What happened
On May 25, 2010, at Nantes Atlantique Airport, an Air France Airbus A318-111, registration F-GUGC, was performing a Category II (CAT II) automatic landing under Low Visibility Procedures (LVP). Simultaneously, a Transavia France Boeing 737-800, registration F-GZHD, was cleared to taxi to holding point Alpha for departure on runway 03.
As the F-GUGC approached the runway threshold, the tower controller observed the F-GZHD approaching the Alpha stop bar. Because the aircraft was positioned in a sensitive ILS area, the controller instructed the F-GZHD crew to take off immediately. During the sequence, the tower controller informed the F-GUGC crew that another aircraft was lining up and then rolling for takeoff.
As the F-GZHD passed the localizer antenna, its physical dimensions caused a momentary disturbance to the localizer signal. This resulted in significant lateral deviations for the F-GUGC during its touchdown roll. The pilot of the F-GUGC eventually had to disconnect the autopilot to maintain the runway centerline after noticing the aircraft drifting.
The investigation
The investigation focused on the separation standards required during LVP and the interaction between the two aircraft. Investigators examined the flight data from the F-GUGC (QAR), which confirmed abnormal localizer deviations for approximately eleven seconds during the landing phase.
Technical analysis revealed that the F-GZHD has a tail height of 12.55 meters. Local airport regulations prohibit CAT II or CAT III approaches if an aircraft with a tail height exceeding 10 meters is positioned between taxiway Bravo and holding point Alpha. The investigation also looked into the functioning of the Alpha stop bar lights and the communication between the ground, tower, and approach controllers.
Findings
- The primary cause was the decision by the tower controller not to instruct the F-GUGC to abort its approach or the F-GZHD to delay its takeoff once it was clear that separation standards were no longer being met.
- The controller's decision was influenced by the assumption that the arriving aircraft was performing a CAT I approach, as the crew did not explicitly announce a CAT II approach.
- The F-GZHD crew's presence in the sensitive ILS area violated the local safety requirement regarding aircraft tail height.
- The F-GUGC crew felt constrained in their decision-making; the pilot chose to continue the approach because they feared that an aborted landing would lead to a loss of separation with the departing aircraft during its initial climb in low visibility.
- There was a lack of standardized procedures for managing taxi movements under LVP, specifically regarding the use of the Alpha stop bar and the monitoring of aircraft positions relative to the ILS sensitive area.