Move to the northwest corner of the building at an altitude of about 850 ft. there is a nook here. Look on the underside of the overhang -- the "ceiling" -- in the nook and you should find a little green switch. The easiest way to hit this switch is to have one player stand on top of the aircraft while it hovers under the switch.
Once this switch is activated, fly directly south and through the large building with the giant, oblong gap near its apex. It is one of the taller buildings in that direction. Fly through the gap in the building and your falcon will suddenly turn into a Pelican. If you are flying a Banshee (you'll need to sky jack it elsewhere in the level), you will turn into a covey dropship