That isn't true at all. 61.195(c) states that the flight instructor must have the category and class on his pilot certificate.
I don't see it.
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61.195 (c) Instrument Rating. A flight instructor who provides instrument flight training for the issuance of an instrument rating or a type rating not limited to VFR must hold
an instrument rating on his or her flight instructor certificate and pilot certificate that is appropriate to the category and class of aircraft in which instrument training is being provided.
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Now, if it said, "...must hold an instrument rating on his or her flight instructor certificate
, and a pilot certificate that is appropriate to the category and class of aircraft in which instrument training is being provided." I'd see the point.
Of course, you'd still have to deal with the fact that you don't see "Notwithstanding subparagraph (b)" in (c), or "Except as provided in subparagraph (c)..." in (b), or one of the other common phrases the FAR uses in other sections to let us know that something, like (b) doesn't count anymore. And, of course, (b) very clearly tells us
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Aircraft ratings. A flight instructor may not conduct flight training in any aircraft for which the flight instructor does not hold:
(1) A pilot certificate and flight instructor certificate with the applicable category and class rating; and
(2) If appropriate, a type rating.
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But...
There is no doubt that the FAA has applied 61.195(c) as though the extra words and provisions were there. The now-defunct Part 61 FAQ even specifically said it was okay.
The issue almost came to a head in 2004. The FAA Eastern Regional Legal Counsel issued an opinion that said, no, you =do= have to have the applicable aircraft ratings on both the CFI and Commercial certificates. Someone pointing out the Opinion to John Lynch, who wrote the FAQ, got a response that said in part, "Looking at § 61.195(c), I now believe my answer is wrong and Ms. Alkalay's (the legal counsel) answer is correct."
There was even a certificate action begun on the west coast (not Alkalay's territory) against a CFII for a violation. Fortunately, at least in part because of the confusion on the issue caused by the FAQ, the certificate action was terminated. I don't know whether the two are related, but the termination of the FAQ came not long after that.
The bad news is that the FAA still hasn't formally resolved the inconsistency.
Now =that's= what I call gray. Gray enough that I'd want a written opinion from the FAA before I'd do it.