What happened
On 24 April 2000, a Gulfstream AA-5B, registration G-PENN, was conducting a private flight from Denham Aerodrome to Le Touquet. The flight was a flying club check of a private pilot, conducted under the supervision of a flying instructor. After departing from Runway 24, the aircraft began to experience engine roughness at approximately 700 feet altitude during a right turn.
Upon noticing the instability, the instructor took control of the aircraft. While maintaining a slow climb, the instructor turned the aircraft back toward the airfield to establish a downwind pattern for Runway 24 and issued a Pan-Pan call to signal an immediate landing. Despite attempts to rectify the issue by switching magnetos and adjusting the carburettor air, the engine continued to run poorly. Fearing a total engine failure, the instructor planned a circuit that allowed for a glide landing. The aircraft touched down on the runway but, due to the aircraft's weight and a minimal headwind, it failed to stop before exiting the runway and striking a small fence. There were no injuries to the four occupants.
The investigation
The investigation examined the engine performance and the circumstances of the landing. Maintenance records and inspections revealed that the engine's rough running was linked to specific component failures. Specifically, investigators identified that one spark plug in the left magneto bank was breaking down, and a second spark plug in the right magneto bank featured a cracked ceramic insulator. Following the replacement of these parts, the engine returned to normal operation.