What happened
On 3 July 2004, an Auster 5J4/100, registration G-AIJT, was conducting a private flight near Whiterashes Airfield, Scotland. After performing two touch-and-go landings on the north runway, the pilot climbed to 1,000 feet to prepare for a landing on the westerly runway. During this phase, the engine began to misfire. The pilot had been using the auxiliary fuel tank, which was nearly empty, and upon noticing the engine trouble, immediately switched to the main fuel tank. Despite this action, the engine failed completely.
At the time of the failure, the aircraft was roughly 4 nm east of the airfield. Although the pilot could not see the airfield, a field south of the runway centreline was identified for an emergency landing. The pilot focused on restart attempts, checking the magnetos and mixture, but the engine would not restart. The chosen landing site contained standing crops and was bordered by trees and telegraph poles. During the landing roll, the left main landing gear sank into soft soil, causing the aircraft to yaw left and resulting in the right wing and propeller striking the ground. There were no fatalities and no injuries to the two occupants.
The investigation
Investigators examined the engine and fuel systems to determine the cause of the power loss. While the fuel in the carburettor bowl was free of contamination, the inspection revealed significant wear on the carburettor butterfly valve spindle and bushing. Additionally, the carburettor heat ON detent on the airbox was worn, preventing the system from maintaining the maximum heat setting.
Regarding the fuel system, the main tank had not been used for approximately three months and lacked a drain. This period of inactivity, combined with the fact that the tank had recently been refuelled, created conditions for water to condense within the tank and enter the fuel line. The investigation also noted that the engine had initially faltered as the auxiliary tank reached empty, a transition that likely introduced air into the fuel system.