Once cleared to fly one class of aircraft, pilots could be asked to ferry any plane in that class even if they had never seen that type of aircraft before. To do so they had Ferry Pilot Notes, a two-ring book of small cards with the critical statistics and notations necessary to ferry each aircraft. A pilot cleared on more than one class could be asked to fly an aircraft in any of the categories on which he or she was qualified. Thus, even a pilot cleared to fly four-engined bombers could be assigned to fly a single-engined trainer if scheduling made this the most efficient way to get the aircraft to its destination.