The helicopter was cruising at about 1,500 ft AGL when the pilot heard a loud bang. The helicopter yawed to the left and the pilot noticed that he no longer had pedal control. He commenced an autorotation and turned into wind. The touchdown was relatively heavy, but the helicopter remained upright. After the pilot evacuated the cabin, he noticed that the auxiliary fuel tank had been damaged by the main drive shaft.

He was able to remove an ELT, survival gear and some drinking water before the helicopter caught fire and was destroyed. Wreckage examination found that the main rotor drive shaft forward flexplate had failed and pieces had punctured the auxiliary fuel tank. The examination determined that the forward flex plate had failed under load as a result of metal fatigue. The fatigue cracking had initiated at an area of corrosion pitting on the forward edge of the flex plate.

Areas of corrosion were also observed under sections of blistered paint at several other sites on the flexplate surface. The edges of the flexplate had been painted with a chromate primer and a protective topcoat. The paint had blistered and formed sites that acted to trap moisture next to the metal. Chlorides contained in the moisture then acted as the electrolytic agent that caused the corrosion. The investigation was not able to determine the source of the chlorides.

However, they could have resulted from environmental factors caused by the helicopter operation in coastal areas or over dry salt lakes. A further possibility was that 'hard' water (containing minerals) from artesian or other sources could have found its way on to the plates. The maintenance records indicate that with respect to main rotor drive shaft alignment, the helicopter was maintained in accordance with the manufacturer’s maintenance procedures.

The maintenance documentation indicated that the failed flexplate (p/n A947-1) had been in service for a total of 1,249 hours. Crack initiation to failure occurred over 350 flights on the flex plate. Prior to this accident, a flexplate fitted to VH-HEW (BASI report 9301775) failed in similar circumstances. A similar failure has occurred in New Zealand. In the New Zealand example, the number of cycles to failure was not determined.

However, the total time in service for this component was 1,486 hours. The Bureau recently obtained a flexplate which had been in service for 4,500 hours and which showed no visible evidence of cracking. The manufacturer does not specify a service life for the flexplates. 

Significant Factors

1. Localised corrosion pitting was created under regions of blistered and lifting paint on the edge of the flexplate.

2. Fatigue cracking had initiated from one area of pitting.

3. The flexplate failed as a result of fatigue cracking.

Safety Action

Based on preliminary information of this and the similar occurrence (report 9301775) the Bureau of Air Safety Investigation made the following Interim Recommendation which was responded to by the CAA:

Interim Recommendation (IR 930272) The Bureau of Air Safety Investigation recommends that the Civil Aviation Authority advise all R22 operators of these failures to the flexplates, institute fleet inspection for drive shaft flexplate integrity and introduce repetitive inspections for cracking at appropriate intervals considering the crack propagation rate of those items which have been examined. Dependent on the results of fleet examination and in consultation with the manufacturer and industry, consideration should be given to the imposition of flexplate life limitations.

The CAA response, in part, stated: 'Your recommendations are generally accepted, however the exact form of our requirement may vary after discussion with the manufacturer and the FAA.' Interim recommendation IR 930272 suggested that the CAA to consider, amongst other things, the imposition of a service life for flexplates.

In the light of information from the manufacturer, review of other flexplates and specialist report 75-93 this part of that recommendation may no longer be appropriate. Specialist report 75-93 on the failed flexplates from these two aircraft identifies that the deteriorated paint treatment on the edge of the flexplates indirectly contributed to the corrosion and ultimately the fatigue failure. It suggests that prevention could be achieved either by maintaining an adherent paint film on the plate or, alternately, by leaving the plate uncoated, thereby eliminating the possible entrapment of corrosives.

Following these two failures (and another in New Zealand) Robinson Helicopters P/L issued SB No. 73 on 15 March 1994. This SB requires an inspection of the forward flexplate Pt. No. A947-1 for corrosion and cracking and proposes an amendment to the R22 Maintenance Manual procedures in respect to this component. Although the bulletin requires an inspection within 25 hours, the status of the bulletin has not been classified mandatory.

The CAA in response to IR 930272 sent a letter to all Certificate of Registration holders of R22 aircraft advising of the flexplate failures. However, there is no mandatory requirement for R22 operators to have their aircraft inspected to determine flexplate serviceability in respect to these failures or to report findings for those who do have their aircraft inspected. The fleet status therefore remains unknown.

The Bureau of Air Safety Investigation therefore makes the following recommendation:

R940092

1. That the Civil Aviation Authority institutes a mandatory inspection to determine the status and condition of in-service flexplates in respect to deteriorated paint finish or the onset of corrosion. The results of these inspections together with component in-service history should be reported and analysed.

2. That the Civil Aviation Authority in conjunction with the manufacturer, whilst considering the fleet status, analyse all of the information now available, review current inspection periods and formulate inspection procedures which will enable the integrity of the flexplate material to be checked.

The pilot was conducting a local flight to maintain his currency. He carried out two circuits and landings before proceeding to the training area. On return to the circuit the pilot completed one circuit and full stop landing on runway 11L. A post flight inspection by the operator, revealed the right wing main spar was fractured, and the right main landing gear leg was displaced rearwards at an angle of about 20 degrees.

