GPS and NAV naviagtion

I know this has nothing to do with infinite flight but in real airplanes, im confused in the difference between NAV and GPS navigation. Could someone explain and when you eould use them?

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This is for Airbus:

The A320 has got 3 ADIRU, 2 GPS and 3 IRS.

IRS 1 sends data to ADIRU 1
IRS 2 sends data to ADIRU 2
IRS 3 sends data to ADIRU 3
GPS 1 sends data to ADIRU 1
GPS 2 sends data to ADIRU 2.

Each ADIRU computes a GPIRS Position (ie. GPS + IRS Position).
So ADIRU 1 calculates GPIRS 1 (ie. GPS 1 + IRS 1)
ADIRU 2 calculates GPIRS 2 (ie. GPS 2 + IRS 2)
ADIRU 3 calculates GPIRS 3 (ie. IRS 3 + GPS 1).

GPIRS 1 is sent to FMGS 1
GPIRS 2 is sent to FMGS 2
GPIRS 3 is generally used as backup.

Each ADIRU also sends each IRS position to each FMGS.

So FMGS 1 and 2 both receive IRS 1, IRS 2 and IRS 3 position. Each FMGS calculates the mix IRS position (IRS 1 + IRS 2 + IRS 3).

It then adds this MIX IRS position to the GPIRS position.

MIX IRS + GPIRS = FM position
This final position is the one used by FMGS to know the aircraft’s position.

If GPS is lost (ie. GPS PRIMARY Failed), each FMGS will tune navaids to help to find it’s position.

NAV is simply the managed lateral navigation mode.

Maybe I have not understood your question :(

Cheers!

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Boeing is completely different from Airbus and I really don’t know how it works:)
Airbus does not use LNAV or VNAV.

HDG is the selected lateral navigation mode.
NAV is the managed lateral navigation mode.

Check A320s Autoflight FCOM :)

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