Has something to do with the cone of ambiguity, or no-course signal
zone. It gets wider the higher the TACAN aircraft is. There's a chart in
the holding pattern manual that shows the distance vs. altitude, and a
DME fix can't even be used if it's within the specified distance,
because the TACAN-only aircraft won't ever receive it while he's in that
cone.

JPH

Roy Smith wrote:
J Haggerty wrote:

TACAN aircraft cannot hold directly over a
VORTAC or TACAN (unless they also have a VOR).


Why not?