Diploma

No, you can not pursue MBA after completing your diploma in aviation only you can pursue MBA after completing your graduation in any stream as MBA is master's degree and also a B.tech Degree holder can pursue MBA. If you want to pursue MBA you need to complete your graduation first as you have done your diploma in aviation. So, you can do BBA In Travel & Tourism management and after that, you can go for MBA in the same. As Tourism industry is spreading wide these days, it has lots of opportunities and career option as it has become one of the fastest growing career industry with the tremendous growth in the economy. Tourism of India is the most attractive and emerging sector in the world and has demanded more number of trained professionals in this field:
http://www.quantumuniversity.edu.in/

Post Graduate Diploma in Computer Application is a course for the students who have completed their graduation and have an interest in computer science. Admission is done on the basis of merit of the student and in India there are many colleges offering this course:
1. Chhatrapati Shahu Ji Maharaj University
This college is formerly known as Kanpur University. College is a state government college Est. in 1966. Spread in 250 acers of campus and give quality education to student since many years.
Our current President Shri. Ram Nath Kovind is a notable alumni of this college.
2. Dibrugarh University Assam.
This college is also a state government college est. in 1965. It has been awarded A grade by NAAC and a member of AIU. This college has also best faculty member and strong alumni network.
3. Annamalani University Tamil Nadu
This college is one of the reputed colleges in all over India est. in 1979. This college offers distance education in this course.
4. Patna Science College
Patna Science College is affiliated to Patna University and is one of the oldest colleges in India, est. in 1917. This college offers both regular and distance education in this course.