What happened
On 13 September 2003, a Grob G11ASS aircraft, registration G-RAFA, was conducting a training flight from RAF Wyton, Cambridge. The crew consisted of an instructor and a student pilot. After completing all necessary pre-flight inspections and a power check, the aircraft departed the airfield with the student at the controls.
As the aircraft climbed through 200 feet above ground level, the crew began retracting the flaps. At this moment, the engine began to lose power and eventually faltered, though the propeller continued to windmill. The instructor immediately assumed control of the aircraft and performed the required forced landing procedures. The instructor successfully executed a landing in a field located beyond the airfield perimeter fence. There were no injuries to the crew and no damage was sustained by the aircraft.
The investigation
The investigation focused on why the engine lost power despite the successful completion of pre-flight checks. It was determined that during the forced landing checks, the crew discovered the fuel cock was in the 'OFF' position.
Investigators examined the cockpit configuration of the Grob G115A. In this specific model, a single fuel cock is located on the centre console. The investigation noted that the student pilot had previous experience flying the Grob Tutor, a later model of the aircraft series. In the Tutor, a fuel tank selector is located in the same position on the console as the fuel cock is in the G115A.
It was concluded that the student likely instinctively moved the lever to a position used for the tank selector on the Tutor, which inadvertently moved the fuel cock on the G-RAFA to the 'OFF' position. Furthermore, a comparison of the aircraft's fuel cock markings with the official Flight Manual revealed that the colour scheme and markings on the aircraft were inconsistent with the manual, which may have hindered the crew's ability to identify the incorrect setting during pre-flight operations.
Findings
- The engine power loss was caused by the fuel cock being placed in the 'OFF' position prior to takeoff.
- The student pilot likely performed the action out of habit from operating the Grob Tutor, where a selector switch occupies the same physical location on the centre console.
- Sufficient fuel remained in the system to allow for takeoff, but the engine failed once the fuel downstream of the cock was exhausted.
- Discrepancies and omissions in the colour-coded markings on the fuel cock made it more difficult to verify the correct position during pre-flight checks.