What happened
On 31 July 1999, a Luscombe Silvaire 8F, registration G-BTJC, was conducting a test flight from Stockton airfield following various radio-related maintenance work. The flight was being operated as a private venture by a single pilot.
During the initial takeoff phase, the airspeed indicator appeared to be operating correctly. However, as the aircraft entered its climb, the airspeed indicator pointer became stuck at 60 mph, while the altimeter and vertical speed indicator began to respond sluggishly. The pilot performed a handling check, noting that the airspeed reading at the point of stall seemed relatively accurate.
During the subsequent approach to the airfield, the aircraft was trimmed in a nose-up configuration, and the airspeed indicator showed a reading of 120 mph. As the aircraft neared the runway threshold, it encountered a sudden sink rate. Despite an immediate increase in engine power, the aircraft landed short of the threshold and nosed-over, eventually coming to rest in an inverted position on the runway. The pilot escaped the wreckage without any injuries.
The investigation
Investigators examined the aircraft's pitot system to determine the cause of the erratic instrument behavior. The investigation established that the pitot system had been partially obstructed by an insect wing.
Findings
- The aircraft sustained damage to the engine, propeller, fin, rudder, and cabin structure.
- The primary cause of the instrument malfunctions was a partial blockage of the pitot system caused by an insect wing.
- The unexpected sink rate during the final approach was linked to the unreliable airspeed and altimeter indications.