Advise prior to altitude change:

[JOhnH]

When flying VFR using flight following and the controller tells you to advise prior to altitude change, then later that controller hands you off to another controller, does the order to advise survive? Do you need to advise the next controller prior to altitude change?

 

[Jim Logajan]

That is how the regulation reads -- no ifs, ands, or buts other than the emergency exception or not being "in an area where air traffic control is exercised," and that's all A, B, C, D, and E space, plus the G-space where there's a tower with no B/C/D/E-space (yes, there are a few, and I suspect that's why they phrased it that way rather than just "in controlled airspace").

At least one court seems to have quoted 91.123 such that it seems to treat paragraph (a) of it is a necessary prerequisite to determining the "area where air traffic control is exercised."

http://mo.findacase.com/research/wfrmDocViewer.aspx/xq/fac.19731212_0000071.EMO.htm/qx

(Even the FAA was trying to argue their instructions in that case were advisory!)

But the judge seemed to feel the need to quote (a) prior to (b). The other thing to consider is that the regulation specifically DOES NOT say "Except in an emergency, no person may operate an aircraft contrary to an ATC instruction in controlled air space." Clearly they could have written that if that was the intent - it is both shorter and "controlled air space" is more clearly defined. Controlled airspace may be a prerequisite, but it appears it was not intended to be sufficient.

I would think, based on a reading of that case and some others that aren't entirely relevant here, that the FAA would rather not have flight following treated as an exercise of air trafic control, lest it find itself liable for all those flights (when it chooses to allow itself to be sued.)

 

[Jim Logajan]

Then please show me the regulation which says when ATC instructions aren't "mandatory," other than, as it says in 91.123(b), when not "in an area in which air traffic control is exercised" (which, as even Steven has pointed out, includes even some G-space).

How about court cases where the feds are pressed to make an assertion one way or the other? Because the feds in at least one past case (1973) have tried to argue that their communications to an airplane well within an "Airport Traffic Area" (Control Zone) - as that airspace was known then - was advisory; specifically the following:
"SIX NINE GOLF IF THAT'S YOU OUT THERE ABOUT TO TURN FINAL PULL OUT TO YOUR AH WELL JUST PROCEED STRAIGHT ON ACROSS THE FINAL AND ENTER ON A LEFT BASE LEG FOR RUNWAY ONE SEVEN. YOU'LL BE FOLLOWING AN OZARK DC-9 TURNING FINAL ABOUT TWO OUT, MAYBE TO YOUR LEFT AND ABOVE YOU, YOU HAVE HIM?"
But of the above "instruction" the court document states the following was argued by the government:
"[...] the Government asserts that the instruction issued by the local controller to proceed straight across final was merely advisory."