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On July 28, 1996, at 1408 mountain daylight time, a Slaybaugh Mustang II, N16WY, was destroyed when it impacted terrain while descending at Crested Butte, Colorado, The commercial pilot (a USAF instructor pilot) and his passenger were fatally injured. Visual meteorological conditions prevailed, and no flight plan was filed for the personal flight conducted under Title 14 CFR Part 91. The flight originated at Gunnison, Colorado, on July 28 approximately 1330.
The accident airplane and another airplane, a Long EZ (also flown by a USAF instructor pilot), were participating in Crested Butte's 22nd annual Aerial Weekend. According to the Long EZ pilot, they were flying abeam of each other over the town at 1200 to 1300 feet agl. The maneuver they were performing was described as a converging turn --- the Long EZ climbing and turning left and the Mustang II climbing and turning right --- with the intention of rejoining. Prior to starting the maneuver, the Mustang II pilot said, "I don't have enough room, hold on a sec." The Long EZ pilot said he interpreted this remark to mean his wingman was too close to a mountain to the south to make a right turn. Shortly thereafter, the Mustang II pilot reported he was ready and the two pilots commenced the maneuver. The Long EZ pilot said that as he completed 45 degrees of the turn, he saw the Mustang II "in what seemed to be 120-135 degrees of left bank" and "approximately 80 degrees nose low" attitude. He lost sight of the airplane momentarily and when he saw it again, the airplane had "approximately 20-30 degrees of left bank" and it appeared the pilot "was trying to pull out from the dive." He then observed the airplane impact the ground.
A retired Air Force brigadier general (and former USAF fighter pilot, instructor pilot, and accident investigator) observed the maneuver and subsequent accident from a nearby golf course. In his statement the general wrote, "I observed the aircraft separating from loose formation with (a Long EZ), taking up a general heading of south. The two had been observed making passes over Crested Butte and Mount Crested Butte since early afternoon the day prior. In each (instance) when I observed, flight conduct appeared routine, safe, and well within FAA restrictions.
"After the aircraft broke formation, the (Mustang II) entered what appeared to be a routine diving turn. It did not appear to be a wing-over, as I did not recall seeing the nose (which was pointed generally towards me) come above the horizon. Neither did the diving turn appear to be loading excessive G's on the aircraft. It looked routine and normal. My impression was the pilot was reversing course to execute a low level pass on the town of Crested Butte. Just at that point of perception, the aircraft continued feeding in more bank and I then perceived he was lining up for his run-in as the wings continued on to hear 180 degrees of bank. I saw nothing extraordinary to cause concern. It appeared he was planning on rolling on through to lose a little more altitude using the rolling G pressure to hold airspeed in tolerances. At this point, the nose began to fall. My thought then was that he was steepening his dive a little excessively which was a surprise...since there had been absolutely no hot-shotting. As the attitude became close to vertical, it was obvious quick recovery would be necessary to avoid a crash."
Several other ground witnesses submitted written statements (enclosed). One witness said the airplane "seemed to try a vertical assault. Near the top, it seemed to me that he 'stalled' the wings of the plane by not having enough forward airspeed. At this point, I heard (engine noise) from the plane. He then went nose down and spiraled into the ground at almost a 90 degree angle. As he went from nose up to nose down, as the fuselage passed horizontal, the wings of the plane were almost vertical (plane was on its side)." Another witness said she saw the plane "spiraling to the ground." Three other witnesses, however, said the airplane "went into a dive" and "went straight down."
The pilot, a U.S. Air Force captain, was on active duty and stationed at Vance Air Force Base, Enid, Oklahoma, as a T-38 instructor pilot. Flight times given elsewhere in this report are a combination of records submitted by the Air Force and a civilian pilot logbook recovered from the wreckage. According to this logbook, the pilot first flew N16WY on December 9, 1995. The last recorded flight was on July 26, 1996. During these 19 months, the pilot had logged no less than 142.1 hours in the Mustang II.
Maintenance records recovered from the wreckage indicate construction of the airplane was completed on January 17, 1992. An overhauled engine was installed on July 27, 1992. The propeller had been overhauled on April 11, 1991. The airplane had received annual conditional inspections, the last being on December 7, 1995. At that time, the airplane had accumulated 110.1 hours time in service. The pitot-static system, altimeter, and transponder were last tested on October 4, 1993.
