What happened
On May 4, 2014, at approximately 1740 EDT, a Messerschmitt-Bolkow-Blohm BK 117 A-4, registration N504TJ, sustained substantial damage during a cruise flight near Hamburg, New York. The aircraft, operated by Mercy Flight Incorporated, was performing a positioning flight from the Women and Children's Hospital Heliport (7NK9) in Buffalo.
While the helicopter was at a cruise altitude of 3,000 feet MSL, the flight nurse notified the pilot and flight paramedic that the left sliding door had opened several inches. As the crew attempted to close the door and the pilot reduced forward airspeed, the lower portion of the door disulated from the lower track assembly and pivoted upward. The door struck the main rotor system and subsequently separated from the airframe. The pilot performed a forced landing in a baseball field. There were no injuries to the pilot or the two passengers.
The investigation
An examination of the door assembly and the main rotor blades was conducted at Airbus Helicopters Incorporated under FAA supervision. Investigators found that the main rotor blades sustained substantial damage.
Regarding the door assembly, the following was observed:
- The upper sliders exhibited excessive wear.
- Both lower door bracket guide assemblies were damaged by impact and partially separated from the composite door structure.
- The aft lower catcher and guide assemblies showed impact damage and partial separation from the door structure.
- A 45-degree section of the forward catch was worn away.
- The door latch was impact damaged but appeared to function properly.
Maintenance records indicated that the door assembly had been inspected 127 hours prior to the accident per an alert service bulletin, with no anomalies noted at that time. However, the maintenance manual specifies that if the minimum measurement of 1.0 + 0.5 mm is not met on one slider, both sliders must be replaced. The sliders on N504TJ were found to be at the minimum tolerance level of 0.5 mm.