The pilot reported a birdstrike during the descent. The strike appeared to cause the left engine to lose power, and it was shut down and secured. Subsequent investigation indicates that the wiring providing indications to the flight crew was damaged and the instrument indications, only, were lost.

An unsafe left main gear indication illuminated when the gear was selected down for landing. Although the standby system indicated three green lights, a single-engine flypast was completed to confirm the gear position.

The crew did not request emergency services. The company agents on the ground at Broome declined to declare a full emergency and local standby only was activated by airport management.

During the later part of the landing roll the pilot lost directional control of the aircraft. He reported brake and steering failure.

The aircraft veered off the sealed runway before the pilot stopped it by application of the emergency brakes.

Ground witnesses reported the loss of directional control may have been the result of the use of reverse thrust on the remaining operating engine.

There were 17 people on board.

Early on Monday morning (the day after the accident) a farmer reported finding the aircraft crashed on his property.

A Flight West crew at Roma had reported that the pilot of an aircraft was having difficulties in finding Roma at about 1835 on Sunday evening. The pilot was asking for a description of the aerodrome in relation to the township and requested that the Flight West crew wait on the ground until their arrival. When the Flight West passengers had disembarked, the crew attempted to contact the aircraft again, but without success.

The aircraft call sign was reported to Flight Service as VH-ECN. When SAR (Brisbane) found VH-ECN at Caboolture and no further reports of a missing aircraft were received, the INCERFA was cancelled.

Last light at Roma was 1804 approximately. The pilot was not rated for night visual flight rules.

FACTUAL INFORMATION

History of the flight

The pilot had commenced mustering at about 0700 EST. At about 1030 the aircraft was refuelled to full tanks during a "smoko" break. The pilot's intention was then to muster about 30 head of cattle which had been separated from the main mob. The pilot had agreed to take a passenger on the flight which was expected to be of relatively short duration. The passenger had been holidaying at the property and was keen to experience a helicopter flight.  The helicopter became airborne at about 1050 and was last heard at 1115. At 1130 a jillaroo realised she could no longer hear the helicopter and began making enquiries on a hand-held radio. When nothing was heard, she began a search on a trail bike and eventually discovered the wreckage and the deceased occupants at about 1420.

Impact sequence

The tail rotor had struck the top branches of a lone 7-metre-high sapling, causing one blade to separate. The tail rotor gearbox then separated, and the main rotor struck the tail boom. The wreckage fell to the ground 30 metres beyond the sapling. The right side of the cabin was crushed. There was no fire.

Wreckage examination

The cabin was crushed on the right (pilot's) side by ground impact. The Perspex bubble was scattered in front of the main wreckage, which was facing south-south-west. The main rotor blades showed evidence of having struck the tail boom and the cabin structure. The tail rotor drive shaft was recovered and showed evidence of torque twisting, indicating that the tail rotor drive shaft was being driven under power when the tail rotor contacted the tree.

The left side of the passenger seat with the seat lap belt attachment, had detached from the fuselage structure and this allowed the passenger to strike the upper door frame during impact. The control systems were examined and appeared to be functioning normally. The engine governor switch in the end of the collective control was found in the off position.

The engine was removed and examined. There were no defects found which would have precluded normal operation.

Weight and balance

The weight and balance of the helicopter was within the limitations published in the aircraft flight manual.

Emergency locator transmitter (ELT)

The Ack Technologies ELT was found undamaged in the mounting bracket at the rear of the engine bay. The arming switch was found in the off position.

ANALYSIS

Civil Aviation Regulation Section 29.10 states that during aerial stock mustering operations, a pilot shall not carry more than one other person and that that person must be essential to the successful conduct of the operation. In this case, the passenger was not essential to the conduct of the operation. The helicopter had been refuelled to full tanks immediately before the flight and, although within the specified weight limitation, it was much heavier with the additional weight of the passenger than the pilot was accustomed to for mustering. Although the pilot was highly experienced, the resultant reduction in performance may have been a factor in his being unable to avoid the collision with the tree.

There were no witnesses to the accident and the final flight path before the collision with the tree could not be determined. However, it was evident that immediately after the tree was struck by the tail rotor, the helicopter was subjected to violent manoeuvres.

The RPM governor is fitted to the engine to prevent decay of rotor RPM when manoeuvring. The aircraft flight manual states that flight is prohibited with the governor switched off, except when there is a system malfunction or for emergency procedures training. The governor switch was found in the off position, but it may have been bumped to this position in the accident sequence. If it was deliberately switched off for the flight, manoeuvring performance of the helicopter may have been reduced.

The possibility that the pilot may have been attempting a precautionary landing for some reason such as an engine malfunction, was considered. There was no evidence found to substantiate such a possibility.

SIGNIFICANT FACTOR

The tail rotor struck a tree, and this precipitated a major structural failure. Why the pilot was unable to avoid the tree could not be determined.

FACTUAL INFORMATION

History of the flight

The pilot had been tasked to ferry the helicopter from Windorah to Cadelga Station in preparation for cattle mustering. Several witnesses saw the helicopter depart at about 1620 EST. It was last seen some time after 1630 as it flew past South Galway Station, 61 km south-west of Windorah.

The track distance was 239 km with an expected flight time of about 1 hour and 40 minutes and an estimated time of arrival of 1800. The helicopter was expected at Cadelga Station before last light at 1829. When it had not arrived, the helicopter was reported missing. An extensive aerial search commenced at first light the next morning. The wreckage of the helicopter was found about 2 km to the right of the direct track and 31 km short of the destination.

Pilot information

The pilot was 20 years of age and had commenced his flying training on Bell 47 helicopters in March 1995. He gained an endorsement on Robinson R22 helicopters in May 1995. He passed his commercial helicopter licence test on 22 June 1995. In February 1996, the pilot passed a check flight with an instructor and obtained mustering training. Since then, he had been employed as a mustering pilot on a full-time basis.

The post-mortem examination report did not reveal any pre-existing physiological problems.

