What happened
On 23 June 2020, a Boeing A75L300 ‘Stearman’, registration G-CGPY, was performing a commercial flight involving wing-walking experience flights. After completing several flights at Chiltern Park Aerodrome in Oxfordshire, the pilot began the return journey to Dunkeswell Airport in Devon.
While flying near the disused Culmhead aerodrome in Somerset, the engine began to struggle at approximately 2,0/00 ft altitude. Despite the application of carburettor heat, the engine continued to run roughly and failed to produce sufficient power. Due to the high descent rate of the aircraft and the presence of obstacles such as a solar farm and industrial buildings in the area, the pilot was forced to perform a curved approach into a nearby grass field. The aircraft sustained damage to the fuselage and wingtip during the landing. There were no fatalities and no injuries to the crew or the passenger on board.
The investigation
The AAIB examined the fuel planning and the aircraft's technical state. The investigation found that the pilot's fuel planning was based on inconsistent assumptions regarding the aircraft's usable fuel capacity and consumption rates. While the pilot believed the aircraft had a larger usable capacity, the investigation noted that fuel starvation could occur at low levels due to the aircraft's design. Furthermore, the pilot had previously reported that the fuel gauge was stuck on empty, which could have hindered accurate monitoring of fuel levels.
Findings
- The engine likely stopped producing power because the aircraft had consumed all available usable fuel.
- There was significant uncertainty regarding the aircraft's actual fuel consumption rate and the true usable fuel capacity.
- Inconsistencies in fuel planning assumptions between the pilots contributed to the event.
- The investigation could not rule out carburettor icing as a potential technical factor, though no mechanical faults were found in the engine itself.
Safety action
Following the accident, the operator implemented several measures, including:
- Mandating a refuel stop after a maximum of 1.5 hours of flight time.
- Requiring all cross-country flights to depart with a full fuel tank.
- Implementing a requirement for pilots to verify fuel quantity using a calibrated dipstick every second wing-walking flight.
- Updating technical logs to include more precise engine running times.
- Introducing an annual technical questionnaire for pilots to refresh safety knowledge.