the standby function mode (fixed frequency radios and transceivers are available for
use by the OCS only) to the emergency function mode (ECS recorder is active and fixed
frequency radios and transceivers are available to ECS consoles only).
A malfunction of NAVAID equipment could place a pilot in a critical position; therefore,
electronic NAVAID monitoring devices (sometimes located in the tower) provide an
automatic means for continuously checking a NAVAID system (see Figure 5-6).
Figure 5-6 -- NAVAID monitor.
Most monitor equipment is similar in that it provides both a light and an aural alarm to
indicate that a particular NAVAID is malfunctioning. Some monitor equipment provides
for an automatic changeover to standby NAVAID equipment when the main system has
failed. Other equipment requires that the standby equipment be "dialed" on, which is a
method similar to dialing a telephone with certain codes dialed for certain functions (see