Entries made in the builder's flight test log on May 27 and June 24, 1993, noted the airplane "broke left" during both power on and power off stalls.
Crested Butte, Colorado, is situated at a surveyed elevation of 8,895 feet msl, and is approximately 26 nm north-northwest of Gunnison County Airport (elevation 7,673 feet msl) from which the airplanes departed. At 1354 (14 minutes before the accident), the airport altimeter setting and temperature were reported to be 30.42 inches of mercury and 79 degrees F. The airport pressure and density altitudes were computed to be 7,173 and 10,016 feet msl, respectively.
A sewage treatment facility, located approximately 1/2 to 3/4-mile from the accident site, was equipped with a temperature recording device. At the approximate time of the accident, the temperature was 76 degrees F., which was the high temperature for that day. The pressure and density altitudes at Crested Butte were computed to be approximately 8,385 and 11,316 feet msl, respectively (see "Tests and Research").
WRECKAGE AND IMPACT INFORMATION
The accident site was located in a marshy area about 1 mile south of Crested Butte. The airplane was embedded in soft earth and required a heavy lift helicopter for its removal. The crater was approximately 48 inches deep. Dirt was pushed up on its forward lip.
The forward and aft portions of the fuselage were aligned on magnetic headings of 196 degrees and 155 degrees, respectively. The left wing trailed the fuselage by 25 degrees, and the right wing led the fuselage by 10 degrees. Both wing leading edges had accordion type crush damage that was more pronounced on the left wing. All structural components remained attached to the airframe, with the exception of the left flap, which was located about 5 feet away. The left side of the firewall and instrument panel were crushed aft by 24 degrees. After removal from the accident site, crush lines on the left and right of the nose were measured at 15 degrees and 33 degrees, respectively.
The elevators and ailerons were attached to the torque tubes, and the rudder and elevator trim tab were attached to the control cables routed through various pulleys. All the pulleys were found in place. Flight control continuity was compromised at the cockpit. The control cables breaks were frayed and the torque tube breaks showed some "necking down."
Examination of the cockpit disclosed the throttle, propeller control, and mixture were full aft. The throttle was bent over 180 degrees. The fuel selector was positioned on the left tank, and the electric boost pump was off. The flaps were retracted. Center of gravity computations indicated the airplane, as loaded, was within limits.
Both blades of the Hartzell constant speed propeller remained attached to the hub, and the hub remained attached to the crankshaft flange. The descending blade was bent 18 degrees aft at midspan, with some forward bending near the tip. Some gouging and scratching were noted on the cambered surface. The ascending blade was bent 40 degrees aft at midspan and bore considerable longitudinal scratching on the cambered surface.
MEDICAL AND PATHOLOGICAL INFORMATION
An autopsy (MMH-CA-64-96) was performed on the pilot by Dr. Thomas Canfield at Montrose, Colorado, Memorial Hospital. Toxicological protocol was performed by FAA's Civil Aeromedical Institute in Oklahoma City, Oklahoma. According to its report (#9600189001), there was no evidence of carboxyhemoglobin in the blood, and there was no evidence of ethanol or drugs in the urine. Cyanide analysis was not possible due to a lack of a suitable specimen.
TESTS AND RESEARCH
The engine and accessories were disassembled and examined at the facilities of Beegles Aircraft Service, Inc., Greeley, Colorado, on July 31, 1996. Both magnetos produced spark when rotated by hand. Ignition harness continuity was established. The fuel flow divider was attached and secure. The diaphragm was undamaged and each fuel nozzle was secure. Residual fuel was found in the flow divider. Fuel was found inside the engine driven fuel pump. The vacuum pump drive was intact, and the pump rotated freely. The propeller governor oil line was securely fastened. No leaks were discernible.
The computed Crested Butte density altitude was 11,316 feet. At that altitude, according to Textron Lycoming Operators' Manual #60297-16 (Section 8, page 8-4), the engine would be capable of producing approximately 68.3% (109.2 hp) of sea level rated horsepower (160 hp). This calculation assumes the propeller is in the low pitch/high rpm configuration.
The wreckage was released to the owner's representative on August 2, 1996. Parties to the investigation included the Federal Aviation Administration and Textron Lycoming. The United States Air Force provided an accredited representative.