NYC03LA033

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.

On December 26, 2002, at 1440 eastern standard time, an MBB (Eurocopter) BK 117 A-4 helicopter, N951AM, operated by Rocky Mountain Holdings LLC, was substantially damaged during engine start-up on a roof-top helipad at the Albany Medical Center, Albany, New York. The certificated commercial pilot and two medical flight personnel were not injured. Visual meteorological conditions prevailed, and a company visual flight rules flight plan was filed for the medevac flight conducted under 14 CFR Part 91.

According to the pilot, the helicopter was positioned on the 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 of the hospital helipad caused the blades to flap excessively. The pilot then heard a series of thumps, and the start was aborted.

Inspection of the helicopter by a Federal Aviation Administration inspector 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 service bulletin included the following information,

"During start-up and shutdown of the engines, the main rotor blades can strike into the endplates if heavy downdrafts occur while the rotor is accelerating from or slowing down to standstill. The presence of very heavy downdrafts which can cause damage to the main rotor blades and to the endplates upon engine startup and shutdown, must be reckoned with at some operational locations, especially between high buildings.

Downward deflections of the main rotor blades which can cause the endplates to be struck cannot be rule out during heavy downdrafts. For this reason, the endplate shall be modified in the potential strike area so that a piece of the endplate will be struck out upon impact, without the main rotor sustaining damage."

The service bulletin had not been applied 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 winds reported by an airport 5 miles north of the heliport, at 1451, were from 300 degrees at 19 knots, gusting to 26 knots.