What happened
On October 3, 2009, at 15:37 UTC, a Chipmunk DH C1, registration HB-TUM, was performing a series of low-altitude flight demonstrations at the Covilhá Aerodrome (LPCV) as part of an aviation festival. The aircraft, operated by a private Swiss association, was performing five planned passes over the runway.
During the second pass, the pilot was flying toward the southeast with the sun directly ahead. After completing the pass, the pilot initiated a left-hand turn to climb toward the crosswind of runway 24. During this maneuver, the aircraft entered an uncontrolled descent to the right. The aircraft struck a large eucalyptus tree, which sheared off the right wing, before the fuselage impacted the ground in a heavily wooded area. Although the aircraft was destroyed, the cockpit remained intact, and the two occupants—the pilot and a passenger—sustained minor injuries and were able to exit the aircraft on their own.
The investigation
The GPIAAF investigation examined the flight history, the pilot's experience, and the aircraft's mechanical condition. The investigation established that the aircraft was in good mechanical condition with no engine failures or technical anomalies present at the time of the accident.
Investigators analyzed the flight maneuvers and noted that the pilot was flying at a very low altitude with the sun causing significant glare, which obscured visual references. The investigation also reviewed the regulatory requirements for airshow participants, noting that while the pilot was properly licensed, his specific experience in this aircraft type was limited. The investigation concluded that the pilot's perception of an upward thermal was actually a loss of airspeed in exchange for altitude, leading to the aerodynamic stall.
Findings
- The aircraft entered a stall during a low-altitude maneuver.
- The pilot's experience in the Chipmunk DH C1 was insufficient for performing low-altitude demonstrations in an unfamiliar environment.
- The sun's position directly in front of the pilot impaired visual references and the ability to monitor airspeed.
- The low altitude of the maneuver left no margin for recovery once the stall occurred.
- The presence of a passenger on board was a deviation from the standard 'flight presentation' regulations, which specify such maneuvers should be performed without passengers.