both Boeing and Airbus have quietly begun double-booking some of their delivery slots, in case a customer collapses.

both Boeing and Airbus have quietly begun double-booking some of their delivery slots, in case a customer collapses.

double-book : ~을 중복으로 예약하다.
some of ~ : ~ 의 일부
double-book some of their delivery slots : 그들의 delivery slot의 일부를 중복으로 예약 하다.