The FAA hass opened an investigation into why Mayor Bloomberg's private helicopter pilot landed in a Meadowlands parking lot last night before a U2 concert.Pilot Toby Mason was on a trial run to this helipad, planning to return later with the boss. Instead he landed the Bloomberg, inc. chopper ½ a mile away as thousands of concert-goers were walking on surrounding pathways.The mayor was hurrying from an appearance in Washington Heights to hear U2's Bono praise him in front of the sell out crowd, while a Bloomberg campaign camera rolled on the scene. After the chopper mishap, he flew instead to Teterboro Airport and drove over. Asked today about the environmental unfriendliness of flying 5 miles, the Mayor responded maybe he should've "swum across the river to save energy."