photo by Faisal Akram
A quick warning: If you are already afraid of flying, this column probably won’t help.
A domestic Jet Airways flight recently departed Mumbai, India carrying 166 passengers and five crew members. A switch in the cockpit remained set to the wrong position, and the cabin never pressurized. As the Boeing 737 gained altitude, some passengers bled from their noses or ears. Eventually, oxygen masks dropped. The flight returned to its point of origin and made a safe landing. While passengers were presumably shaken, and some sustained minor injuries, the flight managed to avoid a major disaster.
We need only look back to 2005 to see an example of how badly this could have played out. A Helios Airways flight from Cyprus to Athens took off with the same incorrectly set cabin pressurization switch. However, in that case, the crew lost consciousness due to oxygen deprivation before they could turn the flight back. The plane climbed to 34,000 feet and proceeded on autopilot, eventually entering a holding pattern over Athens. A flight attendant who had access to a longer-lasting supply of emergency oxygen reportedly made a last-minute attempt to gain control of the plane, but failed. The plane crashed when it ran out of fuel, killing everyone onboard.
Oxygen deprivation, or hypoxia, can deplete your cognitive abilities in less than a minute. The inquiry into the Helios disaster found that the flight crew failed to correctly identify relevant warnings and did not notice indications that masks had deployed; it is likely that hypoxia contributed to their inability to react to the problem in time.
The Helios tragedy – like the more recent averted disaster in India – raises the question of why Boeing 737s have a manual setting for cabin pressure at all when leaving the switch in that position can have such catastrophic consequences. There are various situations when manual control is useful; it allows for pressurization checks on grounded aircraft, flying an empty flight unpressurized if necessary because of damage to the plane, or an emergency option if both of the aircraft’s digital pressurization controllers fail in flight. These are uncommon scenarios, but not unheard of. In fact, an on-ground pressurization check was why the Helios flight’s switch was set to manual prior to takeoff; the engineer failed to reset the switch to automatic after the test was complete, and none of the subsequent crew checks caught the oversight.
Given enough chances, anything that can go wrong eventually will go wrong. The Boeing 737 is one of the workhorses of global air travel, making thousands of flights every day. Boeing calculated that a 737 takes off or lands every two seconds, on average, and that the 737 represents more than one in four commercial plans in service today. So this type of accident was bound to occur sooner or later.
Apparently the situation on the Helios flight was worsened because the cockpit alarm horn that sounded is used to convey information about more than one type of malfunction. The pilots thought they were dealing with something else and, already oxygen-deprived, they did not check the cabin pressure switch. In 2012 the Federal Aviation Administration ordered safety modifications to the Boeing 737 to prevent these situations. Airlines were given until Nov. 7, 2018, to make the modifications. News coverage of the Jet Airways flight did not note whether the aircraft had been modified as per this requirement; this is likely to be a subject of investigation.
Regardless, even the modified aircraft rely on flight crews to check the cabin pressurization setting. This is addressed three times in preflight and takeoff checklists. So the initial error can still occur. In the case of Jet Airways, the pilots correctly diagnosed their problem and returned to ground. Once the plane got below 10,000 feet, the passengers would not have needed supplemental oxygen. The duration of the emergency would have been fairly brief – about 45 minutes altogether, according to one passenger’s tweet, with a much shorter exposure to potential hypoxia.
The ending in 2018 was far better than in 2005. Is this because the modifications have been made and the new “aural warning system” properly alerted the pilots to the nature of the problem? Or was the better outcome just a matter of luck?
I have little doubt that Boeing and the FAA will pay close attention to the investigation in India, which needs to move along quickly given the number of Boeing 737 flights around the world. Air safety agencies like India’s Directorate General of Civil Aviation typically work closely with aircraft manufacturers anyway.
There is not much for ordinary air travelers to do in the meantime except pay attention to their preflight briefings, especially the part about what to do if the oxygen masks descend. Grab yours and put it on immediately. Try to help those around you if necessary only after your mask is secure. Rehearse the procedure in your mind while your fellow passengers struggle to lift their overstuffed carry-ons into the overhead bins.
And maybe keep an eye out for follow-up news to indicate that the tragedy-that-wasn’t in India does not engender a complacent response. If this incident was mere luck, things could go worse next time.