Collision with terrain

The purpose of the flight was to conduct an aerial inspection of a corn crop located approximately 1 km east of the airstrip. Witnesses reported seeing the aircraft in straight and level flight at a height of about 500 ft and hearing a change in the engine noise. A short time later, the right wing dropped, and the aircraft entered a steep, nose down, spiral descent which continued to ground impact.

Examination of the accident site showed that the aircraft had struck the ground while inverted and in a steep nose-down attitude while rotating to the right. The nature and extent of damage to the propeller indicated that the engine was developing significant power at impact. Inspection of the wreckage revealed no faults which might have contributed to the accident.

The evidence suggests that the aircraft probably stalled, causing the right wing to drop and a spiral dive to develop from which the pilot was unable to recover in the height available. The reason for the aircraft entering the manoeuvre was not determined.

Factors

1. The aircraft probably stalled, resulting in a spiral dive developing.

2. The pilot was unable to recover the aircraft to normal flight in the height available.

FACTUAL INFORMATION

Background

The aircraft was engaged in providing support to a mineral exploration operation. The operation required that the drilling rig be disassembled by attaching the various components to the sling of the helicopter and lowering them to the ground.  The rig, associated equipment and personnel were then transported to the new site where the rig was reassembled by using the helicopter to lift the rig components into position.

The drilling rig was operated by the company owner, a driller, and two assistants.  The driller had previously used a helicopter in operations to disassemble, transport and reassemble the rig.  Neither of the assistants had been involved with the use of helicopters in drilling operations.  One of the assistants had practised assembling and disassembling the rig at the driller's base with the use of a crane.  The other had no previous experience with this type of drilling rig.

Sequence of Events

Earlier in the day the helicopter had been used to transport personnel to the drilling site (T9) from the base camp.  It had later flown to a fuel dump and carried a drum of fuel, as an externally slung load, to the next site to be drilled. At this site, the pilot added approximately 30 litres of fuel to the aircraft, removed the sling and net from the external attachment point and stowed them in the cabin of the aircraft.  The aircraft was then flown to T9 from where personnel and equipment were to be transported in preparation for the re-location of the rig to the new site.

At site T9, the pilot remained in the helicopter with the engine operating while the other personnel loaded two batteries and two drill hammers onto the floor of the cabin area. The assistant who was to travel on the helicopter to the next site attached the sling to the external attachment point. The driller and the assistant then boarded the helicopter. They were seated in the cabin opposite each other with one facing forward and the other rearward.

The helicopter then lifted off and, just after commencing forward flight, the end of the sling momentarily contacted the engine of the drilling rig.  The sling was flung upward and struck the helicopter.  As a result, a metre long section of the tip end of one main rotor blade was severed.  A main rotor blade then struck the forward right side of the cockpit area, fatally injuring the pilot.  The tail boom of the helicopter was severed by the damaged main rotor blade and the helicopter fell to the ground, landing on its left side.  Two persons on the ground assisted in evacuating the passengers. One of them remained at the site to assist the passengers and the other walked the considerable distance to the base camp to obtain assistance.

Operational and Briefings Aspects

The helicopter operator's operations manual required that the pilot be qualified on sling operations prior to this type of operation being undertaken.  The manual also required that the pilot brief all personnel involved in the sling operation prior to commencement.

On this occasion, because both the pilot and driller received fatal injuries, it was not possible to determine the extent of the briefing between the two men.  However, the assistants reported that their briefing covered two aspects only; the method of approaching the helicopter when the rotors were turning and the method of manipulating the sections of the drilling rig while they were attached to the sling on the helicopter.

The assistant who attached the sling to the helicopter stated that he had not been instructed on how to complete the task.  When he attached the sling, the pilot waved him away.  The assistant assumed that this was because he was attaching the sling from the wrong direction. He then moved around the helicopter and attached it from a different direction.  Thus, he believed that the pilot was aware that the sling was attached to the helicopter. Whether the pilot was aware the sling was attached and forgot about it during the take-off or believed that the sling was not attached is unknown.  The helicopter was not fitted (nor was it a requirement) with any device that would allow the pilot to ascertain the presence of a sling or the condition of the load on the sling.

