Loss of control

The helicopter sustained a loss of tail rotor control while carrying out a power line inspection. It made approximately 12 to 15 full rotations before landing in a paddock. The pilot and two observers on board received minor injuries. The helicopter sustained minor damage.

Examination of the tail rotor revealed that the loss of control was due to failure of the inner tab of a tang washer. The washer locked the retaining nut holding the drive fork and the tail rotor assemblies onto the transmission output shaft. The failure of the inner tab resulted in looseness of the retaining nut and the split ring becoming dislodged. Consequently, the drive fork and the tail rotor assemblies were allowed to move freely along the transmission output shaft.

The ATSB was advised that at the helicopter rebuild a new tang washer was fitted. To inspect the washer, the retaining nut would have to be removed.

The operator sent the failed tang washer to the helicopter manufacturer to determine nature of the locking tab failure. The report had not been received at the time of writing this report.

A search of the ATSB database, for the 1995 to 2005 period, revealed no records of similar tail rotor control problems. The Civil Aviation Safety Authority Service Difficulty Report database, for the same period, contained only the record of the tail rotor control problem from this occurrence.

The manufacturer advised that they have received two worldwide reports of a broken locking tab since 1988.

ANALYSIS

The final minutes of the recorded Air Traffic Services radar data indicated that the pilot performed a series of turns in a constant descent that was consistent with a forced landing. Given the pilot's history of performing many practice forced landings, it is likely that immediately prior to the accident, the pilot was conducting a practice forced landing.

When radar contact was lost, the aircraft was already below the minimum altitude for a practiced forced landing and there was no indication that the pilot had decreased the rate of descent. That was confirmed by witnesses that indicated that the aircraft was well below 500 ft above ground level.

Based on the pilot's training records and interviews with flight instructors, it is probable that the pilot was fixated on the chosen landing area and descended below the minimum height for a go-around. During the latter stages of the approach recorded by the radar, the pilot performed a tight 360º turn. That may have been intentional to allow the aircraft to lose height and still be positioned for the selected landing area. During the turn, the aircraft lost approximately 25 kts, which reduced the margin above the aircraft's stall speed.

A person near the accident site reported seeing the aircraft at a very low altitude and flying quietly before hearing power applied. However, the atmospheric conditions around the time of the accident were conducive to the formation of serious carburettor ice at descent power and the engine may not have been capable of producing full power when it was applied. Because the person's attention returned to their duties, it was not known if the application of power that they reported was sustained for any length of time. The evidence in the wreckage indicated that there was little or no power applied at impact. The pilot may have removed power as part of the stall recovery procedure. The use of carburettor heat could not be determined and the formation of carburettor ice was a possibility.

The attitude at which the aircraft impacted the ground and the damage to the tail section indicated that the aircraft had stalled before it impacted the ground. The combination of the loss of airspeed during the turn and the pilot's documented difficulty with stall recognition and response, may have led to an inadvertent stall, either during the go-around or in the subsequent climb out. The height at which the aircraft stalled was not sufficient to permit a recovery. It was not possible to determine if carburettor icing had reduced the power available for the go-around and aggravated the situation.

Fatigue

Based on the pilot's activities and sleep patterns prior to the occurrence, it was apparent that the pilot probably obtained only 5 to 6 hours of interrupted sleep on the night before the accident. Even though this was consistent with his normal sleeping patterns, in all likelihood, the pilot may have started the day with a degree of fatigue as a result of insufficient quantity and quality of sleep the previous night. The pilot may have also been experiencing the effects of chronic fatigue given his recurring pattern of interrupted and relatively low quantity of sleep. Consequently, fatigue may have reduced the pilot's ability to fly the aircraft accurately and to develop and maintain awareness of, and make timely decisions in response to, a degraded aircraft state, such as a stall.

Pilot's training history

The pilot had required a significant amount of flying training to meet the General Flying Progress Test standard. The pilot's training was regular, but spread over a considerable period of time. The training records indicated that the pilot had difficulty in acquiring, maintaining and consolidating the skills required to safely operate a light aircraft. Many lessons were repeated to bring the pilot up to the required competency standard. Of particular note is that the pilot consistently demonstrated poor airspeed control during practice forced landings, indecision, a poor awareness of an impending stall, a lack of response to the stall warning horn, and incorrect stall recovery technique. These factors are consistent with the circumstances surrounding the accident.

FACTUAL INFORMATION¹

History of the flight

At about 0945 Eastern Standard Time² on Saturday 23 April 2005, a Cessna Aircraft Company A150L Aerobat aircraft, registered VH-UPS, departed Coldstream Airfield, Vic. for a private flight in the Coldstream General Flying Training Area, with the pilot as the only occupant (Figure 1).

The aircraft was first tracked by the Air Traffic Services (ATS) radar at 0949 heading in a northerly direction consistent with a departure from Coldstream runway 35. Over the next 6 to 7 minutes, the aircraft made a series of right turns that brought the aircraft into an area to the southeast of Steel Hill. The radar track shows the aircraft performing some aerial manoeuvres in this area before heading north-northeast towards Healesville for several minutes, then turning left for another series of aerial manoeuvres.

The final minutes of recorded radar data (Figure 2) show that the aircraft performed a descending orbit into the Yarra Valley before losing radar contact. The aircraft did not reappear on radar. At about that time, a passenger in a vehicle travelling along the Healesville - Koo Wee Rup Road observed the aircraft flying at low level. Shortly after, the aircraft was seen in a steep dive before it disappeared behind an embankment. The occupants of the vehicle located the wreckage of the aircraft in an open field about 1 km west of the Healesville - Koo Wee Rup Road. The aircraft was destroyed by impact forces and the pilot was fatally injured. There was no fire.

Figure1 : Accident location

Figure 2 : Recorded radar track

Recorded radar data showed that the aircraft maintained a fairly constant rate of descent of about 660 ft/min from an altitude of about 2,400 ft Above Mean Sea Level (AMSL), down to about 700 ft AMSL. That placed the aircraft at about 430 ft above ground level (AGL) when radar contact was lost. There was no indication in the radar data that the aircraft had ceased its descent when contact was lost. The accident site was located about 0.7 NM to the north of the last radar return.

At about 1,000 feet AMSL and heading in a north-easterly direction, the aircraft performed a tight 360º turn³ whilst maintaining the descent. During this turn, the radar recorded a decrease in speed of about 25 kts.

An employee working on the property where the accident occurred observed the aircraft pass at a very low level (estimated between 100 and 200 ft AGL) and flying quietly. The aircraft passed within several hundred metres of the employee and was headed in a northerly direction. The employee reported hearing the engine sound increase before returning their attention to their duties. Having worked on the property for some years, and observed many aircraft training in the area, the employee did not notice anything unusual about the aircraft, other than it being very low. Although located only 900 m from the accident site, the employee did not observe the final moments of the flight or the collision with the ground.

Wreckage information

Ground marks and crushing of the left-wing tip indicated that the aircraft had impacted the ground in a left wing-low and approximately 30º nose-down attitude. The direction of flight was approximately 320º (magnetic). The wing flaps were found in the fully retracted position.

The aircraft came to rest about 10 m from the impact point (Figure 3). The fuselage lay on its roof with the left wing wrapped over the cabin and the right wing in a near vertical position. The rear fuselage was bent downward and to the left. The tailplane had separated from the fuselage and the fin, which was lying on the right tailplane, had broken away from its mounting brackets. There were no indications of any pre-existing defects in the aircraft structure.

Figure 3 : Aircraft wreckage

Examination of the propeller, throttle lever position and engine instruments indicated that the engine was operating at low RPM and developing little or no significant engine power at impact. Examination of the engine found no evidence of a mechanical or system failure that would have prevented the production of power prior to impact. Due to the impact damage, the status of the carburettor heat control at impact could not be reliably determined.

Examination of the stall warning system, airspeed indicator and altimeter indicated that they were capable of normal operation during the flight prior to impact.
 

Personnel information

The pilot's flying experience was estimated as:

The pilot commenced part-time flying training on 23 May 2003 and was issued a Student Pilot Licence on 15 November 2003. The pilot's first solo flight on 23 November 2003 was made after receiving 43.7 hours of dual training. A pre-licence check flight was conducted by a senior instructor on 6 January 2004 when the pilot had 77.3 hours of experience. However, it was not until 24 July 2004 that the pilot achieved the General Flying Progress Test (GFPT) after a further 51 hours of flying training. At that time, the pilot had accumulated a total flying time of 128.4 hours, of which 104.9 hours were dual instruction. All of the pilot's flying training was undertaken at the same organisation.

