it was in the hot position. He pumped the throttle, and the engine kept losing and gaining power and then ran normally.

Because of the low height and the terrain ahead, which included a power line, the pilot elected to put the aircraft down in a small clear area. A very heavy touchdown followed, and the aircraft ran through a fence before stopping.

Following the accident the aircraft was found to contain an adequate amount of fuel. No inspection of the engine or its systems was carried out, and the reason for the interruption of power was not determined.

Significant Factors

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

1. A partial engine power loss and engine rough running for an undetermined reason.

2. The decision, by the pilot, to land in a small but immediately adjacent clear area.

3. The aircraft was landed heavily.

After flying through some heavy showers, the pilot detected a vibration in the aircraft. He knew that the main rotor abrasion tapes sometimes came loose in rain, and when he detected a performance loss, he suspected that loose tapes may have been the reason for the vibration. He decided to land to remove the tapes. With maximum power selected, the pilot could not arrest the sink rate during the approach for the run on landing, and the helicopter landed heavily and bounced. As a result of the hard landing, the main rotor blades severed the tail boom.

Damage to the main rotor blades was such that it could not be determined if the blade tape had lifted prior to the accident. No other defects were discovered that could have contributed to the loss of performance.