On November 17, 2010, about 1630 central standard time, an experimental amateur-built Halbrook Rans S-6S airplane, N280JH, was substantially damaged when the left cabin door separated from the fuselage while on final approach to runway 31 at the St. Cloud Regional Airport (KSTC), near St. Cloud, Minnesota. The pilot and his flight instructor were not injured. The airplane was registered to Airflight LLC, and operated by a commercial pilot under the provisions of 14 Code of Federal Regulations Part 91. Day visual meteorological conditions prevailed for the flight, which was operated without a flight plan. The local flight departed KSTC at 1530. 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. While established on final approach, about 1/2 mile from the runway threshold, the door separated from the fuselage. The pilot was able to complete the landing without further incident. A postaccident investigation revealed that the door had impacted the left wing, aft fuselage, left elevator, and the left side of the rudder resulting in substantial damage. Further inspection confirmed that the forward door hinge bolt/nut assembly had backed-off during flight, which precipitated the door separating from the airplane. The airplane’s last condition inspection was completed on April 23, 2010. The airplane had accumulated 219 hours since new at the time of the accident. The builder guidance provided by the kit manufacturer (Rans Aircraft), including the parts listing for the airplane, indicated that a 3/16-inch shear stop nut (AN3641032A) was used in the door hinge assemblies. The gull-wing (upward opening) doors are designed to be easily removed from the fuselage for open-cockpit flight. The same door and hinge design was also incorporated in other Rans models. According to the kit manufacturer, the accident flight was the first documented instance where a door has separated during flight. According to Federal Aviation Administration Advisory Circular 43.13-1B (Acceptable Methods, Techniques, and Practices - Aircraft Inspection and Repair), the use of self-locking nuts, such as the type used on the accident airplane door, is not recommended for parts subject to rotation. Alternatively, the use of self-locking castellated nuts with cotter pins or lockwire is listed as a suitable method to secure rotating parts.