Description

Although the TCAS RA function is inhibited when an aircraft is on the ground or when the aircraft is airborne at very low altitudes, it is very important for operational safety that the system is selected on before take off, to ensure that the RA function will be active as soon as the built-in system constraints allow this during the initial climb. It would be completely impracticable for flight crew to routinely select TCAS on (or off) whilst airborne at low altitude.