What 411A wrote here above is fully correct.
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A first turbojet type rating (FAA) requires a ride in the aircraft, which is expensive.
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So the best way to do, say a B-737 type rating, is first to get a CE-500 rating then you qualify for any turbojet type rating in level D simulators. I heard of a school advertising a CE-500 Citation rating for US$ 4,995...
Then you go for the B-737 rating, I heard it is $6,000 in level D simulators.
Two type ratings CE-500 and B-737 for total of $11,000
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Another little secret of the trade (and twisting FAA regulations and standards to the best of your advantage) is -
(1) If you have only a single engine rating, by getting a CE-500 rating, you get a multiengine rating at the same time.
(2) If you have a CPL/IR only, and ATPL written, by getting a CE-500 rating, you get the ATPL as well. Check ride no different.
All that for $5,000, good deal.
xxx
Happy contrails