Introduction
Flight track data indicated that, approximately 12 minutes after take-off from Canberra, Australian Capital Territory, en route to Armidale, New South Wales, aircraft VH-MSF departed controlled flight and entered a rapid descent shortly before reaching its planned cruising level of 10,000 ft. The aircraft subsequently impacted terrain, fatally injuring all four occupants. A post-impact fire destroyed the aircraft.
Flight Track Data
Up to about 7,000 ft above mean sea level, the aircraft’s flight tracking data showed a normal, stable climb, consistent with two previous flights. This suggested possible use of the autopilot system. All radio exchanges between the pilot and air traffic control were clear and read back correctly. Climbing through approximately 8,300 ft, the flight track data changed from a relatively steady state to variations in heading, altitude, and airspeed, indicating a likely transition to manual control. Potential reasons for this change may have included avoidance of cloud, turbulence, or issues with the autopilot. Around this time, four independent witnesses located below the aircraft’s flight track reported hearing engine surging sounds from an aircraft obscured by cloud.
Aerodynamic Stall
Over the next few minutes, while the aircraft continued to climb, its airspeed decreased to near stall speed on two occasions. As designed, the stall warning system should have sounded when airspeed deteriorated to about 5 kt above stall speed, alerting the pilot. A slight buffet might have been felt as a precursor to the stall. The pilot’s operating handbook (POH) prescribed that, upon stall warning, recovery required immediately reducing back pressure on the control yoke to decrease angle of attack, maintaining safe airspeed, and adding power as needed. Following these two occurrences, the flight data showed a slight descent and an increase in airspeed, possibly indicating a pre-stall recovery, after which the climb resumed.
After a descent, the performance data indicated a climb rate of up to about 1,500 ft/min, with airspeed decreasing from an estimated 96 kt to 70 kt beyond the point of a pre-stall recovery. At a maximum altitude of 9,946 ft, airspeed and altitude rapidly decreased, consistent with an aerodynamic stall and departure from controlled flight. The investigation identified a contributing factor: when approaching 10,000 ft above mean sea level, the aircraft’s climb rate increased significantly combined with a decreasing airspeed, resulting in an aerodynamic stall and departure from controlled flight.
Recovery Actions
The POH procedure for stall recovery required the pilot to reduce back pressure on the control yoke to un-stall the wings and apply power as necessary to accelerate. However, flight data showed that, following the stall at about 9,900 ft, the rate of descent increased to about 13,000 ft/min, inconsistent with a stall recovery. While descending through around 8,000 ft, ground speed reduced, track variations became larger, and the rate of descent started to reduce towards 10,000 ft/min by ground level. These observations, combined with witness reports, wreckage examination, and the manufacturer’s assessment of the flight data, indicated the aircraft had likely entered a spin before impact.
The POH stipulated that following a loss of control when recovery may not be possible, the Cirrus airframe parachute system (CAPS) should be used. It further indicated that the only recovery method from a spin was to deploy the CAPS. The decision to activate the CAPS should be made before an altitude of 2,000 ft above ground level; the POH also suggested activating CAPS regardless of altitude when no other survivable options were available. The ATSB considered there was adequate time (about 44 seconds) to deploy the CAPS after the departure from controlled flight. However, wreckage inspection revealed that the CAPS had not been deployed in flight, but rather due to ground impact forces. Additionally, the pre-deployment procedure of shutting down the engine was not conducted.