ANALYSIS

The circumstances of the accident were consistent with a loss of tail rotor thrust following the failure of the tail rotor drive shaft as the helicopter entered the hover.

The time at which the damage to the drive shaft occurred was not able to be determined. However, given the absence of rotational damage to the tail rotor blades, it is unlikely that it occurred during the accident flight.

The action of the pilot in increasing engine power when faced with the loss of tail rotor thrust was inappropriate and exacerbated the situation.

FACTUAL INFORMATION

At 1215 Eastern Standard Time¹ on 27 September 2004, a Kawasaki Heavy Industries, 47G3B-KH4² helicopter, registered VH-MTF, was being operated on a tourist flight with one adult and a young boy as passengers. The flight included landing on a 1 m high wooden platform in the Teepookana Forest in north-west Tasmania.

The pilot reported that as he brought the helicopter to a 1 m hover above the platform, the helicopter began to rotate slowly to the right. He unsuccessfully attempted to counter the rotation by applying left tail rotor control input. The pilot then increased engine power in an attempt to regain tail rotor control and to move the helicopter clear of the landing platform. That action had the effect of rapidly increasing the rotation of the helicopter to the right and it began to ascend, reaching about 5 m above ground level. The pilot then lowered the collective control and the helicopter impacted the ground heavily on its right side, several metres from the landing platform. The pilot and adult passenger released their seatbelts and then both assisted the young boy to exit the wreckage. The pilot and passengers received minor injuries.

The pilot described the wind conditions at the time of the accident as a headwind with an approximate strength of 8 kts. That assessment was consistent with the wind data for the Strahan area provided by the Bureau of Meteorology³. The pilot also reported that the main rotor RPM indications were normal and that the helicopter had sufficient power to complete the approach⁴. At the time of the accident, the weight and balance of the helicopter were within prescribed limits. There was no evidence that the helicopter had collided with anything during the approach.

The pilot was appropriately qualified and endorsed to operate the helicopter type and held a valid medical certificate. He was a very experienced agricultural aeroplane pilot and had obtained a commercial pilot (helicopter) licence 14 months before the accident. He had accrued at total of 292 hours in helicopters since that time; 286.4 hours of which had been in the Bell 47 helicopter type. The pilot was experienced with operations into and out of the Teepookana Forest landing platform.

The landing platform was located within a dense forest in an area that was cleared of trees but covered by 1 m high scrub. The trees closest to the clearing had been trimmed to a height of about 5 m to allow a 'fly-in, fly-out' approach. There was no requirement to conduct a vertical approach to the platform.

The helicopter's fuselage structure was deformed by the impact and the tail boom was bent in a downward direction at approximately station 100⁵. There was corresponding bending damage to the tail rotor drive shaft assembly long shaft at the same point. The operator reported that examination of the damaged tail rotor pitch control system revealed that the controls were intact and would have been capable of normal operation. All parts of the helicopter were accounted for by the operator at the accident site.

The two-blade tail rotor assembly, mounted on the right side of the tail boom, was intact and correctly attached to the helicopter. There was no evidence of rotational damage to the leading edges or tips of either blade (Figure 1). During the ground impact one blade had been bent outward at the tip and the other was bent in toward the tail rotor gearbox.

Figure 1:     Tail rotor blade damage

The helicopter's tail rotor drive shaft assembly consisted of a series of two short shafts and one long shaft that were situated on the top of the tail boom assembly. The long shaft was supported in eight hanger bearing assemblies and was secured at its front and rear by drive coupling assemblies. The operator inspected the tail rotor drive system and found that the long shaft assembly tubing was fractured and the pin situated through the front drive coupling assembly was sheared. There was also significant distortion of the corresponding pin in the shaft's rear coupling.

Inspection of the tail rotor drive system, including the drive shaft bearings, tail rotor extension housing and tail rotor gearbox, with the exception of the long drive shaft, revealed nothing that would have prevented normal operation.

ATSB specialist examination of the failed components (Appendix A) attributed the tail rotor drive shaft failure to a significant torsional overload event, leading to a loss of coupling security and the subsequent slippage, frictional heating and shear fracture of the shaft. That examination was unable to determine when the torsional overload occurred or what specific events may have contributed to it.

At the time of the accident, the helicopter had logged 72 flight hours since the issue of the current maintenance release. The last recorded maintenance carried out on the helicopter was a spark plug change on 21 September 2004, 1.0 flight hour prior to the accident. On 31 August 2004, 5.7 flight hours prior to the accident, one tail rotor blade was replaced because of delamination of the leading edge wear strip.

Information received from the operator and from the maintenance organisation indicated that there had been no known tail rotor strike or sudden rotor stoppage since the helicopter was placed on the Australian aircraft register in 1992. The helicopter's prior history was not examined.

The company operations manual contained the published normal and emergency procedures affecting aircraft operations. An appendix to the manual contained the flight check systems and operating procedures specific to each aircraft type operated by the company, with the exception of the Kawasaki-Bell 47G3B-KH4 helicopter. The company did however, make available to pilots a copy of the Civil Aviation Safety Authority approved Kawasaki-Bell 47G3B-KH4 helicopter flight manual.

With reference to tail rotor failures, that flight manual stipulated:

1. Immediately execute an autorotative descent and maintain an airspeed of 34 KIAS at least.
2. Execute a normal autorotative descent and landing.

The flight manual did not contain any specific advice for pilots in response to a tail rotor drive failure when hovering.

Information in the company operations manual regarding pilot response to a tail rotor drive failure in another piston-engine helicopter (Robinson R44) included:

LOSS OF TAIL ROTOR THRUST DURING HOVER

1. Failure is usually indicated by right yaw which cannot be stopped by applying left pedal.
2. Immediately roll throttle off into detent spring and allow aircraft to settle.
3. Raise collective just before touchdown to cushion landing

The generally accepted procedure for pilot actions in the event of a tail rotor failure is to quickly roll off the throttle or snap close the throttle and perform a hovering autorotation⁶,⁷,⁸,⁹ For example:

The likely worst place for loss of tail rotor thrust to happen is in the hover, and the reaction is quite simple - get rid of the engine power and land the helicopter from a hovering engine failure condition. Easy to do on those machines that have throttle(s) on the collective¹⁰.

1. The 24-hour clock is used in this report to describe the local time of day, Eastern Standard Time (EST), as particular events occurred. Eastern Standard Time was Coordinated Universal Time (UTC) + 10 hours.
2. The Kawasaki Heavy Industries, 47G3B-KH4 helicopter is a single pilot/single flight control helicopter manufactured under licence from Bell Helicopters. It is commonly known as the KH4 helicopter and is a derivative of the Bell 47.
3. Given that the pilot positioned the helicopter into wind during the approach and landing, the risk of loss of tail rotor effectiveness (LTE) was negligible.
4. There were no external conditions that would have placed the pilot at risk of overpitching or drooping the main rotor.
5. Positioned 100 inches aft of the datum. The datum was located 2 inches forward of the rotor mast centre-line.
6. Coyle, S. (2003). Cyclic & collective - More art and science of flying helicopters. Mojave, CA: Helobooks, pages 341and 342.
7. Federal Aviation Administration. (2000). Rotorcraft flying handbook (FAA-H-8083-21).  Washington, DC: FAA.
8. Newman, R. (1999). Helicopters will take you anywhere: A manual for helicopter pilots. Mentone, Vic: The Helicopter Book Company.
9. Becker, M. (1997). Mike Becker's helicopter handbook. Noosaville, QLD: Becker Helicopters Australia.
10. The Kawasaki-Bell 47G3B-KH4 helicopter had a throttle of this design.

At 1215 Eastern Standard Time on 27 September 2004, the pilot of a Kawasaki Heavy Industries, 47G3B-KH4 helicopter, registered VH-MTF, was being operated on a tourist flight with two passengers in north-west Tasmania. The pilot reported that as he brought the helicopter to a 1 m hover above the raised landing platform, the helicopter began to rotate slowly to the right. The pilot unsuccessfully attempted to counter the rotation by applying left tail rotor control input. The pilot then increased engine power, however, that action had the effect of rapidly increasing the rotation of the helicopter to the right and the helicopter climbed to about 5 m above the ground. After the pilot lowered the collective control, the helicopter impacted the ground heavily on its right side. The pilot and passengers received minor injuries.

The helicopter's tail rotor drive shaft had failed during the occurrence. ATSB specialist examination of the failed drive shaft, attributed the failure to damage from a significant torsional overload event, leading to the shear fracture of the shaft. The examination was unable to determine when the torsional overload occurred, however, examination of the wreckage indicated that it was likely that it had occurred prior to this accident

Information received from the operator and from the maintenance organisation indicated that there had been no known tail rotor strike or sudden rotor stoppage since the helicopter was placed on the Australian aircraft register in 1992. The helicopter's history prior to that time was not examined.

The action of the pilot in increasing engine power when faced with the loss of tail rotor thrust was also examined.

ANALYSIS

The investigation found that there was no evidence of a pre-existing defect in the helicopter that may have contributed to the occurrence, nor was there any evidence of a medical condition that could have affected the pilot's ability to control the helicopter. Consequently, the investigation concluded that in the prevailing environmental conditions, the accident was consistent with pilot spatial disorientation. This analysis examines the development of the occurrence and highlights a significant risk associated with night VFR operations.

The pilot departed for Eurella homestead 6 minutes after civil twilight in moonless, overcast, and probably showery conditions that were likely to restrict visibility to less than the required 5 km. Except for the homestead lights, the ground lighting or celestial illumination required by the Aircraft Flight Manual was not available. Although the pilot had flown at night on two recent occasions (23 and 26 August 2004), those flights did not fully satisfy the night VFR recency requirements and were probably over a well lit area. Given the pilot's limited recent and overall helicopter night flying experience, and the forecast weather conditions, it is unlikely that the pilot planned to conduct the return flight at night. The pilot had probably used the helicopter to move cattle and that task may have taken longer than expected. The proximity of the homestead, the local knowledge of his passenger, the night VFR capability of the aircraft and access to GPS information may have influenced the pilot to attempt the return flight.

