The Harrier is a V/STOL aircraft. In addition to making a landing just as a conventional aircraft would, it may also bring itself to a hover directly over its landing pad and then drop down carefully for a 3 point landing.
To accomplish this feat, the nozzles that redirect the thrust from its engines must be rotated to 90 degrees as it is positioned over its landing pad. Then the throttle can be decreased until it touches the ground, at which point the engines can be completely shutdown.
Because the amount of thrust required to fully lift the
aircraft during a hover maneuver is so great, and because the engines work so hard to produce that thrust, they become dangerously hot. Water is injected into the engines to cool them down. A Harrier can hold 150 lbs.of water, which is enough for only 90 seconds worth of engine cooling. Therefore a pilot only has this much time to carefully position the aircraft into its landing position and complete the maneuver. Otherwise the aircraft will overheat.