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That is exactly what a TCAS RA does, and it relies on "unverified" Mode C.

As I mentioned, this is not as safe as people (i.e. you) would like to
think.

But, a merging target vector should not include an altitude change unless
the
controller has the altitude available, and then only as a last resort to
an
avoidance vector.

Your original question was regarding why vectoring is not part of the ATC
standard procedures for dealing with a VFR target. I'm simply answering
that. You are correct that one could limit the vector to no altitude
changes. But that's simply not how the handbook is written.

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.

I'm not interested in a debate, and I don't see why you seem to be itching
for one. If you really want to debate the matter, call up the FAA and
discuss it with them. They wrote the controller's handbook, not I.

I guess that's a matter of debate. A faulty Mode C readout could cause
a
TCAS unit to cause an accident, rather than avoid one.

Well, so far it has only prevented accidents. Had it been used properly
on the
Swiss border, a lot of folks would still be alive today..

I have a friend who would never wear a seatbelt, because she had a relative
who had been thrown from a car in an accident and walked away unscathed.
The logic she was using is similar to your use of a single example to
justify the use of TCAS.

I assure you that if controllers started using unverified Mode C returns to
provide altitude changes for traffic avoidance on a regular basis,
eventually someone would wind up at the same altitude of traffic that ATC
thought they were moving them away from.

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*.

The controller rules are not written to allow things that are "mostly safe".
They are written to try to make sure that the controller's actions are 100%
safe in ALL situations. In cases where the controller is unable to know for
certain that they are able to separate traffic, the controller is simply not
allowed to attempt it. As such, an unconfirmed Mode C readout is simply not
a piece of information that a controller is allowed to use for positive
control of another aircraft.

It's sort of the Hippocratic Oath of air traffic control. Whatever else
they do, a controller should not make the situation worse.

Pete