Aircraft electrical system operating method

A method of controlling an aircraft electrical system, the electrical system comprising:

• an alternating current electrical machine comprising a plurality of electrical phases, each phase having a nominal power rating, the electrical machine being configured to operate on failure of one or more phases;
• the method comprising:
• determining a power requirement;
• sensing a fault of one or more phases of the electrical machine, and, where a fault is sensed:
• controlling the electrical machine to operate in a fault condition, in which the non-faulty phases of the electrical machine provide the electrical power requirement;
• and
• determining whether the power provided by the remaining non-faulty electrical phases exceeds the nominal power rating of the respective phase, and providing an overrating signal to a flight computer of the aircraft where the power provided by each phase exceeds the nominal power rating of the respective phase.