A320 ADR 1 fail and GPWS

[discountinvestigator]

Hi,

Forgive me please for this basic question which appears to be confusing a few 320 pilots.

If you have an ADR 1 failure, then you switch the system so that Captain's displays get information from ADR 3. ADR 1 feeds into EGPWS and GPWS functions.

Some airlines appear to be switching off GPWS TERR, some GPWS SYS and some both at this point.

So, what does ADR 1 feed? Why do I lose the GPWS rad alt fed functions if ADR 1 fails, or does ADR 1 feed in rad alt information to GPWS. Why do I lose the Glideslope function with ADR 1?

Sorry, but I do not have access to the manuals, merely extracts at the moment. I think I will go back to the P1 compass and a DHC1 shortly.

[sabenaboy]

Here"s what my FCOM says:



And here an extract from FCOM 1.34.10:



And here's a picture:



I'm afraid that that's all I could find in the FCOM.

[discountinvestigator]

simulator experience

Hi, the simulator pops up in the ECAM drills with the requirement to switch the GPWS to OFF. Should it say the GPWS TERR instead? Is this an ECAM error, a simulator error or my brain?

If you switch GPWS to off, then the working RA 1 radio altitude input is eliminated, the ILS box glide function goes as well.

The TERR switch takes out TAD and TCF (sorry, but I do not know what these are) only and leaves Modes 1 to 5 available.

Thank you for the diagram to assist in the debate!

[sabenaboy]

Originally Posted by discountinvestigator

The TERR switch takes out TAD and TCF (sorry, but I do not know what these are)

I don't know either. I hope someone will be able to tell us.

[safetypee]

Originally Posted by discountinvestigator

The TERR switch takes out TAD and TCF (sorry, but I do not know what these are) only and leaves Modes 1 to 5 available.

TAD is the Terrain Awareness Display (EGPWS terrain map) and TCF is Terrain Clearance Floor (EGPWS computation / warning boundary). If these are off i.e Terr Off/Fault then the Enhanced functions of GPWS will not be available, but the old style / standard GPWS (modes 1-5) should work. Remember that the old GPWS does not give you the same standard of protection as EGPWS does – take care.
See: www/egpws.com - ‘Operation’ – ‘Pilots Guides’ for more info