Incident Summary
A pilot reported that after initial takeoff, the cabin door came ajar. The flight returned and landed uneventfully, and the pilot closed the door. The flight then departed again, and the cabin door came ajar a second time. During the second return, the aircraft was landed with the landing gear retracted.
Aircraft Examination
Postaccident examination of the airplane revealed that the landing gear warning system was inoperative. The microswitch for the left throttle/gear warning system was shorted internally, and its roller arm was bent backward. The microswitch for the right throttle/gear warning system was not making contact with the throttle cam, and buckling of the throttle attachment plate was noted. Manual operation of the right microswitch would trip the circuit breaker. When the left microswitch was removed from the circuit, manual activation of the right microswitch activated the warning system.
Examination of the cabin door showed that when closed and latched, the outside door handle extended approximately 1.5 inches away from the door. A rusted and broken spring was observed. An operational check of the door latch mechanism revealed no binding, and the door locked. The upper latch went over center with the door latched, and the aft latch bolt locked properly. Two rivets that secure the pin guide assembly to the door were found broken.
Maintenance History
No written discrepancies pertaining to the cabin door were recorded between May 25, 2000, and September 7, 2001. During that same period, one discrepancy related to the gear warning system was noted: an entry indicating that the throttle warning horn circuit breaker popped during descent before landing gear extension. Airworthiness Directive (AD) 97-14-15, effective September 2, 1997, aimed at preventing unintentional cabin door opening from the interior, was complied with on October 4, 1997. The aircraft had accumulated approximately 1,281 hours since compliance at the time of the accident. A 100-hour inspection was signed off on September 17, 2001, and the aircraft had flown 38 hours since that inspection. The inspection guide for the aircraft includes checks for cabin door security and latching mechanism engagement and ease of operation.