For these 50 Objects, a small Helicopter has proven itself. The Buzzard Helicopter can be found at the bottom right of the map, alternatively you can you buy it for $ 2,000,000. At the beginning of the video you can see the place where you get it.
In the City you will find 2 more helicopters, a Police helicopter and the Medicopters on the roof of the Hospital. Both are a little wider and longer than the Buzzard and 2 Bridges Could there be problems. (15/16)
Thus, a bridge is counted, it is important that you offend neither the helicopter nor with the rotor blades somewhere or touching the water. Looks exactly it comes the yellow message at the bridges, which has counted the bridge. They either did not fly back immediately or load your Save. Should you not do this and end up with 49 / 50 bridges, you must fly again all Bridges to find your missing Bridge.
The overview Map of all 50 Bridges:
Timelinks (match up with Map Numbers):