A FAULTY door which led to a Singapore Airlines (SIA) flight making an emergency landing in Azerbaijan had been found to have a "slightly worn seal" two weeks earlier, investigators have found.
The Airbus A-380 landed safely in the capital, Baku, on Jan 5 after a drop in cabin pressure.
Singapore's Air Accident Investigation Bureau, which is leading an official probe into the incident, has since discovered that checks carried out on Dec 23 last year revealed a "slightly worn seal on the door's upper edge".
In an interim report obtained by The Straits Times, the aircraft investigation arm of the Ministry of Transport said the fault was classified as a defect which did not need immediate attention. The recommendation was for the problem to be fixed within 120 days.
On Jan 4, a day before the emergency landing, the A-380 was en route from Singapore to London when a cabin crew member "noticed a constant, louder-than-normal noise" from the affected door.
When it arrived in London, maintenance personnel checked the door and made the same recommendation as on Dec 23. The fault did not need urgent fixing.
After the plane left London for Singapore with 467 travellers and 27 cabin crew on board, the same noise was heard. This alarmed passengers seated near the door, including bank officer Matthew G. Johnson, who alerted cabin crew.
Apart from the noise, it was smooth flying for the first five hours. At 37,000ft, the cabin pressurisation was normal and equivalent to that at 6,000ft.
But then the pressure started to fall, prompting the pilots to descend the aircraft and deploy passenger oxygen masks.
A "mayday" distress signal was sent to air traffic control in Kabul, Afghanistan, but there was no response.
The pilots wanted to divert the plane to Ashgabat in Turkmenistan, which was first on their list of emergency alternative airports in the area, but it was not able to receive the SIA aircraft.
The A-380 eventually landed safely in Baku.
When inspected, the upper edge of the door was found to be damaged, the interim report said.
"The door skin along this edge had folded outwards which allowed cabin air to leak" and pressure to fall.
The door was removed in Baku and flown to Airbus' facility in Bremen, Germany, for further inspection.
A full report is expected by the end of next month.
The incident led to passengers being stranded for more than 15 hours before they were flown to Singapore in a replacement aircraft. Airbus has since asked all A-380 operators to inspect doors that are reported to be noisy in flight.
The probe by the Air Accident Investigation Bureau of Singapore will focus on what caused the damage to the door as well as the door's assembly and inspection procedures.
Crew actions will also be scrutinised, the authority said.
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