10 hours signed off by a CFII.
WRONG!!!!!! It's 15 hours
61.65 details the requirements for an FAA IR
61.65 (d)(i) mentions 15 hours from an
authorized instructor - The FAA will accept any training done with a JAA instructor (even as part of an IMC course!) to count towards these 15 hours provided they are done under a JAA/CAA (ICAO) approved course (IR or IMC in the UK)..... you’d be a star though if you manage to get to the FAA IR standard in only 15 hours of dual instruction.
There is a major difference in the JAA and the FAA system in the fact that under JAA the schools carry the approvals/restrictions in what courses they can teach while in the FAA system the approvals/restrictions are carried by the instructor (under part 61).
Any other instrument time done with a JAA instructor (ie. ex 19 - instrument appreciation for your JAA PPL) can be counted towards the total 40 hours you need as described in 61.65 (2).
I'll include the link to the regulations for those who are interested
http://ecfr.gpoaccess.gov/cgi/t/text....2.1.4&idno=14
In theory you only need to fly once with an FAA CFII - to obtain the endorsement for a skill test (provided you do a good job on your flight =)) but you may find that most (me included) won't give you the sign off based on one flight performance unless that instructor has been able to follow your progress through the course. Remember that you also need a CFII to endorse your for the theoretical test.
Obtaining TSA approval for an FAA CFI/CFII is relatively straight forward. I registered online for it and a few hours later a guy from the New York IFO called to ask a few questions...and that was it =)
Happy flying!