History of Flight
On September 3, 2008, at 1553 central daylight time, a Socata TB-20 Trinidad, registration N597TB, impacted terrain and caught fire near Cassville, Wisconsin, sustaining substantial damage. Visual meteorological conditions prevailed. The flight was conducted under 14 CFR Part 91 without a flight plan. The commercial pilot in the left seat sustained serious injuries, and the private pilot in the right seat sustained fatal injuries. No injuries occurred on the ground.
The flight originated from Dubuque Regional Airport (DBQ), Dubuque, Iowa, and was en route to Prairie du Chien Airport (PDC), Prairie du Chien, Wisconsin, when it diverted to Cassville Municipal Airport (C74), Cassville, Wisconsin.
A line worker at the fixed base operator refueled the airplane at 1530. According to air traffic control transcripts, N597TB was cleared for takeoff from DBQ at 1353:22 and acknowledged at 1353:28, with no further radio transmissions from the aircraft.
The left seat pilot stated that he and the right seat pilot preflighted the airplane and planned to pick up a friend at PDC. He reported that the right cabin door opened in flight after an unknown time following takeoff. The right seat pilot held the door closed, and the left seat pilot decided to divert to C74, about 21 nautical miles northwest of DBQ. He stated that the approach to C74 "didn't look good," so he performed a go-around during which the right cabin door opened again and the airplane rolled to the right. He said he "lost control" of the airplane and did not know whether a stall occurred or what caused the door to open.
Personnel Information
The left seat pilot was enrolled in the University of Dubuque's Aviation Program and held a commercial pilot certificate with airplane single-engine land and instrument ratings. He had accumulated 329 total flight hours, including 53 hours in Socata TB-20 Trinidad airplanes.
He stated that he had received flight instruction regarding an airplane door opening in flight, using a Cessna airplane with an in-flight door opening.
The right seat pilot was enrolled in the same program in the commercial airplane course. He held a private pilot certificate with airplane single-engine land and instrument ratings, with about 181 total flight hours, including 2.1 hours in the TB-20. He had not completed the required 10 hours of training within the commercial curriculum to receive an instructor sign-off for the TB-20.
Aircraft Information
The 1997 TB-20, serial number 1817, was equipped with gull-wing type doors. For serial numbers 1-9999, doors were made of metal. The doors articulate around a hinge on top of the fuselage, and opening and closing are slowed by a compensating cylinder on the rear part of the door.
According to the manufacturer's representative, the TB-20 had not been flight tested with an open cabin door. The Pilot's Information Manual, Section 2, Limitations, Use of Doors, states: "Flight with doors open and ajar is prohibited."
Wreckage and Impact Information
The main wreckage rested between two motel cottages about 500 feet from the approach end of runway 11 (3,000 feet by 50 feet, asphalt) at C74. The airplane was upright on a tail-to-nose heading of about 140 degrees. The airplane and both cottages were consumed by fire. Slash marks consistent with propeller strikes were noted in the motel driveway.
The landing gear was extended, and the flap jack screw extension indicated a 10-degree flap extension. The fuel selector was in the right fuel tank position.
The right-hand door hinge assembly was attached to the remaining fuselage and door. Only one of four door hook assemblies was found, separated from the door and within the main wreckage. The door hook assembly had two mounting screws attached to a portion of the remaining door, each with three washers. The door hook assembly spring was in place.
Only one of four access door mechanism latching ring assemblies was found. The latch ring was metal, and fracture surfaces within the assembly had a granular appearance consistent with overload.
Tests and Research
Federal Aviation Administration (FAA) aircraft registry records show 23 airplanes registered to the University of Dubuque, including four Socata TB-20 Trinidad airplanes: N597TB (S/N 1817), N1866S (S/N 1866), N1887S (S/N 1887), and N1909S (S/N 1909).
According to the manufacturer's representative, N597TB was equipped with steel door hook assemblies during manufacture. The University's Director of Maintenance stated that the other TB-20 door hook assemblies were checked with a magnet and all were reportedly steel. He said there were no previous reports of cabin doors opening in flight on any of the TB-20s.
The University's maintenance procedures use "squawk" sheets in the aircraft dispatch book, which was not recovered. No archive of squawk sheets or maintenance discrepancies is kept. The University does not voluntarily submit reports to the FAA Service Difficulty Reporting (SDR) database and is not required to retain discrepancies or submit SDRs.
A query of FAA Service Difficulty Reports for TB20 airplanes on November 25, 2008, yielded 34 records, with only one related to a cabin door.