What happened
On 6 July 2018, a Boeing 787-9 Dreamliner, registration G-TUIM, was performing a commercial passenger flight from Tenerife South Airport to London Gatwick Airport. While being vectored for an ILS approach to Runway 2LL, the aircraft began experiencing a progressive loss of normal system functionality.
Following the selection of flaps 1, the crew received alerts indicating primary failures in the slats and flaps systems. As the crew attempted to configure the aircraft for landing, further complications arose involving the landing gear and steering. Specifically, a gear disagree message appeared, indicating the nose landing gear was not in the correct position. While the crew successfully used the alternate system to lower the gear, a fault was subsequently identified in the nosewheel steering system.
Due to the complexity of these unfolding failures, the crew performed a go-around and utilized radar vectors to orbit the airport. This allowed them to execute electronic checklists and formulate a landing plan. The crew decided to land using flaps 20 and planned to use the rudder and differential braking to maintain directional control on the runway. During the approach, the cabin crew were briefed for an emergency landing, with the Senior Cabin Crew Member proactively initiating brace commands as the aircraft neared the ground.
Despite the technical issues, the aircraft landed safely. The crew managed the rollout using the rudder and autobrakes, eventually bringing the aircraft to a stop on the runway. The passengers and crew sustained no injuries.
The investigation
The investigation focused on the cause of the simultaneous degradation of the slats, flaps, landing gear, and nosewheel steering. Investigators noted that this was the third such incident involving G-TUIM within a single week, though previous events had not involved the nose landing gear or steering.
Technical examination revealed that the hydraulic synoptic page showed an issue with the Nose Landing Gear Isolation Valve (NLGIV). Subsequent testing confirmed that the NLGIV failed to open as commanded, which triggered the cascade of system failures.
Findings
- The primary cause of the system degradation was the failure of the Nose Landing Gear Isolation Valve (NLGIV) to open.
- The failure of this valve prevented the normal operation of the leading-edge slats, trailing edge flaps, nose landing gear, and nosewheel steering.
- The crew successfully utilized the alternate electrical system to configure the flaps and lower the nose gear.
- The manufacturer's investigation into the NLGIV identified that the valve could fail under cold-soaked conditions.
Safety action
Following the investigation, the aircraft manufacturer implemented several changes, including:
- Updates to the component Acceptance Test Procedure for the NLGIV.
- Modifications to manufacturing processes to prevent internal component wear known as brinelling.
- Revisions to the Fault Identification Manual and Aircraft Maintenance Manual to include specific operational tests for the valve.