The flying training organisation's pre-GFPT syllabus indicated that the minimum flying training required to the end of the GFPT phase was 23 hours dual and 6 hours solo, a total of 29 hours. The regulatory minimum total flight time required before attempting the GFPT was 20 hours of flight time.

After completing the GFPT, the pilot commenced cross-country navigation training as part of the Private Pilot (Aeroplane) Licence training syllabus. He had also completed 9.7 hours of aerobatic flight training but had not received an aerobatics endorsement. Entries in the pilot's logbook suggested that the pilot had previously engaged in solo aerobatics with a passenger on board the aircraft.

The pilot held a current Class 2 medical certificate that was endorsed with the restriction 'Renew by CASA only'. The results of the post-mortem examination and toxicology screening found no evidence of any physiological factor that may have impaired the pilot's performance during the accident flight.

In the days leading up to the accident flight, the pilot averaged 5 to 6 hours of sleep per night. These sleep periods were interrupted by waking periods late at night and was reported as the pilot's typical sleep pattern.

A review of the pilot's training records indicated that many lessons were repeated before the minimum competency standards were met. The pilot had recurring difficulties in airspeed management, steep and tight turns, identification of impending stall, response to the stall warning horn, recovery from the stall and go-around decision and technique. The pilot's instructors noted that constant reminders to monitor airspeed and altitude and to perform the appropriate recovery technique were required. The training records included several entries relating to inattention, tunnel vision and trouble attending to all parameters. Annotations of these difficulties were associated with many aspects of the pilot's training, but were particularly apparent for practiced forced landings.

The pilot had recorded a large number of practice forced landings during training, the majority of which were with an instructor.

Practice forced landing

The practice forced landing manoeuvre, as used in the flying training organisation's syllabus, typically involved simulating an engine failure by closing the throttle and gliding the aircraft toward a selected landing area.

The main objective of the manoeuvre was to develop judgement and skill in positioning the aircraft for a gliding approach to the selected field. When the manoeuvre is practiced on to an airfield, a landing is made off the approach. However, when the manoeuvre is practiced in the training area, the student is required to demonstrate a go-around from a safe height, usually not below 500 ft AGL. The go-around manoeuvre requires the pilot to apply full power and select the carburettor heat off, raise the flaps (if used) and establish the normal climb. If, for any reason, engine power is not available, the aircraft is ideally positioned for an emergency landing into the selected field.

To prevent the formation of carburettor ice during the practice forced landing, full carburettor heat is applied. A short application of engine power is normally made every 1,000 ft of descent to maintain engine temperatures. If carburettor heat is not selected off during the go-around, full power will not be available. When the normal climb attitude is maintained with less than full power, the aircraft will climb at a slower airspeed and rate of climb.

Aircraft information

The Cessna A150L aircraft was a two-place, high-wing, light aircraft designed for general flying training, but was also capable of aerobatic flight. The aircraft was powered by a Teledyne-Continental Motors O-200-A normally-aspirated piston engine through a fixed-pitch two-bladed propeller.

VH-UPS was imported into Australia in 1990 and had been operated and maintained by the same flying club since that time. It was utilised for both initial flying training and aerobatic training.

The flying club maintained the aircraft in accordance with a CASA approved maintenance system. The last periodic maintenance inspection was carried out on 23 March 2005. The aircraft's maintenance release, recovered from the wreckage, did not list any defects, and the documentation indicated that all required maintenance was completed. The maintenance release was endorsed by a licensed pilot certifying that the daily inspection had been satisfactorily completed on the morning of the accident. The accident flight was the first flight of the day for the aircraft.

Prior to importation into Australia, the aircraft had been fitted with a carburettor ice detection system in accordance with a United States Federal Aviation Administration approved kit. The system consisted of an optical sensor in the carburettor, a control box and a warning light mounted on the instrument panel. The operating instructions indicated that the pilot was required to adjust the sensitivity of the system to suit the local conditions prior to operation. The operational status of the system at the time of the accident could not be determined.

The aircraft had sufficient fuel and was within the weight and centre of gravity limitations for the duration of the flight.

Meteorological information

The Bureau of Meteorology automatic weather station for Coldstream recorded the environmental conditions for Saturday 23 April 2005 as:

The skies were overcast with high level cloud, there was a degree of haze; however, the horizon in the valley was clearly distinguishable. People in the area reported that winds were very light.

Carburettor icing

On the day of the accident, the atmospheric conditions were conducive to the formation of serious carburettor icing at descent power. Refer to Appendix A for a Flight Safety Australia magazine ⁵ article on carburettor icing.

1. Only those investigation areas identified by the headings and subheadings were considered to be relevant to the circumstances of the occurrence.
2. Eastern Standard Time was Coordinated Universal Time (UTC) + 10 hours.
3. The large changes in the aircraft position in this region are likely due to limitations in the radar system at low altitude, however the general pattern of a tight turn is indicated by the data points at 1106, 1006, 906 and 806 ft.
4. Total time in service.
5. Flight Safety Australia magazine is a publication of the Australian Civil Aviation Safety Authority.

At about 0945 Eastern Standard Time on Saturday 23 April 2005, a Cessna Aircraft Company A150L Aerobat aircraft, registered VH-UPS, departed Coldstream Airfield, Vic, for a private flight in the Coldstream General Flying Training Area, with the pilot as the only occupant.

The aircraft was tracked by the Air Traffic Services radar after its departure from Coldstream Airfield. The radar track showed that the aircraft performed some aerial manoeuvres to the east of the airfield before a descending orbit into the Yarra Valley when radar contact was lost. At about that time a passenger in a vehicle travelling along the Healesville - Koo Wee Rup Road observed the aircraft flying at low level. Shortly after, the aircraft was seen in a steep dive before they lost sight of it. The occupants of the vehicle located the wreckage of the aircraft in an open field about 1 km west of the Healesville - Koo Wee Rup Road. The aircraft was destroyed by impact forces and the pilot was fatally injured.

The aircraft had impacted the ground in a left wing-low and nose-down attitude. The fuselage lay on its roof with the left wing wrapped over the cabin and the right wing in a near vertical position. The rear fuselage was bent downward and to the left. The tailplane had separated from the fuselage and the fin had broken away from its mounting brackets. There were no indications of a pre-existing defect in the structure.

The investigation found that it was likely that the pilot was performing a practice forced landing and had descended below the safe altitude when the accident occurred. The airspeed was reduced to a point that the aircraft stalled and the altitude was not sufficient to affect a recovery before impact with the ground. It is possible that carburettor ice was present during the descent.

Related link: 

1. Meteorological conditions were conducive to wind shear, mechanical turbulence or a combination thereof.
2. The pilot took off in a crosswind that exceeded the limitations specified in the Pilots Operating Handbook.

The environmental conditions at the time of the accident required the pilot to take particular account of the prevailing sea conditions and the wind direction and speed, when selecting the area for, and direction of, the take-off. This led to the pilot making a compromise that placed emphasis on an area with a more favourable sea state rather than directly into the prevailing wind.

The local effects of the terrain gave the impression to the pilot that the wind at surface level in the area selected for the take-off was from the north-north-east. Therefore, he assessed that that wind direction was suitable for the take-off. However, it is likely that the aircraft encountered a crosswind during the take-off that exceeded the limitations in the Pilots Operating Handbook (POH). It was also likely that wind shear or mechanical turbulence, or a combination of both these effects, was encountered by the pilot shortly after take-off. At the point where the angle of bank of the aircraft exceeded 45 degrees, it is likely that the aircraft stalled causing it to strike the water.

The pilot reported that he was able to exit the aircraft quickly because of his previous underwater escape training. The Australian Transport Safety Bureau encourages all operators in this environment to ensure that their flight crews have completed similar training. The actions of the rear seat passenger were significant in enabling the remaining occupants to exit the aircraft.

The pilot and passengers did not have the time to retrieve their life jackets from under their seats before exiting the aircraft. This was also the case in the floatplane accident in Tasmania in 2001 (BO/200105932). Although the carriage of life jackets and the stowage of them below each of the seats was in accordance with Civil Aviation Order (CAO) 20.11 parts 5.1.4 and 5.1.5, the wearing of life jackets was not required by CAO 20.11 part 5.1.8, and as a consequence, their availability was not assured after the occupants of the floatplane had exited the aircraft into the water.

The lack of time available to retrieve and don life jackets in the event of an accident when operating close to, or on the water, has the potential to adversely affect the survivability of aircraft occupants after they have exited an aircraft. As highlighted in Federal Aviation Administration Advisory Circular (AC) 91-69A, it is extremely difficult for a person to don a life jacket when they are already in the water, and practically impossible to do so if the person is injured.

