History of the Flight
On 13 October 2001, a Europa aircraft (registration G-BWGH) departed Jersey for Exeter on the final leg of a nine-day tour of northern France. The pilot, a 44-year-old private pilot with 375 hours total experience (26 on type), had performed a thorough pre-flight inspection and found the aircraft serviceable. After refuelling, engine checks were normal, with all pressure and temperature gauges within limits. Both pilot and passenger wore immersion suits and lifejackets.
Climbing to Flight Level 50, at approximately 2,600 feet altitude, the pilot detected a hot smell and observed that the engine oil pressure had dropped to zero. He informed air traffic control of the problem, reporting the aircraft's position midway between Jersey and Guernsey. The engine then began to run roughly and stopped after about 30 seconds. The pilot transmitted a 'Mayday' call, stating his intention to try to reach Sark, about 3 miles away. ATC suggested heading for Guernsey, but the pilot assessed that ditching in the sea was unwise if land could be reached. Despite awareness of a 'no fly' zone around Sark, he decided to head toward the island.
Arriving over Little Sark (an isthmus forming the southern part of Sark) at about 800 feet above mean sea level, the pilot saw that all fields were very small. He spotted slightly larger fields on the main island but felt the aircraft was too low to reach them safely. With no beaches visible, he chose to force-land in a small field below.
The pilot, experienced in landing small fields from microlight flying, selected full flap, switched off the fuel and electrical systems, and initiated a diving turn, maintaining 75 knots. The approach was into wind at about 60 knots, aligned with the diagonal of the field. He landed heavily to reduce forward momentum, then aimed the aircraft toward the top left-hand corner so the left wing would obliquely impact a bank forming the left edge of the field. This caused a ground loop, with the tail absorbing most of the impact. Both pilot and passenger stepped out unhurt. The pilot used a handheld radio to inform ATC that no one was injured.
Engine Examination
The wreckage was recovered to Guernsey, where the AAIB examined the engine and its systems. It was found that the engine contained no oil and had seized. Further inspection revealed that the forward right-hand cylinder rocker cover was loose. This had allowed engine oil to drain overboard while the engine was running. The single steel screw attaching the rocker cover to the aluminium alloy cylinder head had stripped the threads within the cylinder head. The three other rocker cover attachment screws were torqued to 9, 12, and 14 Newton-metres (Nm); the manufacturer's torque requirement was 10 Nm.
Examination of the airframe and engine logbooks showed that the rocker covers had been removed and refitted in May 2001 by an approved overhaul organisation as part of manufacturer's Service Bulletin 7UL96. There were no entries indicating the rocker covers had been disturbed since.
Initial thought was that the screw had been over-torqued, causing damage to the aluminium threads. However, tests by the AAIB and a UK Rotax distributor showed that when over-torqued beyond 10 Nm, the screw failed in tension (between 12 and 17 Nm) without damaging the aluminium threads. On newer engines, Rotax had changed to a stronger screw, which also failed before damaging the aluminium threads (at between 17 and 21 Nm). The stripped aluminium threads clearly led to oil loss and subsequent engine seizure, but there was insufficient evidence to determine the cause of the stripped threads.