Hello,

The optionals subjects listed in UPSC exams are as follows-

Agriculture
Animal Husbandry and Veterinary Science
Anthropology
Botany
Chemistry
Civil Engineering
Commerce & Accountancy
Economics
Electrical EngineeringSyllabus
Geography
GeologySyllabus
History
Law
Management
Mathematics
Mechanical Engineering
Medical Science
Philosophy
Physics
Political Science & International Relations
Psychology
Public Administration
Sociology
Statistics
Zoology

Other than this, there are also literature subjects such as

Assamese,
Bengali,
Bodo,
Dogri,
Gujarat,
Hindi,
Kannada,
Kashmiri,
Konkani,
Maithili,
Malayalam,
Manipuri,
Marathi,
Nepali,
Oriya,
Punjabi,
Sanskrit,
Santhali,
Sindhi,
Tamil,
Telugu,
Urdu,
English

See, aviation as a subject isn't listed here, but if you're comfortable with Mathematics, Physics, or even Chemistry for that matter, you can consider these, these are scoring subjects , also there is good availability of study materials, since your graduation subject isn't listed in optional, I would suggest you to pick a subject which you find interesting, because the syllabus of two optional subject is quite extensive,  it helps if one has his or her graduation subject as it saves a lot of time in starting afresh, however there are many aspirants who do opt for completely different options such as a BTech graduate going for philosophy as an optional, this was of one of the topper, and if you have inclination for humanities subject, and please go through the syllabus to know more about how much to read, what time it will take to complete etc, you can go for geography, history, sociology, political science, economics etc, as there is considerable overlap with the syllabus of General Studies, eventually you have to weigh the pros and cons, and take the decision.

Hey,

The subjects are:

• Geography
• Agriculture
• History
• Law
• Geology
• Management
• Sociology
• Chemistry
• Physics
• Medical science
• Philosophy
• Zoology
• Electrical engineering
• Chemistry
• Civil engineering
• Public administration
• Political science and International relations
• Psychology
• Animal husbandry and veterinary science
• Mechanical engineering
• Statistics
• Botany
• Commerce and accountancy/ economics
• Mathematics

These are the subjects you can choose for the exam. The eligibility criteria is that you have to have a bachelor's degree and you have to prepare for the exams you have chosen in Mains separately if you didn't do them in your bachelor's.

Hope you find this helpful.

ALL THE BEST.