By the mid-60s, the Air Force was receiving 1,000 new UFO sighting reports a year and membership in UFO and "contactee" clubs had swelled. In addition to a steady stream of magazine articles, more than two dozen books on the subject were published between 1966 and 1968.

A much-awaited 1969 congressional report concluded that all UFO sightings could be explained as hoaxes or natural phenomena, and decreed that there was no scientific justification for any further investigations. MacDonald denounced the report as a whitewash and went on to pursue his own independent UFO investigations. But his vehemence regarding UFOs alienated many of his colleagues, and apparently lost him the respect of his audience on the subject of the SST (Supersonic Transport).

"It is my present estimate," MacDonald testified before the House Appropriations Subcommittee for Transportation on Monday, March 1, 1971, "that the operation of SSTs at the now-estimated fleet levels predicted for 1980-85 could so increase transmission of solar ultraviolet radiation as to cause something on the order of 5-10,000 additional skin cancer cases per year in just the U.S. alone."

The government ultimately scrapped the SST program because the plane was so costly and made so much noise.