Harmon Technologies, Inc.

Audio Panel and Marker Beacon Receiver

The audio panel lets the pilot direct audio output from the various radios to either the overhead speaker or the headphones.  Normally, only the active communications radio is enabled although the pilot can switch on the second communications radio if he wishes to monitor a second frequency in the background (perhaps to pick up a weather broadcast).  It is also possible to enable audio output from various navigation radios in order to check their identity or get weather information that is sometimes sent using navigation transmitters. 

A switch on the right side of the audio panel also determines which transmitter is used to communicate to air traffic control. 

In addition to controlling audio, this device has a receiver to receive marker beacon signals.  These signals are very directional signals sent straight up from a point on the ground.  When the airplan passes over the transmitter, a colored light on the instrument panel will flash and (if the pilot has enabled the audio) a distinctive beep will be displayed.  In the past, these beacons were used to measure progress along airways.  Now, they are mostly used to double check progress during an instrument approach.  As the plane descends along the glideslope, the blue light will flash when the plan is about 5 miles from the end of the runway.  This is usually right after the plan starts its descent.  The amber light will flash as the plane passes through 200 feet above the ground.  At this point if the runway is not clearly visible, the airplane must execute a missed approach.  The white light flashes as the airplane passes the runway threshold (projected landing point of the airplane).  Since there are other ways of measuring progress, not all instrument approaches have these marker beacons. 

Copyright © 2004 Harmon Technologies, Inc.