NTSB Identification: ERA11LA428
14 CFR Part 91: General Aviation
Accident occurred Friday, July 29, 2011 in Darlington, MD
Probable Cause Approval Date: 08/29/2012
Aircraft: SCHWEIZER 269C, registration: N39SH
Injuries: 1 Minor.
NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.
The pilot of the helicopter stated that he conducted a light touchdown on the helipad and reduced engine power and applied collective friction for cooldown, per the helicopter’s checklist. About 1 minute after the touchdown, the helicopter began to vibrate violently. The pilot further reduced engine power, but the helicopter continued to vibrate until it fell apart. Before the day's flights, the pilot performed a preflight inspection of the helicopter, during which he visually inspected both forward and aft landing gear dampers and also squeezed them to confirm that they contained oil and were not leaking. He did not observe any anomalies during this inspection. The landing gear dampers were examined by the manufacturer after the accident, and during load testing three of the four dampers did not meet required specifications. The minority owner of the helicopter stated that, based on the helicopter's fuel consumption during the time since its last inspection, he believed that the helicopter was more than 50 hours overdue for a 100-hour inspection. He also stated that, on one occasion, he found the helicopter's Hobbs meter disconnected. The helicopter manufacturer’s maintenance instructions state that, "Incorrect fluid levels, improper pressure or inoperable valving will deteriorate the damping capabilities of the landing gear dampers. These conditions may result in ground resonance and destruction of the helicopter.”
The National Transportation Safety Board determines the probable cause(s) of this accident to be: Inadequate maintenance of the helicopter's landing gear dampers, which resulted in a main rotor out-of-balance condition and ground resonance encounter. Full narrative available
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