One of the requirements to be a flight instructor in the USA is FAA theoretical exams.
Can I sit those exams with EASA ATPL theory basis? Also, do I have the right to sit those exams without completing an official FAA theory exam preparation process?
There is no official theory exam preparation process that is required to be able to take the test, you can do all preparation on your own. If you are asking if having passed the EASA ATP theory exam means you don't have to take the FAA CFI then the answer is no, you definitely would have to take the exam, although I don't think that's your question.
I think what you're asking is if the material in the EASA ATP is the same in the FAA CFI and you don't need to study. While the material is very similar and there will be a lot of overlap the two are not the same, there will be questions which ask specifically about FAA regulations, testing standards and student training which are not obvious and you are not likely to pass without knowing the material.
You are going to have to be a little bit more clear with your question. I don't know exactly what you are asking.
With that said, for the CFI-Airplane initial practical test, you will have to have taken the CFI Aeronautical Knowledge Test (I hope I have the current wording correctly). As far as I know, there are no substitutions, and you must take that test.
Additionally, you will need to take a Fundamentals of Instruction test, unless you already have a Ground Instructor certificate or you are an accredited teacher. Around here if one is "licensed" to teach K or 1st grade, that is considered adequate to waive the FOI test.
The knowledge for a CFI is quite different from the knowledge needed for an ATP (while ATPs may teach in their work). Furthermore, the expectations and rules for CFIs vary between countries. I know Canadian CFIs who have had to struggle with the US CFI coursework, despite their obvious competence and excellent track record in Canada.
One more item worth mentioning: The ability to answer as well as ask questions in a clear and unambiguous manner is an expectation of CFI's in the US. So you will want to hone your skills a bit, based upon the clarity of the question you asked.
The testing requirements are spelled out in 14 CFR §61.183(d)(e)(f), which require you to received a logbook endorsement from an authorized instructor to take the fundamentals of instruction knowledge exam. These requirements can be waived if you are currently employed as a teacher in junior high or high school or are a college professor. The only other requirement is that you pass an aeronautical knowledge exam appropriate to the category and class of aircraft you are applying for on a flight instructor’s certificate.
(d) Receive a logbook endorsement from an authorized instructor on the fundamentals of instructing listed in §61.185 of this part appropriate to the required knowledge test;
(e) Pass a knowledge test on the areas listed in §61.185(a)(1) of this part, unless the applicant:
(1) Holds a flight instructor certificate or ground instructor certificate issued under this part;
(2) Holds a teacher’s certificate issued by a State, county, city, or municipality that authorizes the person to teach at an educational level of the 7th grade or higher; or
(3) Is employed as a teacher at an accredited college or university.
(f) Pass a knowledge test on the aeronautical knowledge areas listed in §61.185(a)(2) and (a)(3) of this part that are appropriate to the flight instructor rating sought;
As to specific preparation for the flight instructor aeronautical knowledge exam, there is no special requirement for this and It does not require a formal ground school or home study course nor an instructor endorsement to take it. You will be required to receive an instructor sign off to take the fundamentals of instruction exam, and a formal study course is recommended as preparation for this.
I’d also recommend a formal ground school with experienced instructors for preparation to obtain an instructor rating. Having the knowledge of how to fly and airplane is one thing. Being able to teach another person how to fly is an entirely different animal. Some formative tutelage by an experienced instructor on all the knowledge and practical nuances required for an instructor certificate can go a long way. The FI and CFI airplane knowledge exams aren’t bad, but the CFI practical test is going to be pretty grueling. Mine was 10 hours long - 7.5 oral, 2.5 flying - and probably the most difficult exam I ever had in my life.
