A Learjet 25D (N333CG) that crashed on approach to Salina, Kan., after losing
elevator control on June 12, was involved in a test flight in connection with obtaining an STC for the installation of Avcon delta fins. According to the NTSB, the jet was
destroyed and the two pilots were seriously injured. The flight-test profile was to
execute a high-speed dive to verify vibration and buffeting characteristics of the
aircraft before a delta-fin modification to the aft-fuselage. The aircraft was to dive from 43,000 ft to 20,400 ft, where a 1.5 g recovery would be made. During the descent, at about 24,000 ft, the control yoke began to vibrate rapidly after which elevator control was lost. Pitch control was established by using the pitch trim of the horizontal
stabilizer. During final approach the nose of the aircraft began to drop and the aircraft landed short of the runway. Avcon Industries of Newton, Kan., has STCs for
installation of its aft delta fins on Learjet 35s and 36s.