Hey Tamseer.

See for appearing in the UPSC exam u must be having any type of degree courses in ur CV. Since u are doing aircraft maintenance engineering u are having a degree courses with u. U can easily apply for the exam.

There is nothing like u must be opting ARTS field for applying in the UPSC exam. Be confident work hard and apply for it with no doubt.

Ask if u are having any query. 

Good luck