Communications and Search and Rescue Aspects

The aircraft was fitted with an Emergency Locator Beacon (ELB) which was not activated during the accident sequence.  The beacon was located on the centre pedestal of the cockpit and positioned so that it was inclined downward.  The operation selector was in the 'Armed' position and a subsequent functional check found that the ELB was serviceable and capable of operation.

The ELB was of the type that is fitted with a single gravity activation switch and the method of mounting it on the pedestal was calculated to allow activation for vertical and forward impacts (those most likely as a result of helicopter accidents). On this occasion the helicopter landed on its left side and the gravity switch was not activated.

No communications network had been set up between the base camp, the helicopter or each drilling site. As a result, there was no provision to either allow the persons at T9 to call for assistance or to alert those at other sites of a potential problem when a schedule was missed.  Also, no one at T9 was aware that the ELB could have been manually activated, thus gaining the assistance of other aircraft in the area. The end result of the lack of a communication network was that a person was required to walk out of the site to obtain assistance.

CONCLUSIONS

Findings

• The pilot was correctly licenced and experienced in the type of operation being conducted.
• The aircraft was serviceable prior to the occurrence.
• The driller had previously conducted similar operations using the support of a helicopter.
• Neither of the driller's assistants had experience working with helicopters.
• The external sling was attached to the helicopter by one of the driller's assistants.
• The pilot could not visually confirm whether or not the external load sling was attached.
• It could not be determined whether the pilot was aware that the sling was attached to the helicopter.
• The pre-operation briefing given to the two drillers assistants was inadequate.
• A metre long section of one main rotor blade was severed by impact with the sling.
• The Emergency Locator Beacon was serviceable and 'armed' prior to the occurrence.
• The Emergency Locator Beacon was not activated by the impact.
• No communications network had been set up between any section of the operation.
• Persons involved in the operation at site T9 were not aware of how to operate the Emergency Locator Beacon.

Significant Factors

• The briefing, by the pilot, of all those involved in the operation was inadequate.
• The helicopter was not fitted with a mirror to enable the pilot to visually confirm the status of the external load sling hook.

SAFETY ACTION

As a result of the investigation the Bureau of Air Safety Investigation issues the following recommendation and safety advisory notices:

1. Recommendation R940190

Summary of Deficiency

A search of the BASI data base revealed that nine accidents involving sling operations had occurred in the past nine years. Of these, six may have been directly related to the pilot being unaware of the presence of a sling or the condition of the winch load.

Regulations relating to sling load and winching operations with helicopters do not require a device to be fitted to allow a pilot to ascertain the status of the sling and load. Additionally, there are no minimum equipment requirements for sling operations specified in Civil Aviation Orders.

Many operators have documented their own requirements relating to minimum equipment for sling/load operations.

Recommendation

The Bureau of Air Safety Investigation recommends that the Civil Aviation Authority:

(i) Review the legislation relating to sling load and winching operations with particular emphasis given to the minimum equipment requirements and the benefits associated with a load checking device, such as a mirror.

(ii) Consider producing effective educational documentation that addresses the issues that pilots and operators should consider in these types of operations.

2. Safety Advisory Notice SAN 940192

Summary of Deficiency

The Civil Aviation Authority is introducing the mandatory carriage of ELTs complying with the US FAA Technical Standard Order 91a (TSO 91a) which comes into effect in July 1995. This does not fully take into account the unique flight characteristics of helicopters.

ELTs with multi-axis gravity switch activation complying with TSO 91a are now available for purchase by operators.

Safety Advisory Notice

The Bureau of Air Safety Investigation suggests that in conjunction with the introduction of the mandatory carriage of ELTs complying with TSO 91a, the Civil Aviation Authority consider introducing a requirement for only multi-axis gravity switch activated ELTs to be fitted to helicopters.

3. Safety Advisory Notice SAN 940194

Summary of Deficiency

Anecdotal evidence collected by the investigation team suggests that it is not unusual for employees to be set down at remote sites with no way of communicating with either their company or outside help.

