What happened
On 19 July 1998, a Rans S6-ESD XL, registration G-MZBD, was performing a private cross-country flight near Sittles Field, Staffordshire. While cruising at approximately 1,000 feet amsl, the pilot experienced a significant drop in engine RPM, which fell from 5,800 to roughly 3,800, accompanied by severe engine roughness. Despite attempts to adjust the throttle, the engine ceased operation entirely within 30 seconds, at which point the aircraft was at an altitude of 1,250 feet amsl.
Due to the low altitude, the pilot opted not to attempt an engine restart. To facilitate a landing, the pilot executed a steep 360-degree right-hand turn to align the aircraft into the wind and toward an uphill slope. However, the maneuver left the aircraft with insufficient airspeed and altitude to complete the necessary round-out. Consequently, the aircraft stalled at approximately 10 feet agl, resulting in no fatalities or injuries but causing significant damage to the cockpit floor and landing gear.
The investigation
Investigators examined the Rotax 503 engine to determine the cause of the power loss. The inspection identified that a needle within one of the carburettor jets had detached and fallen into the jet area. This failure occurred because the needle had broken along the plane of its locating groove. The investigation established that the needle had been subjected to severe machining-type wear caused by the continuous rotation of the needle against its mounting circlip.
Findings
- The engine failure was caused by a carburettor needle detaching and obstructing the fuel jet.
- The detachment resulted from wear in the locating groove, driven by the rotation of the needle relative to the circlip under conditions of vibration and resonance.
- At the time of the accident, the engine had completed 49 total flying hours.