They don’t. However, they often apply a bit of power when they’re close to the runway because they are about to change the flight characteristics of their airplane.
As the plane gets closer to the runway, the pilots will apply “flaps” which are surfaces that make the wing profile thicker to give the plane more lift at lower speeds. However, the last thing the pilot wants to do is to slow the plane down too much – that could result in a stall which, that close to the ground could be a disaster as the only way to get out of it is to apply power and point the nose of the plane down. As such, the pilots will often use auto-throttle to automatically adjust their speed, but will also make sure the plane isn’t slowing down too fast.
About 50 feet from the ground the pilot will “flare” the plane- lift the nose up so the plane has a lot more drag to slow it down as it approaches the runway and to slow down its vertical speed as well so it “touches” the runway rather than “slamming into” the runway. If it’s done right the wing gear take all the force of the landing and the nose falls down slower putting less stress on the nose gear. Again, this is pretty much a maneuver where the point of the exercise is to stall the plane at zero altitude above the ground so the plane goes down and won’t start flying again. Again, a bit of power at this point may be necessary, particularly if the winds are tricky. If a pilot is “late” to flare, the plane may bounce off the runway, meaning the pilots should apply full power and do a go-around rather than trying to land the plane again. Runway bounces happen all the time, but the only time they result in accidents is if the pilots try to force the plane onto the ground again.
Source:Quora
