Peter Duniho wrote:


As far as I know, the language used in the controller's handbook allows
altitude changes any time a controller is supposed to vector an airplane.
It would be a significant change, and would add even more complexity to the
handbook, to call out this particular case as a situation where the
controller is permitted to providing heading guidance but not altitude.

A controller owns a chunk of airspace. As long as I meet the separation
standards I can do whatever I need to with you.



The main reason that TCAS doesn't cause accidents today is that it's used in
a way that is unlikely to cause accidents. Airplanes that are in IMC are
being positively controlled by ATC, and the TCAS should only provide a
warning when ATC has made an egregious error. That doesn't happen very
often. Furthermore, the airplanes involved are both under radar control, so
even though the TCAS doesn't know it, the Mode C *has* been verified.
Airplanes that are in VMC, whether under positive control by ATC or not,
have the ability to use the TCAS to help them *spot traffic*, rather than
just blindly trust the TCAS to tell them what to do. The pilots can then
make a course adjustment as appropriate, based on *what they see*.

TCAS is most useful in class D type tower situations. These are where
you are most likely to have the spam cans flying around with unverified
mode C. If the TCAS gives an RA the airliner must take the action
suggested. Places like Orange County and Pontiac come to mind. Lots
and lots of VFR targets