In the event of an emergency, personnel on the ground at the remote site must either walk out of the site or wait for help to arrive. In cases that are time critical neither of these methods would appear satisfactory.

Safety Advisory Notice

The Bureau of Air Safety Investigation suggests that the Queensland Department of Minerals and Energy, the Mining Industry Standing Committee and The Australian Mining Industry Council consider introducing a minimum acceptable standard of communication between all facets of remote operations as well as setting up a contingency plan for emergency situations at such sites. It is also suggested that these organisations consider implementing education programs for personnel involved in these types of operations.

The flight had progressed from Melbourne to Gunnedah, apparently without incident. After refuelling at Gunnedah, the aircraft departed for Noosa. No flight plan was submitted, nor were any documents indicating an intended route recovered from the accident site. The aircraft was subsequently observed passing over the parachuting centre at Toogoolawah. Weather in that area was poor, with a low cloud base. Parachuting operations had been suspended due to the cloud.

The aircraft apparently tracked north of Kilcoy and eventually around the northern edge of a range before tracking east. The weather on ranges closer to the coast was probably sufficiently poor to deter the pilot from tracking to the coast. Witnesses saw the aircraft in a valley between Conondale and Kenilworth, to the west of Maroochydore airport. Cloud covered all the ranges around the valley. The aircraft was last observed by one witness to be tracking towards Kilcoy. This information was consistent with the position of and direction to the accident site.

Searchers found wreckage of the aircraft at the top of a ridge line east of the main range to the west of Conondale. The aircraft had collided with the upper portion of a tree while in a left bank. Further breakup of the aircraft continued along a direction of 230 degrees, down the side of the ridge and across a small gully. No evidence of any mechanical defect or abnormality was found. From the available evidence, the aircraft was probably either in cloud or at the base of the cloud at the time of the accident. No evidence was found to indicate that the aircraft was equipped with instrumentation appropriate for flight in instrument meteorological conditions.

Significant Factor

1. The pilot continued flight into weather conditions in which he was unable to maintain the visual reference necessary to ensure adequate terrain clearance.

Factual Information

The pilot departed from his property in his ultra-light aircraft at around 0830 EST for a local flight. He flew over several of his friends' properties and over the local township. The weather as reported by witnesses was a sunny day, wind light and variable, scattered high level cloud with a temperature of 18 degrees C.

Witnesses reported that they had observed the aircraft flying in a south westerly direction at an altitude of approximately 150 ft. The aircraft was observed to be flying at a constant speed with the engine noise remaining constant. A father and son said that they waved as the aircraft flew over where they were standing and the pilot acknowledged by waving back to them. The aircraft then banked steeply to the right, with the bank angle estimated to be 90 degrees. At approximately 180 degrees into the turn, the aircraft was observed to stall. At this point the nose dropped, and the aircraft proceeded to rotate. The aircraft was in a steep nose down wings level attitude, when the aircraft crashed through the safety rails of a bridge and impacted the ground, fatally injuring the pilot. The point of impact was approximately 75m from where the witnesses were standing.

Examination of the wreckage did not find any pre-existing defects that would preclude normal operation of the aircraft. There was no evidence that the pilot had any pre-existing medical conditions that would affect his ability to fly the aircraft. The pilot had accumulated some 188 hours flying time in ultra light aircraft, the majority of which was in this aircraft. He was currently undergoing additional flying training to gain his Private Pilot's Licence.

Analysis

The final flight path observed by the witnesses during the turn was consistent with the aircraft stalling and entering an autorotation. In attempting the manoeuvre, the pilot allowed the aircraft performance to degrade by not maintaining sufficient airspeed, resulting in the aircraft departing controlled flight at an altitude insufficient to recover.

