Using GPS for instant wind correction
Under IFR, GPS is the simplest way to navigate in all phases of flight from takeoff to touchdown. But when an ILS approach is selected, GPS is for “monitoring” only. The pilot is expected to use the ILS localizer and glideslope signals for guidance from the final approach fix to the decision height. However, using GPS one can fly the localizer more easily than would otherwise be possible even if the GPS is only used for ”monitoring”.
One of the challenges of flying an ILS approach is figuring out what heading is required to track the localizer course. When there is no wind, the heading to fly is just the inbound course itself. When a crosswind is present the airplane must crab into the wind to prevent being blown off course. Making matters more complicated, wind speed and direction change during the descent along the glideslope. And of course the localizer becomes very sensitive as the airplane approaches the runway.