What happened
On July 3, 2019, a Pipistrel Sinus motorized glider, registration N269PW, was involved in an accident near Lawrence Municipal Airport (LWM) in Lawrence, Massachusetts. The flight was being conducted under 14 CFR Part 91.
After departing LWM and climbing to 3,500 feet MSL, the pilot flew approximately 16 miles toward the coast. Upon reaching a preferred soaring area, the pilot shut down the engine and feathered the propeller to begin unpowered flight. After failing to find thermals and experiencing low wind conditions, the pilot attempted to restart the engine to return to LWM as the aircraft descended through 2,500 feet MSL.
During the restart attempt, the engine began running but produced sluggish performance and higher than normal fuel flow. The pilot attempted to troubleshoot the issue by switching fuel tanks, suspecting fuel contamination or air in the lines, but could not restore normal power. While approaching runway 23, the pilot was unable to maintain altitude. Approximately 1.5 miles from the runway approach end, the aircraft struck a fence on a hilltop at an elevation of 300 feet and slid to a stop near the LMW VOR.
The pilot sustained one minor injury and was not killed in the accident.
The investigation
Post-accident examination of the N269PW revealed substantial damage to the landing gear structure, the left wing, and the lower portion of the fuselage. The two-bladed composite propeller blades sheared approximately 8 inches from the hub upon impact and were found in a feathered position. The propeller control knob in the cockpit also indicated the propeller was feathered.
An inspection of the engine and fuel system found no mechanical discrepancies that would have prevented normal operation. An FAA inspector determined that the pilot did not follow the documented engine restart procedures. According to the aircraft's flight manual, unfeathering the propeller requires reducing airspeed to 90 km/h, pulling the propeller pitch knob base, and rotating it counterclockwise.
Findings
- The engine was operating normally, but the propeller remained in a feathered position.
- The lack of thrust from the feathered propeller prevented the aircraft from maintaining altitude during the return to the airport.
- The pilot failed to follow the specific unfeathering procedure outlined in the flight manual prior to the engine restart.