Background
On 23 December 2001, the helicopter's left forward fuel tank electric booster pump failed. The pilot consulted the locally produced Minimum Equipment List (MEL), which permitted flight with one pump inoperative provided the cross feed system was operative and Rotorcraft Flight Manual (RFM) limitations were observed. The MEL did not specify the RFM limitations. The pilot entered the defect and deferred repair; the maintenance organization requested minimum fuel in the tank for a pump replacement scheduled for 26 December.
History of the Accident Flight
On 25 December, the pilot did not consult the emergency checklist again, having done so the previous day. The helicopter initially carried 340 kg of fuel; after a one-hour flight, 190 kg remained. The afternoon task involved transporting a patient to Morriston Hospital. The pilot calculated fuel requirements and departed with 143 kg, arriving at the hospital after 6 minutes. After shutdown and offload, the helicopter lifted off with 115 kg for the return flight.
Shortly after departure, the aircraft encountered heavy snow showers. The pilot descended to 400 feet agl and reduced speed to 80 KIAS. The FUEL PUMP 2 caution flickered and remained on. The pilot believed both booster pumps had failed but expected the engine-driven pumps to draw fuel by suction. Seconds later, both engines ran down. The pilot lowered the collective to restore rotor RPM, warned passengers, selected gear down, transmitted a MAYDAY distress call, and executed an emergency landing in a clear field. The aircraft landed heavily with low forward speed but a high rate of descent; it remained upright but suffered severe damage to the tail cone, main and tail rotor blades, and landing gear. All three occupants vacated through normal exits and sustained minor injuries (one crew and one passenger).
Safety and Survival
The pilot's MAYDAY was received by London Flight Information Service, and the air observer in the aft cabin transmitted on the operational radio frequency. Emergency services arrived at the scene 12 minutes later. All occupants wore flying helmets; both the pilot and the front seat passenger struck parts of the aircraft with their helmets despite wearing four-point inertia reel harnesses. The helmets were sufficiently damaged to be declared unfit for further use.
Analysis
The investigation noted that the MEL was deficient in not reiterating RFM limitations or providing guidance on the cross feed valve position. The emergency checklist (page 43) required that after a fuel pump failure, the cross feed switch be manually selected to CLOSED. However, in this accident, the cross feed remained open. With the cross feed open, the functioning booster pump pressurized the cross feed line, preventing the left engine-driven pump from drawing fuel by suction from the left forward tank. This rendered the fuel in the left forward tank unusable, leading to fuel starvation to both engines. The pilot had not revisited the checklist before the flight and believed the engine-driven pump could draw fuel; but the open cross feed negated this.