CESSNA 310R — Smyrna, TN

What happened

Shortly after departure, the airplane entered a rapid, full-power, near-vertical descent from about 2,700 feet above ground level to ground impact. The elevator trim actuator was found in the full tab-up or airplane nose-down position after the accident. The 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.

According to the technician who performed the installation and troubleshooting work on the airplane, he had accompanied the pilot on the first flight that day and had spoken to an autopilot manufacturing representative upon their return. Another troubleshooting procedure was performed, the technician left for lunch, and the pilot departed alone on the accident flight. When describing a previous test flight, the technician stated that 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 (autopilot on/off switch and the trim on/off switch) then attempting to trim the airplane with the electric trim that he had just disabled. According to the technician, the pilot yelled at him to turn the system off, and the technician responded that it was off. He said that the pilot’s actions scared him and demonstrated to him that the pilot really didn't have control of the airplane. He noted that, "After the flight, I told [the pilot] he needed to go back and get in the books and learn to operate the system. He seemed very disoriented with the new technology on this flight and previous flights."

Based on the available evidence, it is likely that, after autopilot engagement, the airplane pitched down as a first action of the pitch porpoise, which may have still existed as a discrepancy in the autopilot operation. 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 pilot may have removed one hand from the yoke to again reach for the panel-mounted trim and/or autopilot master switches. With that action, discounting any physical problem, he may have lost his single-handed grip on the control yoke, and the airplane descended in an unrecoverable nose-down attitude.

An editorial "what led to it / how to avoid it" analysis for this accident is generated separately and will appear here.