Something to note, is that most commercial aircraft can glide for anything from 20 to 30 minutes from cruising altitude before they reach sea level. I recall reading many news reports of this particular 747 'plunging' to the earth when all engines failed, but that is not the case.
As noted in the article -
> Eventually, after quarter of an hour without any power, the engines were brought back to life.
In fact, every time your pilot/flight attendant announces that you are on descent to your destination airport, the pilots will have pulled the throttle back to flight idle, and your aircraft is essentially gliding down towards the airport. Engines are pretty much not spooled back up until you are on finals, and the undercarriage/flaps etc. are causing a lot of drag necessitating engine power again to maintain approach speed.