unscheduled

adjectives

not scheduled or not on a regular schedule
"an unscheduled meeting"; "the plane made an unscheduled stop at Gander for refueling"
unscheduled
antonym
scheduled
is similar to
added to a regular schedule
"a special holiday flight"; "put on special buses for the big game"
extra, special
is similar to
made necessary by an unexpected situation or emergency
"a forced landing"
forced