Aircraft and Flight Details
The aircraft involved was a Piper PA-28-161 Warrior II, registration G-BPAU, built in 1978 and powered by a single Lycoming O-320-D3G piston engine. At the time of the accident, it was conducting a circuit check training flight with two occupants: an instructor holding a Basic Commercial Pilot's Licence with Instructor Rating and a Private Pilot's Licence holder. The instructor, aged 60, had 2,625 total flight hours, including 562 on type, with 22 hours in the last 90 days and 2 hours in the last 28 days.
Sequence of Events
Prior to departure, the aircraft was refueled to full tanks. The engine was initially reluctant to start but eventually started and ran normally. Pre-flight power checks, including carburettor heat function, were satisfactory. The aircraft took off from Runway 24 for the first circuit.
During the base leg, with carburettor heat and two stages of flap selected, the pilot initially reduced power and then increased it to adjust altitude. However, increasing power appeared to cause the engine to stop. Operating the throttle had no effect. The instructor took control and maintained gliding speed, determining insufficient height to return to the aerodrome. He turned right to avoid obstacles and selected an alternative landing area in a small field. The left wingtip struck a tree, and the aircraft landed abruptly.
Injuries and Damage
Both occupants sustained minor cuts and bruises and evacuated the aircraft normally. There was some fuel leakage but no fire. The aircraft sustained damage beyond economic repair.
Post-Accident Information
After the accident, the airfield owner checked the fuel supply and found it satisfactory. The instructor noted that carburettor icing might have been the cause but expressed puzzlement because carburettor heat had been selected soon before the engine stoppage.
The Met Office provided an aftercast indicating surface temperature of +14.1°C and dew point of +6.7°C at the time. According to the CAA General Aviation Safety Sense leaflet on piston engine icing, these conditions posed a risk of moderate icing at cruise power and serious icing at descent power.
The flying club at Denham reported several instances of carburettor icing earlier that day and on prior days. A visual inspection of the engine found no major mechanical problems, but no in-depth examination was conducted.
The AAIB is conducting a review of accidents involving suspected carburettor icing and will collate findings to make Safety Recommendations as appropriate.