What happened
On November 21, 2014, a Boeing 787-800 was performing a descent toward Warsaw Chopin Airport (EPWA). During the descent, the flight crew determined it was necessary to change the approach type and the runway direction. However, the aircraft's Flight Management Computer (FMC) failed to allow any modifications to the programmed flight path. No failure warnings or alerts were triggered by the system, and the crew had no means to rectify the unresponsive FMC. Consequently, the crew proceeded to land on runway 33, which had been previously selected in the FMC.
The investigation
The investigation, conducted by the operator, established that the crew was already aware of a Boeing service bulletin regarding similar FMC issues. Previous occurrences of this specific malfunction had been recorded on July 20, 2014, and August 23, 2014.
Technical analysis by the software manufacturer, Honeywell, successfully replicated the reported error. The investigation determined that the malfunction specifically occurs during STAR (Standard Terminal Arrival Route) procedures that contain exactly 14 waypoints when the crew attempts to select an approach not included within that specific procedure.
Findings
- The primary cause of the incident was limitations within the aircraft's onboard system software.
- The issue was identified as a specific logic error within the Flight Management Computer (FMC) related to certain STAR procedures.
- The software manufacturer, Honeywell, proposed a resolution via the FMF Block Point 3 (BP3) modification, which was eventually implemented through Service Bulletins issued in late 2015 and early 2016.
- The operator had been negotiating with the aircraft manufacturer to accelerate the software fix prior to the implementation of the official service bulletins.