What happened
On February 3, 2019, a Cessna 525A Citation Jet CJ2+, registered D-ITMA, was performing a ferry flight from Milan Malpensa to Sion Airport. Following its landing on runway 25, the aircraft exited the runway at intersection Hotel and proceeded along taxiway Sierra.
As the aircraft traveled between intersections Foxtrot and Echo, it drifted to the left, causing the left main landing gear to leave the paved surface and enter a muddy, saturated grass strip. Although the pilot attempted to correct the course, the aircraft continued to slide through the mud for approximately 50 meters before coming to a halt. The incident resulted in minor injuries to the two crew members and caused slight damage to the aircraft, including a small fuel leak from the right wing tank.
The investigation
The investigation focused on the sequence of events leading to the excursion and the environmental conditions at the time. Investigators examined the state of the taxiway surroundings and the cockpit activities of the crew. It was established that the grass area adjacent to taxiway Sierra was heavily saturated with water and mud, which prevented the pilot from successfully regaining control of the aircraft's trajectory once the deviation began.
Findings
Findings indicate that the primary cause of the excursion was pilot distraction. The captain had diverted his attention from the taxiway to scan the airspace for another aircraft performing a visual approach under marginal weather conditions. Simultaneously, the co-pilot was focused on completing the aircraft's technical logbook at the direction of the captain. This lack of monitoring meant the deviation from the taxiway was not detected in time to prevent the aircraft from leaving the paved surface.