Regulations Governing the Handling of Mail Article 22
The term “airmail” refers to a mail item with postage paid based on the airmail rate and transported via airplane.
中文原文 郵件處理規則第22條
郵件交付相關航空資費，以航空郵路寄遞者，為航空郵件。
English translation for reference only; the Chinese text prevails. Not legal advice.