Etihad A6-ETP

The arrival from Sydney

Etihad Airways flight EY455 departed Sydney Kingsford Smith Airport at 10:54 UTC on 18 May 2023 for Abu Dhabi International Airport. The Boeing B777-3FXER, registered A6-ETP, carried 348 passengers, four flight crewmembers and 14 cabin crewmembers, a total of 366 people. Two sets of pilots were assigned to the long range flight. For the landing, the commander was pilot monitoring and the copilot was pilot flying. All four pilots held the required licences, medical certificates and Boeing 777 type ratings.

The aircraft approached runway 13R on the instrument landing system. At 01:39:07 UTC on 19 May, the autopilot was disengaged as the aircraft descended through an indicated altitude of 650 feet, equivalent to a radio height of 530 feet. Its airspeed was 148 knots. Touchdown followed at 01:39:48, about 701 metres beyond the runway threshold, within the normal touchdown zone. The recorded indicated airspeed was 142 knots, the descent rate was about 200 feet per minute, and lateral acceleration was close to zero. The landing weight was approximately 225,950 kilograms.

The crew selected reverse thrust at 01:39:52 and stowed it at 01:40:15. At 01:40:13, with ground speed down to 43 knots, the aircraft began turning right to leave the runway. It passed through taxiway Echo 10 at about 30 knots, continued through Echo 13 and turned onto Foxtrot. The AAIS found that the landing and taxi speeds were normal and that the braking showed no indication of excessive heat. The landing roll and taxi operations did not contribute to the damage to brake number 2.

Flames on the camera display

At 01:43:56, while taxiing along Foxtrot at 18 knots, the crew shut down the right engine under Etihad's reduced engine taxi procedure. Sometime afterwards, they saw flames coming from the left main landing gear on the ground maneuver camera system display. The flame lasted briefly and extinguished itself. Smoke continued to come from the same area.

The crew stopped the aircraft on Foxtrot between Echo 6 and Echo 9. The recorded stop time was 01:44:23, when the parking brake was set. Suspecting a main landing gear fire, the crew made a precautionary MAYDAY call to air traffic control and requested airport rescue and firefighting assistance. They also made an alert call over the passenger address system. Etihad's procedures provided for this cabin alert when an abnormal ground event had occurred or an evacuation might soon be required.

At 01:45, air traffic control declared the ground incident and notified the emergency services. Fire trucks reached the aircraft at 01:46. Firefighters saw smoke and hydraulic oil leaking from the left main landing gear. The fire commander requested shutdown of the remaining engine, and the left engine was shut down at 01:47:50. Firefighters continued watching the gear while the aircraft remained on the taxiway.

Debris, cooling and the tow

The airport began checking the route behind the aircraft. At 01:47, a ground operations team started inspecting the taxiways used after the runway exit. Small fragments of broken metal were found on Echo 13 and reported to air traffic control. At 01:58, the team leader was directed to inspect runway 13R. More metal fragments and pieces of carbon fibre lay on the runway centreline abeam Echo 10.

At 02:04, the inspection team advised that the south runway, 13R/31L, was unsuitable for safe operations. A separate team inspected the north runway, 13L/31R, to prepare it for departures and arrivals while the south runway was restored. The runway and taxiway searches followed the aircraft's route from landing to its stopping place.

An Etihad maintenance engineer reached the aircraft at 02:07 and used convection fan cooling on the left main gear brakes. The engineer inspected the area and confirmed that the wheels could rotate. In consultation with Etihad's Engineering Department, the engineer decided to tow the aircraft to the nearest parking stand. Towing began at 03:00, with a fire truck accompanying the aircraft. It reached stand 301 at 03:05, where all passengers and crewmembers disembarked uneventfully. The airport emergency status ended at 03:23 after the inspections and movement to the stand.

The damaged brake assembly

At the stand, maintenance personnel carried out a high energy brake damage inspection. Brake assembly number 2 was damaged, with hydraulic fluid leaking from one piston. The brake assembly was replaced. A deeper inspection found overheating damage on the axle sleeve, which was also replaced, along with main landing gear wheels 1 and 2. An operational test of the replacement brake showed normal indications and no leakage.

