Incident Details
The helicopter was positioned on a hospital rooftop helipad facing south. After medical crew members boarded, 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 heard a series of thumps and aborted the start.
Damage
Inspection revealed that one of the main rotor blades had contacted the left vertical stabilizer. The impact damaged the tail boom, main rotor blades, and the left vertical stabilizer.
Service Bulletin
On November 30, 1990, the helicopter manufacturer issued service bulletin SB-MBB-BK-30-103. The bulletin 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.
Weather Conditions
The winds reported by the pilot at the time of the engine start were from 340 degrees at 14 knots, gusting to 24 knots.