According to the query of official website of Beihang University Library, the status of the number of books borrowed by readers is shown as loanable. You should go through the entrustment procedures online (library website, WeChat official account, Beihang WeChat applet, Beihang Information) and choose the place to pick up the books. The application will be kept for 5 days. When the book expires, it has not been returned to the library, and readers need to go through the entrustment formalities again.