When the aircraft carries serviceable Mode C transponder, the pilot shall continuously operate this mode:
a. Only when directed by ATC
b. Unless otherwise directed by ATC
c. Only when the aircraft is flying within controlled airspace
d. Regardless of ATC instructions
a. Only when directed by ATC
b. Unless otherwise directed by ATC
c. Only when the aircraft is flying within controlled airspace
d. Regardless of ATC instructions