Accident Overview
On 2 October 2018, a Grob G115E Tutor, registration G-BYUU, experienced an engine failure while returning to RAF Wittering, Cambridgeshire, following a successful air test after an engine change. The aircraft, powered by one Lycoming AEIO-360-B1F piston engine, was engaged in a private flight with a single occupant. The pilot reported no injuries and the aircraft sustained engine failure as the nature of damage.
Sequence of Events
The pilot noted an uncommanded reduction in engine speed. The engine initially recovered, but when the speed reduced again, the pilot made a PAN call. A further loss of power made it impossible to maintain height, prompting a MAYDAY call and preparation to land in a field. The engine stopped prior to landing, and the landing was accomplished without damaging the aircraft.
Examination Findings
Post-incident examination revealed that the engine oil sump drain cap was missing. The loss of the cap resulted in an oil leak and subsequent engine seizure. The Grob 115E is equipped with a modified inverted engine oil system for aerobatic maneuvers, and there is no requirement for the oil cap to be wire locked.
Maintenance Considerations
The maintenance organization responsible for the engine change considered that the most likely scenario is that the drain cap was not correctly secured after the engine was installed. In response, the organization is reviewing their procedures and liaising with the manufacturer about an alternative cap that can be wire locked. In the interim, they have introduced an independent check to ensure the cap is correctly refitted.
Pilot Information
The commander, aged 74, held a Commercial Pilot's Licence and had accumulated 8,100 flying hours, including 100 hours on type. In the last 90 days, he had flown 37 hours, with 3 hours in the last 28 days.