The brake assembly had accumulated 1,188 cycles since installation and 9,250 cycles since new. Seventy eight cycles had elapsed since the most recent tyre change on its mating wheel assembly. The technical log contained no brake defect before departure, and the crew reported no technical anomaly before or during the flight until the taxi incident. The aircraft's alerting system recorded no post flight fault maintenance messages for the flight.

Etihad independently calculated the landing brake energy and brake temperatures and found them within their normal ranges. The brake temperature monitoring system reached a maximum indication of 3.1 units about nine minutes after landing. The report places that value within a normal cooling regime requiring 42 minutes. The temperature tables show brake number 2 at 110 degrees Celsius when the aircraft stopped and 200 degrees Celsius at left engine shutdown. The normal operating indications accompanied a mechanically damaged brake.

How the fire developed

The damaged brake was sent to its manufacturer, Collins, for examination. The pressure plate and piston housing were particularly badly affected. Lugs on stators 1 and 2 had failed, allowing stator clips to become trapped between the heat sink and torque plate. The displaced clips contacted the inner diameters of the rotor assemblies and damaged them. That interference prevented the clamping force from being distributed evenly through the heat sink.

Continued use increased the damage. Uneven loading produced an abnormal wear pattern and wore completely through part of the outboard half of stator 2. The pressure plate lugs eventually sheared, allowing the plate to rotate with the wheel beneath the pistons. Contact between the pistons and rotating pressure plate cut a groove into the plate. The AAIS considered that the additional damage to the outboard part of stator 2 probably occurred on the last cycle after landing.

The combined damage and uneven wear caused the piston at the 7 o'clock position to fail. Hydraulic oil escaped into the heat sink, heated to its flashpoint and produced the brief flame followed by smoke. Other pistons retracted normally during the examination, indicating that they had not been dragging before the failure. Stator 3 remained intact when the fire started, so the brake could still generate some torque.

Collins concluded that the depth of wear and pressure plate damage showed prolonged operation after the original stator lug failure. It considered that the condition would already have existed at the wheel removal 78 cycles earlier. Continued operation destroyed evidence of the original failure. The AAIS could not determine the primary cause of the stator lug damage.

Inspection access and the completed investigation

The investigation examined what flight crews and maintenance personnel could see during normal checks. Exterior inspections and transit checks included looking at the brakes, wear indicator pins and signs of leakage. The AAIS concluded that the wheel assembly concealed the stators and their lug indicators, so their failure could not be seen during these checks. Removing the wheel was necessary to inspect that damage.

The wear indicator pin normally attached securely to the pressure plate and aligned with its guide. The AAIS reasoned that sustained pressure plate rotation would have separated the pin, making its absence visible during an exterior check. It considered the pin most probably intact at Sydney if the checks had been performed properly, and its separation probably occurred after landing. The runway and taxiway searches did not locate it. The manufacturer had considered the pressure plate damage visible with the wheel installed; the AAIS assessed the visibility limitations of the assembled wheel during routine checks.

The wheel and tyre installation task in the aircraft maintenance manual provided a closer inspection opportunity. It required checking the exposed brake for cracks, broken parts, distortion, extensive wear and misaligned index marks on the pressure plate and stator discs. The AAIS found that these steps would have allowed maintenance personnel to examine the assembly in detail. No brake damage findings had been entered in the technical log at the last wheel and tyre replacement.

The AAIS identified the inability to notice the brake defect during exterior inspections and transit checks as a contributing factor. It issued no additional safety recommendation for those routine visual checks, concluding that they offered limited access to the relevant parts. It stated that diligent performance of the existing wheel and tyre installation task would allow such defects to be identified before wheel installation.

The GCAA published its completed investigation as Incident Summary Report AIFN/0007/2023 on 10 January 2024. Its evidence includes flight data from the quick access recorder, information from the ATC communications transcript, brake examination findings, a ground track illustration and brake assembly diagrams. The investigation scope was limited to events leading to the occurrence, with no detailed analysis of factors judged unrelated to it.