Collision with ground, Cessna A150L Aerobat, VH-UPS

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.

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.

FINDINGS

Contributing factors

The investigation identified that the following factors contributed to the accident:

• The aircraft descended below the minimum altitude for a practice forced landing (500 ft above ground level).
• The pilot allowed the aircraft's speed to decrease below the aircraft's stalling speed.
• The aircraft stalled at a height above the ground that was not adequate to permit recovery.
• It is possible that carburettor ice was present during the latter stages of the flight, reducing the available engine power.