What happened
On 14 May 2009, an Aero AT-3 R100, registration G-SACY, was conducting a series of circuits at Sherburn in Elmet Airfield in North Yorkshire. During the fifth circuit, while the pilot was on the downwind leg, the choke was accidentally engaged instead of the carburettor heat. As the pilot transitioned from the downwind leg to the final approach and reduced engine power, the engine ceased operation.
The pilot was forced to perform a landing in a nearby field. During the subsequent landing roll, the aircraft nosed-over, resulting in significant damage to the fuselage and fin. The pilot remained uninjured but required assistance from the Airfield Fire and Rescue Service to exit the cockpit.
The investigation
The investigation focused on the engine failure and the physical configuration of the cockpit controls. It was noted that the choke control, identified by a cylindrical yellow knob, and the carburettor heat control, identified by a square blue knob, are positioned closely together on the centre panel extension. Both controls operate with a similar mechanical action, where pulling the knob activates the system and turning it to the function locks it in the ON position.
Findings
- The engine failure was likely caused by an over-rich fuel mixture resulting from the accidental selection of the choke.
- Alternatively, the engine stoppage may have been caused by carburettor icing due to the failure to select the carburettor heat.
- The proximity and similar operational mechanics of the choke and carburettor heat controls contributed to the inadvertent selection of the wrong control.