FACTUAL INFORMATION

History of flight

The pilot and his passengers arrived at Hotham Heights at about 1735 EST on 21 September 1993. At the time the temperature was minus three degrees Celsius, it was snowing lightly, and the visibility was poor due to low cloud. The pilot parked the helicopter facing in a northerly direction in the day car park overnight. Snow deflector baffles were not fitted to the airframe and covers were not placed in the engine air intakes or on the exhaust stacks. Overnight it snowed enough to cover tracks from the previous day. The average windspeed, recorded from midnight, varied from 4 knots to 13 knots, varying in direction from the north through to the west.

Shortly after 0900 on 22 September 1993 the pilot threw a few cupfuls of water from a bucket into both sides of the particle separator which is the air filtering device for the engine air intake. He also threw water onto the tail rotor assembly and the windshield. Throwing water into the particle separator is not standard practice on a daily inspection prior to flight. About ten minutes later the pilot returned to the helicopter, loaded the two passengers, untied the main rotor, and started the engine. When the main rotor started to spin, snow was flung off the main rotor blades. The pilot ran the engine for five to ten minutes. Then the helicopter lifted into a hover briefly before it departed to the south west and descended into a valley.

The helicopter wreckage was not located until 1245 on 23 September after a prolonged search. The accident site was on a steep, snow covered, timbered slope in mountainous, alpine terrain about 1,300 ft lower than Hotham Heights. The pilot and the two passengers did not survive.

Flight notification

The pilot had telephoned his wife from Hotham Heights at about 0920 on 22 September to say that he would be departing shortly and that he would arrive at Moorabbin by 1200 local time. By about 1315 the pilot's wife became so concerned that her husband had not arrived that she telephoned a friend who contacted Moorabbin Airport to check on the whereabouts of VH-FUX. It was then realised that the helicopter had not arrived, and a search was initiated.

The pilot had not submitted a flight plan to the Civil Aviation Authority (CAA). By telephoning his wife, he had opted for the approved alternative of leaving a Flight Note with a responsible person. The investigation could not determine whether the pilot had acquired a weather forecast before departing Hotham Heights. A post-accident estimate of the fuel on board indicated that it was sufficient for the conduct the flight.

Weather

When the helicopter departed Hotham Heights, the temperature was minus 2.2 degrees Celsius, the relative humidity was 100% and the wind was 256 degrees at 8 kts. It was not snowing. The mountain peaks and tops of the ridges were covered by seven eighths of cloud which was showing signs of dissipating with the sun shining through in patches. The cloud base was slightly below the level of the Hotham Heights day carpark. Cloud conditions on the ridgeline immediately west of the accident site were probably similar. The valley into which the helicopter descended was reported to be clear of cloud with visibility being about 2 km.

Survival

The pilot survived the crash and died from injuries and/or hypothermia before the helicopter wreckage was located.

The helicopter was equipped with a Narco ELT10 survival beacon and a basic survival kit. The survival beacon was ejected from the helicopter at impact and was damaged. Once damaged, the beacon was incapable of transmitting a distress signal to assist in locating the helicopter.

Wreckage examination

Examination of the wreckage did not reveal any pre-existing defects which may have contributed to the accident. Damage sustained by the helicopter during the accident, as well as the damage to the trees, indicated that at initial impact the helicopter had a moderate rate of descent, with low rotor RPM and very little forward airspeed. The helicopter impacted the ground on its left side after which it slid about 20 m down a steep slope before coming to rest against tree trunks. It was within its approved centre of gravity and gross weight limits at the time of the accident.

No evidence of significant torsional twisting was found on any of the drive shafts. The main rotor mast was not torsionally twisted. The engine compressor case-half liners suffered minor internal damage consistent with engine RPM being very low at impact. This evidence is consistent with the engine having flamed out before impact.

The engine was successfully test run after the accident in an approved engine test cell.

Radio transmissions

At 0937, Melbourne Flight Service received a radio mayday call. A call sign was not received, and the Flight Service officer had no idea who transmitted the words 'mayday, mayday, mayday' but did correctly identify which frequency, from the group of frequencies he was monitoring, on which the call was made. He immediately declared the distress phase and notified the search and rescue mission coordinator (SARMC). As no further radio calls were made to indicate that an aircraft was in distress, the search and rescue phase was cancelled.