Wreckage examination

The helicopter wreckage was examined initially at the accident site and later transported to a maintenance facility at Archerfield Airport where a more detailed examination was possible. These examinations revealed that the helicopter had impacted in an attitude about 60 degrees nose-low and banked to the right. The skid gear had separated at impact and the remaining structure of the helicopter was severely compressed.

Significantly, the main rotor had ceased rotating, and the engine had stopped by the time the helicopter struck the ground. Sections of the tail boom were scattered to the right of the main wreckage. Heavy items, such as a jerry can full of oil and the tail rotor assembly, were strewn ahead, along track (approximately 245 degrees M). Lighter items, such as paint flakes and Perspex pieces, were scattered downwind, generally to the north of the main wreckage.

Examination of the main rotor blades found that both pitch-link rods were broken in overload and that both blades were bent into an "S" shape. The tail boom had suffered several main rotor blade strikes. The first blade struck on the flat with the top surface, distorting the tail boom and swinging the tail rotor assembly into the main rotor disc.  The cabin was also struck by one or both main rotor blades.

The engine was bulk stripped at an engineering workshop. Nothing was found that would have prevented the normal operation of the engine. Examination of the exhaust manifold showed that the engine was still hot at impact. Both fuel tanks were holed, subsequently only a small quantity of clean fuel was recovered. The helicopter had undergone a periodic maintenance inspection prior to the flight.

Examination of the helicopter wreckage and of the maintenance documentation did not reveal any abnormalities which could have led to a loss of control.

Weather and environmental issues

An assessment of the weather conditions was obtained from the Bureau of Meteorology and local sources. The wind at 2,000 ft was a southerly at 10-15 kts. The surface wind was a light south-south-easterly, less than 5 kts. Cloud was scattered cumulus at 3,000-4,000 ft with patches of higher altocumulus. Sunset at the crash site was at 1808.

Robinson Helicopter Company research

Research undertaken by the Robinson Helicopter Company found that when the main rotor RPM decreases below 75% RPM, it will continue to decrease regardless of input from the pilot. In a short time span, the engine will stall, and the rotor system will stop completely. During flight with rotor RPM in the normal range, the blades are relatively straight due to centrifugal force. As rotor RPM decreases below the normal range, the main rotor blades bend upwards in a permanent set, the pitch link rods break in overload and the droop stop tusks also break or bend. The main rotor blades are then free to swivel at the mast and flail, striking the tail and cabin structure.

Cabin luggage

Any luggage has to be carried in the cabin of the helicopter: in the space under each seat, on the passenger's seat, or on the cabin floor in front of the passenger's seat.

The pilot carried three bulky items in the cabin: a swag (bedroll), a full 20-L jerry can, and a small overnight bag. The rolled-up swag was later measured at 1,060 mm long by 350 mm in diameter. It was held upright by the lap/sash seat belt on the passenger's seat. The location in the cabin of the 540 x 300 x 200mm overnight bag could not be determined. The jerry can containing engine oil was ejected from the helicopter, indicating that it was not restrained and probably lying on the cabin floor in front of the passenger's seat.

The swag and overnight bag were removed from the wreckage before the investigation team arrived on site. Therefore, any evidence of control interference caused by the luggage was lost. The Bureau's records show that since 1989 there have been four other similar occurrences, three of which resulted in accidents. In each occurrence, control was lost either totally or partially, due to inadequately restrained cargo in the cockpit. The 1989 accident was due to the in-flight movement of a swag and other equipment, held only by the passenger's seat belt.

Emergency locator transmitter

An emergency locator transmitter was not fitted to the helicopter, nor was one carried by the pilot.

ANALYSIS

Loss of control

The loss of main rotor RPM and engine stoppage was preceded by an event which resulted in loss of control. This event was sudden and severe enough to prevent the pilot from taking timely corrective action. An assessment of the helicopter's attitude at impact and the wreckage distribution indicated that this event occurred at an altitude in excess of 500 ft.

There was no physical evidence found to indicate that the swag shifted and interfered with the flight controls.

The event which led to a loss of control could not be identified.

SAFETY ACTION

Since 1989 there have been four similar occurrences, three of which resulted in accidents. In each occurrence, control was lost either totally or partially, due to inadequately restrained cargo in the cockpit.

The Bureau of Air Safety Investigation is considering an article for publication in Asia-Pacific AIR SAFETY highlighting the risks to safety from carriage of cargo in the cockpit of the Robinson R22 helicopter.

During climb out from Dauan Island (Torres Strait), the helicopter suffered an engine power loss. The pilot placed the helicopter in autorotation from approximately 300 feet. Having heavily impacted the water, the helicopter sank and rolled inverted. The pilot and three of the four passengers escaped. The remaining passenger remained in the aircraft as it sank. One of the passengers who survived the ditching did not remain afloat and disappeared from the other survivor's view. The aircraft sank and has not been recovered.

At 2005 EST the pilot conducted an instrument letdown at Flinders Island and then notified air traffic services that he was proceeding night VFR procedures along the coast to Killiecrankie, a private airstrip approximately 15 NM to the north. He made an operations normal transmission at 2020 and advised he would call again by 2045. No further transmissions were received. An air and ground search was commenced.

FACTUAL INFORMATION

History of the flight

The pilot was conducting a charter flight from Roma to Quilpie, Windorah and Tanbar Station 100 km south-west of Windorah. The aircraft was refuelled at Windorah with 170.5 L of Avgas and departed Windorah at 1400 EST for Tanbar.  At 1739 the pilot transmitted flight-plan details to Brisbane Flight Service by radio for the flight to Roma. He advised that the flight would be conducted under the visual flight rules (VFR), and that the aircraft endurance was 250 minutes. He nominated a SARTIME of 2100 for his arrival at Roma.

At 1903 the pilot made an "all stations" broadcast 20 NM west of Charleville. He reported inbound on the 270 VOR radial on descent for a practice VOR approach and said that after a missed approach he would proceed to Roma.

Witnesses at the airport saw the aircraft fly overhead from the west. The aircraft was seen to turn right onto a southerly heading and soon afterwards the sound of the aircraft diminished. A bang was then heard and felt through the ground at about 1915. The aircraft wreckage was located the next day by a search party. The aircraft had struck the ground whilst banked vertically to the right with a 45-degree nose-down attitude, and disintegrated.

