Full FAA Chronology at this link.
19610525: A Special Civil Air Regulation effective this date banned the use of portable FM radios on U.S. civil aircraft. Radios having oscillators operating within or very near the Very High Frequency (VHF) band affected the VHF radio navigation system of the aircraft.
19700525: FAA issued the first supplemental type certificate for installation and operation of area navigation equipment in general aviation aircraft to the Butler National Corporation for use of the Butler Vector Analog Computer. The certificate permitted the use of this equipment during the en route, terminal, and approach phases of operation. (See October 1, 1969.)
19780525: PATCO began intermittent slowdowns to protest the refusal of some U.S. flag carriers to provide controllers with overseas familiarization flights.
This Day in FAA History: May 25th
