Air India’s five Boeing 777-200 LR aircraft, currently used to operate India-US routes, have come under fresh scrutiny with the Bombay High Court directing India’s aviation regulator to dig deep into a particular aspect of its operations. Can it descend safely to 10,000 ft within 12 minutes of a cabin decompression at any point along the route? TOI explains.
Q: What is cabin decompression, and why is the Air India Boeing 777 being singled out for this investigation?
A: Jets like the Boeing 777 cruise at altitudes of 30,000-40,000 ft. To put that in perspective, Mount Everest stands at 29,000 ft.
For human survival, aircraft cabins are sealed and pressurised with conditioned air and oxygen. The aircraft might be cruising at, say, 40,000 ft, but inside the aircraft, the pressurisation system keeps the cabin comfortable as if it is at 8,000 ft. But on rare occasions, the pressurisation system could fail. The pressure and oxygen level in the cabin would then drop, oxygen masks deploy from the overhead panel, supplying vital oxygen for the passengers to breathe.
In the cockpit, the pilots also have their masks on, and they follow the SOP to put the aircraft into a controlled rapid descent of about 5,000 ft per minute or more to level off at 10,000 ft, the altitude at which an external oxygen supply like the one provided by the masks is not needed to support human life.
The higher the amount of oxygen an aircraft carries for a cabin depressurisation emergency, the more leeway there is.
Air India’s five dry-leased Boeing 777s have 12 minutes of oxygen per passenger (pilots get more). Twelve minutes is enough time to descend from higher altitudes to 10,000 ft over plains.
Other Boeing 777 models have 22 minutes of oxygen or more, depending on the airline.
Q: What is the concern then?
A: In Jan 2023, an Air India commander wrote to the airline management seeking instructions to follow if a cabin decompression emergency occurred over mountainous terrain like Greenland. Air India routing to fly between Delhi/Mumbai/Bangalore and New York/San Francisco overflies mountainous terrain.
The concern essentially was that the aircraft would have to level off at 13,000 ft to stay clear of mountain peaks, say in Greenland, which would mean the mandated descent to 10,000 ft would take much longer than 12 minutes. While the pilots have way more than 12 minutes of emergency oxygen, the oxygen requirement for passengers beyond 12 minutes is not met in the flight plan, the letter alleged.
The management had not responded to his query when, on Jan 30 last year, he was rostered to operate a San Francisco to Bengaluru flight on a route that overflew mountainous terrain. The commander refused to operate, citing safety concerns. He eventually did after a longer route that he deemed legal and safe was selected. On Feb 18, 2023, Air India grounded the commander and terminated him in May.
In the following months, the commander wrote to the DGCA about the B777-12-minute oxygen issue, citing the Indian regulator’s safety norms that the airline allegedly violated. In Jan this year, following a show cause notice, the DGCA imposed a fine of Rs 1.1 crore on Air India for operating a US flight using the leased Boeing 777 with 12 minutes of emergency oxygen supply for passengers. In February, the Air India pilot moved Bombay High Court against the DGCA in a writ petition which alleged that the regulator did not give him, the complainant, a hearing in the course of its investigations.
Q: What else did the petition say?
A: Air India continues to operate to/from the US with the leased B777s, the petition said, showing route maps taken from Flightradar 24. During the hearing, Air India refuted the allegations about the flight being unsafe.
“The lives of passengers and crew were at no point endangered,” the airline submitted in its response to the petition. In its defence, Air India said that the “exercise of route mapping/planning is technical, wherein the knowledge available to the pilot is limited”. Air India added that “with the assistance of the CAE software, the aircraft opts for a route where it will descend to 10,000 ft in 12 minutes, in the event of decompression.”
The Bombay High Court, in its order last week, directed DGCA to consider the question of whether Air India’s leased Boeing 777 aircraft, with 12 minutes of oxygen supply, can, in the event of a decompression, achieve descent to 10,000 feet within 12 minutes and land safely at the planned alternate aerodrome. “It is clarified that we have not expressed any view on the merits of the matter,” the court order said.
