Business class passengers are allowed to pre-board the aircraft 20 minutes before economy class.

pre-board 是由前缀 pre-（表示“在...之前”）和动词 board（登机、登船）组成的复合动词，意思是“提前登机”。pre-board 指在常规登机时间之前允许特定乘客先行登机的安排。