What happened
On 26 April 2009, a BAC 167 Strikemaster Mk 80, registration G-UPPI, was conducting a training sortie near Witheridge, Devon. The flight, involving an instructor and a student, included various aerobatic manoeuvres. During the flight, the aircraft was rolled into an inverted position for approximately five seconds. Shortly after returning to a wings-level attitude, the engine experienced a flameout.
Following the engine failure, the instructor attempted to restart the engine twice. However, the aircraft's electrical systems failed during these attempts, preventing the use of the intercom and the transmission of a distress call. The instructor performed a forced landing into a large grass field. While the aircraft cleared a line of trees, it skipped several times on the damp surface before striking an earth bank at the edge of the field. The impact caused extensive damage to the aircraft, including the separation of the left wing. The instructor sustained a serious back injury, while the student suffered a minor injury.
The investigation
The AAIB examined the wreckage and the aircraft's systems. Investigators found that the engine showed no signs of debris ingestion or mechanical failure, but noted a lack of fuel in the main burner feed pipes, which was consistent with fuel starvation. The investigation also focused on the aircraft's electrical state. The aircraft was not fitted with an emergency battery, which is part of the approved configuration for this type.
Testing of the two main batteries revealed they were in a degraded state, with one battery failing a drop test and both showing significantly reduced capacity. The investigation also noted that the aircraft's intercom and radio systems became inoperable when the voltage dropped below critical levels during the engine relight attempts.
Findings
- The engine flameout was caused by fuel starvation, though the specific reason for the fuel interruption could not be determined.
- The inability to successfully restart the engine or communicate distress was due to the failure of the electrical system.
- The loss of electrical power was caused by the depleted state of the two main batteries and the absence of an emergency battery.
- The instructor's injury was exacerbated by an improper bracing position caused by the failure of the aircraft intercommunication system.