The track information recovered from the hand-held GPS showed manoeuvring after 1830 that suggests that the pilot, probably using GPS information, made several attempts to track to the homestead, but was unable to do so. It is likely that during the manoeuvring the pilot was at a low altitude, attempting to maintain visual contact with surface features, possibly with the assistance of the landing lights. Such visual contact would have enabled control of the helicopter and clearance from terrain. In the absence of a consistently discernable horizon, any visual contact with the homestead lights would not have enabled the pilot to determine the helicopter's attitude. Prior to the impact, the pilot may have lost visual contact with the surface due to cloud and/or rain and become spatially disorientated.

The pilot may have attempted to control the helicopter by reference to the flight instruments. However, he had not logged any instrument flight time in a helicopter and had not been exposed to significant night-flight away from metropolitan areas. The relative instability of the helicopter and the different operating environment meant that the pilot's considerable aeroplane night and instrument flight experience was not directly transferable to night VFR helicopter operations. Consequently, spatial disorientation could have developed rapidly.

Flying the helicopter at a low altitude at night with cloud and/or showers in an area with little lighting was a very demanding task with little margin for error. However, once the helicopter became airborne after civil twilight, there were few options available to the pilot. The pilot's lack of helicopter instrument flight experience would probably have precluded consideration of climbing to the lowest safe altitude and tracking to an aerodrome with an instrument approach. Given that the adverse weather was widespread, diversion to another location while maintaining external visual reference was also an unlikely option.

A landing at a location other than the homestead was an option. It is possible that the accident occurred when the pilot became spatially disorientated in the adverse conditions while attempting to land the helicopter. However, it is also possible that, unable to communicate with the homestead, the pilot avoided an out-landing due to the consequent difficulty in reaching the homestead without transport.

Illumination of the clutch light as indicated by the stretched filament may have resulted from clutch operation during flight or from disruption during the impact. If the clutch light had illuminated during flight it may have distracted the pilot and contributed to spatial disorientation.

As a result of the separated ELT antenna cable, the search and rescue effort was significantly affected. However, in this case, the nature of the impact and the extent of injury to the occupants indicated that the search and rescue effort would not have influenced their survivability.

The circumstances of this occurrence highlight the risk of spatial disorientation during night VFR operations and reinforce the significance of the cautions included in the helicopter manufacturer's safety notices SN-18 and SN-26.

SIGNIFICANT FACTOR

The pilot departed after civil twilight in conditions where a natural horizon was probably not discernible and consistent visual reference to surface features was not likely.

FACTUAL INFORMATION

History of the flight

On 8 September 2004, the owner/pilot of a Robinson Helicopter Company R44 Raven II helicopter, registered VH-JWX, conducted a private flight under the visual flight rules (VFR) from Coffs Harbour, NSW to Eurella Station, Qld. The flight included a landing at Roma, Qld where the pilot refuelled the helicopter with 180 L of Avgas from the bulk underground fuel storage supply.¹ The pilot then continued to Eurella Station, located approximately 54 km west of Roma, arriving at 1705 Eastern Standard Time. The pilot shut down the engine and the property owner boarded the helicopter for a pre-arranged local flight. The pilot made several attempts to start the engine, during which it backfired a few times. Once started, the engine seemed to function normally.

The helicopter departed the homestead at 1725 in a northerly direction. A person on an adjoining property about 7 km north of Eurella homestead saw the helicopter operating to the east late in the afternoon. He reported that the helicopter conducted a number of take-offs and landings in what appeared to be the same general area over a period of about 30 minutes. He saw the helicopter depart in a southerly direction at about 1830.

The next reported sighting was by a person at Eurella homestead who, in poor light conditions, saw what appeared to be the helicopter's landing light to the north of the homestead. The light moved toward the west of the homestead. Soon after, that person again saw the light to the west and expected the helicopter to land at the homestead within a few minutes. However, she became concerned when the helicopter did not arrive and telephoned an employee of the property owner to report her concern. The employee contacted the Australian Search and Rescue organisation (AusSAR) and search action was initiated. The helicopter was located the following morning in open, rolling country, 3 km west of Eurella homestead. The two occupants were fatally injured, and the helicopter was destroyed.

Search and rescue

AusSAR reported that it was notified at 1947 that the helicopter was overdue. Weather conditions were unsuitable for an air search, but a surface search was initiated. AusSAR advised that no ELT signal was received on 8 September by satellite or by aircraft at high altitude passing within 130 km of Eurella Station. An ELT signal was detected on two satellite passes early on the morning of 9 September. The signals were identified as originating from separate locations; one approximately 22 km to the south-west, and the other approximately 22 km to the south-east, of Eurella Station. However, those signals were not merged by the satellites as coming from the same source, so they were of little assistance in the search. Local aircraft were tasked to begin a search at daylight on 9 September and the wreckage was located at 0708 by the crew of a search aircraft. Accident site information

The accident site elevation was about 30 m below the ground elevation at the homestead. The homestead was not visible from the accident site.

Figure 1: Aerial view of the accident site

GPS track information

The helicopter was fitted with a fixed global positioning system (GPS) receiver, and also a handheld GPS receiver mounted in a cradle on the instrument panel. The fixed receiver did not contain a non-volatile memory card, but the handheld unit did. Track and ground-speed data for the occurrence flight was retrieved from the non-volatile memory card. Altitude information was not retained in the memory card.

Figure 2 displays the GPS recorded track of the helicopter overlaid in blue on a 1 in 250,000 scale topographical map of the area. The local times that the helicopter was at various locations are depicted.

Figure 2: GPS track overlay, with the landing sites A, B, C and D

The GPS data showed that the helicopter landed five times during the flight. Those positions are depicted on the map and are described as follows:

The data indicated that, after the helicopter departed position B at 1827, it initially tracked almost directly toward the homestead, but that the track then veered south-west. That track was clear of the high ground indicated by the 400 m contour near Mt Muttaby, as depicted on the chart at Figure 2. There are distinct features in the helicopter's track after 1830, indicating that the pilot turned toward the homestead on four separate occasions between 1830 and 1840, only to turn away each time. The accident occurred on the fifth occasion that the helicopter's recorded track turned in the approximate direction of the homestead.

Subsequent to the occurrence, an employee from Eurella Station found that cattle had been moved from the paddock that included positions A, C, and D, to an adjoining paddock. Those paddocks were linked by a gate adjacent to position B. The employee recalled that the property owner had intended to move the cattle to the adjoining paddock and that the gate adjacent to position B was the gate through which he would have expected the cattle to be moved.

Pilot information

The pilot held an air transport (aeroplane) pilot licence and a command multi-engine instrument rating. He had extensive aeroplane flying experience, including regular public transport turbo-jet aircraft and corporate turbo-jet aircraft operations in Australia and overseas. His aeroplane flying experience exceeded 10,000 hours and included 1,418 hours of night flight and 711 hours of instrument flight.

The pilot obtained a private pilot (helicopter) licence on 23 September 1998 and had about 582 hours helicopter experience. He obtained a night VFR (helicopter) rating on 12 September 2000 and since that date had recorded about 11 hours helicopter night flight. Almost all of the logged flights were in the Sydney metropolitan area. Helicopter night flying recorded by the pilot in the two years prior to the occurrence was 0.4 hours on 23 August 2004 and 0.6 hours on 26 August 2004. That night flying most likely occurred during the latter stages of flights to the Sydney metropolitan area.

There was no record of the pilot having received any specific training in operating helicopters in remote areas or dark night conditions where there was little or no ambient lighting. No helicopter instrument flight time was logged.

The pilot held a valid medical certificate. Post-mortem and toxicology examinations did not reveal any pre-existing condition that might have affected the pilot's ability to safely conduct the flight.

Helicopter information

The pilot purchased the helicopter new in early August 2004. At the time of the occurrence the helicopter had operated for 34.1 hours. The maintenance release was valid and the documentation indicated that all applicable maintenance and regulatory requirements had been met.

The helicopter was equipped and certified for night VFR operations. Instrumentation included an airspeed indicator, artificial horizon, sensitive pressure altimeter, turn coordinator, horizontal situation indicator, global positioning system indicator, and vertical speed indicator.

The helicopter was equipped with twin landing lights in the lower nose section. The lights were fitted with 100 watt spot globes and, according to the Aircraft Flight Manual, were 'set at different angles to increase the pilot's field of vision'. Both lights were activated by the one switch which was mounted on the cyclic control centre post.

A row of eight amber warning lights located at the top of the flight instrument panel included a clutch warning light. A further six warning lights were positioned at the top of the centre pedestal.

The helicopter's engine was coupled to the rotor drive system via four double-stranded vee-belts. After engine start, an electric actuator would tension the belts when the pilot engaged the clutch switch. The actuator sensed belt tension and was automatically energised when the tension was less than required. The clutch warning light would illuminate whenever the clutch actuator circuit was activated. The Aircraft Flight Manual included a note regarding the clutch in Section 3, Emergency Procedures. The note stated that stretching of the belts often resulted in illumination of the clutch warning light for brief periods as the drive actuator readjusted belt tension. The note also included actions that the pilot should take after 7 or 8 seconds of illumination of the clutch light. One of those actions was to pull the clutch circuit breaker.

The helicopter was fitted with a Pointer (TSO-C91A) Model 3000-10 emergency locator transmitter (ELT). The unit was located on the left side of the rear fuselage.