The recording of the mayday call was subsequently analysed by BASI and identified as having originated from VH-FUX. The mayday call lasted 2.1 seconds. After voice modulation ceased, there was approximately 0.42 seconds where noise was recorded. A second transmission was made approximately one second later and was approximately 0.23 seconds in duration. The results were compared with the helicopter manufacturer's data and with inflight recordings obtained during inflight trials conducted in VH-FUX on 16 September 1993 when sound and instrument readings were recorded to assist in another accident investigation. A tone which was considered to have been related to aircraft operation was detected and compared with prior recordings of VH-FUX in flight. The tone indicated that the aircraft may have been in an autorotation with the main rotor RPM reducing from 85% to 82% over a 3.3 second period. The normal range for a power off autorotation is 90% to 107%.

Flight in icing conditions

The approved Flight Manual for the Bell 206B states that the helicopter is certified for operations under non-icing conditions. The Flight Manual also states that engine anti-icing shall be selected on for flight in visible moisture in temperatures below plus 4.4 degrees Celsius. At the accident site the anti-ice valve on the engine was found on and the anti-ice switch in the cockpit was found in the on position. It is not known when the pilot selected anti-icing on.

In the Antarctic, the pilot had flown helicopters which were fitted with the same type of engine. He would have been familiar with the potential problems associated with ice. Compressor surge/stall has previously occurred in a Bell 206B in similar weather conditions in the Australian alps. In that case, the surge/stall occurred before the helicopter lifted off. Compressor surge/stall is audible. Witnesses who saw and photographed VH-FUX at Hotham Heights prior to and during its departure, reported no unusual engine noise.

Advice was sought from the Allison engine manufacturer. The engine manufacturer raised the possibility of a slug of ice/slush/snow being sucked into the intake causing a flameout. Such flameouts have been known to occur with the Allison 250 C18 and C20 engines fitted to Hughes 369 helicopters (also known as Hughes 500s) during flights in the Antarctic. In the Antarctic occurrences, the engine flameouts occurred in flight after about 15 to 20 minutes, but the outside air temperatures were colder than in the Australian alps. The Allison 250 B17, which has the same compressor, has been known to flameout in a Nomad floatplane due to water spray during taxiing. A twin engine Bolkow 105 helicopter also suffered a flameout on both of its Allison 250 C20 engines due to snow/sleet ingestion inflight despite the fact that the anti-ice was operating on both engines. In the case of a slug of ice/slush/snow or water causing an engine flameout, usually no damage is subsequently found in the engine.

Tests And Research

An experiment involving throwing cups of water into a particle separator, which was not fitted to an aircraft, proved that a significant amount of water will pass through the swirl vanes of the particle separator into the plenum chamber. There were no drain holes in the plenum chamber. This area is well sealed off to allow only filtered air to enter the engine.

ANALYSIS

Pre-flight actions

Because the helicopter was parked overnight in falling snow and moderate winds, without compressor intake covers installed, it was quite possible that snow made its way into the particle separator. The pilot probably saw frost/snow in the particle separator prior to starting the engine, which would account for his throwing water into it.

However, some of the water thrown into the particle separator by the pilot, plus some of the overnight snow, probably accumulated in the plenum chamber. It is unlikely that the pilot would have been able to see into the plenum chamber, if he tried to check for the presence of snow or water, because the Perspex viewing ports would have been covered in frost. Also, it is normally difficult to see clearly into the chamber except in very bright sunlight or with the aid of a bright torch. The pilot was not seen using a torch and ambient light at the Hotham Heights carpark was diminished by the foggy conditions.

Pilot decisions

The pilot probably elected to depart from Mount Hotham because the cloud on the high ground was just beginning to dissipate, and the valleys appeared clear. As there was no evidence of compressor surging/stalling, it is likely that the pilot turned on the engine anti-ice soon after starting the engine. He then ran the engine for some time, probably to warm it and to determine that there was no intake ice forming. With the rotors turning for several minutes before take-off, the pilot should have been able to feel whether or not the helicopter was vibrating as a result of ice/frost accumulation on the rotor blades.

