GJB 181B is the current edition of the Chinese national military standard specifying the electrical power characteristics of aircraft, and it is the edition against which aircraft and their utilization equipment are qualified today. It continues the structure of the earlier editions, defining the nominal values of the aircraft supply systems, the steady-state voltage and frequency limits, the transient envelope that equipment must tolerate during load switching and generator transfer, the permissible distortion and ripple, and the conditions that arise in abnormal operation. The revision takes account of the changes that have taken place in aircraft electrical systems, among them the increasing use of variable frequency and of higher-voltage direct-current distribution, the greater proportion of the load that is now electronic, and the more stringent expectations placed on power quality by digital avionics. It is applied together with the associated parts of the series, which define the tests and the requirements placed on utilization equipment.