What happened
On the morning of 25 May 2006, a Cessna 150 M, registration EI-CHM, departed Weston Aerodrome for a training flight. The crew, consisting of a flight instructor and a student instructor, was conducting a revision session to prepare the student for an upcoming instructor rating test. The flight proceeded westward through uncontrolled airspace, with the aircraft's transponder providing tracking data to Dublin ATC.
Near the village of Raharly, Co. Westmeath, witnesses observed the aircraft in a vertical spiral. Some observers reported seeing the aircraft at a low altitude, descending at an angle with the engine appearing to sputter or stall before the aircraft disappeared behind a tree line. The aircraft subsequently impacted an open field with high vertical speed and low forward speed. Both occupants were fatally injured in the crash.
The investigation
Investigators from the AAIU examined the wreckage and the engine of the Cessna 150 M. The inspection of the engine revealed no mechanical abnormalities or pre-impact malfunctions in the airframe. However, the investigation focused on the atmospheric conditions and the aircraft's flight profile prior to impact.
Analysis of the engine's heater box showed the flapper valve was stuck in a position corresponding to the carburetor heat being turned off. While the engine was in good working order, the investigators looked into whether environmental factors played a role. Additionally, the investigation reviewed the flight's maneuvers, noting that the aircraft may have been performing a practice forced landing just before the loss of control.
Findings
- The aircraft suffered a loss of airspeed at a low altitude, leading to a stall and a subsequent spiral to the ground.
- Carburetor icing is identified as a likely cause for the loss of engine power, as the temperature and dew point conditions were highly conducive to such icing.
- The aircraft was flying at a low altitude (estimated between 500 and 600 feet) at the time of the incident, leaving insufficient height for a safe recovery.
- There was evidence suggesting the aircraft might have been performing a practice forced landing, and the retraction of flaps to 0°—which increases stalling speed—may have contributed to the loss of control.
- The engine was found to be in good condition, and no structural failures were identified.