While airborne gravity has been available for decades, only with the advent of airborne gravity gradiometry (AGG), and specifically the FALCON AGG installed in a helicopter, has airborne gravity measurement reached a sensitivity and spatial resolution that can be effective for a wide range of engineering applications. Survey examples and gravity models comparing fixed-wing and helicopter AGG measurements demonstrate that voids as small as 10 m, or tunnels of 4 m width can be detected.