14 C.F.R. § 61.7

Obsolete certificates and ratings.

        (a) The holder of a free-balloon pilot certificate issued before November 1, 1973, may not exercise the privileges of that certificate.

        (b) The holder of a pilot certificate that bears any of the following category ratings without an associated class rating may not exercise the privileges of that category rating:

        (1) Rotorcraft.

        (2) Lighter-than-air.

        (3) Helicopter.

        (4) Autogyro.

Official source