An ATSB investigation has found a stalled wing caused a Liberty XL2 to spin upright and crash into a rural property in NSW, killing its pilot.
The final report into the death of John Corbett, on 6 August 2019, was able to confirm that the aircraft’s stall warning system was likely working, but was unable to decipher how long it could have sounded for.
“This investigation highlights the need for pilots to minimise the risk of stalling, particularly when in proximity to the ground, such as during take-off and landing,” said ATSB director transport safety Dr Mike Walker.
The Liberty had flown from Moruya to the property in company (following but not in formation) with a second light aircraft with the view to landing at the property, or if the landing area was deemed unsuitable, continuing on to Camden.
The pilot of the other aircraft, a recreational category aircraft better suited to operating from unprepared landing strips due to its landing gear configuration and higher propeller clearance, successfully landed at the property, but then called the Liberty pilot via mobile to advise that the runway was not suitable for their aircraft.
Recorded data from a flight planning app on the Liberty pilot’s iPad showed that the aircraft approached the landing area from the south-east, overflew the homestead before turning left to circle the landing area with a slowing airspeed.
On a second orbit of the strip, at about 400 feet above ground level, and after crossing the marked end of the landing area, witnesses observed the left wing drop and the aircraft enter a steep rotating descent. The pilot was unable to recover control of the aircraft before it hit the ground.
“The ATSB investigation found that the aircraft departed controlled flight after slowing and turning downwind with no flap selected,” said Dr Walker.
“The left wing stalled, and this resulted in the aircraft entering into an upright spin at an altitude that limited an effective recovery.”
The ATSB has investigated a number of accidents where light aircraft have stalled and crashed into the ground. A stall/spin will result in a steep pitch down and rotation towards the stalled wing. Recovery takes a considerable amount of height, the magnitude of which is dependent on the reaction time of the pilot, and the use of appropriate recovery technique.
“Turning manoeuvres at or close to the aircraft’s critical angle of attack, if mishandled, can lead to a stall that may result in the aircraft entering a spin.
“Pilots can limit their risk of losing control in flight by maintaining situational awareness of the aircraft state while conducting turns, maintaining adequate airspeed through appropriate power application during increased bank angles, and by selecting altitudes to operate at that provide sufficient height to recognise and recover from a stall.”
The investigation established that the aircraft’s stall warning system, which was designed to provide aural warning of impending stall conditions about five knots above the expected stall speed, was most likely functional at the time of the accident. However, it is unknown if and for how long this warning may have sounded. How the pilot reacted to the warning before the aircraft stalled is also unknown.