The total flight time from Roma until the time of the occurrence was about 1 hour 35 minutes. Assuming a fuel usage rate of 60 L per hour, approximately 95 L would have been consumed during that time. On that basis, approximately 95 L should have remained at the time of the occurrence.

Wreckage information

opposite to the helicopter's direction of travel at impact. The impact severely crushed most of the cabin area and deformed the fuselage and tail boom structures.
Two distinct main rotor blade impact marks on the ground forward and to the right of the initial nose impact position, and the damage to the main rotor blades, indicated that the rotor blades were being driven by the engine at impact. The tail-rotor system was intact and there was no evidence that the fuselage was yawing at impact. There was no indication that the helicopter had struck any of the trees in the vicinity of the impact site.

The left fuel tank ruptured during the impact sequence and was empty. The right fuel tank was also empty. With the helicopter lying on its left side, the right fuel tank vent line was at the lowest part of the tank and would have allowed fuel to drain out. There was a strong smell of Avgas in the vicinity of the wreckage on the day after the accident.

The hydraulic system switch was found in the ON position.

Instrument panel light globe and instrument examination confirmed that electrical power was available to the instruments. There was no evidence of malfunction of any of the instruments.

The six warning lights at the top of the centre pedestal were destroyed by impact forces, preventing an assessment being made of their status at impact. The eight warning lights at the top of the flight instrument panel were intact. Examination of those light globes revealed stretching of the clutch warning light filament. Stretching indicates that the filament was hot and that electrical power was applied to the globe when it was subject to forces during the impact sequence. It was not possible to determine the length of time that the globe had been illuminated. Filament stretch was not evident in any of the other seven warning light globes from the top of the instrument panel.

Damage to the landing light globes prevented any assessment being made regarding their status at the time of the occurrence. The damage to the landing light switch indicated that it was in the ON position at impact.

The circuit breaker panel was destroyed by impact forces. The clutch actuator fuse was serviceable. The wreckage examination did not reveal any fault in the clutch system. Although the circuit breaker panel was destroyed, the evidence of electrical power to the clutch warning light indicates that the circuit breaker was engaged, and therefore the system was powered at the time.

The coaxial cable from the ELT unit to the external antenna had separated at the connector to the antenna base on the inside of the antenna mounting panel. The separation of the coaxial cable trapped the transmitted signal within the fuselage compartment. That rendered the ELT unit ineffective and prevented satellite detection of the signal. The separation of the cable appeared to have been as a result of impact forces. As a result, the search and rescue effort was significantly affected.

Specialist examination of the ELT revealed that it had activated upon impact and, when connected to a suitable antenna, was capable of transmitting a normal signal.

The engine was test run after removal from the wreckage and operated normally. The hydraulic pump and three hydraulic servos that formed part of the main rotor flight control system were removed from the wreckage for functional testing. The tests were conducted at the helicopter manufacturer's facility in the USA and supervised on behalf of the ATSB by a representative from the US National Transportation Safety Board. The tests confirmed that the hydraulic system components met the specifications for normal operation.

Meteorological information

Documents found in the helicopter included an Area 41 weather forecast valid from 0900 to 2100 on the day of the occurrence and the Roma terminal area forecast (TAF) valid from 1200 to 2400 on the day of the occurrence.

The area forecast indicated that the weather in the vicinity of Eurella Station would include areas of rain with locally moderate falls, scattered showers and isolated thunderstorms. The Roma TAF indicated that between 1500 and 2400 there would be 60 minute periods in which the visibility would be 2 km in heavy rain, with broken cloud² at 700 ft.

An analysis by the Bureau of Meteorology indicated that during the late afternoon on the day of the occurrence, a surface trough was located from Camooweal to St George, with cold south-west winds to its west and northerlies to its east. The surface trough combined with an upper level trough over the southwest of the state to bring a large cloud band with widespread rain and isolated thunderstorms to the interior. The analysis of satellite imagery and synoptic reports, concluded that there was a high probability of rain in the Eurella Station area around the time of the occurrence, and most likely greater than 5 oktas of cloud cover. However, because the nearest weather radar station was about 200 km distant at Charleville, the amount of cloud cover in the area of the occurrence could not be confirmed.

Persons at and near Eurella Station variously reported that the weather conditions during the day of the accident were windy, with heavy cloud and showers.

Astronomical information

According to information published on the Geoscience Australia website, sunset and twilight times at Eurella Station on the day of the occurrence were:

Sunset 1757³
Civil Twilight 1820⁴

Other information on the website indicated that the moon set at 1409 and was 79 degrees 31 seconds below the horizon at 1830 that evening.

Helicopter night VFR

The pilot's night VFR (helicopter) rating authorised him to act as pilot in command of private or aerial work flights at night under the VFR. Once issued, a night VFR rating remained permanently valid. To exercise the privileges of the rating, a pilot needed to complete a 1-hour night flight during the previous 12 months and one take-off and landing at night during the previous 6 months. There was no requirement for the holder of a night VFR rating to have any recent instrument flight time prior to conducting a flight at night.

A pilot operating under the VFR at night was required to operate in visual meteorological conditions that included a minimum of 5 km visibility. The Aircraft Flight Manual, Section 2, Limitations, included the following statements:

VFR operation at night is permitted when landing, instrument, and anti-collision lights are operational. Orientation during night flight must be maintained by visual reference to ground objects illuminated solely by lights on the ground or adequate celestial illumination.

At the time of the occurrence there was a 1,000 watt flood light on each of the northern and western walls of Eurella homestead, as well as lights in other buildings. However, there were many trees in the vicinity of the homestead, some of which were higher than the homestead roof. Depending on the altitude and position of the helicopter, the trees could have prevented those lights being seen from the helicopter (Figure 1). There was no other lighting in the general area, including at the airstrip adjacent to the homestead. The homestead lights, in effect, formed a 'point' source of light.

Spatial Disorientation

Spatial disorientation refers to a situation in flight in which the pilot fails to sense correctly the position, motion or attitude of the aircraft. When the condition is fully developed, the pilot is unable to tell which way is 'up'.

The risks of non-instrument rated pilots flying in conditions in which they are not able to orientate the aircraft by visual reference have been well known for over 50 years. During testing conducted on a group of non-instrument rated pilots, the average time before loss of control of the aeroplane, after visual reference was lost, was 178 seconds.⁵

US FAA Advisory Circular 60-4A, Pilot's Spatial Disorientation, was published in 1983 and was intended to inform pilots of the hazards associated with disorientation caused by loss of visual reference with the external environment. It included the following information:

Tests conducted with qualified instrument pilots indicate that it can take as much as 35 seconds to establish full control by instruments after the loss of visual reference with the surface.

The helicopter manufacturer issued a safety alert and safety notices (SN) as a result of various occurrences and incidents, and included those notices in the Aircraft Flight Manual Section 10, Safety Tips. Two of the notices related to night flight - SN-18 Loss of Visibility Can Be Fatal, and SN-26 Night Flight Plus Bad Weather Can Be Deadly (see Appendix A). Safety notice SN-18 stated in part:

Helicopters have less inherent stability and much faster roll and pitch rates than airplanes. Loss of the pilot's outside visual references, even for a moment, can result in disorientation, wrong control inputs, and an uncontrolled crash.

Appendix A

On 8 September 2004, the owner/pilot of a Robinson Helicopter Company R44 Raven II helicopter, registered VH-JWX, conducted a private flight under the visual flight rules (VFR) from Coffs Harbour, NSW to Eurella Station, Qld. The flight included a landing at Roma, Qld where the pilot refuelled the helicopter with 180 L of Avgas from the bulk underground fuel storage supply. The pilot then continued to Eurella Station, located approximately 54 km west of Roma, arriving at 1705 Eastern Standard Time. The pilot shut down the engine and the property owner boarded the helicopter for a pre-arranged local flight. The pilot made several attempts to start the engine, during which it backfired a few times. Once started, the engine seemed to function normally.

No defects were found with the cabin door mechanical locking system. Prior to take-off, the locking mechanism of the door was checked by the safety pilot and no problems were reported. When the separated door was located, the external handle was not in the locked position and the latch bolts were not fully extended.

It was possible to move the door locking handle to a high resistance position, where the green line indicators on the latch bolts appeared to line up with the stationary arrow heads in the inspection windows, but the door locking mechanism was not fully engaged. At that position, if the top latch hook sense switch was short circuited due to the proximity of the sense switch terminal and the mounting nut, the door warning light would be extinguished. This condition would provide the crew with no indication that the door was not correctly locked.

Factual Information

The PIC reported that, while passing Flight Level 175 on descent, he heard a loud muffled thud and then air noise, and saw that the cabin door had opened and separated from the aircraft. There had been no door warning indication prior to the door opening.

Following the door separation, the cabin door warning light illuminated and the cabin oxygen masks deployed. The PIC completed emergency checks before diverting the aircraft to Thangool, Queensland.

On 12 September 2004, after a search by the aircraft operator, the cabin door was found approximately 3 NM north of Glenbar, Queensland (see Figure 1). When the door was found, the external handle was not in the locked position and the latch bolts were not fully extended.

Figure 1: Location of recovered door

Aircraft cabin door

The aircraft's cabin door was an outward-opening airstair type, hinged at the bottom, with a diaphragm and mechanical over-centre locking mechanism. It was also fitted with a pressurised seal.

The cabin door mechanical locking system consisted of four latch bolts. Two were located on the rear side of the door and two on the forward side of the door. In addition, two latch hooks located on the top of the door engaged onto stationary locking pins located within the fuselage (see Figure 2).

Figure 2: B300 cabin door locking mechanism

Locking and unlocking of the cabin door was accomplished by means of either the external or internal door handles. Once the aircraft was pressurised, the door's pressure seal inflated. As the pressure differential between the interior and exterior of the aircraft increased, the cabin door's internal diaphragm expanded and locked the interior handle to prevent inadvertent opening in-flight. The cabin door interior trim had three positions marked for the door handle, OPEN, LATCH and LOCK (see Figure 3).

