An active takeoff crack is a dynamic crack that propagates rapidly during the takeoff phase of flight, typically during the high-load conditions encountered during rotation and initial climb. This type of crack often occurs in the heat-treated steel or high-strength aluminum alloys used in landing gear components, such as the gear beam, fork, or axle.

The "active takeoff crack" refers to a critical type of crack that can occur in aircraft, particularly in the landing gear and adjacent structures. This phenomenon is a major concern for aircraft operators, maintainers, and regulatory bodies, as it can lead to catastrophic failures during takeoff, compromising the safety of passengers, crew, and the aircraft itself.