Three Eagle 150 aircraft, VH-EAD, VH-FPO and VH-JBA, were engaged on a training flight for an airshow formation routine. The lead aircraft, EAD, was callsign Eagle 1; FPO was Eagle 2 and JBA was Eagle 3. They were operating at heights between 500 ft and 800 ft. Eagle 2 carried a passenger who was a former Royal Air Force pilot with extensive formation flying experience. The other aircraft did not carry passengers.
The training sequence usually included a formation flypast at 500 ft, followed by a break into a bomb-burst manoeuvre. Following the bomb burst, Eagle 1 would pull up steeply to about 800 ft for some low-speed manoeuvres with flaps extended. Eagles 2 and 3 would remain at 500 ft and complete a pass close to each other as they flew in opposite directions. The aircraft would then rejoin for a formation flypast, followed by a break for a stream landing.
On the day of the accident, the pilots practised their routine (except the stream landing) four times. Then, after the bomb burst during the fifth practice, Eagle 1 climbed to between 700 ft and 800 ft for the low-speed manoeuvres with flaps extended, while Eagles 2 and 3 performed their close pass in opposite directions. As the three aircraft were manoeuvring for a rejoin, the passenger in Eagle 2 observed Eagle 1 roll to the right, flick inverted and begin rotating to the right in a steep nose-down attitude. The rotation stopped after about one revolution, but the aircraft flicked a second time. The rotation ceased again after about one revolution, but the aircraft flicked inverted again. The pilot did not effect recovery before the aircraft impacted the ground.
Examination of the wreckage did not reveal any defect that may have contributed to the accident. Measurement of a flap actuator extension indicated that the wing flaps were extended to 32 degrees (91% of the maximum extension available) at the time of impact. The elevator trim tab was set to 18 degrees up, indicating that the aircraft was trimmed for level flight at 61 kts indicated airspeed with the flaps set to 35 degrees.
The weather conditions at the time of the accident were fine, with a slight sea breeze from the south-east at 2 to 3 kts, with a surface temperature of 13 degrees C, visibility of more than 15 km and no low cloud.
The pilot of Eagle 1 held a Private Pilot Licence with a current Class 2 medical certificate. He had accumulated a total of about 780 flying hours including 47 hours on Eagle aircraft, which he had been flying for about 22 months. About 39 hours of his Eagle experience had been gained on X-TS 150 aircraft and about 8 hours on EAD, a 150 B variant. The X-TS 150 variant is powered by a Continental IO-240A engine driving a McCauley 70-inch diameter propeller of 54-inch fixed pitch, whereas the 150 B variant is powered by a Continental IO-240B engine driving a McCauley 70-inch diameter propeller of 57-inch fixed pitch. There are physical differences between the engines but power outputs are the same. The main difference between the variants was the propeller pitch. Consequently, the performance of the 150B variant, having a propeller with a cruise pitch, would be slower to respond to a rapid increase in power than the X-TS 150.
The pilot had completed a formation flying endorsement approximately 3.5 years previously. Since 26 January 1997 he had accumulated about 47 hours of formation flying in Eagle, Piper Cherokee and Cessna 150 aircraft. He did not hold an aerobatic rating. The pilot's last Biennial Flight Review was completed on 22 November 1998 in an Eagle X-TS 150 aircraft. His last flight before the accident flight had been in EAD 4 days before the accident. The pilot's last airshow routine practice was at Avalon on 16 May 1999.
No pre-existing medical or toxological condition that may have contributed to the accident was identified during the pilot's autopsy.
The Eagle 150 B aircraft was granted Certificate of Type Approval 179-1 by the Civil Aviation Safety Authority (CASA), on 11 November 1997. The process of certification included extensive testing of the aircraft in accordance with Joint Aviation Requirements-Very Light Aeroplanes (JAR-VLA).
The stall characteristics of the Eagle were tested in accordance with JAR - VLA 201, 203, 207 and 221. The flight-test program included stalling the aircraft in more than 200 different combinations of configuration, airspeed, deceleration rate, attitude, flight path and G loading. The aircraft met or exceeded the requirements of JAR-VLA, demonstrating generally benign stall characteristics in all configurations when in balanced flight at the point of stall. Entry into a stall from unbalanced flight could result in an incipient spin.
If a pilot releases pressure on the flight controls after entering an incipient spin, the aircraft should cease rotating and assume a steep nose-down attitude. The pilot can then recover the aircraft to level flight. If the pilot immediately begins spin recovery actions as described in the "Pilot's Operating Handbook and Approved Flight Manual" for the Eagle 150 B, the aircraft should be capable of recovery to level flight from a single-turn incipient spin.
In production test flying, EAD had demonstrated normal stall characteristics.
The Flight Manual, Section 3.7 stated in part:
"Intentional spins are prohibited in this aircraft. Should an inadvertent spin occur, the following recovery procedure should be used:
- Retard the throttle to idle
- Centralise controls
- Retract flaps
If the aircraft continues to spin:
- Determine the direction of rotation by visual method or by reference to the turn indicator (turn and balance indicator)
- Apply and hold full rudder opposite to the direction of rotation
- If the aircraft fails to stop rotating, move control column smoothly forward until rotation stops
- As rotation stops, centralise controls, roll wings level and pull the aircraft out of the dive".
The section included the following note:
"Rotation may seem to increase in speed when forward controls are applied, this is normal and is to be expected just prior to rotation stopping". In this occurrence, the aircraft was observed to roll steeply to the right and then enter a steep nose-down attitude consistent with a stall followed by an incipient spin. Immediately before this, the aircraft was manoeuvring at low airspeed, with flaps extended. The pilot did not retract the flaps in accordance with the aircraft Flight Manual's spin-recovery procedure, but certification test flying had shown that this should not have affected the aircraft's capability to recover.
The pilot had considerably more experience on the X-TS 150 variant than on the 150 B variant, but it is unlikely that differences between the two variants affected the circumstances of the accident.
At the time of the stall, the aircraft was turning right at low airspeed. The passenger in Eagle 2 was giving advice to the pilot of Eagle 1 concerning manoeuvres to enable Eagles 2 and 3 to rejoin formation more efficiently. It is possible the pilot of Eagle 1 was focussing on the rejoin manoeuvre to the extent that he did not recognise the onset of the stall.
The observed manoeuvres are consistent with a stall from an uncoordinated right turn, followed by an incipient spin from which recovery was not effected. The reason the pilot was unable to recover the aircraft from the spin could not be determined.