matt weber wrote:

Note the difficulties US ATC had in locating 757's and 767's on 9/11
after the transponders were turned off, and 757 or 767 has a far far
larger radar cross section than a single engine cessna.

After 9/11, I heard them ask aircraft in the vicinity to assist with
identifying unindentified primary targets on their scopes. And
they didn't seem to have any difficulties painting me as a primary
target whenever my transponder went inop (which was not all that
infrequent in those old single-engine C-210's).

-Mike Marron