What happened
Between November 30 and December 2, 2015, a Boeing 787-800 operated by the user experienced a series of recurring brake system malfunctions while taxiing at Warsaw Chopin Airport (EPWA). On November 30, the crew observed a 'BRAKE SYSTEM INOP (WHEEL 4+8)' alert. Following this indication, the aircraft returned to the stand, where maintenance personnel performed troubleshooting and system tests in accordance with the component maintenance manual. After successful testing, the aircraft was cleared for flight.
Later that same day, the same brake system fault recurred during taxiing. In response, maintenance crews replaced the Electric Brake Actuator Controller (EBAC) as specified in the aircraft maintenance manual. Despite this intervention, the malfunction persisted and reappeared under identical circumstances on December 2, 2015.
The investigation
The investigation focused on the repeated failure of the braking system and the effectiveness of the initial maintenance actions. After consulting with the brake system manufacturer, it was determined that the issue was not limited to the controller itself. The investigation established that a fault within a single Electric Brake Actuator (EBA) unit—one of four units per brake assembly—was capable of triggering the EBAC failure signal.
Findings
- The primary cause of the recurring malfunction was a faulty Electric Brake Actuator (EBA) unit.
- This internal failure within a single EBA block was sufficient to cause the entire EBAC to report a system malfunction.
- The issue was resolved by replacing the complete brake assemblies for wheels 4 and 8.
Safety action
The event was recorded in the operator's Safety Management System (SMS) database and classified according to established criteria. The incident will be included in the airline's Safety Performance Indicators (SPI) for ongoing monitoring as part of their Safety Management Manual protocols.