Pilot in command

The pilot was correctly licensed and endorsed to conduct the flight. Prior to the accident flight, the pilot had only 3.9 hours multi-engine command night experience. Although 6.5 hours single-engine dual night experience was recorded, no multi-engine dual night experience was recorded. The pilot had flown the aircraft in command at night on only three previous occasions. These were on 11 and 12 December 1995 (2.1 hours), and on 4 April 1996 (1.8 hours). The pilot held an instrument rating, but the flight was being conducted under night VFR.

Meteorological conditions

The meteorological aerodrome report (METAR) for Charleville on 16 April 1996 at 1900 hours reported the wind to be a southerly at 6 kts, visibility more than 10 km, and no cloud below 5,000 ft. Witnesses said it was a very dark night with no moonlight.

The VHF omnidirectional radio range (VOR) approach

The pilot broadcast his intention to carry out a practice VOR approach at Charleville when he was 20 NM to the west. The VOR approach is designed to allow an aircraft to descend on specified VOR radials to a specified minimum descent altitude (MDA) in instrument meteorological conditions (IMC). The Charleville runway 12 VOR approach MDA is 1,750 ft or a height above the aerodrome of 727 ft.

To commence the procedure when approaching Charleville from the west, a sector entry is carried out. This entails passing over the aid (VOR) at the initial approach altitude of 2,800 ft and turning right onto a heading of 146 degrees for 1 minute. The aircraft is then turned right to intercept the inbound leg of the holding pattern to overhead the aid. The position of the accident site suggests that this procedure had not been carried out, and that control of the aircraft was lost in the initial right turn from overhead.

Fuel quantity

The pilot refuelled at Windorah before proceeding to Tanbar. The main and auxiliary tanks were filled. No fuel was added to the tip tanks. The main tanks contained 204 L, and the auxiliary tanks 113.5 L, of useable fuel.

Engine instrument indications

During the on-site investigation the engine tachometers were recovered. The left engine tachometer was indicating 2,700 RPM, which is red-line or maximum RPM. The right engine tachometer was indicating 1,600 RPM, which is approximate flight-idle RPM. Both indicators were jammed in position by impact damage.

Fuel selector positions

The left and right fuel selectors and valves were recovered from the wreckage and specialist examination was carried out to determine the selector positions at impact.

The right fuel selector was found selected to MAIN. The selector pin was found secure in the handle although the selector knob was broken off. The pin was positively in the MAIN detent position. The right fuel-selector plate was minimally deformed with two of the three screws securing the plate to its base still in place. This means that the handle probably stayed in contact with the selector plate. That the pin remained, indicates that the selector was in MAIN for the whole impact sequence.

The left fuel-selector handle was found slightly anticlockwise from the MAIN position towards the AUX position. The left fuel-selector handle pin was deformed and depressed into the handle. The handle was thus free to move out of the detents. Examination of the left fuel selector showed deformation of the selector area, the handle subject to impact movement, multiple impact marks around the MAIN position, deformation of the selector plate around MAIN, a clear imprint of the handle above MAIN and an imprint in the plastic base of the selector in the MAIN position. The examination indicated that the left fuel selector was selected to MAIN at impact.

Exhaust pipe examination

Exhaust pipe sections from both engines were examined to assess the temperature at impact. Both exhaust pipe sections exhibited straw/gold coloured heat tinting. A temperature cannot be assigned accurately to a heat tinting colour, since the colour varies not only with temperature but with the time at that temperature. However, the presence of heat tinting does indicate that the exhaust pipes were hot (above 350 deg. C) at the time of impact, and that the engines were operating immediately prior to impact.

Aircraft and engines

Examination of the wreckage did not reveal any defects which may have contributed to the accident. There were no mechanical defects found on the engines which would have prevented the engines from developing normal power.

Emergency locator transmitter

The ACK Technologies emergency locator transmitter (ELT) (which complied with TSO C91a) was found outside the main wreckage unattached. The case was intact, and the three-position (ON-OFF-ARM) function switch was in the centre OFF position. The switch was not guarded and may have been moved in the impact sequence. The unit was functionally tested and found serviceable.

ANALYSIS

At the time of the accident, there was no moon, and the aerodrome pilot activated lighting (PAL) had not been turned on. After passing over the township, which is to the north of the aerodrome, the pilot would have had no visual horizon. The pilot's multi-engine experience at night was 3.9 hours, all of which was in command.

The flight times since the last refuelling at Windorah to arrival overhead at Charleville corresponded to that required to exhaust auxiliary fuel tanks. The pilot was known to have allowed auxiliary tanks to run dry before selecting mains on previous occasions. The fuel supply to the right engine may have been interrupted due to exhaustion of the right auxiliary tank. The operating handbook cautions against using auxiliary tanks in other than level flight due to the possibility of uncovering the tank outlet. Should this occur the engine is likely to lose power, surge and stop. Once the fuel system has ingested air, the engine cannot be restarted until the air is purged and a normal fuel flow restored. The fuel selectors appear to have been selected to the main tanks at impact, but as indicated by the engine tachometer readings, the right engine was not delivering power. This was most likely due to the right engine fuel system having ingested air before the main tank was selected.

The possibility of the pilot carrying out a deliberate asymmetric approach was considered. However, this would seem unlikely due to the demanding nature of the exercise and the pilot's low experience on type at night.

An unexpected power loss while the pilot's attention is concentrated on the flight instruments could be most distracting, even for an experienced pilot. The effect would be for his attention to be immediately diverted to the engine instruments, and then possibly the fuel panel. Cross reference between the attitude and performance instruments is required to perform instrument flight, particularly when there is no visual horizon. This is critical in multi-engine aircraft if an engine fails and asymmetric flight is encountered. Should cross-reference be lost for any reason and the aircraft allowed to get into unbalanced, uncoordinated flight, the aircraft may assume an unusual attitude. The pilot may then become completely disorientated and lose control of the aircraft.

The aircraft attitude at impact suggests that this occurred.