At 1735 eastern summer time on 20 January 2005, a Cessna Aircraft Company A185F floatplane, registered VH-SBH, with one pilot and three passengers on board was taking off on a water departure for a charter flight from Rose Bay aircraft landing area (ALA) to Palm Beach, NSW. Shortly after becoming airborne, the aircraft rolled 45 degrees to the left causing the left wing to strike the water. The aircraft became inverted and was substantially damaged. The four occupants escaped with minor injuries.

The pilot had positioned the floatplane to the eastern side of the ALA, approximately 200 m from the shoreline and to the west of a headland, to achieve more favourable sea conditions for a take-off to the north-north-west. The pilot reported that the wind direction was 010 degrees M at a speed of 20 kts. The intended take-off path ran approximately parallel to the headland in a direction of 350 degrees M.

The pilot reported selecting 20 degrees of flap for the take-off. As the aircraft was about to leave the surface, he selected 30 degrees of flap. This technique was used to help get the aircraft off the surface of the water quickly in difficult sea and/or weather conditions. He also reported that the aircraft took longer than he expected to reach take-off speed. The aircraft became airborne at 45 to 50 kts and he then selected 20 degrees of flap. At approximately 30 ft above the water, the aircraft commenced an uncommanded left roll that he was able to correct with full right aileron input. The aircraft then commenced a second uncommanded left roll that he was unable to correct with control inputs. The pilot, passengers and witnesses, all reported that the aircraft rolled more than 45 degrees to the left before the left wing struck the water.

The floatplane came to rest inverted and shortly after the cabin became submerged. The pilot reported that he had completed Helicopter Underwater Escape Training (HUET) previously, and that he thought that assisted him to exit the cabin quickly through the pilot's door, located on the left of the cabin. The passenger in the copilot's seat, located on the right of the cabin, was momentarily disorientated, but managed to undo his seat belt while the passenger in the middle row was attempting to locate and undo his seatbelt. The rear seat passenger was able to swim towards the front passenger and reported kicking open a door with her foot before pushing the front passenger out of the aircraft. She then returned to the middle row passenger and unfastened his seat belt buckle before pushing him out of the aircraft and then exiting the submerged cabin herself. One passenger reported that he was initially disoriented after the aircraft entered the water. In addition, given the rapid nature of the event and the need to exit the inverted cabin quickly, the passengers did not retrieve the life jackets which were stowed underneath their seats. It was likely that all passengers exited the floatplane via the pilot's door, because the co-pilot's door was still locked closed when the aircraft was recovered.

The floatplane stayed inverted with its floats remaining buoyant. After exiting the aircraft, the passengers were picked up by a passing boat. The pilot remained with the aircraft and secured it to a boat.

The load chart for the flight showed that the aircraft was within weight and balance limitations. The pilot was appropriately licensed and endorsed for the operation and was experienced in floatplane operations in Sydney Harbour. The aircraft was capable of normal operations before flight and there were no known maintenance issues.

A Bureau of Meteorology (BoM) report of the weather in Sydney Harbour at the time of the accident, showed that the prevailing wind around the time of the accident was from the north-east, averaging 26 to 29 kts, with gusts reaching 37 kts. The report also suggested that:

…in considering the wind shear that would have been experienced by a plane taking off from Rose Bay, the sheltering effect of the surrounding topography, especially the shielding of Rose Bay from north easterlies by the southern headland of Sydney Harbour, needs to be taken into account. It is conceivable that in passing from the relatively sheltered inshore waters of Rose Bay to a more exposed location, either through ascent or forward motion or both, that significant wind shear may have been experienced.

The pilot advised that he used a number of cues to determine the wind velocity, particularly the orientation of moored boats and flags, the BoM forecast and the water conditions.

Mountain waves and their turbulence can occur downwind of any obstacle, including an isolated hill a few hundred feet high. If the wind at the altitude of the top of the obstacle is 20 kts or more, there will be noticeable wave turbulence and significant downdrafts. This turbulence will be greatest in the rotor zone in the lee of the obstacle and will be at a maximum at about the same altitude as the top of the obstacle.¹

The company ALA register notation for Rose Bay warned that 'Dumping will be encountered in winds over 20 kts from the North-East, South and West'. The significant downdrafts described in the previous paragraph are what the operator's ALA register referred to as 'dumping'.

A fact sheet on mountain wave turbulence that accompanied Australian Transport Safety Bureau (ATSB) report BO/200104092 into an accident involving mechanical turbulence stated in part that:

In addition to generating turbulence that has demonstrated sufficient ferocity to significantly damage aircraft or lead to loss of control, the more prevailing danger to aircraft in the lower levels in Australia seems to be the effect on an aircraft's climb rate. General Aviation aircraft rarely have the performance capability sufficient to enable the pilot to overcome the effects of a severe downdraft generated by a mountain wave, or the turbulence or the windshear² generated by the rotor.

The Pilots Operating Handbook (POH) for the Cessna 185 indicated that the stalling speed in a 20 degree flap configuration, at a mid-range centre of gravity, was 55 kts. The POH also indicated a maximum demonstrated crosswind velocity for take-off and landing of 13 kts. The investigation determined that the crosswind for the accident flight would have been between 19 and 24 kts.

In December 2001, the ATSB investigated an accident involving a floatplane in Tasmania where the occupants had insufficient time to don life jackets before exiting the aircraft (see ATSB report BO/200105932). That accident investigation highlighted that regulations governing the use of life jackets, do not reflect the operational realities of exiting from an inverted submerged cabin.

Civil Aviation Order (CAO) 20.11 part 5.1.4 stated that:

Amphibious aircraft when operating on water, helicopters equipped with fixed flotation equipment when operating on water, and all seaplanes and flying boats on all flights shall be equipped with:
(a) 1 life jacket for each occupant; and
(b) an additional number of life jackets (equal to at least one-fifth of the total number of occupants) in a readily accessible position near the exits.

CAO 20.11part 5.1.4 stated that:

Life jackets shall be so stowed in the aircraft that 1 life jacket is readily accessible to each occupant and, in the case of passengers, within easy reach of their seats.

CAO 20.11 part 5.1.8 stated that:

Where life jackets are required to be carried in accordance with paragraph 5.1.4 each occupant of a single engine aircraft shall wear a life jacket during flight over water when the aircraft is operated beyond gliding distance from land or water, as appropriate, suitable for an emergency landing. However, occupants need not wear life jackets when the aircraft is taking off or landing at an aerodrome in accordance with a normal navigational procedure for departing from or arriving at that aerodrome, and occupants of aeroplanes need not wear life jackets during flight above 2 000 feet above the water.

Federal Aviation Administration Advisory Circular (AC) 91-69A contained recommendations and revised information for the safe operation of seaplanes. The AC stated that:

Life jackets in sealed pouches can be awkward to remove and don in a flooded aircraft. When a survivor attempts to put on a jacket in the water, it may be difficult to find and fasten its straps and hooks. It would take considerable effort to accomplish the combined maneuver [sic] of pulling a lifejacket over one's head while in the water trying to stay afloat. If a life preserver is not worn before flight, it is practically impossible for a survivor with an injured arm, for example, to don the life preserver in time for it to be effective for survival. Wearing an uninflated TSO C13f life preserver at all times in the seaplane and inflating it only after exiting the seaplane would seem to be the best protection.

Furthermore, the AC stated that after a seaplane accident:

and especially while submerged inverted in water, the passengers are likely to become disoriented and panic.

It also stated that:

Maneuvring [sic] while holding flotation devices can also be disorienting because it occupies the hands, making swimming or treading water difficult.

Additionally the AC stated in Section 1.b. (1)

For-hire operators must use FAA-approved PFD's. A PFD should be worn by each occupant while on the seaplane.

1. Modern Airmanship, Eighth Edition, Van Nostrand Reinhold Company, New York, 1999.

2. A change of wind velocity with distance along an axis at right angles to wind direction, specified vertically or horizontally. Recognised as an extremely dangerous phenomenon because encountered chiefly at low altitude (in squall or local frontal systems) in approach configuration at speed where it makes sudden and potentially disastrous difference to airspeed and thus lift.

Previous recommendation

On 23 October 2002 the ATSB issued the following recommendation as a result of a fatal accident at night near Newman, WA, (ATSB Investigation BO/200100348):

Recommendation R20020193
The Australian Transport Safety Bureau recommends that the Civil Aviation Safety Authority (CASA) review the general operational requirements, training requirements, flight planning requirements and guidance material provided to pilots conducting VFR operations in dark night conditions.

