What happened
On April 21, 2016, an Embraint 170 (E170) operating a scheduled airline flight was cleared to enter runway 29 at Warsaw Chopin Airport (EPWA). During the taxi process, the flight crew reported that a stop bar on taxiway E3 remained illuminated, despite the airport's lighting configuration having been switched from CAT II to CAT I.
This unexpected lighting state forced the aircraft to come to an unnecessary halt before the runway while the air traffic controller worked to resolve the issue. The incident was subsequently reported to the airport's Electrical Service.
The investigation
An analysis performed by the airport's Electrical Service examined the system monitoring logs. The investigation established that there were no hardware or software errors within the lighting control system itself.
Findings revealed that prior to the change in lighting scenario, the air traffic controller had manually deactivated the stop bar on taxiway E3 for a 25-second interval. During this 25-second countdown, the controller transitioned the lighting configuration from CAT II to CAT I. The investigation determined that the system's programmed algorithm does not cancel a pending command to reactivate a stop bar simply because a configuration change has occurred.
Findings
- The primary cause was the timing of the lighting configuration change, which occurred while the system was in the middle of a programmed 25-second delay for the taxiway E3 stop bar.
- The system functioned according to its programmed logic, which does not prioritize configuration changes over active countdowns for stop bar reactivation.
Safety action
- The Polish Air Navigation Services Agency (PAŻP) confirmed that air traffic controllers operating the Touch Screen system have received training regarding the specific operational characteristics of the lighting control system.
- The airport's Electrical Service is working to update the Touch Screen software to include operational counters, showing the remaining time until stop bars are scheduled to reactivate.