Figure 3: Cabin door interior handle in lock position

When the locking mechanism was in the LOCK position, the door handle could not be moved to the LATCH or OPEN position until a release button on the internal diaphragm was depressed.

Each forward and rear latch bolt was marked with green line indicators, which aligned with stationary arrow heads that indicated that the cabin door was locked. The green line indicators were viewed through inspection windows at four locations on the inside of the door.

The recovered door was sent to the Australian Transport Safety Bureau for further examination. The investigation found that the mechanical latching mechanism was intact, however the door's rear latch hook sense switch terminal screw and the sense switch adjustment nut were located in very close proximity and intermittently contacted (see Figure 4).

Figure 4: Rear latch hook sense switch

The rear latch hook sense switch mounting plate showed no significant distortion and there was no evidence of in-service movement of the rear latch hook sense switch adjustment mechanism.

A circuit test of the three sense switches located within the door (two switches for the two latch hooks and one for the door handle position), determined that it was possible for the rear latch hook sense switch terminal to contact the switch mounting plate retaining nut, providing a short circuit to earth. This had the effect of rendering the door handle centre lock sense switch inoperative. In this condition, the door handle centre lock sense switch would not provide an indication to the crew of an unlocked door.

The examination also found that the door handle reached a position of maximum resistance between the LATCH and LOCK position just prior to the mechanism reaching the over-centre and locked position. It was possible to move the locking handle to this high resistance position, where the green line indicators on the latch bolts appeared to align with the stationary arrow heads in the inspection windows, but the latching hook had not yet activated the centre locking mechanism handle sense switch.

On 7 September 2004, at about 0710 Eastern Standard Time, a Raytheon B300 King Air aircraft, registered VH-KJD, was being operated on a private Instrument Flight Rules flight, from Brisbane to Truganinnie, Queensland, with the pilot in command (PIC) and, what the operator termed, a 'safety pilot'. The safety pilot was qualified on the aircraft type. Prior to departure from Brisbane, the aircraft's cabin door had been closed by the safety pilot, who stated that all of the pre-flight cabin door checks had been conducted in accordance with the pilot operating handbook.

On 31 August 2004, at about 1000 eastern standard time, the pilot of a Piper Aircraft Corporation PA-31 (Chieftain), registered VH-LTW, was conducting an instrument flight rules (IFR) flight from King Island to Devonport. The aircraft was maintaining 7,000 feet in visual meteorological conditions. The pilot saw an aircraft flying in the opposite direction passing between 100 ft and 200 ft, down the left of the Chieftain. He took immediate avoiding action. The pilot estimated that there was two to three seconds between initially seeing and then passing the other aircraft.

The other aircraft was later identified as an Aero Commander 500-S (Shrike), registered VH-LET, on a visual flight rules (VFR) flight at 6,500 feet from Launceston to King Island via overhead Devonport. The presence of the Shrike was established when the pilot of that aircraft advised the pilot of a third aircraft, that was east of King Island en route to Wynyard at 7,000 ft, of his position and altitude of 6,500 ft. The pilot of the third aircraft (tracking to Wynyard) had broadcast his intention to descend from 7,000 ft and that radio transmission alerted the Shrike pilot to a possible conflict. The pilots agreed to maintain their respective altitudes until the aircraft had passed. Neither the pilot nor the passenger in the Shrike saw the Chieftain.

At 1001, the Chieftain was 61 NM from Devonport and the pilot advised the controller of the occurrence and requested traffic information on any other aircraft in the area. The controller replied that there was no observed traffic [displayed on the radar].

Both pilots reported operating their aircraft transponders, including the Mode C altitude function, as required by the Aeronautical Information Publication (AIP) procedures. A review of the recorded air traffic control radar data confirmed that both aircraft were cruising at their reported altitudes about 20 minutes before they passed. However, the area where the aircraft passed was not within radar coverage and the investigation could not confirm the altitudes of the aircraft when they passed.

The Chieftain was fitted with two altimeters and the pilot reported that he had set both subscales to the area QNH and had engaged the autopilot. The Shrike was fitted with two altimeters and the pilot reported that he had set both subscales to either the local QNH or, when outside the mandatory broadcast zone (MBZ), the area QNH. The pilot had also engaged the auto-pilot. Both aircraft were maintained to IFR equipment requirements.

The AIP detailed altitudes to be used for aircraft on IFR/VFR flights in an easterly or westerly direction. The altitudes reported by the pilots were in accordance with the AIP.

Both aircraft were fitted with dual very high frequency radios. From about 0954, both pilots were simultaneously monitoring the Melbourne Centre area frequency on 122.6 MHz and the Devonport/Wynyard MBZ frequency on 126.9 MHz. At that time, the Chieftain pilot reported his Devonport estimate of 1020 to the Melbourne Centre controller. The pilot of the Shrike was monitoring Melbourne Centre on 122.6 MHz, but could not recall hearing the position report by the Chieftain pilot to Melbourne Centre. The pilot of the Shrike was not required to make any radio broadcasts. Also, pilots were not required to make any radio broadcasts when leaving an MBZ. A replay of the Melbourne Centre on 122.6 MHz revealed some interruptions by other pilots on that frequency.

Apart from the mandated broadcasts, the procedure in MBZ and Class G airspace is for pilots to listen on the appropriate frequency and to make a radio broadcast if there is the potential for aircraft to come into conflict.

In Class G airspace, air traffic control (ATC) provides traffic information to pilots of aircraft operating an IFR flight about other aircraft operating as IFR flights and military jet aircraft. Pilots operating a VFR flight may request traffic information from ATC, but it is provided subject to workload at the time. Pilots may make additional radio broadcasts at their discretion.

Neither aircraft was fitted with a traffic alert and collision avoidance system, nor was there any legislated requirement to do so.

On 31 August 2004, at about 1000 eastern standard time, the pilot of a Piper Aircraft Corporation PA-31 (Chieftain), registered VH-LTW, was conducting an instrument flight rules (IFR) flight from King Island to Devonport. The aircraft was maintaining 7,000 feet in visual meteorological conditions. The pilot saw an aircraft flying in the opposite direction passing between 100 ft and 200 ft, down the left of the Chieftain. He took immediate avoiding action. The pilot estimated that there was two to three seconds between initially seeing and then passing the other aircraft.

The engine failed after exhaustion of the fuel from the selected tank. Despite the pilot's engine failure recovery actions, 700 to 800 ft of altitude was lost before the engine restarted. If the engine failure had occurred while the aircraft was below 700 ft AGL, it would have resulted in a forced landing.

The different fuel management procedures at the two operational bases led to the inappropriate fuel selector position for operations from Jabiru. The pilot then overlooked the specific fuel tank selection during the pre-flight checks, because he had an expectation that it would already be appropriately positioned. During both the preceding and the occurrence flight, the fuel gauges had the potential to alert the pilot to the developing unsafe condition. This required reliable fuel gauges and regular comparison of their indications with planned fuel usage and fuel tank selection.

The pilot's response to the engine failure was not consistent with the aircraft manufacturer's or the operator's emergency and abnormal checklist instructions. It is likely that sustained operation of the auxiliary fuel pump introduced excessive fuel into the engine preventing an immediate restart. Selection of the fuel pump to the OFF position after priming the engine in accordance with the operator's Cessna 207 emergency and abnormal checklist should have resulted in a quicker restart with minimal altitude loss.

Although the pilot had read the operations manual that contained the relevant checklist, the operator did not require him to be able to recall the specific checklist items following an engine failure. The operator's induction training did not ensure that the pilot was able to follow the type-specific procedure when responding to an engine failure at a relatively low altitude. Standard operating procedures are an accepted means of reducing the risk of aircraft operation. By allowing the use of procedures that were inconsistent with the operations manual, the operator reduced the effectiveness of that risk control.

The chief pilot's belief that emergency procedures learned during early training could be effectively applied to any general aviation aircraft did not allow for significant variations between aircraft systems and in particular fuel systems. For example, the in-flight engine restart procedure for a low-wing aircraft with a carburetted engine that is commonly used for initial flight training is significantly different from the engine restart procedure for the Cessna 207, which is a high-wing aircraft with a fuel injected engine.

Induction training that facilitated memorisation of the Cessna 207 `engine failure during flight (restart procedures)' checklist with the opportunity for in-flight simulated engine failures would have decreased the risk of an inappropriate response to an engine failure.

The Australian Transport Safety Bureau did not conduct an on-scene investigation of this occurrence.

During the early afternoon of 30 August 2004, the pilot and six passengers onboard a Cessna Aircraft Company 207 Stationair (Cessna 207) departed Jabiru, NT for a 30 minute scenic charter flight.

The pilot reported that about 10 minutes after departure and while cruising at about 1,500 ft above ground level (AGL), the engine abruptly failed. The pilot reset the mixture and throttle controls, changed the selector position from the left to the right fuel tank, switched the auxiliary fuel pump to ON and established a glide speed of 80 kts. When the engine did not immediately respond, the pilot positioned the aircraft for a forced landing at a nearby outstation airstrip. At about 750 ft AGL the engine restarted. Unsure of why the engine had lost power, the pilot continued with the approach and transmitted a PAN alert. When assured of a landing he shut down the engine as a precaution against fire and landed.

The left fuel tank was found to contain no usable fuel and the right tank about 100L. The aircraft was ferried back to Jabiru with the right fuel tank selected and was operated on subsequent flights without incident.

The day before the occurrence, the aircraft was relocated to Jabiru from a remote base. The procedure at the remote base was to use the left fuel tank for flight fuel, and the right tank for reserve fuel. The fuel selector was positioned to the left tank when the aircraft arrived at Jabiru. However, for scenic flights from Jabiru the procedure was the opposite. The aircraft was refuelled to provide 40L reserve in the left tank and 100L in the right tank. The operator advised that these procedures were intended to reduce the risk of fuel starvation during scenic flights.