On 13 December 2002, CASA responded to the recommendation as follows:

CASA acknowledges the intent of this Recommendation. As part of the proposed CASR [Civil Aviation Safety Regulations] Part 61, CASA is developing the requirements for night VFR ratings which will be based on the existing Civil Aviation Order CAO 40.2.2. In addition, a draft competency standard for night visual flight operations has been developed for inclusion in the proposed CASR Part 61 Manual of Standards. CASA plans to publish a Notice of Proposed Rule Making [NPRM] in relation to this matter in March 2003.

During July 2003, CASA published NPRM 0309FS Flight Crew Licensing and Draft Part 61 Manual of Standards [MOS]. The draft MOS included a requirement for a periodic flight review of night flying competencies. On 24 November 2004, the Chief Executive Officer of CASA issued two directives related to the regulatory reform process. As of March 2005, CASA was working on the processes necessary to apply the directives to the development of new CASR parts, including Part 61. In a letter to the ATSB dated 6 January 2006, CASA advised that the proposed CASR Part 61 would require night VFR rating holders to undergo flight reviews covering night and instrument flying, in addition to structural changes to the night VFR rating. CASA advised that Part 61 could be completed in the second half of 2006.

During March 2005, the ATSB issued Aviation Safety Investigation report BO/200304282 on the fatal night accident involving a Bell 407 helicopter, registered VH-HTD, which occurred off Cape Hillsborough, Queensland, on 17 October 2003. The report stated that CASA had advised that they intended to issue a CAAP (Civil Aviation Advisory Publication) to clarify safety guidelines for night VFR operations. In a letter to the ATSB dated 6 January 2006, CASA advised that the Night VFR CAAP was in the final stages of preparation, and it was intended that it would be published in the first quarter of 2006. The CAAP would include competency standards for night and instrument flying.

CASA has also advised that copies of a night VFR-related 'Briefing in a Box' were distributed to flying schools in March 2006. The briefings included safety material on night flying and were intended to assist flying instructors and flying schools in providing appropriate training to night VFR pilots.

The investigation was unable to establish why the pilot lost control of the aircraft during a climbing turn while apparently returning to land at Caloundra aerodrome.

However, the following issues are considered to have been significant to the circumstances of the accident.

Aircraft altitude

The altitude of the aircraft as it passed over Bokarina was well below the minimum permissible for a night visual flight rules (VFR) flight, and was also below the minimum for a flight over a populated area. The aircraft's maximum altitude of 742 ft after it crossed the coast provided little margin for inadvertent height loss during the subsequent turn, and was evidently insufficient to allow the pilot to regain control of the aircraft.

Aircraft systems

There was no indication from the recorded radar information that the performance of the aircraft was abnormal. No radio transmission was heard from the pilot to indicate any problem with the aircraft.

Although one witness at Bokarina described the engine noise as abnormal, three other witnesses described the sound as normal and there was clear physical evidence that the engine was operating at high power at impact. There was also evidence that electrical power was being delivered to the lights, and that pneumatic power was being delivered to the gyroscopic instruments.

There was no evidence of a defect that could have affected the controllability of the aircraft. However, impact damage and the unavailability of some parts of the aircraft prevented a comprehensive assessment of the pre-impact serviceability of the flight control system.

Physiological and cognitive factors

The aircraft's recorded cruise altitude of 11,300 ft was above the altitude at which the Civil Aviation Safety Authority (CASA) required supplemental oxygen to be used, but was below the altitude above which oxygen should be used according to the aircraft flight manual.

By flying at 11,300 ft without supplemental oxygen, the pilot increased his risk of developing hypoxia. However, any hypoxic effect on the pilot's performance could not be quantified. The aircraft's steady track and descent profile prior to passing overhead Caloundra suggest that the pilot, probably assisted by the autopilot, was effectively controlling the aircraft. Further, any adverse physiological effects of mild hypoxia would have reduced before the final stages of the flight. However, it is possible that the pilot's cognitive function during the latter part of the flight was affected by earlier exposure to hypoxic conditions.

The duration of the day's flying, together with an inadequate food intake, could have caused the pilot to become fatigued.

Fatigue and hypoxia have been demonstrated to adversely affect areas of cognitive function such as response time, decision-making and risk assessment. Any decrement in cognitive function could have reduced the pilot's ability to identify the reduced level of safety associated with conducting a low-level flight at night over a populated area, and transitioning from an area of extensive ground lighting to an area where surface features and the natural horizon were difficult to discern. However, there was no means of determining if the pilot's cognitive function had been adversely affected. Nor was it possible to determine that if affected, it had not recovered to its normal state once the pilot was no longer exposed to hypoxic conditions.

The pilot's reported difficulties with balance following the April 2002 stapedectomy and subsequent removal of the prosthesis were consistent with expected side-effects of the operations. While these difficulties persisted for some months after the operation, the available evidence indicated that the pilot was not affected by dizziness or balance problems in the months preceding the accident.

Spatial disorientation

The forecast weather conditions did not preclude night VFR flight, and witness reports indicated that there was no reduction in visibility due to smoke or cloud at the time of the accident. The pilot's attention was probably directed outside the cockpit as he positioned the aircraft to fly over his home. Extensive ground lighting associated with the populated Sunshine Coast area would have provided him with good surface and horizon reference during that period. However, after the aircraft turned east, it was heading towards an area of no surface lighting (other than that provided by one or two large ships), and minimal celestial illumination. Consequently, surface features and the natural horizon would have been difficult to discern. Those conditions required that the pilot transition to flight by reference to the aircraft instruments.

The pilot's recorded night flight time indicated that he satisfied the recency requirements for night VFR. Further, the pilot was flying a familiar aircraft, which was suitably equipped (including a standby pneumatic power source) and maintained for instrument flight. However, the pilot had not demonstrated competence in flight solely by reference to instruments since 1998. The Federal Aviation Administration Advisory Circular 60-4A indicated that even qualified instrument pilots can take up to 35 seconds to complete the transition from visual to instrument flight. If the pilot did not achieve a rapid and complete transition to instrument flight during the climbing turn, it is likely that he would have experienced the effects of spatial disorientation.

Because there was no regulatory requirement that the pilot's recurrent aeroplane flight reviews include night VFR or instrument flight, his level of recent competence could not be assessed. The pilot's ability to transition to flight solely by reference to instruments may have been adversely affected by various factors, including a lack of recent experience in instrument flight, possible residual effects of hypoxia, fatigue, and/or a distraction in the cockpit. If the pilot's attention was directed elsewhere, he may not have initially recognised that the aircraft was descending, or the degree to which it was turning after it crossed the coast.

The ability to maintain visual reference with surface features and the natural horizon at night is not assured, even in meteorological conditions that satisfy the night VFR requirements. Consequently, as the Flight Safety Australia (May-June 2005) article advised, it is imperative that night VFR pilots are competent and current in instrument flight. Completing an aeroplane flight review and satisfying the night VFR requirements may not sufficiently reduce the risk of spatial disorientation of a pilot during night VFR operations.

Conclusions

The circumstances of the accident are consistent with a loss of control due to the pilot becoming spatially disoriented after flying into an area of minimal surface and celestial illumination. Physiological and cognitive factors may have contributed to the development of the accident. However, the factors that contributed to the aircraft descending into the water could not be conclusively established.

This accident highlights the need for night VFR pilots to manage the risk of spatial disorientation in dark night conditions by maintaining proficiency in instrument flight.

FACTUAL INFORMATION

History of the flight

At about 1730 Eastern Standard Time on 15 August 2004, the pilot of a Mooney Aircraft Corporation M20K aircraft, registered VH-DXZ, departed Cobar, NSW, on a private flight to Caloundra, Qld. The flight was conducted under the visual flight rules (VFR), with the latter part at night.

At about 2015, several people saw and heard the aircraft, with its wing tip strobe lights flashing, flying low in a northerly direction over Bokarina, 8 km north-north-east of Caloundra aerodrome. One witness said that the engine sounded as though it was 'struggling and cutting out'. Two other witnesses described the engine sound as a 'steady drone', while another said it sounded like it was 'turning at low [revolutions], as if it was powered down for a landing'.

The aircraft was then observed to turn east and cross the coast before descending steeply and impacting the water. The impact was accompanied by a bright flash. The aircraft wreckage was located 4 days later, approximately 1.5 km east of Bokarina beach, at a depth of about 16 m. The pilot, who owned the aircraft and was the sole occupant, did not survive the impact.

Earlier that afternoon, the pilot had flown from Caloundra to Cobar with one passenger. The passenger remained at Cobar and reported that the flight from Caloundra had been uneventful and that they arrived at Cobar at about 1700. The refueller advised that the pilot refuelled the aircraft with 156 L of avgas (apparently to full tanks) and checked the engine oil before departing on the return flight to Caloundra.

