NTSB Identification: NYC03LA033.
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Accident occurred Thursday, December 26, 2002 in Albany, NY
Probable Cause Approval Date: 06/30/2004
Aircraft: MBB BK 117 A-4, registration: N951AM
Injuries: 3 Uninjured.

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 helicopter was positioned on the hospital rooftop helipad facing in a southerly direction. After the medical crew boarded the helicopter, the number 1 engine was started. As the main rotor blades began to turn, an unexpected gust of wind traveling over the rooftop caused the blades to flap excessively. The pilot then heard a series of thumps, and aborted the start. Inspection of the helicopter revealed that one of the main rotor blades had come in contact with the left vertical stabilizer, damaging the tail boom, main rotor blades, and the left vertical stabilizer. On November 30, 1990, the helicopter manufacturer issued service bulletin SB-MBB-BK-30-103, which called for a triangle section to be cut out of the stabilizer fin assembly, in an area where a potential strike from a main rotor blade could occur, and replaced with a foam core insert. The operator did not apply the service bulletin to the accident helicopter. The winds reported by the pilot at the time of the engine start were from 340 degrees at 14 knots, gusting to 24 knots.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

The inadvertent encounter with a downdraft during engine start, which flexed the main rotor blades and subsequently damaged the tail boom assembly. A factor related to the accident was the failure of the operator to comply with a service bulletin.

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