Forced/precautionary landing

The pilot performed a daily inspection of the aircraft with the intention of flying to Dysart. During this time, he filled the aircraft fuel tanks with Avgas and carried out a fuel contamination check. A small amount of water was drained from the left fuel system. During the engine run-up checks, all pressures and temperatures were within normal operating tolerances.

The pilot reported that following a normal take-off, at about 100 ft, and after landing gear retraction, the right engine lost power. He transmitted a MAYDAY broadcast which was received by Brisbane Flight Service. While carrying out the engine failure vital actions, he thought that the engine may have regained power. However, when the engine did not respond to throttle movements, he completed the vital actions, which included feathering the right propeller. The pilot observed that the indicated airspeed was below the best single-engine climb speed and that the aircraft was not climbing. He was aware of rising terrain ahead and decided to land the aircraft in a flat field beyond the aerodrome boundary. He selected the landing gear down, but the aircraft touched down heavily before the gear had extended. The left tip tank ruptured and caught fire on impact. The aircraft slid for 120 m. and when it stopped, the pilot and passenger exited the aircraft, and the pilot extinguished the fire with the fire extinguisher from the aircraft.

A witness reported that the aircraft took off normally but then suddenly diverged left of the extended runway centreline. A short time later, he lost site of the aircraft behind buildings. The investigation did not determine why the aircraft diverged left after the right engine failed.

Examination of the right propeller indicated that it had been feathered prior to the impact, while damage to the left propeller was indicative of a low-power setting at impact.

Extensive examination of the engines and their systems failed to identify any deficiencies which might have contributed to the reported engine failure. The examination included operating the engines at various power settings.

The flight was planned as a familiarisation flight for the passenger. The pilot did not detect any fault with the engine during the pre-flight inspection, and he reported that the compression on all cylinders appeared normal. The aircraft was close to its maximum weight at take-off.

During the take-off roll engine RPM was 2800. Maximum RPM permitted was 3300 however, the manufacturer reported that the engine/propeller combination fitted to the aircraft was only expected to produce between 2900 and 2950 RPM. Although the take-off performance appeared below normal, the pilot believed it was caused by the aircraft being close to its maximum weight. Witnesses reported that the aircraft used almost all of the 900 m strip for its take-off roll. The manufacturer reported that the take-off roll in a Jabiru 1600 at maximum weight should be between 250 and 300 m.

After becoming airborne the aircraft would not climb, and engine RPM had fallen to 2700. The pilot turned to follow the road in case the engine lost more power. He completed trouble checks but was unable to identify the reason for the loss of performance. Shortly after, the engine regained some power, and the pilot decided to attempt a return to the airstrip.

During the subsequent turn the engine stopped completely. The pilot then attempted a forced landing in a tree covered area. Whilst attempting to avoid a medium sized tree, at a height of approximately 20 ft above the ground, one wing collided with the tree and the aircraft stalled and crashed. The fuselage turned through 180 degrees and slid backwards into another tree before coming to a stop.

Although the aircraft was extensively damaged the cockpit area was relatively intact. A fuel filter had fractured allowing fuel into the cockpit however, there was no fire. The pilot turned the fuel off and secured the electrical system before he and the passenger exited the wreckage.

An inspection of the engine disclosed that the exhaust valve, seat and spring on the No. 3 cylinder had been subjected to excessive heating. The valve guide was loose in the cylinder head and the valve spring had lost its tension. There was an accumulation of grease and metal shavings in the rocker cover which had been there for sufficient time to congeal indicating that the valve, seat and spring had been in this condition for some time. The faults meant that the valve might or might not seat correctly during engine operation. The variable nature of the valve operation could lead to an intermittent power loss at those times when the valve was not seated correctly. It is possible that the valve was seated correctly when the pilot checked the compression during the pre-flight inspection; however, the post-accident investigation was unable to reproduce normal cylinder compression. It is possible that the low RPM and excessive take-off distance, reported by the pilot, was a symptom of the valve problem.

The engine was fitted with a reconditioned cylinder head and the manufacturer reported that there had been other cases of valve guides coming loose. To manage this type of problem the manufacturer had included a compression check and, if this proved irregular, a tappet check in the daily inspection requirements. Although the precise reason for the valve guide failure could not be determined the guide is held in place by a using a temperature-dependent shrink-fit. As there was an indication of excessive heating, it is possible this caused the fit to come loose.

Although the valve position could lead to a loss of power, experience indicates it would not normally be sufficient to stop the engine. It could not be determined why the engine stopped. The manufacturer reported that any reduction in power, during three cylinder operation, might stop the engine. The pilot reported that he did not reduce power.

At the low speeds, normally used during a forced landing, any abrupt manoeuvres made to avoid trees would probably cause the aircraft to stall.

