What aircraft was involved and where did it happen?

The accident on null involved a aircraft, registration G-BTMS, at IE.

What was the probable cause of the accident?

The engine stopped due to a suspected vapour lock in the fuel supply system, potentially exacerbated by inadequate venting of the header tank.

Engine Failure Leads to Sea Ditching of Avid Mk. IV

A pilot successfully ditched an Avid Mk. IV Speedwing in the Irish Sea after a sudden engine failure caused by suspected fuel vapour lock.

What happened

On 11 August 2009, an Avid Mk. IV Speedwing, registration G-BTMS, departed Haverfordwest Airport in Wales, bound for County Wexford, Ireland. During the flight, approximately 55 minutes into the journey, the engine stopped abruptly without any prior warning or mechanical symptoms.

While crossing the sea, the pilot issued a MAYDAY call. In an attempt to restore power, the pilot switched the fuel selector to the right tank and tried to restart the engine. However, as the aircraft descended through 900 feet, the pilot abandoned the restart attempt and executed a controlled ditching in the sea, roughly 5 nautical miles southwest of Tuskar.

Following the impact, the aircraft began to fill with water. The pilot, wearing a flotation jacket, waited for the water level to rise sufficiently to open the doors and evacuate. The pilot was subsequently rescued by an Irish Coast Guard helicopter and sustained no injuries.

The investigation

The AAIU examined the wreckage, which was recovered from the sea near Carna Beach. The investigation focused on the fuel system, the engine, and the pilot's pre-flight procedures.

Investigators found that the engine itself had no mechanical defects. However, the fuel system in G-BTMS was noted to be non-standard, differing from the manufacturer's manual. Specifically, the vent line was routed in a way that did not comply with standard specifications. Analysis of the fuel revealed a mixture of MOGAS and AVGAS, which had been stored in the tanks for five months.

Additionally, the investigation identified that a bungee cord used for ground securing had been left attached to the control stick, which restricted the movement of the flight controls. The pilot also had not performed a thorough pre-flight inspection, specifically omitting a water check of the fuel.

Findings

The engine stoppage was likely caused by vapour lock within the fuel supply system.

The use of a fuel mixture containing MOGAS increased the risk of vapour-related issues.

The fuel system's venting was potentially inadequate because the header tank vent valve was closed during flight.

The pilot's pre-flight checks were not sufficiently thorough, and no flight plan had been filed for the flight.

The pilot's prompt distress call was the primary reason search and rescue services were alerted so quickly.