Korean Air Flight 631

Korean Air Flight 631 was a scheduled international passenger flight operating from Incheon International Airport near Seoul, South Korea to Mactan–Cebu International Airport in Metro Cebu, Philippines. On 23 October 2022, the Airbus A330 operating this flight overran the runway while landing in Cebu due to a failure with the hydraulics system. No one was killed, but 20 people were injured.

The aircraft was damaged beyond repair and written off as a result of the accident, and also resulted in the 14th hull loss of an Airbus A330 worldwide.

The accident resulted in the first hull loss of a Korean Air aircraft since Korean Air Cargo Flight 8509 crashed in Great Hallingbury, United Kingdom, nearly 23 years prior.

Accident

The flight departed Seoul at 19:20 KST (10:20 UTC) and was scheduled to land at Cebu at 22:00 PHT (14:00 UTC). At about 22:12 PHT (14:12 UTC) KE631 was on final approach to Mactan–Cebu International Airport. There was scattered thunderstorm and the crew received instruction from the control tower to land on runway 4 to avoid landing with a tailwind. As they were descending and before the final approach, the wind direction changed and they were instructed to use runway 22 instead. During their descend at low attitude, the plane encountered a heavy rain shower that obstructed visibility so the pilots executed a go-around. During the second landing attempt the plane encountered turbulence at 300 ft that pushed the plane below the glide path. The responding pilot maneuver overcorrected and raised the plane above the glide path before the subsequent pilot action overcorrected to the down side and pushed the plane below the glide path. The pilot reacted by pitching the plane's nose up to attempt to bring the aircraft to the correct altitude. At this moment, the crosswind shifted to a tailwind with an additional downdraft pushing the plane from the top, which nullified the pilot's nose up maneuver and kept the plane below its correct altitude. The plane was flying too low and at 22:26 and less than 75 ft from the ground, the pilots attempted a second go-around. However, the plane's right gear struck the ground two meters short of the runway before it could take off and the right gear was severely damaged.

After the plane flew to above 1,500 ft, several fault messages were displayed that alerted the pilots of the seriousness of their situation. The plane could no longer detect gear status and the crew had no idea if the gear was up or down (it was down). The normal braking system with anti-skid, reverse thrust, and ground spoilers were disabled because the gear had lost communication with the system and in its place, the alternate braking system was enabled. The aircraft circled northeast of Cebu for approximately 30 minutes before conducting a third approach.

Unbeknown to anyone at this point, the aircraft had been leaking hydraulic fluid inside the Pressure Relief Valve (PRV) for some time before the accident. The hydraulic fluid was leaked into another fluid line and pumped back into circulation so neither the flight nor the maintenance crew noticed the fault. However, with the right gear damaged, the hydraulic fluid was now leaking out of the airplane. This means the alternate braking system was compromised. A fault warning was displayed and the pilots responded according to operation manual to turn off the alternate brakes to stop fluid from leaking and to rely on the emergency brakes instead. However, because the PRV had been leaking, the accumulator pressure that the emergency brakes relied on was also compromised. In essence, the airplane had virtually no braking power but the flight crew was unaware.

On the third attempt, the aircraft touched down at 23:08, but was unable to stop on the runway and it ran off the runway at 83 knots. The aircraft continued past the end of the runway, striking an instrument landing system lighting array before stopping 300 m beyond the runway threshold. According to eyewitness accounts, "The instrument landing system lighting array laid over the wings of the aircraft once the aircraft was stopped in the marsh."

Weather reports indicated that the wind speed was 9 kn from the south-west at 220 degrees. As the aircraft landed on runway 22, there was a 9 kn headwind present. Visibility was 8,000 m at the time of the accident, with thunderstorms and rain in the area; there were no reports of lightning. Cumulonimbus clouds were scattered at 1,800 m and overcast at 9,000 m above Cebu. Other planes decided to divert due to weather prior to KE631's landing attempts, but there is no information on the time span between the other diversions and the Korean Air flight.