Incident Overview
On April 21, 2016, at Warsaw Chopin Airport (EPWA), an incident occurred involving a Embraer 170 aircraft. The air traffic control tower (TWR) reported abnormal operation of the navigation lighting control system. After conducting a CAT II lighting test, the stop bar on taxiway E3 remained illuminated when the system was switched to CAT I. The crew of the Embraer 170, which had been cleared to occupy runway 29, reported the stop bar as being on. The time required to turn off the stop bar caused an unnecessary stop of the aircraft before the runway.
Investigation Findings
The investigation, conducted by the airport operator, analyzed monitoring recordings of the system's operation. The analysis revealed no errors in either the software or the hardware. Before changing the lighting scenario from CAT II to CAT I, the TWR controller had turned off the stop bar on TWY E3 for a period of 25 seconds. During the 25-second countdown for the stop bar to re-engage, the TWR controller changed the lighting scenario from CAT II to CAT I. According to the programmed algorithm of the system, changing the lighting scenario does not cancel the command to re-engage the stop bar after the requested time has elapsed.
Cause
The cause of the incident was the change of the lighting scenario from CAT II to CAT I while the stop bar on TWY E3 was turned off for 25 seconds. After the countdown ended, the stop bar returned to the re-engaged state. This situation resulted from the specific operation of the lighting control system.
Preventive Actions
The airport operator informed the Polish Air Navigation Services Agency (PAŻP) and confirmed that TWR controllers operating the Touch Screen system have been trained on the described system behavior. The Energy Service is working on a software update for the Touch Screen system, which will include counters for operating time and the time remaining until stop bars re-engage. No safety recommendations were issued by the investigation commission.