On March 12, 2000, approximately 0840 mountain standard time, a Learjet 60, N240FX, was substantially damaged when it overran runway 18 during landing roll at Jackson Hole Airport, Jackson, Wyoming. The airline transport pilot and the airline transport copilot were not injured. The airplane was owned by Bombardier Aerospace Corp., of Dallas, Texas, and was being operated by FlexJet, also of Dallas, Texas, under Title 14 CFR Part 91. Visual meteorological conditions prevailed at the time of the accident. The cross-country repositioning flight originated from Provo, Utah, approximately 43 minutes before the accident. An IFR flight plan had been filed. The pilots had spent the night in Provo, Utah, and they received this assignment on the morning of the accident. The captain said that they departed Provo with the airplane's thrust reversers mechanically pinned to the forward thrust position due to a maintenance discrepancy. As they approached Jackson, the airplane's cockpit voice recorder (CVR) documented that they planned to fly an Instrument Landing System (ILS) approach to runway 18 (6,299 x 150 feet, and -.611% gradient). The Automatic Weather Observation System (AWOS) recorded that the cloud ceiling was 1,200 feet above the ground and the wind was 030 degrees at 9 knots. Approximately 90 seconds before touchdown, the CVR recorded the AWOS wind as, 010 degrees at 7 knots (6.5 knot tailwind). The airport manager said that snow had fallen the night before the accident. He said that airport ground crews had plowed the runway and broomed it. The runway condition report prepared at 0516 indicated thin ice on the runway, and braking action was fair. The captain said that he was told that the braking action on the runway was fair. He flew the final approach at "Vref plus a couple of knots, continued the approach and made a normal touchdown approximately 800 to 1,000 feet down the runway." He said that he applied brakes approximately 500 to 800 feet after touchdown, and "noticed very little deceleration." The captain reported, on the National Transportation Safety Board's Pilot/Operator Aircraft Accident Report, that he used maximum braking effort to stop the airplane. The pilot reported to a FlexJet official, immediately after the accident, that he had used "emergency braking," because of the apparent lack of aircraft deceleration. Later, when interviewed by the NTSB Investigator-In-Charge, he could not remember if he had used emergency braking. According to the captain, at approximately runway midfield, the airplane began to slide left, then right, and then left back to centerline where "maximum braking continued." He said that they departed the end of the runway at approximately 40 knots, and continued forward (in an estimated 2 feet of snow) for approximately 160 feet. Subsequently, the nose landing gear separated and penetrated the airplane's pressure vessel. A manufacturer's representative said that if the emergency braking system were used, a very loud high pitched sound would be heard in the cockpit as the high-pressure air went into the brake lines. The CVR recorded a "high pitch" sound at 0839:44, and the pilots immediately began making verbal exclamations. The CVR documentation suggests that the airplane left the runway at 0840:00. The manufacturer's Airplane Flight Manual indicates that when emergency braking is utilized, the anti-skid protection is deactivated. The Airplane Flight Manual also limits landing on contaminated runways to the following: A. Winds must be zero or a headwind of less than 30 knots (i.e. no tailwind). B. The runway gradient must be between -1% and +2.2%. C. The anti-skid system must be operational.