Early on the day of the occurrence, the pilot conducted a daily inspection of the aircraft and by dipping the tanks, visually confirmed that the fuel quantity accorded with the operator's procedure. He then conducted a 30 minute scenic flight without incident. As the total fuel on board for the occurrence flight was adequate, the quantity of fuel in each tank was not verified visually. The operator stated that the fuel gauges were serviceable. However, the pilot stated that the fuel gauge indicators constantly flickered between full and empty, which prompted him to disregard them.

The operator's maintenance controller informed the ATSB that the maintenance release had not been annotated with details of a fuel gauge defect. A check following the incident revealed that the indications on the aircraft's fuel gauges matched the dip stick measurements for the left and right fuel tanks. He advised that the aircraft was returned to service and there has been no report of a fuel gauge defect.

The aircraft's fuel selector valve had LEFT, OFF and RIGHT positions. The pilot said that, during the pre-flight cockpit checks for both the preceding flight and the occurrence flight, he had checked that the fuel selector was positioned to a fuel tank, but did not realise that it was positioned to the tank containing only reserve fuel.

The Cessna 207 `engine failure during flight (restart procedures) checklist' in the operations manual was similar to the corresponding procedure produced by the aircraft manufacturer. Importantly, both identified the need to use the auxiliary fuel pump only briefly. However, the pilot said that he had applied a memorised generic engine failure procedure that he had learnt in initial flight training. That procedure did not address specific use of the auxiliary fuel pump. The pilot said that, had there been more time after the engine failure, he would have referred to the copy of the operations manual checklist in the aircraft.

Information provided by the operator indicated that, one week prior to the occurrence, the pilot's induction training had included discussion of engine failure procedures based on a generic procedure similar to that used by the pilot. That training did not include the Cessna 207 `engine failure during flight (restart procedures) checklist' in the operations manual, or in-flight simulated engine failures.

The chief pilot reported that the operator's pilots were required to apply whatever normal and emergency/abnormal procedures they had learnt during early training. The chief pilot stated that: `Once learnt, I believe these checks stand a pilot in good stead for their entire flying career in GA [general aviation] and cannot see any reason to change that approach.' The chief pilot added that: `… all pilots are told when time permits to use the supplied check lists in an emergency.'

The ATSB recently completed an investigation into an engine failure involving a similar aircraft type (Cessna 206, ATSB report 200402049). Although there was fuel on board and no identified aircraft defects, the engine did not restart. The four occupants were seriously injured during the subsequent forced landing. The investigation found that the in-flight engine restart procedures published by the aircraft manufacturer were not followed.

Preparation for take-off

The pilot was qualified, appropriately endorsed and reported to be fit and well for the flight. The available aircraft and maintenance documentation, results of the recent 50-hourly inspection and subsequent engine ground run, and the successful 2-hour flight to El Questro indicated that there were no known pre-existing aircraft anomalies that might have contributed to the occurrence.

Although it was reported that the pilot most likely observed the El Questro Aircraft Landing Area (ALA) in June 2003, the investigation was unable to determine the means by which the pilot satisfied himself prior to arriving on 28 August 2004 that the ALA was suitable for his operation in accordance with the requirements of Civil Aviation Regulation 92. The runway width and length satisfied the guidance provided by Civil Aviation Advisory Publication (CAAP) 92-1(1) for the aircraft. While the tree that was initially struck by the aircraft may have infringed the lateral transitional slope, the pilot had indicated his acceptance of the suitability of the ALA for his operation and had landed without incident on 28 August 2004.

The results of the fuel tests, and the large number of other aircraft that had also used the Broome fuel supply without any reported problems, indicated that the quality of that fuel supply had not contributed to the development of the occurrence. The reported conduct by the pilot of the left underwing fuel drain test and observed presence of the pilot underneath the right wing tended to suggest that the pilot had completed the fuel drain and sump checks. That supported the consistent reports from all witnesses that the aircraft's engines sounded 'normal' throughout the take-off, and decreased the likelihood that water or other particulate contamination of the aircraft's fuel supply to the engines had any effect during the take-off.

The pilot's extensive and recent experience in the operation of this type of aircraft, and apparent intimate knowledge of its systems and procedures, would have reduced the likelihood of the pilot omitting to unlock the aircraft's controls prior to commencing the take-off. In any case, the ability of the pilot to fly the aircraft from the runway meant that the control column and optional rudder gust locks were unlocked at that time. Therefore, the pilot should have been able to react to the reported initially slight left bank after take-off.

The Broome engineer's report that the engines had started and run normally after the 50-hourly inspection, and the lack of any indication by the pilot during his stay at El Questro of any problems affecting the flight to El Questro indicated that the aircraft probably did not have a recurring engine starting problem. The action by the pilot to continue the engines start, taxi and take-off without interruption indicated that the pilot was unconcerned by the reported initial difficulty starting the left engine, or by the 'frequency vibration' that was reported by the passenger witnesses at the runway 32 parking area. In addition, given the history of extensive efforts by the pilot during the flight to Australia to at all times ensure the serviceability of the aircraft, it was likely that the pilot would have attended to any engine(s) start or after-start anomaly as soon as it became evident. The investigation concluded that the start and after-start passenger witness reports probably resulted from observations that were accepted as 'normal' by the pilot and also by the pilot witness who was also located at the runway 32 parking area.

Take-off

The action to conduct a rolling take-off was consistent with an attempt by the pilot to minimise the potential for damage to the propeller blades and underside of the aircraft as a result of the dislodgement from the runway surface of pebbles and other potentially damaging debris. The investigation considered whether the pilot may have attempted to lift off the runway earlier than normal in an attempt to minimise the possibility of such damage. However, this was considered unlikely given the report from the pilot witness, that the lift-off appeared to reflect other twin-engine aircraft take-offs that he had observed, and the approximation of the length of the take-off roll to that predicted by the Pilot's Operating Handbook (POH) performance charts.

The reports from the witnesses at the runway 32 parking area that there had been no smoke or fumes observed emanating from the aircraft and that nothing fell from it during the take-off, corroborated the results of the after-accident runway inspection. That, along with the identification of all control surfaces at the accident site, and the distribution of the aircraft wreckage, indicated that there had been no aircraft break-up or detachment of the aircraft's control surfaces prior to the impact with the trees and ground.

There was no evidence of any pre-existing failure or anomaly in either engine or their supporting assemblies or components that were able to be tested, that might have adversely influenced the performance of the engines during the take-off. In addition, the nature of the damage to the propellers and propeller hubs was consistent with the delivery of comparable amounts of power to both propellers from within the engines' upper operating range at the time of ground impact. There was no evidence of an enduring power failure of either engine during the take-off.

The investigation considered a number of possible factors that could have had the potential to affect the lateral control of the aircraft. Those factors included: the possibility of a lateral weight imbalance; an aerodynamic influence on the performance of the aircraft; and whether the pilot might have either intentionally or inadvertently manoeuvred the aircraft to the left of the runway immediately after lift-off.

Given that all of the baggage was observed being stowed in the aircraft cabin, there was minimal potential for the baggage distribution on take-off to have adversely affected the lateral control of the aircraft. The pilot's high and recent experience operating the aircraft minimised the possibility that he might have neglected to check the correct engine fuel selections on the three occasions (at least) required by the POH during the flight to El Questro. Similarly, had the pilot inadvertently mis-selected the engines' fuel supply, the nature of the aircraft checks meant that it was unlikely that a mis-selection would remain undetected by the pilot for the duration of the flight to El Questro. Therefore, it was considered that the potential for a lateral fuel load imbalance, and therefore aircraft weight imbalance to have developed during the flight to El Questro was minimal.

In any case, given the short taxi to runway 32 from the parking area and the rolling take-off, any disparity that may have existed in the lateral fuel distribution for the take-off was estimated to have been within 50 pounds of that for the landing at El Questro. That meant that the pilot would have been aware of the potential for any associated aircraft roll during the take-off and would have been ready to compensate. In addition, as indicated in the POH, the relatively benign nature of the ambient conditions and reported 'normal' appearance of the take-off ought to have allowed the pilot to control the aircraft even had there been a lateral fuel imbalance.

The aerodynamic factors with the potential to have affected the lateral control of the aircraft included the effects of asymmetric or 'split' flap and a wing stall. The damage to the left flap meant that, in the first instance, the investigation could not discount that split flap might have occurred during the lift-off. However, given that the right flap was confirmed retracted at ground impact, the only possibility was that the left flap might have self-extended. In that case, the aircraft would have rolled to the right after lift-off. That was not consistent with the witness reports that the aircraft banked to the left after lift-off before striking the trees to the left of the runway. On that basis, the investigation discounted that split flaps had occurred.

It was considered most likely that the experienced and proficient pilot would have raised the nose wheel at 95 knots indicated air speed (KIAS) and lifted the aircraft from the runway at 100 KIAS in accordance with the procedures recommended in the POH.

The pilot witness's description of the take-off and initial slight left bank after take-off could be construed as normal manoeuvring. In that case and given the reported lack of a very steep pitch angle after take-off, it ought to have been difficult for the pilot to have stalled the aircraft. In addition, the pilot's high experience and proficiency in the aircraft, and intimate knowledge of its systems meant that it was highly unlikely that he might have: allowed the speed to decrease to between about 88 to 93 KIAS in order for the stall warning to have activated; to have then reacted inappropriately, or not at all to that warning; to have finally not, or inappropriately, reacted to any developing mild and then increasing aerodynamic buffet; and, instead allowed a continuing reduction in airspeed until reaching about 83 KIAS whereupon the aircraft stalled. On that basis, it was concluded that an aerodynamic stall had most likely not occurred.