Had the weather conditions caused the accumulation of significant airframe icing before departure, particularly on the rotors, the pilot and the passengers would probably have felt significant airframe vibrations soon after the engine was started. Such vibrations would have prompted the pilot to shut down the engine and postpone the departure. Also, if the aircraft had suffered serious airframe icing after departure, it would more likely have crashed under power, which was not the case.

A likely scenario is that the pilot, while flying in the valleys, saw a possibility of tracking north west and attempted to track in that direction in the hope of clearing the alpine area sooner than if he persisted in the valleys. In so doing, the pilot is likely to have flown at reduced airspeed as he approached the ridgeline which was slightly north west of the impact site. The evidence indicates that there probably was low cloud on or near the ridgeline as well as associated reduced inflight visibility.

Engine flameout

Given the weather conditions which prevailed in the Mount Hotham area at the time of the accident, there are two likely reasons for a flameout of the helicopter's Allison 250 C20 engine - compressor intake icing or a slug of ice/slush/snow being ingested into the compressor intake.

If the pilot had left the anti-ice switch in the off position for some time, ice could have built up on the engine compressor intake and caused the engine to surge/stall or even flameout. However, the pilot's actions after start, and the lack of any evidence of surge/stall at that time, make this less likely.

The helicopter probably encountered a slightly higher outside air temperature as it flew in the valleys. Also, the particle separator may have warmed up slightly as a result of engine heat soak, particularly if the helicopter was flying at low forward airspeed. An increase in temperature probably caused a large enough slug of ice/slush/snow to dislodge from the plenum area and the particle separator and enter the engine compressor intake causing an instant flameout. The helicopter was not fitted with the optional auto reignition system which relights the engine very quickly in the event of a flameout.

Because of the low height above the ground the pilot would not have had time to restart the engine. The combination of a flameout, low height, low airspeed, mountainous terrain, and tall trees resulted in a very heavy landing. The low height and lack of time would also account for the pilot not managing to transmit his call sign during the mayday call.

Survival

Had the Emergency Locator Transmitter (ELT) beacon been capable of transmitting a distress signal, it is possible that the signal would have been intercepted by the monitoring satellite or by an overflying aircraft. The time taken to locate the helicopter could have been significantly shorter in duration, which may have increased the pilot's chances of survival.

CONCLUSIONS

Findings

1. The pilot parked the helicopter outdoors and did not fit it with engine intake covers.
2. The helicopter was exposed to blowing snow and freezing conditions overnight.
3. The engine anti-ice switch was found in the on position.
4. The helicopter was not fitted with the optional engine auto-reignition system.
5. The ELT fitted to the helicopter was damaged during the impact and could not transmit a distress signal.
6. The pilot survived the initial crash impact but died from injuries and/or hypothermia before the helicopter was located.

Significant Factors

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

1. The helicopter was parked overnight, without engine intake covers being fitted, in conditions of blowing snow.
2. The pilot may not have inspected the plenum chamber for snow or water accumulation before take-off.
3. An engine flameout occurred at a low height over terrain unsuitable for a forced landing.

SAFETY ACTION

The issues relating to the ELT survival beacon raised in this report are being considered in the light of this and several other occurrences. They will be the subject of a future Bureau of Air Safety Investigation report.

The pilot was returning from a local sheep mustering flight on his property. When the gyroplane failed to return to the airstrip, and the pilot could not be contacted by CB radio, a search was commenced. The wreckage of the gyroplane was found about 230 metres west of the airstrip, having struck the ground in a steep descent with little forward speed, fatally injuring the pilot. The weather conditions at the time of the accident were reported to have been affected by strong gusting north- westerly winds, associated with blowing dust and reduced visibility.

An inspection of the wreckage revealed no evidence of any pre-existing mechanical fault or defect. However, whilst the gyroplane was in flight, the rotors had struck the tailplane and fractured the tail boom to the rear of the engine mounting. This damage was consistent with excessive flapping of the rotor blades associated with air flow reversal through the rotor disc. Air flow through the rotor disc normally enters from beneath the plane of the disc and exits above. Other effects of reversal of airflow are the irreversible deceleration of the rotor blades, and a nose down pitch change. In this accident the gyroplane appeared to have tumbled end over end, as well as rotating about the vertical axis.

