What happened
On 18 January 2000, a Cessna T310R, registration G-GREN, was conducting a private flight from Southend Airport, Essex, to Weston Airfield, Eire. While cruising at FL80 near the North Wales coast, the aircraft's left engine ceased operation. The pilot, who was in contact with London Flight Information Service, secured the engine and issued a MAYDAY call. Following instructions to squawk 7700 and switch to the emergency frequency, the right engine also failed.
Noting an airfield visible on the coast below, the pilot decided to perform an emergency landing. Llanbedr Air Traffic Control identified the emergency via radar and frequency monitoring, subsequently coordinating with the Distress and Diversion centre to provide the pilot with airfield details. During a visual approach to Runway 36, the pilot determined the aircraft would land short of the runway. He notified ATC of his intention to land in a field outside the aerodrome boundary. The aircraft landed in a field with no damage and no injuries to the pilot.
The investigation
The investigation established that the aircraft's main tanks contained enough fuel for the intended flight to Ireland. However, the engines were being fed from the auxiliary tanks, which had run dry. The pilot's report indicated that the fuel system had been mismanaged.
Investigators examined the specific design of the Cessna T310R fuel system, noting that while the main tanks can be used at any time, the auxiliary tanks are intended for use during cruise. A critical feature of this system is that excess fuel from the auxiliary tanks is returned to the main tanks, meaning the actual endurance of the auxiliary tanks can be significantly lower than their initial volume suggests. Furthermore, the fuel gauges do not explicitly indicate which specific tank is currently supplying the engines, a factor that can lead to pilot confusion, particularly for those with limited experience on this specific model.
Findings
- The primary cause of the dual engine failure was the pilot's mismanagement of the fuel system, leading to the exhaustion of the auxiliary fuel supply.
- The pilot had limited experience on this specific aircraft type, with only 15 hours logged on the model.
- The design of the fuel system, where auxiliary tank endurance is unpredictable due to fuel return to the main tanks, contributed to the error.
- The lack of clear indication on the fuel gauges regarding which tank was being depleted increased the risk of confusion.