- do you mean that for a rating you do not need a TSA nor a M-1 ? I am surprised by that.
TSA approval is required for:
- An initial airmens rating (aka your initial PPL or other initial license)
- A multi-engine rating
- An instrument rating
- A type rating for aircraft over a certain number of pounds (17.000 or so, from memory)
Taildragger, seaplane and such are exempted. The TSA is only interested in people coming to the US to significantly enhance their ability to fly a large airliner into a building. (Sounds cruel but that's almost the exact wording in the various TSA bills etc.)
An M1 visa is required if the primary reason for your visit to the US is getting trained for something. But since your primary reason is work-related and the flight training is only incidental to that, you need a visa for whatever work-related thing you're doing. Or, if the work-related thing qualifies, and you are otherwise qualified, you can get in under the Visa Waiver Program. (But don't forget ESTA in that case.)
However, as Adam points out, you need an FAA license to put the seaplane rating on. If its a 61.95 "piggyback" FAA PPL then you can simply pick that up (after a little paperwork exercise between you, the FAA and the CAA) at the nearest FSDO but you need to remember that you're building a house of cards: Your seaplane rating is based on your FAA PPL, which is based on your CAA PPL and your medical. If any of these crumble (for instance because the number of your CAA license changes) the house of cards comes tumbling down. Is that important? If you're just doing the seaplane rating as a thrill activity, with no serious intention to use it ever after, it's probably not. But you wouldn't want to get an instrument rating and put it on such a piggyback certificate.
The alternative is to get a standalone FAA PPL. But this is going to require a little more training than just the BFR for the 61.95 piggyback and it'll be harder to argue that you still don't need an M1 visa. Also, we've had a heated debate on here a while ago about whether you need TSA clearance to do a standalone FAA PPL when you are already the holder of another ICAO PPL. I think you don't, and others think you do, and the discussion ended inconclusively - in the end nobody involved went as far as getting the TSA interpretation in writing. Look up the discussion if you want to, and see who you agree with. This is not the place to repeat it.
- Furthermore, can the FAA instructor give you the seaplane rating on your JAR? Am a bit more surprised
No, he can not. He can only give you the FAA seaplane rating on your FAA PPL (piggyback or standalone).
Also I think the requirements of the JAA seaplane rating and FAA seaplane rating are different enough that the CAA will not give you your JAA seaplane rating solely based on your FAA seaplane rating. I would assume that the training would be accepted, but not the various exams, so you would have to do some further exams over here. But I haven't dived deep enough into the regulations to be sure.