Hiller UH-12B Helicopter Accident at Aachen-Merzbrück

Incident Overview and Aircraft Details On 15 December 2007, a Hiller UH-12B helicopter, manufactured in 1951 with serial number 624, was involved in an accident near Aachen-Merzbrück, Germany. The aircraft was powered by a Franklin 6V-335-B engine producing 210 horsepower and had a total airframe time of 3,530 hours. Its last annual inspection was completed on 6 September 2007, with 30 hours of operation since then. The helicopter was not equipped with flight data recorders, as they were not required by applicable regulations. ## Flight Sequence and Pilot Actions The 57-year-old pilot, holding a private pilot license for helicopters, intended to fly from Aachen-Merzbrück to Bonn-Hangelar. After a 10-minute taxi for engine warm-up, he took off from runway 08 at approximately 13:37 local time into a 9-knot wind with gusts up to 22 knots. During the climb, the pilot observed an indicated airspeed of 60 knots and attempted to reduce it to 45 knots, the best climb speed, while simultaneously adjusting the throttle to bring the engine speed into the green range. This simultaneous maneuver resulted in a drop in main rotor speed. Despite attempts to increase engine power and adjust the collective pitch lever, the pilot could not restore the rotor speed. The helicopter lost altitude, rolled about its longitudinal axis, turned right out of the wind, and impacted the ground in a field approximately 600 meters beyond the runway end. The engine was manually shut down on the ground. ## Investigation Findings and Contributing Factors The investigation determined that the accident was caused by pilot error, specifically a simultaneous maneuver that led to a main rotor speed drop and a hard landing. Contributing factors included the pilot's limited total flight experience of 111 hours on helicopters, with only 30 hours on the UH-12B type, and the aircraft's relatively weak engine power for its takeoff weight. The aircraft was in good maintenance condition, and no technical defects were found that contributed to the accident. The pilot sustained no injuries, and the helicopter was heavily damaged, with the right skid broken off and significant damage to the main and tail rotor blades.