James Robinson wrote:

A Guy Called Tyketto wrote:

When did the Wake Turbulence advisory become standard in the
.65? From what I've read (I got into aviation in 2000), it happened
shortly after the King Air crash at KSNA that killed the founder of
In-N-Out Burger. It was concluded that the King Air had been caught
in the UAL B757's wake, rolled into a steep descent and crashed.

I don't know when it started, but might be able to narrow it a bit.

There were extensive tests done by NASA in the 1950s into the subject,
and various Advisory Circulars were issued warning pilots of the
danger. One I found that dates from early 1965 mentions that
controllers might use the expression "Caution, wake turbulence". It
therefore goes back at least that far.

(That should have been NACA, which was NASA's predecessor.)

In looking a bit more, it seems that 7110.65 evolved in the 1970s from
simply a cautionary warning to establishing separations based on aircraft
type and size. There is an historic discussion in the following link:

http://www.flightsafety.org/fsd/fsd_mar-apr02.pdf