The official definition of a base turn in ICAO Doc 8168, PANS Ops Volume 1 is, "A turn executed by the aircraft during the initial approach between the end of the outbound track and the beginning of the intermediate or final approach track". In the turn construction parameters the angle of bank is assumed to be 25 degrees and the timing to be one minute from the start of the turn for Cat A and B aircraft and 1 minute 15 seconds for Cat C,D and E aircraft.