Given the pilot's predominant recent experience during the flight to Australia of landing and taking off from major or international aerodromes, the occurrence take-off was potentially his first from an airstrip and surface such as that at the El Questro ALA for some time. In addition, as a result of the pilot having landed the aircraft on runway 14, the take-off from runway 32 was potentially his first opportunity to have comprehended the relative proximity of the trees to the left of the runway. That comprehension was probably only possible during the conduct of the occurrence take-off and may have influenced the pilot's awareness of the need to maintain the aircraft overhead the runway centreline during the take-off.

The absence of bird or other animal remains along the runway surface, and the reported absence of any thermal activity or dust devils, indicated that the pilot most likely was not required to intentionally manoeuvre the aircraft as a result of those potential influences on the take-off. Also, the nature of the pilot's recent flying experience, the number and variety of the exotic locations visited during his flight to Australia, the pilot's age and total flying experience, and his probable desire to not compound any apprehension on the part of the passenger meant that it was most unlikely that the pilot was performing the early stages of any sort of intentional low-level manoeuvre.

The investigation could not discount that the pilot might have been momentarily distracted during the lift-off from the runway to the extent that the aircraft developed an unintended slight left bank and drift. The probable small amount of time for the pilot to have reacted once he perceived any unintended movement of the aircraft would have minimised the possibility for the pilot to have avoided impacting the trees to the left of the runway.

Summary

There was no documentary, physical or witness evidence identified during the investigation that indicated that an anomaly or failure in the aircraft or its systems contributed to the development of the occurrence. In addition, there was no evidence to indicate that the reported slight left bank after lift-off from the runway was the result of a lateral imbalance of the aircraft, an aerodynamic effect or an intentional control input by the pilot. However, the investigation was unable to determine whether the pilot might have been distracted during the lift-off by an unidentified event to the extent that he did not notice or was unable to react to any unintentional left bank and drift of the aircraft in sufficient time to prevent the aircraft impacting the trees to the left of the runway.

CONCLUSIONS

Findings

Pilot

• The pilot was qualified and appropriately endorsed for the flight.
• The pilot was reported to have 975 hours experience flying the Cessna 421 B and C models over the preceding 10-year period and at least 2,100 total flying hours.
• The pilot held a valid Class 2 medical certificate.
• The pilot was reported to be fit and well and in good spirits prior to the flight.
• There was no evidence of any pre-existing medical disease, sudden illness or incapacitation that may have affected the pilot's ability to control the aircraft.

Aircraft

• Export Certificate of Airworthiness number 3588/04 was issued for the Swiss-registered aircraft by Swiss regulatory authorities on 27 February 2004.
• The quality of the fuel that was supplied from the Broome supplier was not a factor in the occurrence.
• There was sufficient fuel onboard the aircraft to complete the flight to Broome.
• The aircraft weight and balance was estimated to be within the published limits at the time of the take-off.
• The ability of the pilot to lift the aircraft from the runway meant that the control column lock and optional rudder gust lock were unlocked at that time.
• There was no break-up of the aircraft or detachment of the aircraft's control surfaces prior to the impact with the trees and ground at the accident site.
• There was no evidence of any pre-existing failure or anomaly in either engine or their supporting assemblies or components.
• Comparable amounts of power were being delivered to both propellers from within both engines' upper operating range when the aircraft impacted the ground.

Other findings

• Witness reports indicated that, shortly after lift-off from the runway, the aircraft banked and drifted to the left slightly, before striking the trees to the side of the runway and impacting the ground.
• There was no evidence that the ambient conditions contributed to the circumstances of the occurrence.
• The pilot indicated that the El Questro ALA was suitable for his operation.
• There was no distress radio transmission by the pilot.
• Based on the available evidence, it was considered most unlikely that the pilot was performing the early stages of any sort of intentional low-level manoeuvre.
• The investigation could not discount that the pilot might have been momentarily distracted during the lift-off, resulting in the development of an unintentional slight left bank and drift of the aircraft.
• The relative proximity of the trees to the left of the runway would have adversely affected the time available for the pilot to have reacted to the development of any unintentional left bank and drift.
• The destruction of the aircraft cockpit and cabin from the combined effects of the impact forces and post-impact fire rendered the accident non-survivable.

Sequence of events¹

On 30 August 2004, shortly before 1200 Western Standard Time, the owner-pilot of a twin-engine Cessna Aircraft Company 421C Golden Eagle (C421) aircraft, registered HB-LRW, commenced his take-off from runway 32 at El Questro Aircraft Landing Area (ALA). The private flight was to Broome, where the pilot intended resuming the aircraft delivery flight from Switzerland to Perth. The available documentation indicated that the flight segments en route to Australia had all been to international or major aerodromes.

The pilot of a Cessna Aircraft Company 210 (C210) and his two passengers in the runway 32 parking area witnessed the take-off. Those witnesses reported that the C421 pilot carried out a pre-flight inspection of the aircraft prior to boarding for the take-off. During that inspection, he was observed preparing for and conducting a fuel drain check under the left wing, and to have removed some weed-like material from the right main wheel. He then loaded a small amount of personal luggage into the aircraft cabin, before he and the sole passenger boarded.

The C210 pilot witness, who reported having observed a number of twin-engine aircraft operations at another aerodrome, did not comment on the nature of the pilot's start and engines run-up checks. The passenger witnesses reported that the pilot of the C421 made a number of unsuccessful attempts to start the left engine, before reverting to starting the right engine. He then started the left engine and moved the aircraft clear of the C210 in order to conduct his engine run-up checks. The passenger witnesses reported that during those checks they heard a 'frequency vibration' as the C421 pilot manipulated the engines' controls.

The witnesses at the parking area reported that the C421 pilot taxied the aircraft onto the runway and applied power to commence a rolling take-off.² They, together with a hearing witness³ located to the north of the ALA indicated that the engines sounded 'normal' throughout the take-off. Witnesses who observed the take-off reported that the aircraft accelerated away 'briskly'. The pilot witness stated that the take-off roll and lift-off from the runway appeared similar to other twin-engine aircraft take-offs that he had observed.

The witnesses at the parking area also stated that, shortly after lift-off from the runway, the aircraft banked slightly to the left at an estimated 10 to 15 degrees angle of bank and drifted left before striking the trees along the side of the runway and impacting the ground. There was no report of any objects falling from the aircraft, or of any smoke or vapour emanating from the aircraft during the take-off. The aircraft was destroyed by the impact forces and post-impact fire. The pilot and passenger were fatally injured.

Personnel information

The 60-year-old pilot was appropriately licensed and held the relevant aircraft and other endorsements to conduct the flight. It was reported that the pilot had accumulated more than 975 hours experience flying the Cessna 421 B and C model aircraft over the preceding 10 year period and had at least 2,100 total flying hours. The pilot had flown about 50 to 60 hours in the aircraft since March 2004 and held a valid Class 2 medical certificate. He last underwent an electro cardiogram examination (ECG) in support of the revalidation of his medical certificate, on 22 September 1999. That included an annotation by the consulting doctor that the ECG was 'normal'. The pilot's family indicated that the pilot's personal logbook would have been in the aircraft at the time of the accident.

The passenger had accompanied the pilot for the majority of the flight from Switzerland to Australia, but was reported to have been a little nervous about take-offs and landings.

The pilot and passenger arrived at the El Questro ALA at about 1330 on 28 August 2004 and landed on runway 14. They were reported to have spent the next two days relaxing in the tourist resort and homestead. During that time, the pilot was observed by staff to have retired for bed by about 2200 and appeared from his room by about 0930 each day. During his stay the pilot ate regularly, drank alcohol only socially, and recounted many of his experiences during the delivery flight to staff and other guests. That did not include the discussion of any difficulty starting the aircraft engines, of any anomalies during the after-start checks and procedures, or during the flight to El Questro. The pilot was reported to be fit and well and in good spirits on the morning of the accident.

Aircraft information

General information

All of the aircraft's original maintenance documentation was reported to be on board the aircraft for the flight to Australia and was subsequently destroyed in the post-impact fire. The loss of the aircraft's maintenance documentation and historical records precluded a thorough review of the aircraft's documentation concerning compliance with applicable airworthiness directives and service bulletins. Aircraft and engine maintenance and airworthiness-related issues were reconstructed from available secondary documentation, including: pilot and other relevant party e-mails and facsimile messages, and data from international regulatory and other agencies.

E-mail correspondence from the pilot dated 16 September 2003 indicated that the aircraft was equipped with the Robertson Short Take-off and Landing (R-STOL) Kit. That kit included the following changes to the configuration of the aircraft:

• Replacement of the existing trailing-edge split flaps with R-STOL slotted flaps for use with the flaps extended 10°. The effect was to reduce the aircraft stall speed and the best single-engine climb speed.
• Introduction of a scissors-type aileron bell crank that allows symmetrical aileron droop with extension of the flaps. This had the effect of further reducing the aircraft stall speed.
• Introduction of a spring/cable flap/elevator interconnect to minimise pitch trim changes with flap extension or retraction.

In this instance, and as discussed in the wreckage examination discussion at page 13, and the asymmetric or 'split' flap discussion at page 19, the aircraft flaps were retracted. In that case, the R-STOL kit would have had no effect on the aircraft take-off performance, and the aircraft's performance would have been in accordance with a standard C421C in a flaps retracted configuration.

The aircraft's take-off weight and centre of gravity were estimated by the investigation to be within the limits published in the C421C's Pilot's Operating Handbook (POH). The POH also included a Normal Take-off Distance prediction chart. Application of the estimated aircraft take-off weight and reported ambient conditions for a normally configured C421C to that chart resulted in a predicted take-off roll that approximated the estimated take-off distance reported by the witnesses located at the runway 32 parking area.

