Originally Posted by
Twin Wasp
As they say, the revision to 61.51 was supposed to make it clearer that 61.129 and 61.51(e)(iv) go hand in hand.
But they don't. 61.51(e)(iv) requires that the pilot already be rated for the aircraft.
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(iv) When the pilot performs the duties of pilot in command while under the supervision of a qualified pilot in command provided--
(A) The pilot performing the duties of pilot in command
holds a commercial or airline transport pilot certificate and aircraft rating that is appropriate to the category and class of aircraft being flown, if a class rating is appropriate;
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The Commercial ME applicant generally doesn't already have a commercial certificate and an ME rating.