Operation. The NAV control panels have an active frequency indicator and a standby frequency indicator

The NAV control panels have an active frequency indicator and a standby frequency indicator. The frequency that shows in the active frequency indicator is the frequency the navigation radios use for operation. The standby frequency indicator shows the next frequency you will use.

The frequency transfer switch is a momentary action switch. It transfers the frequency in the standby frequency indicator to the active frequency indicator. When you push the switch, the frequency in the active frequency indicator transfers to the standby frequency indicator.

The frequency selectors are continuous rotary selectors. There is an inner selector and an outer selector. The outer selector sets the tens and ones numbers. The inner selector sets the tenth and one hundredth numbers. The frequency selectors only change the numbers in the standby frequency indicator. At power up, the frequency displays show the last frequency entry before power down.

The NAV control panel continuous BITE function monitors the operation. The NAV control panel shows FAIL in the active and the standby frequency indicators when there is a control panel failure.

An internal monitor in the NAV control panel monitors the 28v dc input. If the monitor does not see the 28v dc, it shows the message BLANK in the active and the standby frequency indicators.

Test

When you push the NAV control panel test switch, a test command goes out on the data bus. If a VOR frequency is active, the VOR receiver starts a self test. If an ILS frequency is active, the MMR receiver starts a self test. If a DME frequency is paired with the VOR or ILS frequency, the DME interrogator starts a self test at the same time.

When you do a test of the master dim and test system, the NAV control panel shows 188.88. The display shows for two seconds on, then one second off until the test is complete.