Aircraft history

The aircraft was manufactured in the United States (US) and was US-registered until 1992, when it was exported to Switzerland. It was operated in Switzerland in the private category until purchased by the pilot in December 2003. E-mail correspondence from the pilot and dated 4 December 2003 indicated that a Swiss maintenance organisation would commence a 'new annual/200-hours check' on 10 December 2003. The available aircraft maintenance records indicated that the total aircraft flight hours were 3,192 hours 40 minutes as at 10 December 2003. That corresponded with the initial entry made by the pilot in the aircraft maintenance record after a flight in the aircraft on 2 March 2004. The last entry in the aircraft's maintenance record, that was available to the investigation, was a total of 3,233.6 aircraft flight hours at Ahmedabad, India on 9 August 2004.

A number of aircraft anomalies or maintenance requirements needed resolution while the aircraft was en-route from Switzerland to Australia. They included:

• In Malta, where an approved maintenance facility:
• replaced leaking right engine push rod tube seals
• replaced a faulty left engine vacuum pump
• identified a leaking right main landing gear oleo and disassembled the landing gear oleo and installed new packings and 'o' ring seals before reinstalling the oleo on the aircraft.
• In Cyprus, where a crack was discovered in the right engine crankcase that necessitated the replacement of that engine.
• In the United Arab Emirates and Oman, where a number of attempts were made by local engineering companies to resolve a problem with the operation of the aircraft's landing gear. That ultimately required the replacement of a selector valve and hydraulic line.

In addition, the pilot established communications with a twin-engine Cessna owners group in an effort to fault analyse ongoing problems with:

• the left and right hydraulic pumps that supplied the necessary hydraulic pressure to extend and retract the landing gear, and
• the right alternator warning light, which was reported to commence flickering after about 30 minutes flight time. That anomaly was reported to have commenced in July 2004.

The resolution or otherwise of those two anomalies was not documented by the pilot.

On arrival in Australia, a 50-hourly inspection of the aircraft was carried out by a Broome aircraft maintenance company on 26 August 2004. The total airframe hours at the time of that inspection were not noted on the inspection work sheet. At the conclusion of the inspection, a company engineer carried out a ground run of the engines with the pilot accompanying him in the right front seat. The engineer reported that during that ground run, both engines started on the first attempt and ran normally without any anomalies being noted.

Engines and propellers

The aircraft engine details were as follows:

The available right engine documentation indicated that it had been certified by a US Federal Aviation Administration-approved maintenance organisation. In addition, the documentation confirmed that the engine complied with all of the engine manufacturer's service bulletins and service letters that affected the engine up to and including 17 May 2004.

The details of the propellers, including their relationship to their respective engines, were determined from examination of the pilot's e-mail correspondence and the aircraft sales brochures, and included:

Meteorological information

A Bureau of Meteorology (BoM) post-accident assessment of the wind at the ALA at the time of the accident was that it would have been a light southerly at around 5 kts. An estimation of the ambient temperature and humidity at the ALA was not included in the BoM assessment. The BoM indicated that any difference between the BoM estimation of the prevailing wind and that reported by any witnesses could have been due to local topographical effects at the site. The BoM advised that a possible influencing factor on the aircraft's take-off could have been the presence of a dust devil⁹, but that the presence of that phenomenon would also require confirmation by any witnesses at the scene of the accident.

The witnesses at the landing area estimated that the wind affecting the runway was south-easterly at 5 to 10 kts at the time of the take-off. There were no dust devils reported in the vicinity of the runway at that time, and another pilot who was conducting charter work in the vicinity of the landing area indicated that there was minimal thermal activity.

Aerodrome and communications information

Aerodrome

The El Questro ALA, designation YEQO, is located at 16°00.5'S, 127°58.5'E and is at an elevation of 300 ft above mean sea level. The dirt runway is aligned south-east (runway 14) to north-west (runway 32) and is 1,400 m long and about 15 m wide. Windsocks are located at the northern side of the threshold to runway 14 and at the tourist resort homestead, which is located about 1 km south-east of the landing area.

The manager of the tourist resort indicated that when making bookings with the resort, visiting pilots generally included that they were 'self-fliers'. That was the case with the occurrence pilot. In addition, it was reported that the pilot telephoned the resort manager on the morning of 28 August 2004 and nominated a SARTIME¹⁰ for his arrival at El Questro. During that call, the pilot confirmed that he was comfortable with the location and details of the ALA. Other twin-engine aircraft of similar size to the C421 Golden Eagle were reported by the resort manager to have operated to, and continue to operate to, the El Questro ALA.

It was reported that in mid-March each year, just prior to the commencement of each tourist season, resort staff conducted a routine inspection of the runway and environs. As a result of those inspections, any newly growing vegetation was cleared from the runway and its surrounds, runway markers were repainted as required and other actions were undertaken by resort staff as and when required. In addition, the resort manager stated that he routinely consulted with aircraft operators who regularly fly to the resort, in order to confirm the ongoing suitability of the ALA for aircraft operations.

Communications

The charter pilot indicated that just prior to 1200, he exchanged a number of radio transmissions with the pilot of an unknown aircraft on frequency 126.7 Mhz in order to coordinate that pilot's take-off from the ALA. The charter pilot reported observing a plume of smoke from the vicinity of the ALA shortly thereafter, and that he did not hear a distress radio transmission. There was no facility at the ALA to record pilots' radio transmissions.

Wreckage information

The impact forces and post-impact fire sustained by aircraft structures in occurrences of this type can result in erroneous control position indications. In general, the position of the flight controls after impact cannot be relied upon as evidence of the aircraft's pre-impact configuration.

Overview of accident site and aircraft wreckage

The accident site was located on level ground, alongside a dry creek bed about 106 m to the left of the runway centreline and abeam a point on the runway about 888 m from the runway 32 threshold. A photograph of the general location of the accident site is at Figure 1. Groupings of rocks were located about the site and the surrounding light scrub was interspersed with isolated larger Boab and other trees.

Figure 1: General location of the accident site

A number of trees to the left of the runway were struck by the aircraft before it impacted the ground. Those trees were oriented along a line at about 15° to the left of the runway heading. Laser range equipment was used to measure the distances of those tree strikes from the aircraft wreckage. Trigonometry was then applied to the laser ranges in order to estimate the height of the strikes above ground level as follows:

• The initial tree strike was to a tree located about 66 m to the left of the runway centreline and at an estimated height of about 8.2 m (27 feet (ft)).
• The final tree that was struck prior to ground impact was located about 97 m from the runway centreline. That tree was struck at an estimated height of about 10.7 m (36 ft). The location of the left-wing tip and remnants of the left navigation light in the immediate vicinity of that tree indicated that tree strike had been by the left wing.

The aircraft impacted the ground about 33 m beyond the last tree, in a left-wing low attitude and cartwheeled counter-clockwise. The right wing and tail then struck the ground. During the impact sequence, the right engine separated from the airframe mounts and was thrown about 26 m from the main wreckage and the tail section separated from the aircraft. The main wreckage came to rest upright, with the nose of the aircraft facing south-east. All structural components and flight control surfaces were accounted for in the vicinity of the impact point. A severe post-impact fire destroyed the majority of the aircraft's fuselage, wings, tail section, cockpit and cabin, and damaged the left engine. The right engine sustained minor fire damage from a scrub fire that was started by the aircraft fire. A photograph of the aircraft wreckage is shown at Figure 2.

Figure 2: Aircraft wreckage

Wreckage examination

The investigation conducted a post-accident inspection of runway 32 from the threshold of the runway to a point on the runway abeam the ground impact point. That inspection found no evidence of any: bird or other animal remains; gouges, scrapes or other abnormal ground marks; or the presence of any detached aircraft items or components.

Very few ground impact scars or marks were able to be examined at the accident site due to them having been partially obliterated by the vehicles and personnel involved in the initial firefighting and rescue response. However, a number of rocks located in the dry creek bed had evidence of propeller impacts at substantial propeller revolutions per minute (RPM).

Both wing structures were destroyed by the fire. The right-wing forward attachment point was intact, and the aft spar was fractured in overload consistent with upward loads in excess of design limits. The left-wing structure had separated at the wing spar outboard of the engine nacelle, having also failed in overload due to the ground impact.

The fire severely damaged the aircraft fuel system. Both wing tanks were destroyed, and their associated auxiliary pumps were severely damaged. The left- and right-over-wing filler caps were secure. Damage during the impact, and the post-impact fire precluded the recovery of a fuel sample from the wreckage.

Both of the engines' air boxes and both turbocharger compressor turbines, together with their associated valves were fire damaged. On-site examination of the turbochargers did not reveal any anomalies, or foreign object, or other damage that might have adversely affected their operation. Deformation damage to the right engine's exhaust system was consistent with engine operation at ground impact. The left and right engines were recovered from the accident site and transported to an authorised overhaul facility for subsequent inspection under the supervision of the Australian Transport Safety Bureau (ATSB).

All six propeller blades separated from their respective hubs during the ground impact. Four intact propeller blades and segments from the remaining two blades were recovered from the accident site for subsequent technical examination.

Both engine propeller hubs flanges displayed indications of rotation at high RPM at the time of ground impact and were recovered from the accident site for subsequent technical examination. Severe impact damage to the propeller static stops prevented any determination of the propeller pitch settings at the time of ground impact. All of the propeller counterweights were recovered and examined on site. That examination identified overload of the threaded inserts, to the extent that a number of the counterweights had separated from their housing. That corroborated the earlier evidence of high engine RPM at the time of ground impact.

