What happened
On 18 May 2011, a Beech 90, registration N46BM, was performing a private flight from Bournemouth Airport to Manchester Airport. The flight was operated by a single pilot with one passenger. After completing pre-flight checks, the aircraft was cleared for takeoff from Runway 26.
Shortly after becoming airborne, the pilot noticed the aircraft was not climbing as expected. While the engine instruments appeared normal and no master warnings were triggered, the aircraft's rate of climb was insufficient to maintain altitude. The pilot attempted to return to the airport but, realizing the aircraft was descending, made the decision to perform a forced landing in a field approximately two miles west of the airfield.
The aircraft struck young trees at the field boundary and touched down heavily. The landing gear collapsed upon impact, and the aircraft slid along the ground before coming to a halt. There were no injuries to the pilot or the passenger, though the airframe and powerplants sustained substantial damage.
The investigation
The AAIB investigation examined the aircraft's engines, the cockpit controls, and recorded data from the EGPWS and airport radar. Investigators analyzed the engine components, specifically the Pratt & Whitney PT6A-28 turboprop engines, to check for mechanical defects or fuel contamination. Fuel samples were tested and found to be within specification, with no evidence of water or biological contaminants.
Engine disassembly revealed that both engines were in a serviceable condition. While the left engine showed some evidence of being 'alight' during the impact due to scorched grass in the casing, no significant mechanical defects were found that could have caused a power loss. The investigation also reviewed the pilot's takeoff technique, noting that the propeller levers were positioned approximately half an inch behind the fully forward position, a practice the pilot used to prevent exceeding RPM limits.
Findings
- The aircraft experienced a symmetrical power loss sufficient to prevent sustained level flight.
- The cause of the apparent reduction in engine performance could not be determined.
- Fuel contamination was discounted as a cause.
- The pilot's decision to perform a forced landing was made effectively, maintaining control of the aircraft and ensuring the safety of the occupants.
- The aircraft's takeoff performance was deficient, though it was not determined if this was due to the power lever settings or an unidentified factor.