What happened
On November 24, 2012, a Tunisair Boeing 737-600, registration TS-IOL, was performing an ILS approach to runway 23 at Geneva Airport under low visibility procedures. The weather conditions were characterized by fog, with vertical visibility of only 200 feet and runway visual range between 375 and 550 meters.
During the landing phase, the aircraft experienced a significant vertical acceleration of 2.5 g. Shortly after touchdown, the left main landing gear veered off the runway, traveling approximately 120 meters onto the grass. This excursion caused the destruction of two runway edge lights and left ruts in the terrain. The impact of the gear on the lighting infrastructure triggered a total failure alarm for the runway edge lighting system (BALUPI).
The investigation
The Swiss Transportation Safety Investigation Board (SUST) examined the flight data, cockpit voice recordings, and airport infrastructure. The investigation focused on the flight crew's use of automated systems, the meteorological conditions, and the airport's monitoring of lighting failures. Investigators also reviewed the operational procedures for low visibility and the communication between the cockpit and air traffic control.
Findings
- The primary cause of the excursion was a momentary loss of control resulting from spatial disorientation.
- The improper use of automatic flight control systems contributed to the incident.
- The crew engaged both autopilots during the final approach but disconnected them at the decision altitude.
- The aircraft experienced a hard landing with the left side of the aircraft off the centerline.
- Autopilots and autothrottle systems remained engaged for approximately two seconds after the aircraft touched the runway.
- Air traffic controllers were not immediately aware of the specific nature of the lighting failure; the presence of debris on the runway was only discovered during a routine inspection three hours later.
Safety action
Following the investigation, a safety recommendation was issued to the Federal Office of Civil Aviation. The recommendation (No. 495) states that controllers in the control tower should have a means to immediately identify the specific details of a runway lighting alarm to ensure rapid response to infrastructure damage.