SIGNIFICANT FACTORS

1. The pilot was inexperienced on multi-engine aircraft at night and had not undergone night flying training on the aircraft type.
2. The aircraft carried sufficient fuel for the flight, and it is likely that auxiliary tank fuel was depleted or nearly depleted when the aircraft arrived overhead Charleville.
3. The weather was fine, but with no moon and no visible horizon, was unsuitable for VFR operations at night.
4. The pilot was conducting a practice VOR approach at Charleville.
5. The right engine was not developing power, most probably due to fuel starvation.
6. The pilot lost control of the aircraft for undetermined reasons during a practice instrument approach and the aircraft impacted the ground.

The aircraft crashed into the back yard of a property in Munro Street. Initial information indicates the aircraft was about to land at St George after a flight from Toowoomba. The aircraft operator advises that the aircraft was privately hired for a return flight to St George.

The aircraft took off from runway 23 at Ballarat for a test flight. The take-off was witnessed by many operations and maintenance personnel who work on the airfield.

Witnesses advised that shortly after take-off they heard some loud bangs from the engine, which some described as backfiring, and then engine noise ceased. They estimated that the aircraft was 300 ft above the ground at this point. The aircraft then turned steeply to the left without much loss of height. After turning through approximately 180 degrees and levelling, the nose dropped and the aircraft spiralled steeply towards the ground. Immediately before impact, the engine surged to high power. Impact was

approximately 250 m beyond the end of the runway and 206 m to the left of the extended centreline.

The aircraft was destroyed by impact forces and fire. The impact was not survivable.

The terrain beyond the end of the runway was flat farming land with dispersed buildings and trees but provided suitable forced landing sites. Extensive fencing was the main hazard to a forced landing in this area.

The pilot of the aircraft was a licensed aircraft maintenance engineer (LAME) and his passenger was an apprenticed aircraft maintenance engineer. Both worked at the aerodrome. The pilot was also the owner of the aircraft, having restored it to flying condition approximately 5 years prior to the accident.

The pilot commenced flying in 1972. He flew regularly and in December 1990 was issued with a rating to fly at night under visual flight rules. In December 1992, he obtained his commercial pilot licence. At the time of the accident, he had flown approximately 890 hours, 240 of which were in the accident aircraft.

Persons who worked with the pilot at the airfield advised that in November 1995, 3 months before the accident, the aircraft was flown interstate by another pilot. During that flight, the engine was reported to have hesitated, run rough and had reduced power available. The aircraft was examined by a LAME but no fault was found. After the aircraft returned to Ballarat, the owner removed the engine-fuel nozzles and fuel distributor valve for testing. The test was satisfactory and the owner reinstalled the components.

The aircraft operated until 20 February 1996 when, as a result of further rough running and reports of the engine cutting out on take-off, the pilot removed the engine-driven fuel pump, the fuel control unit, and the throttle assembly for testing. The bushes on the mixture shaft of the fuel control unit were replaced, and some minor lint contamination was cleaned from the fuel control unit filter; otherwise, the units were found to be serviceable.

The pilot reinstalled the units and, on 29 February, the day of the accident, carried out engine test runs. After some initial setting up problems, the engine was reported to have operated satisfactorily, and the pilot was observed to taxi out to the runway and take off. The take-off was reported to be normal until the backfiring that preceded the accident.

It was determined that there was sufficient fuel on the aircraft for the flight as it had only been flown for about 1 hour since having the main tanks filled. The investigation was able to determine that at the time of the main impact, the fuel selector was selected to the right main fuel tank. The investigation could not determine the distribution of the fuel within the tanks, nor the exact quantity on board.

No abnormalities were found during the examination of the engine and components except that five pebbles were discovered in the cockpit- mounted fuel selector. Three were located in three of the five fuel passages in the strainer body. The other two were loose in the cavity between the main rotor and the strainer body and were able to sit over and partially block the fuel-feed passage.

The investigation is to be continued by the Victoria Police.

Synopsis

This report outlines the circumstances surrounding a fatal accident involving a Cessna 337 aircraft near Albany, in Western Australia on 13 March 1996. The aircraft crashed during a low-level inspection of a bay on the coastline to the east of Albany.

The accident occurred after the pilot lost control of the aircraft at low level. Loss of control was precipitated by a loss of power on both engines whilst the aircraft was being flown in a maximum-performance turn.

Loss of power on the rear engine was the result of fuel starvation, probably caused by un-porting of the fuel supply line during prolonged unbalanced flight. The reason for loss of power on the front engine could not be determined although it is possible that the pilot inadvertently selected the front engine to off whilst attempting to change the fuel selection on the rear engine from the main to the auxiliary fuel tank.

History of the flight

Witness evidence indicates the aircraft and pilot were hired so the passengers, Federal and State officers, could complete an aerial inspection of some unidentified drums located in a small bay 45 km east of Albany. An attempt to reach the drums on foot had failed because of dense undergrowth.

The pilot's post-flight report form shows the flight departed Albany Airport at 0901. Passengers' watches indicate the accident occurred between 0920 and 0925. There were no witnesses to the route flown or the accident.

The aircraft was reported missing at 1500, and the wreckage was located at 1615, on the edge of the bay containing the drums.

Pilot information

The pilot held a current commercial pilot licence with a Cessna 337 type rating. He was approved to conduct low-level operations. He was experienced in low-level operations, having worked as an agricultural and whale-spotting pilot for many years. He should also have been familiar with the coastline in the area of the crash, having operated in the area as a whale spotter.

The pilot held a Class 1 medical certificate. Post-mortem examination did not disclose any medical condition that may have been a factor in the accident.

Aircraft information

Cessna 337C VH-FAM was manufactured in the USA in 1968 and placed on the Australian register on 16 October 1968. The aircraft had completed 5,390 hours time in service. The rear engine, Serial Number IO-360-C-10344, had completed 393 hours of its 1,500-hour service life. The front engine, Serial Number IO-360-C-10014, had completed 1,726 hours of its 1,800-hour service life. The additional 300 hours available on the front engine were the result of earlier maintenance which extended the service life of that engine. An inspection of the aircraft's logbooks revealed that it had been maintained in accordance with the manufacturer's and regulatory requirements. A valid maintenance release was in force and no unserviceable items were recorded prior to the final flight.

