RAMAH, CO, USA
N28TP
NORTH AMERICAN T-28B
WHILE MANEUVERING IN VISUAL METEOROLOGICAL CONDITIONS, THE AIRPLANE SUSTAINED AN IN-FLIGHT STRUCTURAL FAILURE THAT RESULTED IN SEPARATION OF THE LEFT AND RIGHT WINGS AND THE HORIZONTAL TAIL ASSEMBLIES. INVESTIGATION REVEALED THAT THE PRINCIPAL FAILURE MODES WERE GROSS POSITIVE (UPWARD) OVERLOADS ON BOTH THE WINGS AND THE HORIZONTAL STABILIZERS, WITH FAILURE OF THE STABILIZERS OCCURRING PRIMARILY DUE TO POSITIVE UPWARD LEADING EDGE TORSION. THE PILOT-OWNER POSSESSED A CURRENT LETTER OF AUTHORIZATION TO SERVE AS PILOT-IN-COMMAND OF THE T-28; THE SECOND PILOT'S LETTER OF AUTHORIZATION HAD EXPIRED.
HISTORY OF FLIGHT On July 9, 1995, at 0852 mountain daylight time, a North American T-28B, N28TP, was destroyed when it broke up in flight and impacted terrain while maneuvering three miles west of Ramah, Colorado. The two private pilots were fatally injured. Visual meteorological conditions prevailed at the time, and no flight plan was filed for the personal flight conducted under 14 CFR Part 91. The local flight originated at Englewood, Colorado, on July 9 at 0831 MDT. One witness said she saw the airplane in a wings level, shallow descent and travelling "at a high rate of speed, faster than the other airplanes you see around here." The airplane was south of U.S. Highway 24 and flying in an easterly direction. She said the airplane entered a left bank with its right wing and nose up. She heard "popping" noises and said the airplane appeared to "explode" in midair. Another witness said she saw the airplane "humming right along." She then heard a loud boom, looked up, and saw pieces of the airplane falling slowly to the ground. PERSONNEL INFORMATION According to an FAA Flight Standards District Office inspector in Denver, Colorado, the pilot-owner was issued a Letter of Authorization (LOA), dated September 22, 1994, to serve as pilot-in-command of the North American T-28B. The inspector said an LOA for a reciprocating engine-powered airplane is valid for 12 calendar months. The other pilot held similar LOAs to serve as pilot-in-command of the T-28B airplane. The only LOAs found in his personal files were dated March 27, 1989, January 17, 1990, and February 6, 1990. FAA reported having no current LOA on file for the second pilot. FLIGHT RECORDERS Two video cameras were aboard the airplane: one was mounted in the left wing leading edge (originally used for armament), and the other was mounted in the rear cockpit and aimed at the face of the rear seat occupant. The tape deck and cassette were recovered from the wreckage. The cassette tape was examined by the NTSB's CVR laboratory. According to the technician, the tape was blank. WRECKAGE AND IMPACT INFORMATION Both wings separated from the airplane; the ailerons remained attached but both flaps separated. Both wings were broken in two pieces at the outboard splice. Both horizontal stabilizers separated from the airplane, and both elevators separated from the horizontal stabilizers. The left elevator was broken in three places, and the right elevator was broken in two. All separated components were found within 1/4-mile of the fuselage. The fuselage was on its left side on the south side of U.S. Highway 24. The vertical stabilizer and rudder remained attached to the airframe. The engine was buried in the middle of the highway (see attached Wreckage Diagram). MEDICAL AND PATHOLOGICAL INFORMATION Autopsies were performed on both occupants by the El Paso County Coroner's Office. FAA's Civil Aeromedical Institute (CAMI) performed toxicological screens on both occupants. According to CAMI's reports, 1890.5 ug/ml salicylate (a compound found in aspirin) was detected in the pilot-owner's urine; none was detected in the kidney fluid. Chloroquine (a drug used in the treatment of malaria) was found in the second pilot's liver tissue fluid. According to a CAMI toxicologist, he did not consider either of these findings to be significant or causal to the accident. FIRE A small fuel and oil-fed fire erupted on the highway where the engine was embedded. There was no evidence of an in-flight airframe fire. SURVIVAL ASPECTS Both occupants wore parachutes. The second pilot was found in the front seat with both seat belt and shoulder harness fastened. The pilot-owner was found about 30 feet from the fuselage. His parachute had not been deployed. TESTS AND RESEARCH An NTSB specialist in airframe structures and an independent metallurgist from the University of Denver examined the wreckage. According to the Structures Group Chairman's Report, the lower main (rear) spar cap on the right horizontal stabilizer main spar showed evidence of "a tensile failure and upward bending deformation." The upper main spar cap "was twisted (forward) relative to the stabilizer, reflecting failure-separation of the stabilizer in an upward bending, aft-twisting motion." The upper surfaces of the left horizontal stabilizer showed evidence of "pronounced upward bending along a line extending from the middle hinge location forward and inboard at about a 30 degree angle." A section of the lower spar cap showed evidence of "a tensile failure." The inboard skin of the right elevator showed evidence of "distortion and diagonal buckling consistent with relative movement of the outboard section in an aft direction." Damage to the right elevator trim tab was indicative of "relative movement of the elevator in an aft direction." Both elevators showed evidence of "elevator overtravel...in the up direction." The left elevator and trim tab exhibited similar damage. The right wing's root fairing deformation was "consistent with upward bending." The left wing's forward and rear top spar caps and lower forward spar web section showed evidence of tensile overload, and the inboard portion of the forward top spar cap and web were "twisted (relative to the wing section) in the wing leading edge down direction...Deformation of the wing root fairing was consistent with upward bending or deformation of the wing. Both upper and lower spar caps of the wing center section-carry through structure were bent upwards and showed evidence of tensile overload. According to a University of Denver metallurgist who examined the airplane, all the fractured surfaces were consistent with, and indicative of, tensile overload. He said there was no evidence of fatigue, corrosion, material or manufacturing defects. ADDITIONAL INFORMATION The wreckage was released on July 20, 1995, to a representative of the pilot's estate. The release was accepted on September 13, 1995.
THE AIRCREW ALLOWED THE AIRPLANE'S DESIGN STRESS LIMITS TO BE EXCEEDED.
Source: NTSB Aviation Accident Database
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