Chris Brooks wrote:
Thanks, that is a good reply.

Do you confirm that if you hear "cross HAIGS at 4000 feet", that you can
immediately descend from whatever altitude you are at. Say you are at 5,000
feet (as I was). If you hear that you can descend to 4,000? Usually won't
the controller issue you a descent to 4,000 and then the crossing
restriction? Such as "descend maintain 4,000... cross HAIGS at 4,000,
cleared ILS 27".

By providing an approach clearance and a crossing restriction, the
controller has authorized you to descend to that altitude immediately,
and to maintain that altitude until you reach the fix where the altitude
restriction applies.

What if they just said "descend maintain 4,000, cleared ILS
27"... is that not proper procedure?

No, that's similar to what was given to TWA 514 (the airliner crash that
initiated the requirement for specific altitudes and clearances). In
that situation, the pilot was established at 7000 when cleared for the
approach, but not yet on a published portion of the procedure. The rules
were less clear back then, but the pilot should have been told to
maintain a specific altitude, as well as a point where that altitude no
longer applied (i.e., maintain 7000 until crossing XXXXX). When the
controller says "maintain 4000" they're supposed to also state the point
where the 4000 restriction no longer applies. It should be "maintain
4000 until HAIGS" if you intercept East of HAIGS, or "4000 until
established on the localizer" if interception is inside of HAIGS. I'm
concerned that some controllers feel that intercepting a localizer
anywhere is all that is needed, but that only works if the localizer
intercept point is within a published part of the procedure, or for this
approach, inside HAIGS.
You can review the TWA crash details at
http://www.aopa.org/asf/asfarticles/sp9806.html