I am fully aware what constitutes an M1 Visa, regarding the 18 hour of study a week.
However, US Immigration, and particularly the officer for South East Florida, will be more than happy to inform you that flight training of any kind requires a visa, and was more than happy to send someone home during my time in the states this year. "If training is required, visa is required" is how it was summarised.
Agreed, the reference material is grey, and sometimes hard to find.
I certainly wouldn't take the chance.
I just pity the guy who was sent home / or to the Bahamas to change his visa
