2010 Bell 412 HP accident at Berlin-Marzahn

Incident Overview and Aircraft Details On 6 September 2010, a Bell 412 HP helicopter operated by a German air-ambulance service was being prepared for a patient transport from the Unfallkrankenhaus Berlin-Marzahn to the Krankenhaus Berlin-Friedrichshain. The aircraft, manufactured in 1993 with serial number 36066, was equipped with a raised skid landing gear and powered by two Pratt & Whitney PT6T-3BE turboshaft engines. At the time of the incident, the helicopter had accumulated 9,199 flight hours and 26,518 landings. ## Sequence of Events The helicopter was parked on a landing platform on the hospital roof, with its nose facing west. At approximately 20:00 local time, a patient was loaded into the cabin and secured on a stretcher. As the crew began pre-flight preparations, a loud noise was heard, and the rear cross-tube of the skid landing gear fractured. The aircraft tilted approximately 15 degrees to the right and pitched slightly upward, with the nose pointing about 10 degrees up. The four crew members and the patient were not injured. ## Investigation Findings The fractured rear cross-tube was examined by the German Federal Bureau of Aircraft Accident Investigation (BFU) and the Institute of Materials at Braunschweig Technical University. Microscopic analysis revealed that the failure was caused by a fatigue crack that initiated at the most highly stressed area of the component, near the right clamp of the mounting bracket on the underside of the tube. The crack propagated due to cyclic loading, and the final fracture occurred by ductile overload. No local surface defect was identified as the initiating cause. ## Maintenance and Service History The rear cross-tube, serial number 710, was originally installed on another helicopter in 2000 and transferred to the accident aircraft on 21 August 2002. In May 2008, it underwent inspection and overhaul in accordance with Alert Service Bulletin No. AA-07109 from Aeronautical Accessories Inc. (AAI), which corresponds to Bell Helicopter ASB 412-08-129. The inspection found no defects, and the component was returned to service. By the time of the accident, the cross-tube had accumulated 6,245 hours and 17,690 landings, including 1,410 hours and 4,120 landings since the last overhaul. ## Additional Context A similar failure of a rear cross-tube on an identical landing gear occurred in 2007 with the same operator. In April 2008, AAI issued Alert Service Bulletin No. AA-07109, which established a service limit of 20,000 landings for the component and mandated periodic inspections for cracks and permanent deformation. The accident occurred under visual meteorological conditions with a wind from the east-northeast at seven knots. The helicopter was not equipped with a cockpit voice recorder or flight data recorder.