Abstract: A runway approach lighting system with fault monitor includes an oscillator which develops clock pulses which are accumulated by a counter. The output of the counter is used to develop trigger signals which control the sequential energization of runway alignment indicator lights. The operation of each light is sensed and is compared with the oscillator pulses, and a fault signal is generated each time a light fails to operate in response to a trigger signal. The number of fault signals generated in an energization cycle is accumulated, and a fault indication is generated once a predetermined number of faults has occurred.