What happened
On February 7, 2016, at approximately 14:30, a Cessna Citation 525A, registration D-ISCO, was preparing for a repositioning flight at Chambéry Aix-les-Bains airport. Following a previous flight from Poznan, Poland, the aircraft had been moved to parking stand 26.
After completing a walk-around inspection, the co-pilot entered the cockpit and signaled the ground agent to remove the wheel chocks. After the chocks were removed, the aircraft began to roll backward slowly. The movement was not immediately detected by the crew due to reduced visibility caused by rain on the windshield. The aircraft eventually left the paved surface, traveled across a grassy area, and the main landing gear became lodged in a ditch approximately one meter deep. The incident resulted in heavy damage to the aircraft, including deformation of the main landing gear and structural damage to the rear fuselage frames.
The investigation
The investigation focused on the sequence of events leading to the uncontrolled movement and the cockpit communications. Investigators examined the wreckage and found no malfunctions within the braking system itself.
Interviews with the crew revealed that while the commander had tested the brakes by applying pedal pressure and checking hydraulic pressure, the parking brake was not engaged. During the pre-departure checks, the co-pilot asked the commander if the brakes were "OK." The commander responded affirmatively, but the investigation determined that the co-pilot's inquiry was ambiguous; while the co-pilot was referring to the parking brake, the commander interpreted the question as a confirmation of the service brakes' functionality.
Additionally, the investigation noted that the parking area, situated on a former taxiway, featured a slight slope for rainwater drainage, which contributed to the aircraft's movement once the chocks were removed.
Findings
- The commander verified the service brakes during pre-start procedures but failed to engage the parking brake.
- Ambiguous communication between the crew members regarding the status of the brakes led the co-pilot to signal the ground agent to remove the chocks while the aircraft was unsecured.
- Rainwater on the windshield obscured the commander's view, preventing the timely detection of the aircraft's backward movement.
Safety action
Following the accident, the airport operator implemented new procedures for ground agents working in this specific parking area, now requiring chocks to be placed on the nose gear until the aircraft's departure. Furthermore, a NOTAM was issued to alert flight crews to the specific characteristics of this parking area, and an amendment to the airport's Visual Approach Chart (VAC) is being processed.