Incident Overview
On August 23, 2014, at Warsaw Chopin Airport (EPWA), a Boeing 787-800 aircraft experienced a flight management system lateral (FMCL) fault while the flight crew was modifying an approach in the Control Display Unit (CDU). The fault resulted in the loss of the active route, performance data, autopilot, autothrottle, and both VNAV and LNAV modes. The crew successfully restored the lost data by reprogramming the Flight Management Computer (FMC) multiple times until the fault cleared.
Recurring Issue
The captain reported encountering a similar issue three times in the preceding weeks. However, the airline's Safety Department had no records of any pilot reports regarding these anomalies. A comparable event had previously occurred on July 20, 2014 (report 1130/14).
Investigation Findings
Honeywell, the manufacturer of the Boeing 787 software, was able to reproduce the reported problem. Their investigation revealed that the issue manifested exclusively during Standard Terminal Arrival Route (STAR) procedures containing exactly 14 waypoints and occurred when the crew attempted to select a different approach not included in that STAR procedure.
Corrective Actions
A fix was initially proposed via a Flight Management Function (FMF) modification known as Block Point 3 (BP3), scheduled for release in the fourth quarter of 2015. In the interim, Honeywell explored alternative solutions, including a modification to the navigation database. Boeing subsequently announced a revised navigation database version incorporating the correction.
The operator (PLL LOT) negotiated with Boeing to expedite the solution but without success. On December 23, 2015, Boeing issued Service Bulletin B787-81205-SB340013-00, which was revised on May 6, 2016 (Revision 02). This bulletin introduced software modifications for the Flight Management System (FMS), Thrust Management System (TMS), and Communication Management Function (CMF), collectively referred to as BP3. These modifications addressed the underlying software limitations. The operator informed the State Commission on Aircraft Accident Investigation (PKBWL) that work was underway to implement these modifications.
Probable Cause
The cause of the incident was determined to be limitations in the software of the Boeing 787 aircraft systems.
Preventive Measures
The operator's Engineering Department (OTE PLL LOT) engaged in negotiations with Boeing to resolve the problem, with correspondence attached to the report. The operator also informed the commission of the progress toward implementing the BP3 modifications.