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Many state agencies are investigating the use of unmanned aerial systems (UASs) for bridge inspections. Some agencies are receiving pressure from consultants and their own administrations to implement UAS inspections with limited knowledge of their efficacy. This paper studies the feasibility of using UASs for fatigue crack detection in bridges with fracture critical members (FCMs) through real-time and postflight visual inspection. The effects of surface illumination on the maximum crack-to-camera (MCC) distance at which a fatigue crack can be detected were investigated in the laboratory. Mock field inspections evaluated the achievable crack-to-platform (ACP) distance in Global Positioning System (GPS)-denied and windy environments to determine whether known cracks can be identified at achievable standoff distances. Finally, two FCM inspections demonstrated the field performance of UASs in identifying …