SAFETY ACTION

The manufacturer has discontinued production of the 1600 cc engine and replaced it with a 2200 cc engine which is manufactured using a different process.

This will alleviate the problem with the valve guides. The manufacturer is also working to relocate the fuel filter to prevent fuel from entering the cockpit in the event of a failure.

The pilot reported that he was in the Coolangatta training area practising forced landing procedures with a student pilot. An autorotation was entered by lowering collective initially, then the throttle was wound off. Carburettor heat was selected fully on, carburettor air temperature was indicating approximately 12 degrees Celsius, and the engine was idling. The pilot said he turned towards the forced landing area and was briefing the student on the wind direction. The rotor RPM was in the green range and indicated airspeed was 55 knots, the correct autorotation airspeed. The pilot said that at this stage he was downwind (5-10 knots approx) and was ready to turn into wind at approximately 300 ft AGL. The collective was raised and the throttle was opened fully, but the manifold pressure increased only to 14-15 inches, there was a definite lack of power and the rotor RPM decayed. He maintained heading and airspeed and re-entered autorotation heading for the forced landing area when he noticed the engine had stopped. He said he attempted a restart but at this stage he was too low to risk a turn and accepted his present direction. The landing was made onto a tree lined track. The main rotor contacted trees and the aircraft rolled over to the right on the sandy surface. The pilot suspected that carburettor icing may have been the problem.

The weather conditions at the time were light drizzle or rain with a temperature of 18 -20 deg C. These conditions were conducive to carburettor icing. The pilot said that he had experienced power loss with this type of helicopter in similar situations, but usually on the initial entry into the autorotation. The aircraft manufacturer carried a technical investigation and found no evidence of any failure or malfunction that may have led to the accident. The manufacturer stated that the carburettor heat fully applied in autorotation produces an indication on the carb air temp gauge of full scale deflection. However, this has not been the operators experience. The operator advised that with full carb heat the temperature remains in the mid (caution) range and pilots have been advised to terminate autorotations and apply power if the carb air temp falls below this value. The operator now requires pilots to practice autorotations over a clear landing site, so that a landing may be terminated should the situation recurr.

HISTORY OF THE FLIGHT

The pilot and the passenger, who was also the owner of the aircraft, performed a pre-flight check of the aircraft. Seated at the right control position, the pilot then taxied the aircraft for departure with the intention of conducting cross wind circuits. The airstrip was aligned approximately 020 degrees magnetic.

Shortly after take-off, when the aircraft was about tree top height, the passenger became aware that the aircraft did not appear to be performing normally. At about the same time the pilot assessed that the nose attitude was too steep. He lowered the nose and felt the aircraft descend. He confirmed that the throttle was set at full power and, assuming that the aircraft was stalling, lowered the nose further. When the aircraft continued to descend, the pilot attempted to land in an area about 100 m beyond the end of the airstrip.

The aircraft collided with a stack of several large posts and concrete pipes and came to rest inverted 120 m from the northern end of the airstrip but displaced about 50 m to the west of the airstrip alignment.

Both the pilot and the passenger sustained serious injuries.

At the time of the take-off the pilot had estimated that there was an easterly crosswind of about five knots, with a headwind component of about three knots. The windsock was located to the north-west of, and close to the hangar and farm buildings. A worker employed on Tartrus reported that the wind had been a light south-easterly.

The pilot normally flew and instructed in Cessna C172 or Piper PA28 type aircraft. He held an Australian Ultralight Federation pilot's certificate, but had limited experience flying ultralight aircraft. He had previously flown the aircraft at Tartrus Station four or five times.

Both the pilot and the passenger indicated that although the engine seemed to operate normally the aircraft had lacked performance. The passenger noticed that when the nose of the aircraft was aligned approximately with the horizon, the aircraft was descending. She was aware that there was a large performance degradation with two people on board and would normally fly the aircraft alone. When flying with a passenger she preferred the cooler hours of the day and would make as much use of ground effect as possible after lift-off.

AIRCRAFT EXAMINATION

The Hughes Lightwing GA-55 was manufactured in Ballina, NSW, and was powered by an Aeropower (modified Volkswagen) four cylinder, four stroke, air cooled engine driving a two bladed wooden propeller. The airframe was of high wing monoplane design. An Artex E03 emergency locator beacon was mounted behind the pilot's seat and was activated by the impact.

The aircraft forward fuselage area below and in front of the rudder pedals had sustained substantial damage.

No pre-existing defect which may have affected the controllability of the aircraft was found.

Examination of the fuel tanks found that the tanks were empty but the soil beneath the right fuel tank filler cap was found to be soaked with fuel to a depth of about eight centimetres.

