What happened
On November 13, 2011, a Messerschmitt-Bolkow-Blohm BK 117 B-2, registration N330SL, was undergoing an engine shutdown procedure following an emergency medical services flight in Carbondale, Illinois. During this procedure, a main rotor blade struck the left vertical stabilizer, resulting in substantial damage. The impact caused the main rotor blade to break near its root and resulted in dents to the tailboom and the tail rotor driveshaft cover. There were no injuries resulting from the incident.
At the time of the event, weather conditions were VMC with visibility of 10 statute miles. Local winds were recorded at 190 degrees at 25 knots, with gusts reaching 34 knots.
The investigation
Investigators determined that the damage to the aircraft was consistent with the main rotor blade flapping due to strong, gusty wind conditions, which led to the contact with the stabilizer. The operator reported that there were no mechanical malfunctions with the helicopter prior to the accident.