On June 26, 2018, about 0850 mountain daylight time (MDT), a Bombardier Learjet 60 airplane, N57Z, sustained substantial damage when it was involved in an accident at Salt Lake City International Airport (KSLC), Salt Lake City, Utah. The two pilots and one technician were uninjured. The airplane was operated as a Title 14 Code of Federal Regulations Part 135 flight. The mission-specific modified airplane was registered to and operated by the Federal Aviation Administration (FAA) and was used to perform flight inspections of the National Airspace navigational systems. The captain was the pilot flying at the time of the accident. According to the flight crew, while taxiing to the runway for departure, the nose wheel steering seemed unusually sensitive and the airplane pulled slightly to the right. As they neared the runway threshold, they smelled what they thought was overheated brakes. The crew confirmed the position of the parking brake handle and the airplane moved more freely. The crew then cancelled their takeoff clearance and taxied the airplane to the runup area to allow the brakes to cool. Shortly thereafter, the control tower notified the crew that the airplane was on fire. The crew secured and then evacuated the airplane. The cockpit voice recorder (CVR) recorded the captain’s and first officer’s comments and revealed that, as the airplane taxied, both pilots felt that the airplane’s movement was jerky and they could hear a squealing noise that was not audible on the CVR. The captain indicated that the airplane wanted to pull to the right and that it seemed like more power was required to taxi. The first officer indicated that it felt like the captain was "riding" the brakes. Shortly thereafter, the captain realized the parking brake was not completely released. Examination of the airplane by an FAA inspector revealed that the right tire and landing gear were fire-damaged, and that the underside of the fuselage and right wing was substantially damaged due to the fire. A detailed examination of the airplane’s brake system revealed no pre-accident mechanical failures or malfunctions that would have precluded normal operation. The parking brake handle was located on the pedestal below the thrust levers and labeled PARKING BRAKE. The parking brake was operated by depressing and holding the toe brakes and pulling the parking brake handle to set the brakes. The parking brake was released by returning the handle to the off, or in, position. Whenever the parking brake handle was not fully in, the PARK BRAKE light would illuminate. A review of the Lear 60 Single Card Checklist, Revision 1, dated June 4, 2017, revealed that the Before Taxi, Taxi and Before Takeoff, Quick Turnaround, and Taxi checklists did not contain a line item for the release of the parking brake.