NTSB Identification: DEN05FA032.
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Accident occurred Tuesday, December 07, 2004 in Montgomery, TX
Probable Cause Approval Date: 02/28/2006
Aircraft: Beech A45, registration: N141SW
Injuries: 2 Fatal.
NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.
While maneuvering during an upset recovery training flight, the left wing separated from the airframe, which resulted in an uncontrolled descent and impact with terrain. A review of an on-board video revealed the instructor and student were performing training maneuvers which included steep turns, stalls, accelerated stalls, unusual attitudes and recoveries from these to a wings level attitude using several techniques. During the final maneuver, the instructor asked the student to lower the nose to "about a hundred and forty knots", and afterwards told the student to slowly pitch the nose upward "until we're pointed straight up." The airplane was seen climbing vertically up and visual contact with the ground disappeared. The instructor then told the student to "pull the way we just did a minute ago and pull the airplane into a stall." A brief stall occurred, and then the airplane continued to pitch in the same direction, and its path resembled the remainder of an inside loop. As the ground reappeared into the view, the aircraft was inverted and descending. There was a slight roll to the left as the airplane was descending while its pitch attitude continued in the same trend toward a vertical nose down attitude. While in a steep nose down attitude (no sky visible in the view), the instructor told the student to "pull it into a stall right now." At that moment, the recording ended. The main wreckage came to rest on the side of a hard surface gravel road, and the left wing, left horizontal stabilizer, inboard section of left elevator, aft canopy frame, and a portion of the left wing skin were located in a wooded area approximately 0.4 miles southwest of the main wreckage. The true history of the airframe could not be substantiated. All applicable Federal Aviation Administration Airworthiness Directives had been complied with at the time of the accident. Examination of the wing and carry-through structure revealed the structure failed as the result of extensive and widespread fatigue cracking in the -31 and -33 channels and the -3 and -85 webs. The cracks in the channels were in hidden areas and probably could not have been directly detected without extensive disassembly of the structure. However, the cracks in the webs would have been easily detected, and the crack in the forward web apparently was detected, based on the stop-drilled hole and the notes in the maintenance records. The materials of the structure were in compliance with required specifications. However, the workmanship was poor as indicated by the trapped debris and damaged holes. This may have been acceptable standards of workmanship at the time of manufacture, but have since been recognized as having a large negative impact on fatigue life of the structures. The fractured hole in the rear spar was recently inspected with no indication of cracks. It is highly unlikely that the cracks initiated and grew to the current sizes in less than 40 hours of flight time since the inspection. The localized damage and enlargement of the hole could have reduced the effectiveness of the inspection. The fatigue cracking in the carry-through, the rear wing spar, and the horizontal stabilizer indicate that the fatigue life of the entire aircraft structure has been expended. It is strongly suspected that these conditions may exist in other T-34 airframes.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: the in-flight separation of the left wing as a result of extensive fatigue cracking throughout the wing carry-through structure. Full narrative available
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