A Style A PAPI system comprises a plurality of identical lamp housing assemblies, each with one or more lamps and each housing assembly including a tilt circuit. A master control includes a microcontroller that supplies an inverted 1 KHz, 50% duty cycle pulse signal to each tilt circuit through a corresponding blocking diode. Each of the tilt circuits includes an optical pendulum tilt switch that responds to tilting of the housing assembly. DC power is developed in each tilt circuit from one phase of the pulse signal. A pair of steering diodes and a voltage divider network enable return pulses to be supplied back to the microcontroller via the same wires that deliver the pulse train. The returned pulses exhibit different voltages corresponding to tilt and no tilt conditions of the tilt switch. Visual indications of the status of each tilt circuit are presented at the tilt circuits and at the master control. The microcontroller disables all of the lamps in the system unless a no tilt voltage is received from every lamp housing assembly.
