But the engines stopped working too. And an airliners glide ratio is only a little better than a rock under the best of circumstances. And hydraulic systems in airliners are power assisted. Without the power they are extremely hard to maneuver. And if the plane was not flying straight and level when it happened the loss of engines and loss or serious degradation of control surfaces would probably put it into a flat spin, which is what was depicted on screen. Most airliners in around cities are in some kind of holding pattern waiting for or maneuvering to follow landing instructions or maneuvering to reach flight corridors for those leaving.
My dad is a pilot and had a chance to fly a restored B-17 that was flying around the country. He said it was a beast to maneuver with the old style simple hydraulics. That matches with what I have read about those old bombers and even early airliners.
And, WW II movies aside, the glide ratio's of most large aircraft suck. Hell, even the F4U Corsair, one of the best FIGHTERS of the war had only a 1 to 1 ratio. Most modern fighters and bombers have no better. And airliners glide really no better than a bomber, usually not as well.
Light aircraft would do better. They are lighter with more relative lifting surface than most larger craft. Many of them would be able to glide to a landing if they could find a flat empty spot.
As someone who has been around pilots and airports his whole life, as well as someone who has been fascinated by the history of flight and aircraft, I would say that the falling planes were probably the most realistic part of the show.
It was just a lot of the other stuff that was kinda questionable.