The Cessna 337 is a twin-engine aircraft with the engines located fore and aft on the main fuselage. The rear engine is reported by the manufacturer to be the critical engine. Single-engine performance is less with only the front engine operating rather than the rear. In addition, the front engine is positioned below the total thrust line and the rear engine above it. Any loss of power in the rear engine will result in a nose-up pitching moment.

The estimated weight of the aircraft at the time of the accident was 1,927 kg. Maximum allowable weight was 1,996 kg. The pilot and one passenger were seated in the front row. The other two passengers were seated in each of the other two rows. The centre of gravity was within the defined envelope.

Meteorological information

The surface wind at 0900 at Albany was recorded as coming from 080 degrees at 16-18 kts. Meteorological advice indicates that the terrain around the crash site is conducive to the formation of small-scale eddies or rotors which cause turbulence. The pilot of the search helicopter reported that, 7 hours after the crash, conditions in the bay at low level were very turbulent. Wind conditions appeared to be significantly affected by the surrounding terrain. It was reported that the average wind conditions tended to push any aircraft operating in the bay towards the hills around the bay.

Communications

A review of the air traffic service recording tapes indicates that no radio transmissions from the pilot were recorded before or during the flight. There was no requirement for the pilot to contact an air traffic service agency. Wreckage and impact information

On-site inspection

It was apparent from aircraft and foliage damage that the aircraft impacted at a nose-down angle of approximately 60 degrees with the wings level. The left wingtip contacted the ground first, because of the slope of the terrain, followed by the lower, forward fuselage. Damage to the cockpit/cabin area was extensive. The fuselage section, aft of the wings, exhibited only moderate damage. The wreckage remained upright and mostly intact after the impact. There was no wreckage trail.

The direction of the impact indicated that the aircraft was flying towards the north, following the coastline in the bay, when it crashed.

The front engine was torn from the fuselage and suffered considerable impact damage to the crankcase, cylinders, and accessories. Engine oil was found on the ground under the engine. The rear engine suffered minor damage only, although the engine mounts fractured on impact.

The front propeller drive shaft fractured during the crash. Whilst both blades on the front propeller and one blade on the rear propeller were bent, neither propeller exhibited damage consistent with being under power at impact.

The landing gear was retracted.

The position of the flap motor worm drive indicated the flaps were extended to half travel.

All control surfaces were present, and all systems appeared to be working correctly prior to the accident. All damage was consistent with being caused by the impact.

Both wings were destroyed. The main fuel tanks, two in each wing, were split at the seams and exhibited severe distortion caused by the movement of fuel. The auxiliary fuel tanks, one in each wing, were intact although each had been breached. They also exhibited severe distortion caused by the movement of fuel. The distortion made it possible to determine that the main tanks were almost full and the auxiliary tanks half full, at impact. The right auxiliary was the only wing tank still containing fuel (3 L) at the time of the inspection. All other wing fuel had drained from the damaged areas. Both fuel sumps, one in each tail boom, were intact and undamaged. Only the left sump contained fuel.

The fuel lines running from the main and auxiliary tanks to their respective engine fuel filters were intact (right tanks to the rear engine and left tanks to the front engine). The fuel supply line from the filter to the rear engine was intact. The line on the front engine had been severed although fuel in the line was trapped by crimping adjacent to the fracture and the angle at which the wreckage was lying. No pre-existing blockages were found in the fuel system.

Approximately 50 mL of fuel was removed from the fuel supply line, filter, and engine-driven fuel pump for the rear engine. This amount is representative of residual unusable fuel. The right fuel sump was empty although beach-marks indicated that it contained approximately 1.25 L of fuel at impact. Approximately 250 mL of fuel was recovered from the lines and filter for the front engine, the amount expected from a fully charged system. The left fuel sump contained 1.3 L of fuel and beach-marks indicated that it had been full at the time of impact. No water was evident in any of the fuel recovered. The fuel colour and smell indicated it was 100/130 avgas. The difference in the amount of observed fuel and fuel at the time of the crash was probably the result of evaporation. The on-site wreckage inspection took place 5 weeks after the crash (due to the unavailability of a suitable winching helicopter). Both fuel sumps were open to the atmosphere as a result of main tank damage and were lying at an angle which placed open lines above the fuel. The amount of evaporation was about the same for each sump.

Despite the damage to the main fuel tanks, the wreckage situation was such that it was possible for fuel to pool in the leading edge of the inboard left main tank following the accident. This fuel could have recharged the left fuel supply lines after the crash, leading to the fuel found during the post-crash investigation. A similar situation did not exist on the right side of the wreckage.

Although the cockpit/cabin area was destroyed, the engine control panel was recovered intact. The throttles, propellers and mixture levers were found set at a cruise power setting. There was evidence they had been locked in their pre-crash position by the impact. The ignition and battery switches were on, and the auxiliary fuel pump switches were off. The flap selector was set to just below the first detent. This corresponded with the position of the flap motor drive shaft.

The fuel selector panel indicated that the front engine was selected to the left main tank and the rear engine to the right auxiliary tank. The left fuel selector valve was also set to the left main tank: the cable was intact and exhibited little damage. The fact that the selected position corresponded with the valve position and that cable stretch was minimal indicates that the control position was probably the selected position. The right selector valve was set between the main tank and off positions. The cable was severely stretched and kinked. The centre wire had been pulled from a clamp on the actuating arm at the fuel selector panel. Stretching of the right fuel selector cable could move the selector valve from the auxiliary position, through the main tank and towards the off position. There was some restriction to movement of the right selector valve.

Propeller examination

The fractured drive shaft from the front propeller was examined in detail. No evidence was found in either the mode of failure (bending) or in the nitride coating on the shaft, to indicate the propeller was under any power at impact.