The reason for the onset of airflow reversal on this occasion could not be positively established. However, in conditions of strong gusty winds, large changes in the vertical wind component could lead to airflow reversal. The likelihood of such an occurrence would have been increased if the gyroplane was being flown at relatively high speed.

The pilot suffered from epilepsy and was taking prescribed medication at the time of the accident. It could not be determined if the pilot's medical condition was a factor in this accident.

The pilot who had assembled the aircraft was also distributing the aircraft in Queensland. He had planned to fly the aircraft from Caboolture to an airshow at Hervey Bay.

The flight from Caboolture to Gympie took about two hours because of headwinds encountered en route. At Gympie the pilot refilled the left fuel tank of the aircraft from a 20-litre container he carried in the aircraft. He was then given a ride to a nearby service station where the container was refilled. Upon returning to the aircraft the refilled container was strapped to the seat beside the pilot. The pilot boarded the aircraft and after starting the engine the aircraft was taxied for take-off. Witnesses reported that after the aircraft became airborne it climbed overhead the airfield before setting course to the north. The witnesses also stated that the aircraft appeared to be operating normally and that engine operation was also normal.

About five minutes later the aircraft was observed to the east of Gympie flying in a northerly direction. The engine was then reported to have misfired and stopped. The aircraft was turned to the west and overflew a golf course. The western side of the course was bounded by pine trees about 10 metres in height and the Bruce Highway. The aircraft cleared the pine trees but impacted the highway directly in front of a vehicle. The vehicle struck the fuselage of the aircraft which was dragged underneath the vehicle for a short distance.

The fuselage and inboard section of the wing were severely damaged by ground and vehicle impact. However, an inspection of the wreckage did not reveal any faults that may have contributed to the accident. The engine was removed from the aircraft and inspected. Apart from some minor accident damage it appeared in good condition. The engine was internally inspected and the only fault found was some minor scoring on the forward face of the number 1 piston which would indicate that the piston may have partially seized previously. The effect of this scoring on the operation of the engine prior to the accident could not be determined.

The pilot was experienced in the operation of ultralight aircraft and a senior ultralight flying instructor. He had operated this particular aircraft for all of the 25 hours it had flown since assembly. Following the reported engine problems, the aircraft was flown over the golf course which contained several fairways that would have been suitable for landing the aircraft in an emergency.

SIGNIFICANT FACTORS

1. The reason for the reported loss of engine power could not be positively determined.

2. The pilot overflew suitable landing areas without attempting a landing.

3. The pilot lost control of the aircraft at an altitude that was too low to effect recovery.

On Friday 11 June 1993, at about 1918 EST, Piper PA31-350 Navajo Chieftain aircraft, VH-NDU, while on a right base leg for a landing approach to runway 01 in conditions of low cloud and darkness, struck trees at a height of 275 feet above the elevation of the aerodrome at Young, New South Wales, and crashed. The aircraft, which was being operated as Monarch Airlines flight OB301 on a regular public transport service from Sydney to Young, was destroyed by impact forces and post-crash fire. All seven occupants, including the two pilots, suffered fatal injuries.

The investigation found that the circumstances of the accident were consistent with controlled flight into terrain. Descent below the minimum circling altitude without adequate visual reference was the culminating factor in a combination of local contributing factors and organisational failures. The local contributing factors included poor weather conditions, equipment deficiencies, inadequate procedures, inaccurate visual perception, and possible skill fatigue. Organisational failures were identified relating to the management of the airline by the company, and the regulation and licensing of its operations by the Civil Aviation Authority.

During the investigation a number of interim safety recommendations were issued by the Bureau. The recommendations and responses are summarised in Section 4 of this report.

