Mark,

It's pretty clear that your instructor is mistaken, as you have
cited chapter and verse of the pertinent regulatory article.

This also agrees with the FAA's Instrument Flying Handbook,
publication faa-h-8083, pages 8-23 and 8-24, in which the approach
category speeds are based on being 1.3 times the stall speed of the
aircraft in the landing configuration at gross weight. Stall speeds are
never predicated on ground speed. The error in doing so should be
readily apparent.

If your instructor is basing his instruction and recommendation on
"ground speed" then challenge him to show you chapter and verse where
ground speed is the acceptable determining factor. Your ground speed
comes into play on instrument approaces in timing the approach and in
determining your rate of descent for a given glidepath angle. Your
instructor, while well intentioned appears to be "reading too much into
the situation". Using a lower category than authorized can result in a
bust of minimums. Using a higher category than required can result in
not being able to take full advantage of lower minimums.

It would behoove you at this point to also read and know not only
the instrument PTS, but also the FAA Instrument Flying handbook as well
as whatever texts your instructor is using for your ground based
instruction.

Good Luck
Dave

Mark Hansen wrote:
I'm an Instrument Airplane student, and am having a disagreement
with my instructor on one topic - that of Aircraft Approach Categories.

According to 14 CFR Part 97.3 (b), it provides the speed ranges for
the different aircraft categories (A-E). In all the documentation I've
read, this "speed" is the IAS of the airplane.

However, my CFI says that this is based on the Ground Speed. When
we are flying an approach with a tail wind and can see that, although
we are remaining below 90kts IAS, our Ground Speed (shown by the GPS unit)
is just over 90kts, he said I must use the category B minimums.

I understand his reasoning (in that the faster we're moving across
the ground, the faster we'll move out of the protection zone, etc.),
but from what I can find, the FAR doesn't mention ground speed at all.

If I use the minimums associated with the higher of the IAS or
Ground Speed, would I get dinged during a proficiency check?

The reason I ask is that I've been asked questions before where the
examiner was trying to make sure that I completely understood the
rule, and I'm worried that selecting minimums that are higher than
necessary will show that I don't really understand it.

Thanks,