Event
On 24 April 2000, a Gulfstream AA-5B (registration G-PENN) experienced engine roughness shortly after departure from Denham Aerodrome. The aircraft, operated by a flying club, was conducting a cross-channel sector to Le Touquet with a private pilot under supervision of a flying instructor. The surface wind was 180°/15 kt.
The aircraft departed from Runway 24. After turning right at about 700 feet agl, the engine began to run roughly. The instructor took control, turned back towards the airfield, and made a Pan call to land immediately. Despite switching magnetos and selecting carburettor air to hot, the engine continued to run roughly.
The instructor planned a circuit anticipating possible engine failure, turning base leg at a point where a glide landing on the runway would be possible. Full flap was selected on final approach. The aircraft touched down normally but further along the runway than ideal. The aircraft was heavy and there was little headwind, so it could not be stopped before running into a small fence just beyond the runway end. Groundspeed was very low, resulting in minor damage to wing leading edges and the underside of the engine cowling.
Airfield fire services arrived rapidly. All four occupants, wearing lap and diagonal upper torso restraints, escaped unaided via the main canopy; there were no injuries.
Investigation
Subsequent investigation by the maintenance organisation found that one spark plug in the left magneto bank was breaking down, and another in the right magneto bank had a cracked ceramic insulator. Both were replaced, after which the engine performed normally. The organisation expressed the opinion that these faulty spark plugs caused the rough running experienced in flight.
Outcome
The aircraft sustained minor damage. No injuries were reported.