What happened
On August 19, 2019, a Boeing 787-8, registration SP-LRE, was climbing through FL 310 when the crew received a "LANDING GEAR DISAGREE" warning on the Engine Indicating and Crew Alerting System (EICAS). In response to the alert, the crew leveled off at FL 330 to perform the required "GEAR DISAGREE" checklist. To manage the situation, the crew reduced the aircraft speed to 270 knots and requested holding at waypoint HAPIE to remain within the Boston FIR. No emergency was declared during this phase.
The landing gear indications remained unstable, with the EICAS message appearing and disappearing approximately once or twice per minute. The cockpit displays showed fluctuating statuses, including "LEFT MAIN GEAR DOWN/REST UP" and "ALL GEAR IN TRANSIT." After consulting with the Maintenance Coordination Centre (MCC), the captain decided to return to the departure airport, KJFK.
During the descent through FL 190, the crew extended the landing gear to verify its operational status. While the indications initially returned to normal after extension, the crew remained uncertain about the safety of the landing due to the aircraft's weight being near the maximum landing mass. They initially opted for runway 22R, the longer runway, but elected to perform a missed approach procedure to ensure safety. During this maneuver, the landing gear retracted, causing the warning messages and erratic indications to reappear. Following the completion of non-standard checklists, the crew performed a second approach to runway 22L, landing without further incident.
The investigation
The investigation focused on the electrical signaling and the physical connection between the aircraft's wiring and the landing gear assembly. The investigation examined the continuity of the electrical signals within the wiring harness and the stability of the intermediate connector socket.
Findings
- The primary cause of the incident was intermittent signal transmission within an electrical wiring harness, which failed when the wiring assumed certain positions during flight.
- The issue was exacerbated by a loose intermediate connector socket, which had become loosened due to vibrations, affecting the connection between the aircraft wiring and the wiring mounted on the landing gear strut.