The rear propeller was still attached to the engine. There was no evidence of any rotational damage on the blades. There was some evidence that the rear of the spinner had rubbed against the engine cowl during the crash. The rub marks were minor, indicating that, whilst the propeller was rotating, it was not under power. The rear propeller was lying across one tail boom following the crash. There were no strike marks on the boom.

Engine examination

The engines were examined at an engine overhaul facility. The inspection indicated that both engines should have been capable of normal operation prior to the crash. No faults were found with the engine's electrical and fuel systems.

Aircraft fuel system

Fuel contents

The aircraft was refuelled to full main tanks 1 month prior to the final flight. At that time, the auxiliary tanks were estimated to be half full. The aircraft was kept locked in a hangar when not in use. The distortion of the fuel tanks during the crash confirmed that there was sufficient fuel on board at the time. There were no witnesses to the pilot's pre-flight inspection; therefore, it could not be confirmed that he had completed a fuel check, including a check for water. Fuel recovered at the crash site did not contain any water and there was no other evidence that fuel contamination was a factor.

Fuel caps

All fuel caps were fitted with vents and the vents were clear.

Fuel selector panel

The Cessna 337C fuel selector panel is mounted in the cockpit/cabin roof. There are separate selector knobs for the front and rear engines. The knobs are the same shape and size and are mounted longitudinally, with the knob for the rear engine at the rear.

To move the rear engine fuel selector from the main to the auxiliary tank position, the knob is turned one notch to the right. Moving the front engine fuel selector one notch to the right from the left main tank position, turns the fuel off. There is no bar to prevent accidental selection to the off position on either selector, as the knob must be moved through off to select crossfeed.

Selection of auxiliary on either selector depresses a button which changes the fuel gauge indication from main to auxiliary tank. The button is depressed as the lever moves and does not need to be depressed to move the lever. The normal method of fuel selection in the Cessna 337 is to operate the front engine from the left fuel system and the rear engine from the right fuel system.

The selector panel was dismantled and inspected. As was noted above, the operating cable for the rear engine/right fuel selector had been pulled from a clamp at the selector end of the cable. There were marks on the selector actuator arm which indicated that it had been pulled hard against the pinion gear shaft before the cable was pulled from the clamp. It was apparent that separation occurred during the crash process. Although the rear selector knob was set to the auxiliary tank position, it was free to move as a result of the separated cable. This, coupled with the witness marks on the selector actuator arm, indicates that the final knob position was not the selected position.

Fuel selector valves

The fuel selector valves were examined. Both valves appeared capable of normal operation. The restriction to movement reported in the right valve was determined to be excessive friction caused by a build-up of corrosion. It could not be determined if the corrosion was present prior to the crash.

The selector operation had been checked during the periodic servicing which took place 41 flying hours prior to the crash. Evidence was also available that the fuel selector controls and valves had operated correctly two flights prior to the final one. The selector had not been moved on the penultimate flight.

Fuel tanks

In the Cessna 337C the auxiliary fuel tanks, mounted inboard of the tail booms, feed directly to the engines via their respective selector valves.

The main fuel tanks, mounted outboard of the tail booms, feed the engines via a fuel sump located in each tail boom. Each sump has a capacity of 2.7 L and is gravity-fed from the main tanks. Fuel is drawn through an outlet, located in the top of the sump, by the engine-driven fuel pump. The outlet is displaced to the inboard side of the sump centreline. As a result, the unusable fuel, in a 45-degree banked turn, varies from 1 L to 1.25 L, depending on the direction of the turn. The unusable fuel in the right sump in a right turn is 1.25 L. The unusable sump fuel, in level flight, was measured at 500 mL. An auxiliary fuel pump is provided in the event of engine-driven pump failure.

Under normal conditions (balanced flight), unusable fuel is not a consideration as the fuel system is designed to keep the sumps full. In some circumstances (unbalanced flight), it is possible that gravity feed to the sump may cease. For example, in an unbalanced turn to the right, if the pilot introduces left rudder to help keep the nose up as bank angle is increased, gravity feed from the main fuel tanks to the right fuel sump will stop. The sump is above the main tanks and gravity and centrifugal force will tend to move the fuel downwards and away from the main tank outlet. Fuel will continue to feed to the left sump as the situation is reversed. Selection of the right auxiliary tank will overcome this problem as it bypasses the sump, and the outlet is on the lower part of the tank in a right turn.

At cruise fuel consumption rates (37.5 L/hour/engine), it will take just over 2 minutes for the rear engine to use the 1.45 L of useable fuel available in the right sump in an unbalanced turn. If the fuel selector is selected off or moved to a position were fuel supply is interrupted, tests indicate power loss will occur after approximately 9 seconds, as fuel supply is stopped downstream from the sump.

In the Cessna 337D and later models the auxiliary fuel tank is interconnected with the main tank and also feeds the sumps. This arrangement overcomes any possible fuel feed problems that might occur during an unbalanced turn.

Survival aspects

The crash was not considered survivable. Crashworthiness information indicates that aircraft occupants are unlikely to survive an impact at 60 degrees to the horizontal if the airspeed is more than 55 kts. As the stalling speed was probably in excess of 80 kts, impact speed would have exceeded 55 kts.

Although no evidence was found that the pilot had left a formal flight note with a responsible person, an associate of one of the passengers raised the alarm when the aircraft had not returned. Initial concerns were expressed to the manager of Albany Airport at 1330. A formal search was started by the Melbourne Search and Rescue Centre at 1500, once local attempts to establish the whereabouts of the aircraft had failed. The wreckage was located at 1615 by aircraft from the Western Australian Police Air Wing. The search aircraft initially flew over the wreckage without sighting it. The crew were directed back to the site by the signal from the emergency locator transmitter.

The aircraft was fitted with a fixed installation emergency locator transmitter that complied with TSO C91a. The transmitter was activated by the crash. However, its signal was not received by the search-and-rescue satellite until the day after the accident and therefore did not provide an early indication that a crash had occurred. The coaxial cable from the transmitter to the fixed aerial had been severed at the aerial. Movement of the coaxial cable during recovery of the bodies probably led to the signal being received by the satellite.

