Once the pilot announces that the plane is making its final descent, everybody relaxes.
(Maybe not the people that hate the moments of takeoff and landing, but pretty much everybody else...)
Once you reach that point, everyone just assumes that the flight has been a success and that they'll soon be released from the small-seated, metal, claustrophobia tube that they've been strapped into for what felt like a lifetime.
For the 175 people on British Airways flight BA422 from London to Valencia, Spain, though, those moments of peace and reprieve quickly became moments of panic and fear when the entire cabin filled with smoke.
Lucy Brown, a passenger on the plane, said the smoke had a metallic, chemical odor to it.
"Passengers started shouting they couldn't breathe. We covered our mouths with our clothes. We don't know why oxygen masks didn't deploy."
According to British Airways, although the pilots' oxygen masks and goggles were deployed, the passengers' were not because the system simply isn't designed that way.
"Oxygen masks are used for loss of pressurization. It is not standard procedure for oxygen masks to be used when there is smoke in the cabin and at low altitude.... unlike pilot and cabin crew oxygen systems, are not designed to be used in smoke events as they mix the oxygen supply with the ambient air."
According to CNN, three passengers were taken to the hospital, but they were all discharged.