Cathay Pacific Flight 256 was a flight from London Heathrow Airport to Hong Kong on 11 September 2010. As the flight climbed through 9000ft, the cabin didn't pressurize and a safe landing was made back at London Heathrow Airport. Aircraft The aircraft involved was an Boeing 747-467, registration B-HOP. It was manufactured in 1989 and first flew as VR-HOP before being re-registered B-HOP after the 1997 handover of Hong Kong to China. Accident Cathay Pacific Flight 256 took off from London's Heathrow Airport at 00:42am local time (23:42 UTC). During the climb through 9000ft over Harlow, Essex, the cabin failed to pressurize due to a stuck outflow valve. The aircraft made a safe landing at London Heathrow Airport at 02:09am local time (01:09 UTC). The problem was repaired and departed for Hong Kong's Chep Lap Kok Airport with a delay of 18 hours 30 minutes.