The aircraft took off from the strip near the homestead at about 0645 hours to conduct cattle spotting operations. At about 0930 hours, the pilot reported by radio that he had completed the spotting task and was directed by the property manager to fly to the western section of the property and check the status of three bores. When the manager arrived back at the homestead at about 1200 hours, he found that the aircraft had not returned. Search arrangements were initiated and the wreckage of the aircraft was later found approximately one kilometre from the second in the series of bores to be checked. There were no witnesses to the accident.

On-site investigation revealed that the aircraft had crashed on flat, open terrain while heading in a north-easterly direction. The aircraft initially contacted the ground with the left wingtip followed by the propeller 14 metres beyond this point. There was evidence of a flash fire at this location, and of the aircraft then cartwheeling, before coming to rest 60 metres from the initial impact point. The relationship between the wingtip ground impact mark and the propeller impact point suggested that, at initial impact, the aircraft was in a slightly nose down attitude and banked steeply to the left.

The aircraft was severely damaged by a combination of impact forces and post impact fire. Examination of the wreckage did not disclose any condition or fault which might have contributed to the accident, although fire damage precluded a complete examination of some components, particularly the instruments and controls in the cockpit area.

The weather in the area around the time of the accident was reported to have been fine and hot with a light and variable wind. There were no restrictions to visibility. Flying conditions as described by occupants of the search aircraft were good with only light turbulence.

The broader area over which the aircraft was operating was covered with lush knee-high grass. Advice from the Bureau of Meteorology indicated that the chances of a dust devil (willy-willy) forming in these conditions were very small. Dust devil formation usually required barren, very hot and very dry conditions. No dust devils were observed in the area during the on-site phase of the investigation.

Considerable bird activity was noted around bores on the property. However, no evidence of the aircraft having struck a bird was found, although the post-crash fire could have destroyed any bird remains which might have entered the cabin area.

The notepad apparently used by the pilot to record information on each bore was found along the wreckage trail. Writing in pencil on the notepad indicated that the pilot had inspected the first bore (D-15) and recorded his observations. Beneath this writing was an incomplete recording of information on the second bore (X-8). At the end of this writing was a pencil mark similar to that which might be expected if the writing platform or the pencil was bumped or disturbed.

Bore inspections were a regular aspect of the pilot's flying duties. Inspections involved flying over the bore and checking the amount of water in the holding tank along with the condition of the adjacent animal drinking trough. The task could be readily accomplished from a flying height of 500 feet above ground level.

There was no indication of any physiological or psychological condition which might have affected the pilot's ability to operate the aircraft. He had been flying in the area for some 14 months during which time he had conducted many bore inspection flights. The pilot completed a course in low flying in January 1993.

Factors

The factors which contributed to this accident could not be determined.

The pilot and his wife flew their own aircraft from Bankstown to The Oaks where a set of spark plugs was purchased. As the engine had operated normally during this flight, the pilot declined an offer by the seller to fit the new spark plugs to the engine. Three days earlier an engine ignition system unserviceability was rectified by a licenced aircraft maintenance engineer who replaced two spark plugs.

The aircraft was taxied to the southern end of the airstrip where an engine run up check was carried out prior to take-off. The passenger noted no irregularities during this check.

The take-off was commenced in a northerly direction. After the aircraft became airborne the engine began to run roughly, accompanied by a significant loss of power. The pilot was able to maintain a shallow climb at an indicated airspeed of 45 knots.

After travelling for approximately 1.5 kms in a northerly direction and reaching a height of between 200 and 300 feet, the pilot commenced a level turn to the left. When the aircraft had turned through about 40 degrees the left wing dropped, and the aircraft entered a steep nose down spiral dive. Although rotation ceased, the aircraft struck the ground heavily. The pilot received fatal injuries, and the passenger was seriously injured.

The loss of control occurred at a height insufficient for the pilot to effect a safe recovery.

An examination and testing of the engine and its systems did not reveal the reason for the significant loss of engine power.

Significant Factors

1. Immediately after liftoff, the engine suffered a significant loss of power.

2. The climb performance was substantially reduced.

3. The aircraft stalled during a left turn and entered a spiral dive at an insufficient height to permit recovery.