Air India in a statement said an aircraft undergoes multiple engineering checks before it is cleared for flight operations, with top priority given to safety issues, and the June 1 Delhi-Hong Kong flight too went through the process.
Also Read: Eye on AI (Air India) "A hissing sound started emanating from the decorative door panel mid-flight, and after assessing that there was no risk to safety, crew took action to alleviate the noise. After landing in Hong Kong airport, the aircraft underwent checks by the engineering team.
"All safety parameters were found to be in compliance and the aircraft was cleared for service. There was no such noise during the return flight AI315 from Hong Kong to Delhi. We would like to reiterate that the safety of our customers and crew remains top priority," the Air India statement added.
So what could have caused the problem?
"As the aircraft climbs, the atmospheric pressure difference within and outside the aircraft increases. The pressure inside the B787 passenger cabin is what you would experience at around 6,000 ft altitude. But the aircraft could be cruising at 40,000 ft. If the door seal is compromised, pressurised air (meant to circulate in the passenger cabin) could leak through it, making these noises," said a source, requesting anonymity.
Also Read: Air India fares drop after Boeing 787 crash; fleet inspections lead to flight cancellations and reduced operationsUnlike the Boeing 777 or 737 aircraft, Boeing 787 has an advanced plug-type door which is electronically monitored. The door swings outward and then moves forward to open. To close, it is plugged into the fuselage for pressurisation. The B777 door on the other hand is operated manually, while the narrow body B737 has a manual, mechanical plug-type door.
TOI looked into door plug problems reported by airlines worldwide. The most recent documented case occurred in Oct 2022, when an American Airlines Boeing 787-800 flight to Paris returned to Philadelphia after fumes were detected around two doors.
Flight attendants checked lavatories and other places but couldn't find the source of the fumes and when they began spreading in the passenger cabin, the crew declared an emergency and diverted to land safely.
In Feb 2022, a TUI airlines B787-800 flying from Amsterdam to Punta Cana in the Dominican Republic returned to Amsterdam after a howling noise came from door 2L. A small hole in the door seal caused the sounds and the pilots decided to divert.
In Aug 2019, a Japan Airlines flight from Tokyo to Bangkok landed back in Tokyo two hours after departure. Passengers complained of growling sounds and vibrations coming from the main door towards the front of the Boeing 787-800 Dreamliner, according to reports. On ground inspection a small gap was found in the door seal through which pressurised air was escaping, creating strange noises and vibrations. There were no cabin pressurisation problems, and no oxygen masks were deployed. The aircraft was returned to service about 30 hours after the incident.
In none of these three cases did the aircraft suffer from a cabin depressurisation problem. A senior commander said, "This kind of leak can happen if a door seal is slightly out of place or it has gone old. It does not affect cabin pressurisation at all. Hypothetically if we assume all 8 doors develop this problem, even then pilots get enough advance warning to initiate a descent down to 10,000 ft as is the standard practice in a cabin decompression emergency."
Capt Amit Singh, an air safety expert, said, "The question is, was it a one-off thing or is it a regular occurrence? It could be a combination of maintenance issues and how the door was closed."