All of the cockpit and cabin seats and structures, along with the seat belts and their attachments, were destroyed by the fire. Most of the cabin fittings and cockpit, including instrumentation and switches were also destroyed. The nature of the damage to the switches was such that their position prior to the ground impact could not be ascertained. The control columns and flap actuator were destroyed in the fire and the engine controls, and the cockpit instruments and radios were severely damaged. While that prevented the examination of most of the instruments, the attitude indicators and annunciator panel were recovered for subsequent technical examination.

Pre-impact flight control continuity was confirmed for the elevator and rudder control surfaces. Flight control continuity was evident for the ailerons, from the cockpit controls aft to the point where the wing impact damage occurred. A continuity check of the engine controls was not possible as a result of the fire damage. The nature of the damage to the right flap indicated that it was retracted at the time of ground impact. The more extensive damage to the left flap precluded a definitive assessment of its position at ground impact. The landing gear was fully extended. The tyres were destroyed by the fire. The severe disruption of the tail structure rendered the determination of the aircraft trim measurements inconclusive.

Examination of components recovered from the wreckage

The left and right engines were disassembled and inspected at an authorised overhaul facility under the supervision of the ATSB and with the engine manufacturer's representative in attendance. That inspection found no evidence of internal mechanical failure within either engine, or of their associated accessories or components that would have prevented the normal operation of either engine prior to the accident.

Technical examination of the propellers and propeller segments indicated multiple high-energy hard object impact signatures on all blade surfaces. Several of those impacts were of sufficient force to have caused ductile shear of the outer airfoil sections. In addition, there was backward curling or loss of material from the blades' leading edges, with associated chordwise scoring and gouging across the airfoil sections. That was consistent with each propeller being actively driven by a comparable amount of power from within the respective engine's upper operating range at the time of ground impact.

Both engine propeller hubs sustained similar multiple fractures to their aluminium alloy housings that was consistent with ductile overload during the accident sequence. There was no indication of any pre-impact cracking or manufacturing defects. The propeller hubs were exposed to gross bending loads through the blade sockets, which was assessed as being consistent with the magnitude of the impact forces that damaged the propellers.

The technical examination of the primary attitude indicator proved inconclusive due to the extensive heat damage to the instrument. There was evidence of rotational scoring to the inside of the secondary attitude indicator's instrument case and to the gyro armature, which indicated that pneumatic drive was available to the aircraft's vacuum instruments at the time of ground impact.

The filaments from the annunciator panel globes were distorted and encased in molten glass as a result of the fire. That prevented the analysis of whether any of those lights had been illuminated at the time of ground impact.

Medical and pathological information

A review of the pilot's aviation-related medical records and the results of the pilot's postmortem examination found no evidence of any pre-existing medical disease, sudden illness or incapacitation that may have affected his ability to control the aircraft.

Fire

There was no report by the witnesses to the take-off, or evidence, of an in-flight fire. The tourist resort volunteer fire-fighting crew responded to the accident site and scrub fires.

The source of the intense post-impact fire was fuel that had spilled from the ruptured wing fuel tanks. The ignition source of the fire could not be confirmed but was likely the hot engine exhausts.

Survival aspects

The emergency locator transmitter (ELT) was destroyed in the post-impact fire. There was no report from the charter pilot, or from the search and rescue authorities to indicate that the ELT had activated on ground impact.

The destruction of the cockpit and cabin from the combined effects of the impact forces and fire rendered the accident non-survivable.

Tests and research - aircraft fuel

The last recorded refuel of the aircraft was the addition of 594 litres of aviation gasoline 100 at Broome on 27 August 2004. It was reported that the pilot refuelled the aircraft's tanks to capacity. The investigation team quarantined a sample of that fuel for subsequent analysis by an approved National Association of Testing Authorities facility. That analysis indicated that the fuel:

• was clear and bright
• was free from water and sediment
• conformed to specification for aviation gasoline 100.

Examination of the Broome fuel supplier's records confirmed that 18 other aircraft were refuelled from that source after the occurrence aircraft on that day. There were no reports from the pilots of those aircraft of any fuel-related problems.

There were no aircraft refuelling facilities at El Questro.

Additional information

Use of aerodromes

Civil Aviation Regulation 92 places responsibility for ensuring that an aircraft landing area is suitable for landing or take-off with the pilot in command. In addition, the regulation requires the pilot to have regard to the prevailing weather conditions and other circumstances affecting the proposed landing or take-off. The determination by a pilot of which other circumstances should be considered is not stated in that regulation.

Civil Aviation Advisory Publication (CAAP) 92-1(1): Guidelines for Aeroplane Landing Areas includes guidance on the factors that may be considered by a pilot when determining the suitability of a potential landing area. While there was no evidence that the pilot had considered the requirements of the CAAP prior to planning his arrival at the El Questro ALA, the investigation applied the minimum landing area physical characteristics recommended by the CAAP to the pilot's take-off from runway 32 until the point at which the aircraft first struck a tree to the left of the runway. That examination determined the following relevant recommended parameters for the take-off:

• minimum runway width - 15 m
• required runway length - about 624 m
• suitable lateral transitional slope, which the CAAP notes could allow for a desirable area of increased lateral clearance during the take-off and may reduce wind shear if near tall trees - maximum obstacle height of about 7.2 m at 66 m from the runway centreline.

The pilot's family indicated that the pilot had operated at a gravel airstrip in the south-west of Western Australia on a number of occasions over the previous 3 years. In addition, the family reported that the pilot drove to El Questro in June 2003 and, during that visit, most likely observed the ALA.

Preparation for flight

The pilot submitted a flight notification to Airservices Australia on the morning of the accident, for a 2 hours 15 minutes flight under the Visual Flight Rules from El Questro to Broome. The investigation estimated that 740 lbs of fuel remained after the reported 2-hour flight from Broome to El Questro, and the POH stated that 50 lbs of fuel was required for 'taxiing for take-off'. That, and the endurance nominated by the pilot in the flight notification, indicated that sufficient fuel was carried for the planned flight to Broome.

The POH stated that the aircraft equipment included a control column lock that restricted control column movement and held the ailerons in a neutral position and the elevators at about 10° trailing edge down. The aircraft manufacturer indicated that the design of the control column lock was such that, if inadvertently left engaged by a pilot, the aircraft would be unable to take-off. The available documentation indicated that an optional rudder gust lock was also included in the aircraft equipment. The POH stated that engagement of that lock required the rudder to be centralised and the elevators to be moved to the fully 'down' position. Disengagement of the rudder lock was possible either manually during the aircraft pre-flight, or automatically as the elevator was moved up through the 6° 'down' position. Due to the damage to the aircraft, the investigation was unable to confirm the position of these locks.

Manufacturer data

The POH promulgated the necessary checks to be carried out by the pilot when operating the aircraft. That included confirmation of the selection of the left and right engines to the left and right main fuel tanks respectively as part of the following checks: before start, before take-off and during the descent. In addition, the POH stated that:

A take-off with one main tank full and the opposite tank low on fuel creates a lateral unbalance. This is not recommended since gusty air or premature lift-off could create a serious control problem.

The published take-off technique included the requirement for the pilot to raise the nose wheel at 95 kts indicated air speed (KIAS) and lift the aircraft from the runway at 100 KIAS. In addition, the POH included a description of the aircraft stall including that:

• the stall characteristics are conventional
• there is an aural stall warning device that operates at 5 to 10 KIAS above the stall in all configurations
• the stall is preceded by a mild, aerodynamic buffet, which increases in intensity as the stall is approached
• the power-on stall occurs at a very steep pitch angle, either with or without flaps extended
• it is difficult to inadvertently stall the aircraft during normal manoeuvring.

Stall speeds were published in the POH for a number of aircraft configurations. None of those configurations reflected the aircraft's take-off configuration. At the estimated aircraft weight and with wings level, the maximum stall speed for the published configurations was calculated as 83 KIAS. The increase in stall speed at 15° angle of bank for all published configurations was about 2 KIAS.

The manufacturer's Pilot Safety and Warning Supplements identified a rare, but potentially serious problem known as 'split wing flaps'. Split or asymmetric wing flaps may result from a mechanical failure in the flap system and cause the flap position on one wing to differ from that of the opposite wing flap. The result is a tendency for the aircraft to roll in the direction of the retracted flap. Depending on the experience and proficiency of a pilot, the manufacturer indicated that any rolling tendency caused by a split flap situation may be controlled with opposite aileron. In addition, there was the potential for a pilot to apply differential power in a multi-engine aircraft to assist in managing the condition. This is discussed further in the Analysis under 'Take-off'.

1. Only those investigation areas identified by the headings and subheadings were considered to be relevant to the circumstances of the occurrence.
2. A take-off commenced by a pilot without pausing an aircraft in a stationary position on a runway, or decreasing the speed of an aircraft on arriving at a runway intended for use for a take-off.
3. A witness that heard, but did not observe the take-off.
4. On 14 November 2003, the pilot submitted an application to the Australian Civil Aviation Safety Authority (CASA) to reserve an Australian aircraft registration in anticipation of registering the aircraft in Australia. That reservation was granted by CASA.
5. Based on the 50-hourly inspection that was carried out in Broome on 26 August 2004 being conducted within the potential 10-hour extension period that had been authorised by the Swiss regulatory authorities. That was between 50 and 60 hours after an annual/200 hours check that was reported as being commenced in Switzerland on 10 December 2003, and included the 2.0 hour flight to El Questro ALA.
6. Derived from e-mail correspondence from the pilot dated over the period 16 September 2003 to 24 August 2004 and the available aircraft and engine documentation.
7. Derived from the right engine Export Certificate of Airworthiness of 19 May 2004 and e-mail correspondence from the pilot dated 29 July to 19 August 2004.
8. Precise date not available.
9. A miniature whirlwind with the potential to be of considerable intensity, and to pick up dust and perhaps other items and carry them some distance into the air.
10. The time nominated by a pilot for the initiation of Search and Rescue action if a report has not been received by the nominated unit.