What happened
On 9 November 2016, an Emirates Airbus A380-861, registration A6-EDQ, was operating a scheduled passenger flight from London Heathrow to Dubai International Airport. During the flight, the crew received an alert indicating that the green hydraulic system had overheated. Following standard operating procedures, the crew isolated the green hydraulic system to manage the temperature. This isolation introduced several operational limitations, including restricted nose gear steering and the requirement to use the emergency free-fall method for landing gear extension.
As the aircraft approached Dubai at approximately 4,000 feet, the crew selected the landing gear to the down position. While most of the gear locked into place, the cockpit indications revealed that the left wing landing gear remained in its bay. Despite the emergency declaration, the commander decided to proceed with the landing, citing fuel considerations and the fact that a go-around would have significantly increased drag and fuel consumption. After landing, the aircraft was towed to a stand, where it was discovered that the left wing gear had failed to release via the emergency system.
The investigation
The UAE Air Accident Investigation Sector (AAIS) conducted a technical examination of the aircraft's landing gear systems and the emergency unlock actuators. The investigation focused on why the free-fall extension method failed to actuate the left wing gear. Investigators examined the wiring of the emergency unlock actuators and analyzed the hydraulic system's behavior following the isolation of the green system. The probe also reviewed the operator's communication procedures and the adequacy of the manufacturer's manuals regarding aircraft towing during emergencies.
Findings
- The primary cause of the failure was flexure endurance fatigue damage affecting the command wires for both channel A and channel B of the emergency unlock actuator.
- This fatigue was caused by aerodynamic forces acting on an inadequately secured wiring loom during the operation of the landing gear.
- The aircraft's network control center was unaware that an emergency had been declared by the crew prior to landing.
- Existing documentation lacked specific instructions for safely towing an aircraft with passengers and cargo onboard under these specific abnormal conditions.
Safety action
Following the investigation, the AAIS issued several safety recommendations. To the European Aviation Safety Agency (EASA), the investigators recommended that the manufacturer determine the root cause of the wire damage and implement a design improvement to prevent future failures. For the operator, recommendations were made to update network control center procedures to ensure better monitoring of declared emergencies and to establish clear instructions for towing aircraft with passengers onboard.