Messerschmitt-Bolkow-Blohm BK 117 N504TJ accident near Hamburg, New York

Probable cause

Wear in the left cabin door assembly parts, which resulted in the door partially opening in flight, dislodging from the lower door track assembly, and then separating from the helicopter.

NTSB analysis

The pilot reported that, during a repositioning flight of the emergency medical services helicopter and while at cruise altitude, the flight nurse notified him and the paramedic that the left cabin door had partially opened. As the flight nurse and paramedic were attempting to close the door, it dislodged from the lower track assembly, pivoted up, and struck the main rotor system; the door subsequently separated from the helicopter. The pilot then initiated a forced landing to a field.

Examination of the door assembly revealed that both of the lower door's bracket guides and the aft lower catcher and guide assemblies were worn and that the door's upper sliders were worn down to their minimum tolerances. The Airplane Maintenance Manual states that, if one of the two sliders does not meet the minimum tolerance, "both sliders must be replaced with new ones." A review of the maintenance logbook revealed that the door assembly had been inspected 127 hours before the accident in accordance with an alert service bulletin but that no anomalies with the door assembly were noted at that time.

Text from the NTSB. Open the NTSB docket for ERA14LA223 for the full record.