LAX08FA117 · Cessna 510

As the airplane approached the destination airport, the pilot selected vertical speed mode on the autopilot. While descending, the copilot's Primary Flight Display (PFD) began to flicker. About 5 minutes later, as the airplane transitioned through 28,000 feet mean sea level, the left PFD flashed a "PFT" alert indicating that the autopilot had disconnected. The pilot said he immediately felt heavy control forces on the control yoke that he had to exert to fly the airplane. Shortly thereafter, the pilot discovered that the electric pitch trim was not operational. While hand-flying the airplane the pilot entered instrument meteorological conditions as the airplane descended through a 2,400-foot-thick cloud layer. Thereafter, the pilot continued a visual approach to the 4,897-foot-long runway. The pilot noted that he was overwhelmed with the electrical failures and fatigued from maneuvering the airplane by hand for such a long duration (which he approximated was around 45 minutes). The airplane crossed the runway threshold about 15 knots faster than the correct landing speed and the airplane touched down past the midpoint of the runway. The pilot realized that despite his braking attempts the airplane was going to continue off the runway surface over a small downsloping cliff at the end. He determined that he would not be able to abort the landing due to the airplane's diminished ground speed and elected to perform a 180-degree turn. The airplane ground looped, coming to rest in a dirt area south of the runway; the main landing gear collapsed and the flaps folded under the wings. According to the pilot, he never attempted to reset the autopilot system. The autopilot was designed for an automatic disengagement when there is a system failure, invalid sensor data, or yaw damper failure. On the manufacturer's current Pilots' Abbreviated Checklist, Emergency Procedures section, it states that if the autopilot preflight test fail warning (red "PFT" warning on the PFD) illuminates, the pilot should reset the associated circuit breaker to clear the fault. A post-accident examination of the airplane's systems revealed no mechanical malfunctions or failures, with the exception of a flickering PFD screen.

Verbatim NTSB analysis and probable cause from the NTSB dataset