Flight History
On 11 May 2011, at approximately 15:15 hours local time, a Schweizer 269D helicopter (registration PH-HHF) was on a return flight from Kempen Airport to its home base at Lelystad Airport with the pilot as the sole occupant. While cruising at about 1000 feet near Veghel, the pilot heard a noise immediately followed by a pitch-up and left roll motion. Suspecting a tail rotor drive failure, the pilot reduced the throttle to idle and initiated an autorotation. The helicopter made a hard tailwind landing in a grass field. After landing, the pilot attempted to shut down the engine but encountered difficulty with the throttle detent release system. He eventually pulled the fuel cut-off knob to stop the engine. After exiting, he briefly returned to switch off electrical systems and retrieve items. Shortly thereafter, a fire broke out, destroying the helicopter. The pilot suffered no injuries.
Investigation and Analysis
Technical investigation was conducted with assistance from the National Aerospace Laboratory of the Netherlands (NLR), the National Transportation Safety Board (NTSB), and experts from the helicopter and engine manufacturers. Examination revealed that the helicopter's engine-to-main-gearbox drive train was interrupted due to a broken KaFlex coupling at the engine power takeoff. The fracture was found to be caused by metal fatigue. The driveshaft had accumulated 2599 flight hours since conversion to configuration A 333, with a remaining service life of 5001 hours. The last inspection occurred at 6929 flight hours, and maintenance records indicated that scheduled inspections were performed per manufacturer specifications. The post-crash fire originated from fuel released when a fuel hose end was fractured during impact, igniting on hot engine components.
Conclusions
The investigation concluded that the sudden disruption of power to the main rotor caused an immediate drop in rotor RPM, resulting in the pitch-up and left roll. The helicopter impacted with high vertical velocity, causing structural damage and a post-crash fire. The KaFlex forward coupling drive lug fractured due to metal fatigue, though the root cause of the fatigue could not be positively identified. Following the incident, the helicopter manufacturer issued an alert service bulletin requiring engine alignment checks at reduced intervals to prevent similar occurrences.