OK, here we go again.
Just to make a long story short, the M-1 visa was NOT originally intended to be a flight training visa.
Prior to 2001 a visa was not required for flight training.
Since there was no specific flight training visa, flight training was added to whatever else you could do on the M-1.
Which also means that not all of the M-1 rules may apply to flight training:
The academic student is defined as a "bona fide student qualified to pursue a full course of study and who seeks to enter the United States temporarily and solely for the purpose of pursuing such a course of study consistent with section 214(l) at an established college, university, seminary, conservatory, academic high school, elementary school, or other academic institution or in a language training program in the United States." The vocational student is defined as "an alien having a residence in a foreign country which he has no intention of abandoning who seeks to enter the United States temporarily and solely for the purpose of pursuing a full course of study at an established vocational or other recognized nonacademic institution (other than in a language training program) in the United States." 8 USC § 1101(a)(15)(f) and (m). A "full course of studies" is defined separately for academic and vocational students. For vocational students, a "full course of studies" is defined as at least 12 semester hours if the school is a community college or junior college, 12 hours per week if it is a postsecondary vocational or business school, 18 clock hours of attendance a week if the dominant part of the course consists of classroom instruction in a vocational school, and 22 clock hours of attendance a week if the dominant part of the course of study consists of "shop or laboratory work." 8 CFR § 214.2(m)(9). For academic students, the hours required for a "full course of studies" depend on the type of program (e.g., postgraduate, undergraduate, language school) that the student is taking. 8 CFR § 214.2(f)(6). Students who do not meet these hourly requirements do not qualify for an M-1 or F-1 visa. However, they can be admitted under a B-1/B-2 visa if the inspector determines that their course of study is incidental to their primary purpose of pleasure or for a business related purpose.
Highlights in blue: I don't see flight training specifically mentioned there so the assume that it is included is very risky.
Do not qualify is not the same as "do not need one".
Selfin is correct in his post in that you can enter under business visa if the flying is incidental to your stay and less than 18 (or 22) hours per week
I beg to differ, it does NOT mention flying anywhere in the above quoted rule.
It mentions class room instruction or "shop or laboratory".
Only Part 141 certified schools can accept foreign students and have the capability to issue the I-20 which is the visa application form.
Schools that tell you that you do not need a visa are either blatantly lying or simply misinformed. IN ANY CASE, THEY ARE NOT AT RISK, YOU ARE.
An Immigration official will not accept and "I didn't know" or "they told me so" story and you will be forced to quit your training and be deported with an immigration violation which will barr you from entering the USA for up to 10 years.
Guitarboy, you DO NOT NEED A VISA for flight training, you may need a visa to enter, depends which country you are from.
You already hold all the certificates for which a flight training visa is required.
And your M-1 visa may be valid but an M-1 can only be used if it is accompagnied by a valid I-20 issued by a school which has the authority to do so. So attempting to enter the US on your M-1 (without the I-20) will not work and you will likely be denied.