General Aviation News will often reprint excerpts from US National Transportation Safety Board (NTSB) accident reports, including one dated March 2011 that involved a Cessna 310 with a new autopilot system in Smyrna, Tennessee, that proved fatal for the pilot.
According to the accident investigation, the technician who performed the autopilot installation and troubleshooting work on the aircraft had accompanied the pilot on the first flight of the day and he indicated the pilot seemed to be unfamiliar with the autopilot operation:
The pilot worked the yoke against the autopilot, and, in response, the autopilot ran the elevator trim to the full nose-down position. The pilot responded by swiping both panel-mounted master switches to the off position then attempted to trim the airplane with the electric trim that he had just disabled.
The technician even stated the pilot’s actions had scared him and showed the pilot really didn’t have control of the airplane as he appeared to be “very disoriented with the new technology.”
The second flight of the day turned out to be the fatal flight and was the fourth in a series of maintenance acceptance flights after the installation of a new avionics suite and a new autopilot system. All of the autopilot system’s features were tested satisfactorily on the ground. However, the system did not yet function as designed in flight because the aircraft had a pitch-porpoise tendency when the altitude hold feature was engaged.
During the fatal accident flight, its believed the airplane pitched down as a first action of the pitch porpoise after the autopilot was engaged. The pilot likely pulled back on the yoke to try and stop the aircraft’s decent while the autopilot would have commanded the trim further toward the nose-down position. The aircraft ended up descending in an unrecoverable nose-down attitude.
The NTSB ruled that the probable cause of the accident was the pilot’s improper response to a known autopilot pitch divergence anomaly while the pilot’s decision to perform a test flight on a system for which he lacked a complete working knowledge was ruled a contributory factor. However, a commenter named Guido posted the following comment:
The newly installed autopilot doesn’t work correctly and all blame goes to the pilot? The installer dodged one that time……
Someone named Dennis Reiley then responded by commenting:
I agree Guido, what use is an auto pilot that when engaged in level flight immediately causes the aircraft to pitch the nose down? The answer is none! May I never encounter that technician nor his work.
Both comments are good points as the pilot is not around to provide his side of the story – meaning the NTSB must rely on the testimony of any technician or mechanic involved in the installation work. Moreover and if the pilot’s actions were “scary,” why did the technicians or mechanics allow the pilot to go up for another flight on his own?