1. Air tickets and train tickets usually require a one-time payment, while online loans are mainly small short-term loans, which can't meet the capital demand for buying air tickets or train tickets.

2. Online loans usually have higher interest rates and extra fees. If it is used to buy high-priced tickets, it may lead to excessive burden and increase the difficulty of repayment.

3. Online loans often have restrictions, such as the borrower's credit rating and proof of income. These conditions may be difficult to meet the requirements of purchasing air tickets or train tickets.

4. Buying air tickets or train tickets belongs to personal consumption, which is inconsistent with the purpose that online loans are generally used for emergency or capital turnover.

Summary: Due to the characteristics and limitations of online lending, it cannot be used to buy airline tickets or train tickets. It is suggested to consider other financing methods or plan savings according to personal economic situation.