Incident Overview
On November 8, 2011, at approximately 1100 mountain standard time, a Piper PA-31T Cheyenne II, registration N39EH, executed a precautionary landing at Cheyenne Regional/Jerry Olson Field Airport (CYS) in Cheyenne, Wyoming. The landing followed the in-flight separation of the airplane's main cabin door, which occurred about 20 miles north of the airport. The aircraft, registered to La Stella of Wilmington, Delaware, and operated by Travelaire Service, Inc., of Pueblo, Colorado, was conducting an on-demand air medical flight under 14 Code of Federal Regulations Part 135. Visual meteorological conditions prevailed, and an instrument flight rules flight plan was filed for the cross-country journey. The flight had originated from CYS at approximately 1040, with Sheridan, Wyoming (SHR) as its intended destination.
Pilot Report
The pilot reported that while climbing through 7,500 feet en route to a planned altitude of 12,500 feet, a pressurization issue was noted. The airplane was leveled at 8,500 feet, and the pilot consulted the checklist but was unable to resolve the problem. A turn back to the departure airport was initiated. Shortly thereafter, the master caution horn sounded, and the door unsafe light illuminated, followed by a rush of air in the cockpit. The pilot returned to CYS and landed without further incident.
Medical Crew Report
The medical flight crew reported that approximately 20 minutes after takeoff, the main cabin door opened in-flight and subsequently separated from the aircraft.
Door Examination
The main cabin door was recovered and examined by a senior materials engineer at the National Transportation Safety Board's materials laboratory in Washington, DC. Examination revealed that the door hinge was fractured at the lower end of the door, while the hinge remained attached to the airplane. Rivets at the forward end of the hinge line were fractured, and the door outer skin was fractured along the hinge rivet line. Skin fractured around several rivets, with a saw-tooth pattern of fracture propagation indicative of forward-to-aft progression. Deformation was observed on the outer skin at the lower end of the door, consistent with the door rotating downward and aft relative to the hinge attachment. Fracture surfaces exhibited deformation and features on slant planes consistent with ductile overstress fracture. No evidence of preexisting cracks was found.
Internal panels were disassembled to examine the door structure and latching mechanism. All pushrods, latch pins, and associated bellcranks were in place and intact. Wear was observed on the upper side of the forward pins at the middle and upper positions; however, the latching mechanism travel and pin extension were correct. No other anomalies were noted. A complete materials laboratory examination report is contained in the public docket for this accident.