The damage was consistent with a hard landing. The pilot, who was inexperienced, said he was unaware the touchdown was sufficiently hard to damage the aircraft. His final landing was conducted in wind conditions swinging from 090 to 120 degrees, 10 to 15 knots gusting to 20 knots, with a maximum crosswind component of 8 knots on runway 11.

An aero club fly-in was organised at a property strip. One of the activities organised was a session of assessing skill and judgement in the form of flour bombing. The target was placed near the southern threshold of the north/south strip, and the contestants were to fly at 60 -65 knots, at 200ft AGL, drop the flour bomb and land straight ahead on the remaining section of the strip.

The passenger in the accident aircraft was a private pilot whose licence was not current. He sat in the left control seat whilst the pilot flew the aircraft from the right control seat. After take-off into the north, the pilot flew a left circuit followed by a level approach at about 200ft AGL towards the target. The passenger dispensed one flour bomb out of the left window and the aircraft then descended as if to land straight ahead but then entered a climb.

As the aircraft climbed, it was observed to drift left of the strip before commencing a teardrop turn to the right with increasing angle of bank. During this manoeuvre, the aircraft suddenly adopted a nose-low attitude and dived into the ground from a height estimated by witnesses to have been 130-150 feet AGL. The flaps were in the retracted position at impact. The passenger reported hearing the stall warning horn operate during the turn shortly before impact.

The helicopter was engaged on local joy flights, each flight being of about 7 minutes duration. After completing several flights, the pilot said he dipped the fuel tanks and determined the remaining fuel quantity to be 70 litres. At the completion of two more flights, the pilot decided to proceed to Albion Park aerodrome to refuel. As the helicopter passed through an altitude of 700 feet on descent to Albion Park the engine stopped. The pilot gave a Mayday call and carried out a trouble check but was unable to identify the reason for the engine failure.

An autorotative landing was subsequently conducted onto swampy grasslands near the northern shore of Lake Illawarra. It was reported that the helicopter touched down on the heels of its skids and pitched forward, decelerating rapidly due to long grass and soft surface conditions. As the helicopter pitched forward the main rotor blades severed the tail boom. A subsequent inspection of the engine failed to reveal the reason for the engine failure.

VH-NJC, was en route from Cairns to Ayers Rock cruising at flight level (FL)280. VH-TAJ was en route Darwin to Adelaide, cruising at FL330. The crossing point of the two tracks was approximately 100 nautical miles east of Alice Springs. Near the intersection of the two tracks, the pilot of VH-TAJ requested a clearance from air traffic control to descend to FL270. This was approved.

Subsequently the air traffic controller realised VH-TAJ did not have the required lateral separation from VH-NJC. He checked the level of VH-TAJ, but the aircraft had left FL285 on descent. The aircraft was allowed to continue the descent as both aircraft were well clear of each other, but within the area of lateral confliction.

The pilot was taking off to the north with a wind from approximately 340 degrees at about 40 knots. During the take-off run the wind veered to the west and the pilot lost directional control. The aircraft ran off the strip to the left and collided with a ditch, breaking off the nosewheel and damaging the propeller. The pilot reported that he had previously flown in similar wind conditions but on this occasion was caught by the sudden wind change.

About 200 feet above the ground on initial climb after take-off, the engine began to run roughly and within seconds it stopped. The pilot attempted a forced landing into the paddock off the end of the airstrip. During the forced landing the aircraft clipped a farm fence and landed heavily. Subsequently, a Civil Aviation Authority Airworthiness Surveyor examined the wrecked aircraft and conducted a successful engine ground run with its ROTAX 532 engine. No defects were found with the aircraft. The nature of the engine failure was consistent with carburettor icing.

Conditions at the time were conducive to carburettor icing; the temperature was 7 degrees Celsius and the dewpoint 5 degrees. A Cessna 152 suffered an engine failure due to carburettor icing while taxiing at the same airport minutes after the accident. This Kitfox was not equipped with carburettor heat. The Civil Aviation Authority is assessing the need for the mandatory installation of a suitable carburettor heat device to the Kitfox.

Significant Factors

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

1. The aircraft was not equipped with carburettor heat.

2. The aircraft encountered conditions conducive to carburettor icing.

Soon after take-off, on initial climb, the left engine lost power because the mechanical fuel pump failed. The pilot feathered the left propeller and landed safely back at Yarrawonga.

Significant Factor

The following factor was considered relevant to the development of the incident:

1. The engine driven mechanical fuel pump failed in flight.

After the aircraft cleared the runway after landing, the tower reported what appeared to be a fire in the starboard engine. The engine was shut down and the fire bottle discharged. The aircraft then taxied to its allocated parking bay followed by the RFFS vehicles.

Investigation revealed there had been no engine fire, but the APU was 'torching' from the tail pipe. The APU igniter plug, fuel atomiser and combustor liner were changed and the APU then operated normally.

The aircraft was being landed in a crosswind by a pilot undergoing a check by the operator. It bounced three times, and the pilot decided to go around. After lift-off, as the landing gear was retracting, the pilot reported that the aircraft was affected by windshear and touched down again. The aircraft came to rest on the runway.