GJB 181A is the Chinese national military standard that specifies the electrical power characteristics of aircraft. Its scope is the power produced and distributed by the aircraft system, defined as a set of conditions that the utilizing equipment must be designed for, rather than the requirements imposed on the equipment itself, which are dealt with in the associated documents of the series. The standard establishes the nominal voltage and frequency of the several aircraft supply systems, the steady-state tolerances that apply in normal operation, the transient voltage envelope that appears on the bus when large loads are switched or when a generator is connected or disconnected, the distortion and the ripple that may be present, and the conditions that arise during abnormal operation such as the failure of one generator and the transfer of the bus to the remaining source. It also defines the reference measurement points and the instrumentation by which the characteristics are verified during type testing of an aircraft.