What happened
On September 27, 2015, a McDonnell-Douglas MD 500E, registration SP-SOO, was conducting specialized aerial inspections of medium-voltage power lines near Wałbrzych. After completing an initial three-hour flight, the crew—consisting of a pilot and an operator—landed near Burkatów to refuel.
Upon resuming the mission, the pilot attempted a left turn at approximately 220 degrees to capture a transformer on the thermal camera. During the maneuver, the pilot reduced airspeed to between 20 and 30 knots and adjusted the collective pitch. During this deceleration, the helicopter experienced a sudden, uncontrollable yaw to the right. The pilot attempted to correct the deviation by applying left pedal, but the aircraft failed to respond and began a rapid descent.
In an attempt to manage the descent, the pilot reduced engine RPM and collective pitch, eventually entering an autorotation. During the high-rate vertical descent, the pilot increased the collective to maximum. The aircraft struck a power line, hit a tree, and clipped an electric pole before impacting the ground at high speed on its right side. The two crew members sustained minor injuries and were able to exit the wreckage on their own.
The investigation
The PKBWL investigation confirmed that the aircraft was properly maintained, documented, and within weight and balance limits. The pilot was fully qualified, well-rested, and not under the influence of alcohol. The investigation focused on the aerodynamic behavior of the aircraft during the low-speed maneuver and the environmental conditions present at the time of the accident.
Findings
- The primary cause of the accident was loss of control by the pilot.
- Variable wind speeds and directions, caused by the mountainous terrain and nearby structures, acted as contributing factors.
- The aircraft was performing a specialized inspection at a low altitude (approximately 37 meters above the power line tops), which left minimal margin for error during the loss of directional stability.