The admission criteria for the course is varied as various institutes have their very own criteria and process of admission. The admission in any of the IIT in this course is through the candidates performance in the Graduate Aptitude Test in Engineering (GATE). Each candidate seeking admission to M. Tech. Aircraft (Aerospace) Engineering is supposed to take the GATE and on the performance in the test and academic record seats are allotted and the private institutes also follow their own process to provide admission in above mentioned course.

For more information about Aerospace Engineering, you can go through below article also -
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http://www.engineering.careers360.com/aerospace-engineering

Good Luck!!!