Accident Overview
During an instrument landing system (ILS) Z approach to Runway 26 at Clermont-Ferrand-Auvergne Airport in instrument meteorological conditions (IMC), the pilot of a single-engine aircraft was instructed by air traffic control (ATC) to climb to 6,000 feet to the TIS VOR via a right turn because he had failed to follow the published missed approach procedures. The aircraft departed the approach path, and control was lost after it completed several turns during climbs and descents. It entered a high nose-down attitude and struck the ground at high speed approximately 6 kilometers short of the runway. The aircraft disintegrated on impact, and all three occupants, aged 70, 73, and 76, were killed. They were completing an intermediate stop at Clermont-Ferrand to pick up two additional passengers before continuing to Biarritz.
Approach and Missed Approach
Radar data showed that the aircraft followed the ILS Z 26 procedure track in the horizontal plane to about 6.4 nautical miles from the runway threshold. This was consistent with the autopilot tracking the procedure entered into the flight management system (FMS) in GPS mode. The transition from GPS to localizer (LOC) mode occurred after the final approach point (FAP). Although the approach (APP) mode was engaged, the aircraft did not descend as expected by the pilot. It continued in line with the localizer but in level flight at 4,000 feet for more than one nautical mile. The pilot attempted to catch up with the glide path from above. Unable to stabilize his course, he aborted the approach without following the prescribed go-around path or the heading and altitude instructions provided by the controller. He made a succession of left and right turns, climbs, and descents.
Loss of Control
The track and readbacks indicated that the pilot lost situational awareness. The airspeed regression following the last climb caused the pilot to lose control of the aircraft, which collided with the ground. The entire approach was flown with no outside visibility.
Probable Cause and Contributing Factors
According to the official investigation, the probable cause is that the aircraft followed the ILS Z 26 procedure track horizontally to about 6.4 NM from the threshold, consistent with autopilot tracking in GPS mode. The transition from GPS to LOC occurred after the FAP. Despite APP mode engagement, the aircraft did not descend as expected. The pilot attempted to intercept the glide path from above but, unable to stabilize, aborted the approach without following prescribed procedures or ATC instructions. After a series of turns and altitude changes, he lost situational awareness, and a loss of airspeed following the last climb led to loss of control and collision with the ground. Contributing factors included a coding error in the Garmin 1000 avionics suite database that prevented automatic GPS-to-LOC transition, the pilot's overconfidence in the autopilot, lack of knowledge of autopilot conditions for glide path capture, lack of consistency verification between coded procedure and breakthrough sheet, lack of recent instrument flight experience, sensory illusions from numerous attitude changes, and ineffective acquisition of experience with safety pilots outside regulatory training frameworks.