The pilot lived at Bokarina and family members reported that he did not normally fly over his home on returning from a flight. They indicated that the pilot's car was at the aerodrome, so he did not need to be met and driven home. They assumed that the purpose of flying over the house was to let them know that he would be home soon.

Recorded information

The pilot was not required to report to air traffic control during the flight and there was no record of him having done so. The Caloundra Common Traffic Advisory Frequency did not have a recording capability.

A pilot conducting a VFR flight was required to operate the aircraft's secondary surveillance radar (SSR) transponder on code 1200 in airspace not subject to air traffic control. The Mooney's SSR track for the flight was recorded by The

Australian Advanced Air Traffic System. That data showed that the aircraft first appeared on radar at 1903, north of Moree, NSW, on the direct track from Cobar to Caloundra at 11,300 ft. The aircraft maintained that altitude until 1937, when it commenced descent, passing through 10,000 ft at about 1940, and 5,000 ft at about 1958. It maintained a steady track and descent profile, and was overhead Caloundra at 2014, at 1,140 ft. The aircraft then maintained a relatively constant altitude and tracked north towards Bokarina (Figure 1).

At 2015, the aircraft commenced a further descent and when overhead Bokarina, turned right and headed east-north-east, towards the ocean. Radar data indicated that the aircraft descended to 442 ft about the time it flew over the beach. The aircraft's altitude then increased, reaching a maximum of 742 ft. The last valid radar information was recorded at 2016:13, and indicated that the aircraft had entered a descending right turn. The recorded radar data did not reveal any abrupt or abnormal changes in the aircraft's altitude, groundspeed, or track. The recorded speeds were consistent with normal cruise and descent speeds for the aircraft type (Appendix A).

Figure 1: The aircraft's radar-recorded track

Pilot information

The pilot purchased the aircraft in May 1994, and was issued with a private pilot (aeroplane) licence in July 1994. His logbook recorded his total flying experience at the time of the accident as about 1800 hours, 142 of which were at night. In April, May and June 2004, the pilot logged 5, 0.5 and 5.4 hours night flying respectively, all in DXZ. In those same months, he also logged 20.8, 12.3, and 25.4 hours day flying. The pilot last flew at night on 19 June 2004, and in actual or simulated instrument meteorological conditions, during 1998. His total instrument flight time was recorded as 32.4 hours.

The pilot was issued with a night VFR rating on 11 June 1998. There was no evidence that he had ever held an instrument rating. His three most recent flight reviews were completed on 29 March 2003, 18 November 2001, and 24 November 2000. They were logged as day flights, with no instrument or night flight recorded.

The pilot's family reported that he was well rested before the flight, was not affected by any illness and had never smoked cigarettes.

A person who spoke to the pilot while he was at Cobar reported that he said that it had been a busy day, and that he had not had any lunch, but was carrying some nuts and a drink on the aircraft.

Aircraft information

The aircraft was manufactured in the US in 1988 and was imported into Australia in the same year. At the time of the accident, it had accumulated about 2,868 flight hours. The aircraft was equipped and maintained in the instrument flight rules (IFR) category. It was fitted with a turbo-charged, piston engine which had accumulated about 180 hours since the last overhaul.

The aircraft cabin was not pressurised but was fitted with a supplemental oxygen system. The organisation that maintained the aircraft reported that the supplemental oxygen system tank was empty. There was no indication that the oxygen tank had been charged at Cobar.

A review of the aircraft's maintenance records revealed that the requirements of Airworthiness Directives (AD) RAD/43 and RAD/47¹ were due to be completed in July 2004 but had not been carried out. No other discrepancies were noted, and no defects had been recorded on the maintenance release.

The aircraft was fitted with an electrically driven standby vacuum system for providing pneumatic power to the gyroscopic instruments, and a Century 2000 autopilot system.

Meteorological information

Information provided by the Bureau of Meteorology indicated that the weather conditions in the Bokarina area at the time of the accident were benign. Smoke areas were forecast below 6,000 ft with visibility reducing to 4,000 m in smoke, and 1,000 m in thick smoke. The terminal area forecast for Maroochydore aerodrome (15 km north-north-west of Bokarina), issued at 1813, predicted visibility greater than 10 km and scattered cloud at 3,000 ft. None of the witnesses reported that smoke, cloud or haze affected their ability to see the aircraft.

The QNH² recorded by the automatic weather station at Maroochydore at 2020 on the day of the accident was 1014 hPa.

On 15 August 2004 at the accident location, astronomical twilight occurred at 1846 and the moon set at 1637³. Two cargo ships were located east of Maroochydore at the time of the occurrence, at least one of which was at anchor, and therefore displaying lights⁴. Several hours after the accident, witnesses observed two large ships moored east of Maroochydore which were displaying deck lights.

Wreckage and impact information

The wreckage was raised from the seabed on 28 August 2004 (Figure 2). Most of the aircraft was recovered, including the engine, fuselage, left wing, all three propeller blades and the propeller hub. The right horizontal stabiliser, right elevator, and parts of the right wing were not recovered.

An examination of the wreckage indicated that:

• The aircraft was banked right, and in a nose-down attitude of approximately 45 degrees when it struck the water.
• The nature of the damage to the engine crankshaft and the propeller blades was consistent with the engine delivering high power at impact.
• The frangible plastic drive shaft of the engine driven vacuum pump had failed under a sideways load. The drive shaft of the electrically driven vacuum pump was intact.
• Damage to the gyroscopes in the artificial horizon and directional indicator flight instruments was consistent with gyroscopic rotation at impact.
• The light globes in the artificial horizon and the directional indicator flight instruments were receiving electrical power at impact.
• The landing gear was retracted, and the wing flaps were extended about 10 degrees, at impact.
• The altimeter subscale was set at 1015.
• There was evidence of a short duration, post-impact fire.

Impact and saltwater corrosion damage precluded a determination of the serviceability of the automatic pilot system and its operational status during the final stages of the flight. None of the windscreen was recovered. There was no evidence in the recovered wreckage that the aircraft had struck a bird or a bat during flight.

The extent of airframe disruption and the missing parts of the right wing, horizontal stabiliser and right elevator prevented a comprehensive assessment of the functionality of the flight controls at impact.

Figure 2: Recovery of the main wreckage

Regulatory aspects

The pilot's night VFR rating authorised him to act as pilot in command of private or aerial work flights at night under the VFR. Civil Aviation Order (CAO) 40.2.2 detailed the flight tests and other requirements for the issue of a night VFR rating. The test requirements included recovery from unusual attitudes, basic turns, and straight and level flight, which were required to be conducted solely by reference to flight instruments. The CAO also required that training for the issue of a night VFR rating included at least one landing at an aerodrome 'that is not in an area that has sufficient ground lighting to create a discernible horizon'.

Once issued, a night VFR rating remained permanently valid. To exercise the privileges of the rating, a pilot needed to meet certain minimum recent experience requirements. 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 ⁵.

Except during take-off, landing, or radar vectoring, the pilot of a night VFR flight was required to ensure than the aircraft remained at or above the calculated lowest safe altitude (LSALT) while further than 3 NM from the destination aerodrome. The minimum LSALT for the Bokarina area was 1,500 ft. Aircraft operating overpopulated areas were generally required to remain at or above 1,000 ft.

A pilot was required to satisfactorily complete an aeroplane flight review every 2 years. There were no published requirements or guidance material regarding theoretical knowledge or practical skills (such as flight conducted solely by reference to flight instruments) required to be demonstrated by pilots undergoing an aeroplane flight review.

Medical and pathological information

The pilot held a valid Class 2 Medical Certificate at the time of the occurrence. His medical records indicated that he had undergone a stapedectomy⁶ operation on his left ear about 22 years before the accident. He underwent a stapedectomy on his right ear on 11 April 2002 because of hearing loss. However, due to a post-operative decline in hearing and persistent balance problems, the prosthesis was removed on 24 April 2002. During two subsequent telephone conversations with the surgeon in June and July 2002, the pilot reported that he was still dizzy, couldn't look up and down quickly, and was still unsteady.

The pilot underwent a Class 2 aviation medical examination on 1 March 2004. The designated aviation medical examiner who performed that examination reported that the pilot had advised of no ongoing dizziness, disorientation, or other related problems.

A pathological examination did not identify any indication of a pre-existing medical condition that could have contributed to the development of the accident. It was not possible to establish when, or what, the pilot had last eaten.

