Beam Approach Visual Indicator Ref 10Q/4 RAF

This is a WWII and Cold War-era Beam Approach Visual Indicator, Ref 10Q/4, Mod 27 as used in bomber aircraft of the Royal Air Force such as the Avro Lancaster (see illustration of the Lancaster instrument panel from the Pilots Notes showing the location of the indicator).   Per the Rochester Avionics Archives: The Standard Beam Approach System is similar to the ILS system used in Modern aircraft. Beam Approach Beacon System – BABS – was a homing device used to help pilots land in poor visibility; it was fitted to the Lancaster, Halifax, and Whitley. Radio beacons on the airfield transmitted signals, which were picked up by aircraft on their approach to land.The Main Beacon at the end of the runway transmitted a signal in the form of a narrow beam. When the pilot was lined up correctly on this beam the signal received was steady and he knew he was heading straight towards the runway. If he was too far to the left or right, the signal received was a stream of dots or dashes and he correc