A method of managing an electrical power supply outage on board an aircraft, including the following operations: —detection of an electrical power supply outage, —measurement of a duration of the power supply outage by measuring a discharge time of a capacitor and comparing this measured duration with a threshold duration, —saving a long outage indication when the duration of the outage is greater than a threshold duration. The disclosed embodiments also relates to a system implementing this method and including: —a circuit for detecting an electrical power supply outage, —a circuit for measuring a duration of the power supply outage, and—a circuit for managing indications able to manage emissions of signals according to the measured duration of the power supply outage.