Hypoxia

Hypoxia is a condition in which there is reduced oxygen supply to the body. Available oxygen decreases with increased altitude, such that at 12,000 ft, brain oxygen saturation is approximately 87%, compared with sea level saturation of 96%.
The investigation calculated that if the entire cruise segment of the flight had been conducted at 11,300 ft, the aircraft would have been at that level for almost 2 hours.

The US Federal Aviation Administration⁷ (FAA) recommended that pilots use supplemental oxygen when flying above 10,000 ft during the day and above 5,000 ft at night when the eyes become more sensitive to oxygen deprivation.

The Mooney M20K Aircraft Flight Manual stated that 'supplemental oxygen should be used when cruising above 12,500 feet. It is often advisable to use oxygen at altitude lower than 12,500 feet under conditions of night flying, fatigue, …'.
Civil Aviation Order (CAO) Part 20.4 paragraph 6.1 stated:

A flight crew member who is on flight deck duty in an unpressurised aircraft must be provided with, and continuously use, supplemental oxygen at all times during which the aircraft flies above 10,000 feet altitude.

An article⁸ in Flight Safety Australia magazine stated '[a]fter vision, the tissues most affected by hypoxia are those areas of the brain associated with judgement, self-criticism and the accurate performance of mental tasks'. An associated article⁹ in the same magazine indicated that the use of oxygen during night flight below 10,000 ft resulted in an increase in alertness and cognitive function, and a reduction in fatigue. Studies of the effects of exposure to altitudes between 10,000 ft and 15,000 ft have consistently shown small to moderate effects on human performance. Those effects included a reduction in night and peripheral vision, increased drowsiness, decreased response time, decreased short-term memory capacity, and poorer performance on complex and reasoning tasks.

The FAA Civil Aerospace Medical Institute Human Factors Research Laboratory in Oklahoma City, USA advised that restoration of a sea level atmosphere following exposure to hypoxic conditions caused rapid physiological recovery, but that cognitive recovery was slower.

Fatigue

Fatigue results from inadequate rest over a period of time, and leads to physical and mental impairment. The effects of fatigue include decreased short-term memory, slowed reaction time, decreased work efficiency, increased variability in work performance, a tendency to accept lower levels of performance and not correct errors. Not consuming food regularly is known to exacerbate the effects of fatigue.
Based on previous flights recorded in the pilot's logbook, the total flight time for the trip from Caloundra to Cobar and return to Caloundra would probably have been between 6.4 and 6.9 hours.

Stapedectomy

Stapedectomy involved a small risk of ongoing episodes of dizziness and hearing loss¹⁰. However, according to an article published in 1998 in the journal Otolaryngology - Head and Neck Surgery¹¹,

The FAA [Federal Aviation Administration] has always had the most experience with aircrew returning to flying duties after stapedectomy. The civilian track record is excellent with no reported cases of sudden incapacitating vertigo, sudden hearing loss, or other poststapedectomy related sequelae.

Spatial disorientation

Spatial disorientation describes an in-flight situation in which a pilot does not correctly sense the position, motion or attitude of the aircraft, and may be unable to tell which way is up. A pilot operating under the VFR determines the attitude of an aircraft by reference to the natural horizon or surface features. If these references are not visible, the pilot must use the flight instruments to determine the aircraft's attitude.

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 aircraft, after visual reference was lost, was 178 seconds¹². An article titled 'Fatal Night Flight' in the Civil Aviation Safety Authority (CASA) magazine Flight Safety Australia (May-June 2005) stated that:

[v]isual disorientation is a distinct possibility on dark nights or away from areas of extensive ground lighting. Disorientation can be caused by sudden loss of visual reference such as when turning away from a well lighted area towards an area without ground lighting.

The article also stated that 'it is imperative that Night VFR pilots are competent and current in instrument flight'.

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 surface. 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.

Surface references and the natural horizon may at times become obscured, although visibility may be above visual flight rule minimums. The lack of natural horizon or surface reference is common on over water flights, at night, and especially at night in extremely sparsely populated areas, or in low visibility conditions.

Recent night VFR accident

On the evening of 17 October 2003, an air ambulance Bell 407 helicopter descended into the sea near Mackay, Qld. The ATSB investigation (200304282) was unable to determine, with certainty, what factors led to loss of control of the helicopter. The investigation considered that although the forecast weather conditions did not necessarily preclude flight under the night VFR rules, the lack of a visible horizon and surface lighting, and the pilot's limited instrument flying experience may have contributed to the accident. The investigation concluded that the circumstances of the accident were consistent with loss of control due to the pilot becoming spatially disoriented.

1. AD/RAD/43 required a biennial altimeter and encoder check and AD/RAD/47 required a biennial transponder check.
2. Sea-level atmospheric pressure.
3. Information obtained from Geoscience Australia website http://www.ga.gov.au/nmd/geodesy/astro/
4. Vessels over 100 m long and at anchor are required to display white lights at either end of the vessel and available working lights or equivalent to illuminate the decks.
5. In contrast, the holder of an instrument rating was required to undergo an annual instrument flight test, and comply with flight and instrument approach recency requirements, in order to keep the instrument rating current.
6. Stapedectomy is an operation to remove the fixed stapes [the third middle ear bone] and to replace it with a prosthesis. That allows sound vibrations to be transmitted properly to the inner ear for improved hearing. http://www.bcm.edu/oto/clinic/educate/stapled.html
7. Federal Aviation Administration. 2003. Advisory Circular AC 61-107A Operations of Aircraft at Altitudes Above 25,000 feet MSL and/or Mach Numbers (MMO) Greater than .75.
8. Brock, J. & Bencke, R. 1998. Hypoxia. Flight Safety Australia. Volume 3 Number 1. Civil Aviation Safety Authority. Canberra.
9. Thom, A. 1998. Improved Performance. Flight Safety Australia. Volume 3 Number 1. Civil Aviation Safety Authority. Canberra.
10. http://www.bcm.edu/oto/clinic/educate/stapled.html
11. Thiringer, J.K. & Arriaga, M.A. 1998. Stapedectomy in Military Aircrew. Otolaryngology - Head and Neck Surgery. Volume 118 Number 1. January 1998.
12. Bryan, L.A., Stonecipher, J.W. & Aron, K. 1954. 180-degree turn experiment. University of Illinois Bulletin. 54(11), 1-52.

At about 2017 Eastern Standard Time on 15 August 2004, a Mooney Aircraft Corporation M20K aircraft, registered VH-DXZ, descended into the ocean off Bokarina, Queensland. The pilot, who owned the aircraft and was the sole occupant, did not survive the impact.

The pilot held a private pilot (aeroplane) licence and a night visual flight rules (VFR) rating. His logbook recorded his total flying experience at the time of the accident as about 1800 hours, 142 of which were at night.  The pilot last flew at night on 19 June 2004, and in actual or simulated instrument meteorological conditions, during 1998. His three most recent flight reviews were logged as day flights, with no instrument or night flight recorded.

The weather conditions in the area at the time of the occurrence were benign. Astronomical twilight occurred at 1846 and the moon set at 1637.

The wreckage was recovered 13 days after the accident. An examination revealed that at the time of impact; the engine was delivering high power, the instrument lights were receiving electrical power, and the gyroscopic instruments were receiving pneumatic power.

The circumstances of the accident are consistent with a loss of control due to the pilot becoming spatially disoriented after flying into an area of minimal surface and celestial illumination. Physiological and cognitive factors may have contributed to the development of the accident. However, the factors that contributed to the aircraft descending into the water could not be conclusively established.

This accident highlights the need for night VFR pilots to manage the risk of spatial disorientation in dark night conditions by maintaining proficiency in instrument flight.

At approximately 1211 Eastern Standard Time on 2 April 2004, the pilot of a Bell Helicopter Company 47G Soloy helicopter, registered VH-UTY, was conducting fire-ant baiting operations at Nudgee, about 5 km north-west of Brisbane Airport. The operator's chief pilot occupied the right control position and was supervising the pilot.

Near the end of a baiting run, the chief pilot told the pilot that he wanted to demonstrate a procedural turn and asked the pilot to follow him through the manoeuvre. Both pilots reported that, during the turn, the helicopter began to yaw right. The chief pilot then said that he was taking control of the helicopter. He reduced engine power but was unable to arrest the right yaw. The helicopter continued to descend towards a canal and struck the water slightly nose down and banked to the right. Both occupants were injured in the impact but were able to exit from the helicopter unaided.

The pilot reported that he had completed two previous baiting operations in the helicopter during that day without incident.

A subsequent examination of the helicopter found that the tail rotor control pedals installed at the right control position operated in the reverse sense, compared with the tail rotor control pedals installed at the left control position. That meant that tail rotor control pedal inputs made by the chief pilot would have produced a yaw response opposite to that which would normally be expected.