The engine was fitted with a standard aircraft magneto and dual electronic modules. The electronic modules were found to be impact damaged and could not be tested. Specialist examination of the engine indicated that the magneto external timing was advanced 10 degrees beyond the recommended setting but was serviceable. No evidence was found that the magneto timing adjustment was altered during the impact sequence. No other pre-existing defect was found.

ANALYSIS

It is likely that the position of the windsock resulted in a shielding effect when the wind was south-easterly. This may have caused the pilot to incorrectly assess both the wind direction and the strength. Consequently, it is possible that the marginal performance of the aircraft was further degraded when, shortly after take-off, the aircraft encountered a crosswind with a tailwind component.

The pilot's limited experience flying this aircraft type, and ultralight aircraft generally, may have led him to apply an inappropriate handling technique in response to the low performance.

SIGNIFICANT FACTORS

1. The aircraft had marginal performance characteristics when carrying a passenger.

2. The pilot was inexperienced on the aircraft type.

3. The pilot did not maintain adequate flying speed after take-off.

The aircraft had been operating on the mustering flight for about 45 minutes. With the helicopter at 70 feet above the ground and 50 kts indicated airspeed, the pilot reported that he had just commenced a climbing turn to approach a small mob of cattle when he heard a loud noise from the rear of the cabin. The engine oversped and the rotor speed decayed. A forced landing was conducted but the pilot was unable to retain adequate rotor speed to prevent a heavy landing.

Following the take-off with 850 L of chemical for another spray task, the engine began to vibrate and lose power. The pilot dumped the load and conducted a forced landing into a paddock about 4 km from the departure airstrip. During the landing one main landing gear leg was torn off, the wings were creased, and the propeller was bent rearwards. After an examination of the engine the pilot found that the number 6 cylinder had cracked between the spark plug holes.

The helicopter was in a steady cruise at 80 kts at 1,500 ft above ground level when the pilot heard a loud bang. He immediately initiated auto-rotation and believed that there had been a failure of the tail rotor drive. The pilot attempted a landing in the nearest clear area but the nature and slope of the terrain coupled with some rotation of the helicopter resulted in it rolling over and sustaining severe damage during the landing.

Examination of the helicopter revealed that the intermediate flex plate failed. This flex plate consists of the front and rear yokes plus the flex plate itself, all joined by four bolts. The examination found that one of the two front lugs was missing. The adjoining flex plate lug was present and bent forward. The bolt joining the missing front yoke lug to the adjoining flex plate lug was also not present. Neither the bolt nor the front yoke lug were found at the accident site.

The hole in the flex plate lug, opposite the missing front yoke lug, was worn and enlarged suggesting that, after the bolt was liberated, the shaft's axis of rotation changed. Such an event would have led to failure of the tail rotor drive and given the symptoms described by the pilot.

The pilot had conducted a brief pleasure flight. He intended to land to the west on a 330 m grass airstrip on his own property. The strip ran east west with a 12.5 degree upslope to the west. He estimated the wind components to be 5 kt headwind and 15 kt crosswind. However, on short final, the aircraft encountered moderate turbulence and windshear. The pilot elected to overshoot, but because of the steep upslope, this required a turn north or south. He advised that from past experience in PNG, having landed on many bush strips, he would normally have turned into wind during an overshoot into a one-way uphill airstrip. However, on this occasion he inadvertently turned downwind and encountered more windshear and loss of airspeed.

With the aircraft facing downwind and very low in airspeed, he elected to land straight ahead in the paddock. During the latter part of the landing roll the aircraft nosewheel collided with a rock and the aircraft overturned. 

The pilot subsequently advised that the aircraft had recently undergone a complete overhaul and that had not contributed to the accident.

At about 200 ft after takeoff the engine began to run roughly. The pilot elected to abandon the takeoff so that the aircraft could be landed on the remaining length of runway. After a high flare for landing the aircraft touched down heavily. The left landing gear leg was broken off and the aircraft came to rest off the left side of the runway.

The relative humidity was assessed as being around 80% and there had been recent light rain at the aerodrome. The pilot reported that the aircraft manufacturer considered carburettor icing as the cause of the rough running.

The pilot reported that he was engaged in moving cattle on a flooded property. On board the helicopter with the pilot was the property owner. While hovering at about 30-40 feet behind some cattle, the pilot's attention was diverted momentarily allowing the engine and main rotor RPM to decay. He was unable to regain rotor RPM and elected to attempt a landing onto a nearby dry patch of ground. In turning the helicopter towards the dry ground, the pilot inadvertently turned down wind, overpitching the main rotor blades. During the ensuing deep flare to land, the tail rotor contacted the water and the main rotor blades severed the tail boom. The helicopter then settled into the water and rolled over. Both the pilot and passenger were able to exit the helicopter safely.