§ 65.50 Currency requirements.
The holder of an air traffic control tower operator certificate may not perform any duties under that certificate unless—
(a) He has served for at least three of the preceding 6 months as an air traffic control tower operator at the control tower to which his facility rating applies, or at the operating positions for which he has qualified; or
(b) He has shown that he meets the requirements for his certificate and facility rating at the control tower concerned, or for operating at positions for which he has previously qualified.