Since thats the case what I would suggest is to explain that, or ask the aviation school to state that on the letter i.e. that you can start at any time and no deadline, upon approval of your visa of course.Actually in my course there is anytime intake throughout the year. As it was a flight training course. But it was necessary to state a date for course augment so we selected august 1,2019 . Because I had confidence that it will be approved. But it didn't so ..
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As you said when i applied 2nd time the LOA was still valid and 12 days were left as per LOA date. Now it has surpassed the date so after getting the new LOA ....will it help or still question arise
Not sure how long is your training course or for what purpose, but if you are just taking it for pleasure or extra hours and if its for couple of months only then in my opinion it might not be a strong student visa application, compared to someone for example who just finished high-school and going to attend a 2-4 year program. Not discouraging you but making sure you know what could affect your application so you don't get rejected many times. Wish you the best on your next application.