Organisational and management information

The operator held an appropriate air operators’ certificate. No organisational or management issues were identified as contributing directly to the accident. The drums were later found underneath bush on the edge of the bay. They were not visible from the air. A State Police helicopter was operating in the area of the crash site at the time but was not used in the search for the drums.

Terrain

The bay in which the accident occurred is open to the south-east and surrounded by hills up to 1,843 ft high. The average ground slope, which starts at the waterline, is 33 degrees. The bay is rectangular in shape and 300 m wide and 400 m deep. Calculation based on the manufacturer-supplied performance figures indicates a Cessna 337 cannot out-climb the terrain from inside the bay with only one engine operating.

Stalling speeds

The Cessna 337 owner’s manual details the expected stalling speeds for various configurations. At 1,905 kg the stalling speeds are:

• At 0 degrees of bank: 65 kts with flap up, 60 kts with flap at one-third and 55 kts with full flap.
• At 30 degrees of bank: 69 kts with flap up, 64 kts with flap one-third and 59 kts with full flap.
• At 60 degrees of bank: 91 kts with flap up, 85 kts with flap one-third and 78 kts with full flap.

Thus, stalling speed reduces with the application of flap but increases significantly with increasing bank angles. The estimated stalling speed for the aircraft configuration was between 80 kts and 85 kts.

Post-accident inspection flights and other operational information

During the investigation, flights were conducted in a twin- and a single-engine aircraft over the bay area. The pilot of the twin-engine aircraft reported he could not remain inside the bay in a right turn with less than 60 degrees of bank selected. He was operating at a higher speed (120 kts) than the Cessna 337's assumed operating speed. The investigator in charge inspected the bay in a Cessna 182. His pilot flew a pattern which he thought was the best way to view the bay: this consisted of commencing an orbit over the bay at 900 ft (clear of the terrain and turbulence). When the drums were not sighted, he descended in a continuous 30–45-degree banked turn, at 75 kts with flap set, to 500 ft (the limit because of turbulence and safety).

Discussion with experienced pilots indicates that during low-level inspections it is not unusual for a pilot to introduce top rudder in a turn to allow bank angle to be increased and thereby improve the view below the aircraft without losing altitude in the process.

Flight tests and calculations indicate that to operate a maximum-weight Cessna 337 with half flap set, with both engines operating at cruise power, in nil-wind conditions and at low level in the bay area, requires a steep turn of more than 51 degrees of bank and an airspeed of no more than 90 kts. Once committed to the turn inside the bay, a pilot would have no option but to continue the turn to exit. Any adverse wind conditions would cause an increase in the bank angle required.

Experience indicates that operations at low level in confined situations place pilots in a high workload environment where they need to concentrate their attention outside the cockpit. In previous investigations it has been determined that this type of operation often leads to poor airspeed control. It can also lead to the unsighted operation of ancillary controls such as fuel selectors, particularly if the pilot is experienced on the aircraft type and does not need to look at the control to confirm where it is or how it operates.

Information from fuel starvation occurrences indicates that an engine will usually start surging rather than just stop when the fuel quantity available is low, particularly when operating in turbulent conditions. Usually, the first action by the pilot in the event of a sudden and unexpected power loss in cruise flight is to move the fuel selector to another tank that has fuel in it. If there is no response, this action is usually followed by selection of the auxiliary fuel pump. Fuel pump selection varies, depending on aircraft type.

Tests and research

BASI Report 87-116 (Australian Aviation Occurrences Involving Fuel Starvation & Exhaustion 1969-1986) concludes that pilot factors were involved in 89% of fuel exhaustion occurrences and in 45% of the fuel starvation occurrences reviewed. It goes on to report that 71% of the factors involved mismanagement of the fuel system. The report looked at all types of general aviation aircraft, both single and multi-engine.

To further refine the information obtained from Report 87-116, the air safety occurrence databases of the Bureau and the US National Transportation Safety Board were reviewed to determine the types of events that led to loss of power to both engines in twin-engine aircraft in general and to loss of power in one or both engines in the Cessna 337.

The following are explanations of some of the terms used.

Fuel exhaustion occurs when all the useable fuel in the aircraft has been consumed. Pilot miscalculation is often the main factor, although there are some occasions where problems with the fuel system may give the pilot false information or fuel is lost overboard.

Fuel starvation occurs when there is still adequate fuel on board the aircraft, but it is not being supplied to the engine(s) for some reason. Mismanagement of the fuel system is often the main factor. However, there are occasions where such problems as fuel contamination or fuel blockage may be factors.

Un-porting occurs when the fuel tank outlet is uncovered, and air enters the system. A low fuel state or unusual manoeuvres can lead to un-porting.

Mechanical failure/malfunction includes failure of an engine component or accessory, low oil pressure, low fuel pressure, fouled spark plugs and rough running.

"Undetermined" covers those factors which could not be or were not determined by the investigating authority.

The events listed as "other" include one-off occurrences such as icing conditions.

The review of the Bureau's database covered the years 1969-1996 and included power-loss occurrences (accidents and incidents) in all types of aircraft and the Cessna 337 in particular.

Fifty-nine occurrences involving loss of power in both engines in all types were identified. Of these, 31 were the result of fuel exhaustion, 20 of fuel starvation, six for other reasons and two were of undetermined origin. Sixty-five percent of the fuel starvation occurrences involved pilot factors.

There were 67 occurrences involving a loss of power on one engine in the Cessna 337. Of these, 52 were the result of mechanical failure/malfunction, 12 were due to fuel starvation and three were for undetermined reasons. There were seven occurrences where there was a loss of power on both engines in a Cessna 337. Four were the result of fuel exhaustion and three involved fuel starvation. Two of the three involved pilot factors. The factors in the third were undetermined.

The review of the National Transportation Safety Board's database covered the years 1985-1995 and Cessna 337 accidents involving a loss of power on one or both engines.

There were 12 accidents involving loss of power on one engine and 23 accidents involving loss of power on both engines. Four single-engine accidents resulted from mechanical failure/malfunction, four were for undetermined reasons, two were from fuel starvation and two occurred for other reasons. The records for the multiple-engine failure accidents indicate 11 resulted from fuel exhaustion, eight from fuel starvation, three were for undetermined reasons and one was the result of un-porting of the fuel supply lines. A breakdown of factors in the National Transportation Safety Board's recorded accidents could not be determined from the information available.

