What happened
On February 9, 2016, an incident occurred at Warsaw Chopin Airport (EPWA) involving the airport's navigation lighting control system. Following the completion of a CAT II lighting test, the tower air traffic controller observed that a stop bar on taxiway D2 remained illuminated, even though the system settings had been switched to CAT I configurations.
The investigation
The investigation, conducted by the airport management, included a detailed analysis of the system's monitoring logs. The review found no hardware malfunctions or software errors within the lighting control system itself. The investigation established that prior to the transition from CAT II to CAT I settings, the air traffic controller had manually deactivated the D2 stop bar for a 40-second interval. During this 40-second countdown, the system settings were changed from CAT II to CAT I. Due to the system's existing operational algorithm, the change in lighting mode did not cancel the previously programmed instruction to reactivate the stop bar once the 40-second timer expired.
Findings
- The primary cause of the incident was the selection of new lighting settings while a temporary deactivation timer was still active, which caused the stop bar to automatically re-engage after the countdown ended.
Safety action
- The electrical services department is working to update the lighting control system software to include visible countdown timers, showing the remaining time until stop bars automatically reactivate.