What happened
On July 29, 2015, at 12:22 UTC, an Airbus A320, registration HA-LPR, operated by WizzAir Hungary Ltd, was performing a landing approach on runway 33 at Warsaw Chopin Airport (EPWA). During the approach, the pilot reported that the PAPI lights for runway 33 had automatically switched off.
At the Air Traffic Control Tower (ADC TWR) lighting control panel, the status window for the PAPI lights displayed the number 5, indicating a 100% intensity setting. However, the indicator was gray, signifying that the lights were actually inactive. The controller attempted to restore the lights by cycling the intensity setting from 4 back to 5, which successfully re-engaged the PAPI lights, a change confirmed by the flight crew of HA-LPR.
The investigation
Following the incident, airport technical services were notified. At 12:47 UTC, technical staff at Warsaw Chopin Airport confirmed that a system error had occurred.
Findings
- The primary cause of the incident was an error within the updated software of the navigation lighting control and monitoring system.
- This specific software bug had not been detected during testing in a virtual environment.