(a) The holder of a senior rating on August 31, 1970, may at any time
after that date exchange his rating for a facility rating at the same air
traffic control tower. However, if he does not do so before August 31,
1971, he may not thereafter exercise the privileges of his senior rating
at the control tower concerned until he makes the exchange.
(b) The holder of a junior rating on August 31, 1970, may not control
air traffic, at any operating position at the control tower concerned,
until he has met the applicable requirements of §65.37 of this part.
However, before meeting those requirements he may control air traffic
under the supervision, where required, of an operator with a senior rating
(or facility rating) in accordance with §65.41 of this part in effect
before August 31, 1970