What happened
On 28 October 2014, a Piper PA-28-181 Cherokee Archer II, registration G-BSIM, was performing a local general handling flight from RAF Henlow. The flight, conducted by a single pilot, proceeded normally through three takeoff and landing cycles. However, during the fourth circuit, as the aircraft transitioned onto the base leg, the pilot applied carburettor heat. Immediately following this action, the engine experienced a significant drop in RPM accompanied by increased noise.
Despite the pilot's attempts to manage the throttle and restore engine stability, the power delivery remained erratic. Realising that the engine could no longer sustain the power required to reach the runway, the pilot declared an emergency and selected a nearby field for a forced landing. While the initial touchdown on the main wheels was stable, the aircraft subsequently struck a small land drain. This impact deformed the left landing gear and caused damage to the left wing and fuselage. The aircraft eventually came to a halt after yawing 90 degrees from its original landing direction. The pilot sustained no injuries.
The investigation
The investigation focused on the sudden degradation of engine performance following the application of carburettor heat. Investigators examined meteorological data from Luton Airport, which indicated temperatures between 14°C and 16°C with dew points between 11°C and 13°C. Analysis of these atmospheric conditions against standard induction system icing risk models demonstrated that the environment was highly susceptible to ice formation. Specifically, the data suggested that the engine was at risk of moderate icing at cruise power and serious icing at lower power settings.
Findings
- The primary cause of the engine power loss was carburettor icing.
- Atmospheric conditions, characterized by the recorded temperature and dew point, were conducive to the formation of ice within the induction system.
- The application of carburettor heat during the landing circuit coincided with the onset of the engine malfunction.