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Does the crew manually tune-in frequencies, or does the FMC automatically switch the radios as the flight plan progresses?
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The FMC automatically tunes in VOR freqs along the route for auto updating and actually prefers DME. It compares that info with either IRS and/or GPS (depending upon aircraft and avionics installed)position to continually update the FMC(s).
The pilot can override or force the FMC to use another VOR station by either typing the station identifier and selecting it into the FMC or selecting a "manual" mode on the MCP. This allows us to get a quick bearing and/or DME from that station the the RDMI indicator. We can also tell the FMC to not use a certain station if it was NOTAM out of service or as a problem. The FMC doesn't know about NOTAMs, only where the station is suppose to be and it's freq.
Normally, the FMC's are allowed to do their own thing without our interference and the entire flight is flown in a "nav or Lnav" mode. This means, the route is programmed into the FMC (which is normally a stored route in the database), a pretty picture of our route including airways, VORs and airports are displayed on the moving map. The aircraft simply follows that FMC generated course line as it's being constantly updated by GPS, IRS or VORs.
We don't normally manually tune in VOR station along the route since the FMC is an approved method of navigating from point "A" to "B" using it's designed updating capabilities.
We do, however, have to back up the FMC data using raw data during IFR approaches. This means that one of the pilots has to select "HSI" on his nav display. He'll continue to backup the flying pilot's progress against what the FMC/moving map is displaying.
BTW, one or both FMC can be inop (doesn't happen very often)and we can be dispatched for a flight. We'll just back to the basics of manually tuning in VORs and using the HSI mode of our moving map.
Disclaimer: The above pertains to older glass cockpit aircraft such as the B75/76 and A300 and may not apply to newer aircraft such as the B777, MD11 or newer Airbuses. Your mileage may vary. Please consult your owner's manual.
