Background
Three company pilots, including the president of Sky Train Air Inc., were returning to McAllen, Texas, from Thermopolis, Wyoming. They made a fueling stop in Casper, Wyoming.
Refueling Stop
At the Casper airport, a lineman added 320 gallons of Jet-A with Prist to the left wing tank and 260 gallons to the right, noting a fuel imbalance. The crew was aware of this imbalance. A total of 585 gallons filled the wing tanks to capacity; no fuel transferring was required. The lineman believed the fuselage tank was full because the nosegear strut extended 6 to 12 inches. A ground power unit was used to start the engines, and no issues were observed during preflight checks.
Departure and Flight
The president, listed as pilot-in-command, filed an IFR flight plan to McAllen at Flight Level 450, true airspeed 450 knots, with a route via J170 to Denver, J17 to Amarillo, J17 to San Antonio, J25 to Corpus Christi, then direct to McAllen. En route time was estimated at 2 hours 20 minutes with 3 hours 40 minutes of fuel. A weather briefing was not provided as the crew already had weather information. The crew received taxi clearance from Casper Tower at 1352:08 and departed Runway 21 at 1357:02.
Loss of Contact and Crash
At 1449:39, while cruising at FL450, the crew made initial contact with Albuquerque ARTCC Sector 71, squawking transponder code 0670. Around 1458, a new controller took over. At 1459:36, he issued a frequency change but received no response. The controller noticed no transponder target and made several attempts to contact the aircraft until 1501:39. Radar contact was lost at 1458:07 at FL447.
Five witnesses in Felt, Oklahoma, heard an aircraft overhead at very high speed. One witness reported a vibration indicating overspeeding, and another stated the aircraft appeared to be about to break the sound barrier. One witness momentarily saw the aircraft in a 45° descent with wings rocking up and down. All witnesses heard an explosion and saw a mushroom cloud of black smoke. The aircraft crashed 2.5 miles southwest of Felt at approximately 1502 local time. All three occupants were killed.
Probable Cause
The official probable cause states: A loss of control, possibly initiated by an unexpected encounter with moderate to severe clear air turbulence, which caused the aircraft to depart the narrow flight envelope boundaries in which it was operating and from which recovery was not effected; the flightcrew's lack of adequate training and experience in the Learjet; and the aircraft's marginal controllability characteristics near and beyond the boundaries of its flight envelope. Contributing to the accident was the flightcrew's probable extension of the spoilers in an overspeed situation, a procedure that had been prescribed in the approved aircraft flight manual until 1 year before the accident.