YX28 means: Y means economy class, and X28 means special air tickets sold 28 days in advance.
Extended data:
Domestic air ticket
The cabins of domestic passenger tickets are mainly divided into first class (cabin code F), business class (cabin code C) and economy class (cabin code Y).
Economy class is divided into different seating classes (cabin codes are B, K, H, L, M, Q, X, E, and each airline has different logos and different prices). Discount cabins are arranged in turn. Although these prices belong to economy class, the service enjoyed by the lower cabin is different from that enjoyed by the higher cabin.
The most obvious thing is to book seats and meals on the plane in advance (that is, even if you book seats and meals in advance, you may encounter impossible situations on the plane). There is a very low shipping space that cannot be returned.
International air ticket
The cabins of international air tickets are mainly divided into first class (cabin code F A), business class (cabin code C D J) and economy class (cabin code Y).
The seat level of economy class subordinates is similar to that in China, and there are also regulations that cannot be refunded. However, I can't refund the ticket except for the extremely low shipping space. If I want to cancel my trip, I must call the airline to inform me that I want to cancel my seat. Otherwise, the airline will charge you a fine for not being present (not being present means occupying a seat).
References:
Baidu encyclopedia-aviation