In article .net,
says...


When is it not the right thing to do?




When you are over, or very close to the station - you expect it to go
full-scale, and you have to wait it out a bit. (VOR)

In turbulence, you may see a momentary, full-scale GS needle (it only takes
0.7°, either way). If you see it happen and you are confident in recovering
rapidly. (GS)

When another aircraft passes (or parks!!) in front of the loc emitter, you may
get a momentary spurious deflection. (LOC)

When you are in sight of the runway, and able to make a normal landing, to the
intended runway, using normal maneuvers!


I don't mean to be facetious in stating the "obvious" - but perhaps that's why
there's no specific rule. We are not mechanical "needle-chasers"- we're
expected to understand what we're doing, and exercise good judgment. On the
other hand, if you are in IMC and you have one or the other pegged for some
time, you have not flown the approach to an acceptable standard and the only
logical thing to do is to break it off. Failing to do so may not be a direct
violation of regs the instant the needle goes to the peg, but after some time
you are likely to run afoul of FARs or terrain. G/S high? You haven't busted
minimum altitude, but you haven't flown the published approach either (a
requirement) Too high and you can get a false GS. GS low - no comment.