The following is part of the Henry McKay Archives. It is used here on The Black Vault, with permission:
The following is a transcript from an audio cassette recording of Henry McKay, around the 42 second mark. This would have been at either one of his lectures or his course.
The cassette is simply labelled as “UFO Talk H.H.M”. Date unknown. From the files of the Henry McKay UFO Archives:
Now, the three broad categories of UFO:
The “A” category is the astronomical or aerial observation. Of the UFO reports, this would comprise of approximately 75-80%. Now, unfortunately, I do not have any training in astronomy.
A lot of the activity that’s unidentified that’s going on in space may have some military background to it and it’s difficult to extract the information from the authorities.
So, I do not pursue that particular area.
The “B” category is below normal aircraft altitude, or at tree-top level if you will.
And the “C” category is contact with the ground or communication with humans.
That’s the three broad categories. “A” astronomical. “B” below normal aircraft altitude or at 500 foot distance if you will. And “C” category is contact with the ground or some sort of communication.”
– Henry McKay