The helicopter operator reported that the tail rotor control pedals for the right control position had been refitted to the helicopter before the accident flight.

In 1954, the Bell Aircraft Corporation, as it was then known, issued Service Bulletin (SB) 98. The SB required installation of a stop assembly (part number 47-722-165-1), under both control position footrests. The purpose of the stop assembly was to prevent the incorrect re-installation of the tail rotor control pedals. UTY was manufactured in 1966, and the stop assembly would have been incorporated as a standard build item during manufacture.

In October 1971, the then Australian Department of Civil Aviation issued Airworthiness Directive (AD) AD/Bell47/69 titled Tail Rotor Control Pedal Assembly Interference Bracket. That AD, which mandated the installation of the interference (stop) brackets to all Bell 47G series helicopters as introduced by Bell SB 98, was still current at the time of the accident.

Examination of the helicopter showed that only part of the tail rotor control pedal assembly bracket as specified in AD/Bell 47/69, remained fitted in the helicopter. The majority of the bracket had previously been removed. There was no evidence to indicate that the removal was as a result of wear or damage sustained in the accident. The maintenance organisation that certified for the last scheduled maintenance check advised that the bracket was in place, and that the co-pilot tail rotor control pedals were not fitted at that time.

The helicopter's maintenance documentation contained no record of the installation of the right tail rotor control pedals, or of the required independent inspection of the flight controls after the installation of the tail rotor control pedals.

The helicopter examination also found that the forward section of the tail rotor drive output shaft, from the main gearbox to just forward of the first bearing hanger assembly, had separated. The separated section was not found. Examination of the remaining broken section of the drive shaft indicated that it had separated due to overload forces that occurred during the accident impact sequence. There was no evidence found of any pre-existing fault in the shaft.

At approximately 1211 Eastern Standard Time on 2 April 2004, the pilot of a Bell Helicopter Company 47G Soloy helicopter, registered VH-UTY, was conducting fire-ant baiting operations at Nudgee, about 5 km north-west of Brisbane Airport. The operator’s chief pilot occupied the right control position and was supervising the pilot.

1. The pilot was not recently experienced on the occurrence helicopter type.
2. The pilot in command allowed the helicopter to move laterally during the lift-off to the hover.
3. The pilot in command did not raise the helicopter to a hover height sufficient to prevent contact with the mobile platform.

Post-occurrence technical examination of the helicopter did not reveal any evidence of an airframe, engine or system fault that may have contributed to the accident. In addition, examination of the mobile platform did not reveal any evidence of it having moved throughout the rollover sequence.

The circumstances of the accident are consistent with the phenomenon known as dynamic rollover. Scrape marks from the helicopter's right skid were found on the lip along the right side of the mobile platform. That indicated that the helicopter was not raised to a height sufficient to clear the platform in the event of lateral movement. There was no wind reported at the time of the occurrence that could have contributed to the lateral movement. The pilot had extensive flying experience and normally flew a mix of different types, including a mix of European and North American types. Due to that experience, the investigation considered that confusion with respect to correct flight control input to control yaw was unlikely.

If the pilot had prevented the lateral movement of the helicopter during the lift off to the hover, and had raised the helicopter to a hover height sufficient to clear the platform, dynamic rollover would most probably have not occurred. Therefore, the investigation considered that the design or use of the mobile platform was not a factor in the occurrence.

The pilot had not flown a Bell 47 type helicopter during the preceding three months, and had not previously flown a turbine-powered Bell 47. It is likely that the pilot's lack of recency in the helicopter type, combined with his not having flown a turbine-powered Bell 47 previously, contributed to his:

• not making sufficient flight control input to correct the right lateral movement during the lift-off to the hover
• not raising the helicopter to a hover height sufficient to prevent contact with the platform.

The pilot's injuries were consistent with him being struck by the main transmission assembly as it separated from its mount as a result of the dynamics associated with main rotor ground contact.

History of the flight

At approximately 0830 EST, the pilot of the Bell 47G-4A turbine-powered (Soloy) helicopter, registered VH-MTX, was conducting a lift-off to the hover from a mobile helicopter landing site (HLS)¹ at Caboolture aerodrome, when the helicopter rolled onto its right side. Weather conditions at the time of the occurrence were reported to be '…little or no wind, warm and humid, some cloud but clearing.' The helicopter was substantially damaged and there was no post-occurrence fire. The pilot, who occupied the left seat², was fatally injured and the passenger, who occupied the right seat, sustained minor injuries.

Pilot in command

The pilot held an Airline Transport Pilot (Helicopter) Licence, a Commercial Pilot (Aeroplane) Licence, a Command Multi Engine Instrument Rating (CMEIR) (Helicopter), a CMEIR (Aeroplane), and a Grade 1 Instructor (Helicopter) Rating. According to his pilot flying logbooks, he had accumulated approximately 8,293 hours total flying experience, of which approximately 7,180 hours was on helicopters, including 14.8 hours on the Bell 47G helicopter type. He had flown 2.0 hours in the last 30 days and 15.7 hours in the preceding 90 days. His last flight prior to the occurrence flight was nine days previously in a Bell 206 type helicopter. He had last flown a Bell 47G type helicopter on 19 December 2002, including taking off from and landing back on the mobile platform involved in the occurrence. He had not previously flown a turbine-powered Bell 47G helicopter.

The pilot was endorsed to fly Bell 47G type helicopters in accordance with Section 40.3.0 of the Civil Aviation Orders (CAO). In accordance with paragraph 3.3 of those orders, he was permitted to fly turbine-powered Bell 47G helicopters without further endorsement. The operator also reported that, in accordance with paragraph 3A.4 of CAO 40.3.0, prior to the occurrence flight, the pilot was offered refresher training in the turbine-powered Bell 47G type, however the pilot declined that offer.

The pilot met the recency requirements of Civil Aviation Regulation 5.178, having completed CMEIR (Helicopter) and Instructor (Helicopter) Rating renewals on 13 May 2002, in a Bell 412 helicopter type.

Due to the nature of his employment, the pilot had flown 10 aircraft types in the preceding 12 months, of which 7 were helicopters. Those helicopter types included a mix of European and North American types, a mix of single engine and multi-engine types³, and a mix of turbine and piston engine types. Most of the pilot's helicopter flying experience was in turbine engine types. The pilot was experienced in operating helicopters from mobile platforms.

Passenger

The passenger was employed by the same organisation as the pilot in command. He was an experienced helicopter pilot, who reported that he had accumulated approximately 4,700 hours total flying experience, of which approximately 4,500 hours was on helicopters. He reported that he was not in current flying experience. According to witnesses, he did not have his hands or feet near the flying controls during the occurrence.

Medical information

The pilot's aviation medical certificate was valid and carried a restriction for him to have available reading vision correction. A review of his medical records, investigation interviews, results of the post-mortem examination and toxicological testing, found no evidence of pre-existing medical conditions or the presence of any substance that may have influenced his performance.

Survival information

Four-point restraint harnesses with inertia reel shoulder straps were fitted at the pilot and right side passenger positions. Post-occurrence technical examination revealed that they were firmly secured to their mounts, and the inertia reels appeared to operate normally. The pilot occupied the left seat and remained restrained during the rollover sequence. He sustained severe impact injuries to the rear of the upper torso and lacerations to the back of the head.

Helicopter information

Type: Bell 47 helicopter
Model: 47G-4A (Soloy)
Registration: VH-MTX
Serial Number: 7765
Year of manufacture 1971
Engine: Rolls Royce 250-C18
Total time in service: Approximately 5,570 hours
Maintenance release: Number 09425 issued 14/03/03 at 5,549.7 hours

The helicopter had been imported from Japan in October 2002, receiving an Australian Certificate of Airworthiness in December 2002. The helicopter was maintained in accordance with the manufacturer's and CASA approved documents and schedules, and had flown approximately 20 hours since its last 100-hourly inspection.

Damage to the helicopter

The helicopter came to rest on its right side, with its right skid landing gear resting on the right rear corner of the platform. The canopy bubble had shattered. The main rotor, mast and transmission assembly had detached from the helicopter as a single unit and was located next to the helicopter. The 'white' main rotor blade⁴ was lying across the cockpit. Evidence, in the form of multiple main and tail rotor impact marks, was observed in the ground with an area of burned grass beneath the helicopter's engine exhaust. One of the tail rotor blades had detached and was located approximately 30 metres from the helicopter. The tip of the 'red' main rotor blade was found approximately 150 metres to the east of the helicopter. Both arms of the main rotor stabiliser bar had fractured and were found within 20 metres of the helicopter. All major components were located and identified at the site. Post-occurrence technical examination of the helicopter did not reveal any evidence of an airframe, engine or system fault that may have contributed to the accident.