No occurrences were identified, in either database, where a loss of power in both engines resulted from mechanical failure/malfunction.

The one report of un-porting in a Cessna 337 involved a pilot entering a wings-level, steep descent whilst there was minimum fuel in the tanks. Both engines stopped during the descent as a result of un-porting of the fuel lines.

The manufacturer reported that a military version of the Cessna 337C was used extensively as a forward air control aircraft in Vietnam without any similar fuel feed problems being reported. Forward air control often results in extreme flight attitudes.

Anecdotal evidence indicates that the rear engine of early model Cessna 337s occasionally stopped without warning during varying phases of flight. Some of these stoppages led to accidents when the loss of power was not identified early enough by the pilot. A common reason for these stoppages was not formally identified.

Overview

It is evident from information provided on the purpose of the flight, the location of the crash, the impact direction, and the damage, that the pilot was conducting a low-level inspection of the bay area in an attempt to find the drums. To complete this task, he had to fly the aircraft in a steep, right turn at a slow speed. During the turn both engines lost power. The loss of power led to a loss of control and the pilot was unable to recover the situation prior to impact.

Engine power loss

The lack of rotational damage to either propeller indicates that both engines had lost power prior to impact.

The lack of fuel in the system supplying the rear engine suggests fuel starvation contributed to its loss of power. The fact that the sump was depleted indicates that the fuel supply to it was interrupted. As no blockages were found, the most probable reason is that a prolonged, unbalanced, right turn stopped fuel feed to the right fuel sump from the right main tank. In less than 3 minutes, all useable fuel in the sump had been consumed and the engine stopped.

One flight conducted during the investigation indicated that the accident aircraft probably commenced an orbit over the bay area at a higher altitude than that used for the final circuit. When unable to see the drums, the pilot probably descended until he entered the bay on the final orbit at low level. As a result, the turning-time required to deplete the useable fuel in the sump could have been exceeded.

No direct evidence was available to establish why the front engine was not producing power. The investigation found that fuel was available and that all the engine systems were probably serviceable. The engine controls were all selected to the operating position at impact.

The research indicates there are no recorded occurrences where a loss of power to both engines resulted from mechanical failure/malfunction of the engines. The most common reasons for loss of power to both engines in a twin-engine aircraft (and in particular the Cessna 337) are either fuel exhaustion or fuel starvation. There was adequate fuel on board the aircraft; therefore, fuel exhaustion is not a consideration. As a result, fuel starvation is considered to be the most likely reason for the loss of power to the front engine. Pilot factors were identified in 45% of fuel starvation occurrences in all types of aircraft and in 65% of those involving twin-engine aircraft. In the absence of any evidence indicating a problem with the aircraft systems, pilot factors are considered the most probable contributors to loss of power to the front engine.

As it is common practice to select a different fuel tank following sudden power loss, it is possible that the pilot inadvertently selected the front engine off whilst he was attempting to restart the rear engine by changing the fuel tank selection. The design of the fuel selector switches and the pilot's concentration outside the cockpit may have contributed to his action. Fuel supply to the engine was probably re-established when the pilot realised his mistake and reversed the selection. Fuel then flowed backed into the lines, but the engine had insufficient time to restart.

Loss of control

The pilot had extended the flaps to reduce the stalling speed and increase his safety margin. Evidence indicates the aircraft was probably flying at 85-90 kts. This speed gave the pilot a small margin above the stall and allowed the aircraft to remain inside the bay. Under the circumstances, any interruption to engine power would have resulted in a sudden reduction in flying speed. This may have been sufficient to cause the aircraft to stall. If the rear engine lost power first, the nose-up pitching moment would have exacerbated the situation. The tendency for the prevailing wind to push the aircraft towards the hills could have resulted in an unconscious action by the pilot to increase bank and tighten the turn, thereby further reducing the safety margin. Turbulence may also have been a factor.

Impact sequence

The steep nose-down attitude indicates the aircraft was probably in an aerodynamically stalled condition for some time prior to impact. Considering the pilot's experience, the stalled condition probably resulted from a loss of control at inspection height. In a more controlled situation, the pilot would have attempted to manoeuvre the aircraft to a crash landing, and any last-minute stall would have been less severe. The relatively intact nature of the wreckage and the lack of severe damage to the aft fuselage indicates the loss of control occurred at low altitude.

Summary

As the right sump fuel contents approached the unusable level, it is likely the rear engine began to surge rather than just lose all power immediately. Re-establishment of fuel supply from the auxiliary tank would have corrected the situation and prevented complete power loss. The pilot probably attempted to change the tank selection. The lack of fuel in the rear fuel supply lines indicates that this did not occur. Although there is no substantive evidence to explain the loss of power to the front engine, it is possible the pilot inadvertently selected it off instead of selecting the rear engine to the auxiliary tank.

Failure of the rear engine alone may have been sufficient to cause the loss of control, particularly if the pilot was distracted from flying the aircraft by the engine/fuel situation. Failure of both engines at a critical point in a maximum-performance turn in a confined area will almost certainly lead to loss of control.

The low operating altitude probably prevented recovery from the loss of control situation before impact.

1. The task requirements and the terrain conditions meant the pilot had to fly the aircraft in a continuous maximum-performance right turn at low level. Whilst they approached the limits, these conditions were still within the aircraft's and the pilot's capabilities. As the aircraft was operating at or near the limits, there was little margin for error. The margin available was insufficient to prevent loss of control when the situation changed unexpectedly.
2. To improve visibility, the pilot probably introduced left rudder and increased the angle of bank, thereby creating an out-of-balance condition.
3. A prolonged, unbalanced turn probably led to fuel starvation and loss of power to one engine.
4. A sudden, unexpected loss of power during a maximum-performance turn resulted in loss of aircraft control.
5. The loss of power and control occurred at low altitude and there was insufficient height to effect recovery.