Accident Summary
On May 4, 2014, at approximately 1740 eastern daylight time, a BK-117 A-4 helicopter, registration N504TJ, was substantially damaged while in cruise flight near Hamburg, New York. The cabin door separated from the aircraft and struck the main rotor blades. The commercial pilot and two passengers were not injured. The helicopter, operated by Mercy Flight Incorporated under 14 CFR Part 91 as a positioning flight, had departed Women and Children's Hospital Heliport (7NK9) in Buffalo, New York, at 1730. Visual meteorological conditions prevailed, and no flight plan was filed.
Pilot Report
According to the pilot, the helicopter was cruising at 3,000 feet mean sea level when the flight nurse reported that the left sliding door had opened several inches. The flight nurse and flight paramedic attempted to close the door. As the pilot reduced forward airspeed, the lower portion of the door dislodged from its lower track assembly, pivoted upward, and struck the main rotor system. The door then separated from the airframe. The pilot initiated a forced landing to a baseball field, and the door was recovered for examination. The pilot stated that the flight paramedic had performed a preflight walk-around, inspected the doors, and secured his own door before takeoff. The door caution lights were extinguished prior to departure and did not illuminate until the left door opened at cruise altitude.
Post-Accident Examination
A cursory examination by the operator found the door broken into several pieces. The airframe latch assembly showed no anomalies, but the door latch and spring assembly were questioned for possible failure. The operator noted that they lacked engineering staff to further analyze the latch assembly. The door and main rotor blades were examined at Airbus Helicopters Incorporated under FAA supervision. The main rotor blades were substantially damaged, and the door's upper sliders exhibited excessive wear. Both lower door bracket guide assemblies were impact-damaged and partially separated from the composite door structure. Guide brackets on the door assembly were worn. The aft lower catcher and guide assemblies showed impact damage and partial separation, with a 45-degree worn-away section at the forward catch. The door latch, though impact-damaged, appeared to operate properly. According to Maintenance Manual MBB-BK117 Chapter 21, page 16B, sliders must be replaced if the minimum measurement of 1.0 + 0.5 mm is not reached on either slider; the sliders were at the minimum tolerance of 0.5 mm. Logbook excerpts indicated the door assembly had been inspected 127 flight hours prior to the incident in compliance with Alert Service Bulletin MBB-BK117 No. ASB-MBB-BK117-20-111, with no anomalies noted.