Mobile platform information

The mobile platform was a flat-based metal construction on wheels, measuring 365 x 300 cm and was approximately 22 cm above the ground. A 5 cm high metal lip ran along both sides of the platform. There were no metal lips at the front or rear of the platform. The front wheels were positioned forward of the base and were approximately 27 cm in diameter. The rear wheel axles were in line with the platform base, allowing the 38 cm-diameter wheels to sit approximately 18 cm above the base. There were two prominent worn strips along the base approximately 38 cm from the side lips, which indicated the usual positioning of the helicopter skids on the platform. At the time of the occurrence, the platform was connected to a small tractor. The tractor brake was engaged and there was no evidence of the tractor having moved throughout the accident sequence.

Civil Aviation Regulation 92 (1) states that:

An aircraft shall not land at, or take-off from, any place unless:

(d) the place… is suitable for use as an aerodrome for the purposes of the landing and taking-off of aircraft;

and, having regard to all the circumstances of the proposed landing or take-off (including prevailing weather conditions), the aircraft can land at, or take-off from, the place in safety.

GEN 2.2 of the Aeronautical Information Publication, defines an aerodrome as:

A defined area of land or water (including any buildings, installations and equipment) intended to be used either wholly or in part for the arrival, departure and movement of aircraft.

Guidelines for the establishment and use of HLS are at Civil Aviation Advisory Publication (CAAP) 92-2 (1), which defined an HLS as:

…a place that may be used as an aerodrome for the purposes of landing or taking off of helicopters.

The definition of '…place…' in CAAP 92-2 (1) included '…on a structure…'.

There is no CASA regulation or guidance concerning the design or use of mobile platforms. Additionally, international standards and recommended practices contained in Annex 14 to the International Civil Aviation Organization (ICAO) Convention on International Civil Aviation, Aerodromes, Volume II - Heliports, do not refer to mobile platforms. A search of international regulatory authorities found no documentary guidance regarding design or use of mobile platforms.

The investigation found that mobile platforms of varying design are used throughout the Australian civil helicopter industry. Some of those designs incorporated side lips and others had no protrusions above the platform surface. Most of the platforms were tractor-towed.

Damage to the mobile platform

Examination of the mobile platform revealed two fresh scratch marks on the right lip approximately 50-85 cm from the rear of the platform. Also evident were fresh gouges on the rear edge of the platform, adjacent to the right wheel axle, which indicated that the helicopter had been moving rearwards as it contacted the lip. Examination of the platform did not reveal any evidence of it having moved throughout the rollover sequence.

Organisational information

Pilot employees from the same organisation as the occurrence pilot reported that they each received funding for up to 40 flying hours each financial year to maintain recency on selected aircraft types. They also reported that, due to the nature of their employment, some pilots had a requirement to maintain recency on a number of types simultaneously.

Dynamic rollover

The phenomenon known as dynamic rollover was described in helicopter textbooks, training manuals and industry and safety publications. It was included at:

• items 10.7 and 12.1 of the CASA Day (VFR) Syllabus - Helicopters, Issue 3, January 1999, which applied from Student through to Commercial Helicopter Licence standard
• item 2.1.14 of the Air Transport Pilot (Helicopter) Licence - Aeronautical Knowledge Syllabus, Issue 3, January 1999.

Dynamic rollover has been defined as:

The occurrence of a rolling motion, while any part of the landing gear is acting as a pivot that causes the aircraft to exceed a critical angle and roll over⁵.

Another definition states that:

Put simply, dynamic rollover is the result of the helicopter developing excess angular momentum about the skid in contact⁶...

Dynamic rollover typically occurs when a critical rollover angle is exceeded. That angle is dependent upon control limits and in most helicopters is in the order of 15 degrees. Accidents attributed to dynamic rollover have occurred previously on a number of surfaces, including open flat grassed surfaces.

Planned activities on the 9 December 2002 flight had indicated that the aircraft became laterally unstable as the aircraft approached the stall speed. Recorded flight data indicated that the aircraft also entered a stall during the flight on 9 December, even though this was not planned. It is possible that this stall was an unplanned activity. There was no evidence that any of the aircraft's performance and handling characteristics encountered in this unplanned stall, such as stalling airspeed, were considered when preparing for the flight when the accident occurred, when stalls were part of the test program.

Lateral instability, as the aircraft speed approached the stall speed, had been experienced and noted in a previous flight. The test flight program did not include a lateral stability test for the flight and the recorded aircraft data did not indicate that a lateral stability test had been undertaken on the flight. It is possible that the notes referred to a tendency for the aircraft to drop a wing as it approached the stall, or stalled, as similarly experienced during the accident flight.

During the flight when the accident occurred, the aircraft departed controlled flight from a deliberately induced stall during a test flight. The aircraft then descended rapidly, at an airspeed that was not consistent with a stalled or spinning configuration.

The aircraft instruments displayed a stall speed that was significantly below the actual stall speed in that configuration. It is possible that the stall occurred before the flight crew expected it.

The aircraft was based on an established aircraft design, but had significant design changes from the original. Those design changes were likely to have changed the performance and handling characteristics of the aircraft and the cumulative effect of those changes would have been hard to predict.

The test flight program had been developed in accordance with some of the approved advisory material. The advisory material gave detailed guidance on what was to be done, and how it should be done. It did not give detailed guidance on defining what should be expected during the test program, and what to do if something unexpected occurred during the program. As an example, a particular aircraft design is normally expected to stall at a particular airspeed for a given configuration and flight condition. The particular handling characteristics as the aircraft approaches and passes through a stall should also be predictable and expected. When these characteristics are examined during a test flight, they would be expected to fall within a defined range. The guidance material did not detail what to do if any of the performance or handling characteristics were outside the expected ranges.

There was no evidence of a significant risk management process, other than preflight briefings conducted by the pilot of the first two flights, throughout the design, construction, or test flight program development for the aircraft. Such a program could have assisted in identifying hazards and their attendant risks, and for managing them appropriately from initial construction though to certification. While there was no requirement for an owner/builder to have a risk management process, such a process would have been prudent considering the significant changes made to the aircraft.

The test program did not incorporate flight instrument calibration and therefore the accuracy of the flight instruments was unknown. It would not have been possible to confidently establish the exact speeds at which the aircraft's handling and performance were assessed.

The test flight program only required one person on board the aircraft for test flights. The investigation was not able to identify an operational reason for the owner/builder to be on board the aircraft.

The investigation could not determine the reason for the pilot losing control of the aircraft. There was no physical evidence indicating that the right wheel destroying two taxiway lights during take-off damaged any major structural element or in any way contributed to the accident. Also, no evidence was found to support the reported observations of the left or the right wings folding up or a part of the aircraft separating in flight. The evidence suggested that the portion of the right-wing rear spar interplane strut that was found approximately 73 metres from the accident site, was thrown to its location as a result of impact forces when the right wings struck the tree.

The aircraft was observed cruising in level flight when it apparently departed controlled flight. It was not observed changing altitude or commencing a turn and would have been experiencing approximately 1g loads only, well below the minimum design load of 5g.

The timber examination reports noted failures of the laminated members, on wings of the original manufacture. This was probably due to the Casein glue having been attacked by micro-organisms after the wood and the glue moisture content rose above 18%. The attack by micro-organisms was least evident in areas close to the edges of the glued joints. Circulating air quickly dries these areas causing any attack by micro-organisms to cease while it can continue on the inner areas of the joint that remain moist. This, and the fact that the glued joints were further secured by nails, bolts and screws would most likely prevent detection of any glued joint that had been attacked by micro-organisms. It is also considered likely that the presence of `Irish linen' and the thick coat of paint on the propeller would disguise any underlying delamination.

The wreckage and the exposed wood were soaked wet while on site. The possibility of attack by micro-organisms commencing at that time was not considered likely, because once the wreckage was removed from the site it was stored in dry environment. That prevented elevated moisture content and attack by micro-organisms.

CONCLUSIONS

The pilot was appropriately qualified and endorsed on the aircraft.

No evidence was found indicating that the aircraft striking and destroying two taxiway lights during take-off contributed to the accident.

It could not be determined if any part of the aircraft structure or the propeller failed prior to the aircraft departing from the level flight.

The wood that the wings were constructed from was of a high quality and there was no evidence to indicate that a failure of wood was a factor in the accident.

A number of laminated members on three wings of the original manufacture and the propeller failed at the glue line rather than in the wood, probably as a result of Casein glue having been attacked by micro-organisms.

Current inspection procedures would not allow detection of delaminated Casein glued joints.