Accident Details
A helicopter on an instructional flight was observed by witnesses flying along a beach at an altitude between 100 and 200 feet above ground level. Approximately 45 minutes after departure, one witness reported that the helicopter made contact with a kite. Immediately following the contact, witnesses heard a loud cracking or popping sound, after which the main rotor separated from the helicopter. The aircraft then entered an uncontrolled descent and impacted the water.
Examination Findings
Post-accident examination of the main rotor mast fracture surfaces showed signatures consistent with overload. The cockpit exhibited damage consistent with contact by the main rotor blades. Investigators noted no evidence of any pre-impact mechanical malfunction or failure.
Relevant Handbook Information
The pilot's operating handbook for the helicopter contains a warning regarding low-G (weightless) flight conditions. It states that pushing the cyclic forward following a pull-up or rapid climb, or even from level flight, produces a low-G condition and that mast bumping can occur. The handbook further notes that severe in-flight mast bumping usually results in main rotor shaft separation and/or rotor blade contact with the fuselage.