On May 7, 2000, an Eurocopter BK-117-A4 (registration N911NC) was involved in an aviation accident near Cincinnati, OH. Investigators recorded the probable cause as: the pilot's misjudgment of his closure rate, while turning to land on the rooftop helipad, which resulted in a collision with the building. Factors in the accident were the tailwind and the stuck windsock. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
A helicopter struck a hangar and the landing area during a night approach to a rooftop helipad. The pilot reported a loud bang and uncontrolled rotation. Examination revealed tail rotor blade fragmentation and strike marks on the hangar.
Incident Details
The pilot reported approaching a lighted rooftop helipad from the southwest at night under light wind conditions. The helipad and an adjacent hangar were directly ahead. The pilot initiated a right pedal turn to align the helicopter toward the south. During the turn, a loud bang was heard, and the helicopter began an uncontrollable right-nose rotation. The pilot lowered the collective, causing the helicopter to strike the landing area.
Examination Findings
Post-accident examination of the helicopter revealed that the tail rotor blade tips were fragmented. Corresponding strike marks were found on the top corner of the hangar, consistent with contact from the tail rotor blades. The hydraulic pump and tail rotor actuator were examined and showed no evidence of failure or malfunction.
Environmental Conditions
The pilot's approach was constrained to the southwest because other helicopters occupied the ramp. The wind was estimated from 220 degrees at 10 knots with gusts to 15 knots. Personnel noted that the windsock occasionally became caught on its support structure, failing to indicate the true wind direction and speed. No other wind information was available to the pilot.