Description

A Pushbutton Switch Indicator (PBSI) is a switch that also functions as an indicator of system status.

Many pushbutton switches in modern aircraft function both as switches and status indicators. For example, on the Embraer ERJ-170/190, the switch to activate ground power is a PBSI. If a Ground Power Unit (GPU) is connected to the aircraft, and the power has the correct voltage, frequency, and phase sequence, an AVAIL light will illuminate within the PBSI. If the pilot presses in the button to activate ground power, the light indication changes to IN USE.

Similarly, PBSIs are often used for cargo compartment fire suppression systems. If a cargo compartment fire is indicated, the pushbutton for that particular compartment will illuminate in red. That provides the crew with a quick reference for which pushbutton to press. 

Other applications include audio panels. For example, if a pilot presses a button to transmit on the number one VHF radio, that button will illuminate to provide quick reference that VHF #1 has been selected.