Aircraft: Cessna 310. Injuries: 1 Fatal. Location: Smyrna, Tenn. Aircraft damage: Substantial.
What reportedly happened: According to the technician who performed the autopilot installation and troubleshooting work on the airplane, when he accompanied the pilot on the first flight that day 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 said that the pilot’s actions scared him and demonstrated to him that the pilot really didn’t have control of the airplane. The mechanic told investigators that the pilot appeared to be “very disoriented with the new technology.”
The accident flight was the second flight of the day and was the fourth in a series of maintenance acceptance flights after the installation of a new avionics suite and a new autopilot system. Before the accident flight, all of the features of the autopilot system tested satisfactorily on the ground but did not yet function as designed in flight, as the airplane demonstrated a pitch-porpoise tendency when the altitude hold feature was engaged.
Based on the available evidence, it is likely that, after autopilot engagement, the airplane pitched down as a first action of the pitch porpoise. In response to the downward movement of the airplane, the pilot likely pulled back on the yoke in an effort to arrest the airplane’s descent. As a result, the autopilot would have commanded the trim further toward the nose-down position. Such a scenario would require a greater and ever-increasing physical effort by the pilot to overcome the growing aerodynamic force that would result from the nose-down pitch and increasing speed of the airplane. The airplane descended in an unrecoverable nose-down attitude.
Probable cause: The pilot’s improper response to a known autopilot pitch divergence anomaly. Contributing to the accident was the pilot’s decision to perform a test flight on a system for which he lacked a complete working knowledge.
This March 2011 accident report is provided by the National Transportation Safety Board. Published as an educational tool, it is intended to help pilots learn from the misfortunes of others.