Before it suffered the deadliest crash in South Korea's history, budget airline Jeju Air was moving fast: racking up record passenger numbers and flying its aircraft more than domestic rivals and many of its global peers, data show. The high "utilisation rate" of Jeju Air's planes - the number of hours they fly in a day - is not problematic in itself, experts say, but means scheduling enough time for required maintenance is crucial. Authorities have suggested a bird strike contributed to the accident, but as part of their probe into the incident aboard Boeing 737-800, police have raided the airlines' Seoul office to seize documents related to the operation and maintenance of the plane.