Amateur-built Rans S-6S N280JH accident near St. Cloud, Minnesota

Probable cause

The airplane kit manufacturer’s recommended use of an improper nut type for securing the door hinge.

NTSB analysis

The pilot reported that while practicing touch-and-go landings he noticed that the nut from the forward door hinge of the left cabin door was missing. He decided to make a full stop landing to inspect further. During final approach, the door separated from the fuselage; the pilot was able to complete the landing without further incident. A postaccident examination confirmed that the forward door hinge bolt/nut assembly had backed-off during flight, which precipitated the door separating from the airplane.

The airplane kit manufacturer guidance indicated that a shear stop nut was to be used in the gull-wing (upward opening) door hinge assemblies. However, the Federal Aviation Administration (FAA) advises (in Advisory Circular 43.13-1B) that self-locking nuts, such as the type used on the accident airplane door, are not recommended for use on parts subject to rotation. The FAA further advises that the use of self-locking castellated nuts with cotter pins or lockwire is a more suitable method to secure rotating parts. According to the kit manufacturer, the accident flight was the first documented instance where a door separated during flight.

Text from the NTSB. Open the NTSB docket for CEN11LA077 for the full record.