Why do I get a warning when Radar Altimeter is disabled?

How come I still get a ground collision audio warning when I have Radar Altimeter disabled? I thought that disabling this switch disabled the GCAS? I think they call her Betty, (Hmm Betty) and she warns me of a ground collision even though the Radar Altimeter switch is disabled?

I can call you Betty

And Betty when you call me

You can call me Al

(as for the original question ... no idea, sry)

A shot in the dark: GCAS warnings may be generated with the digital terrain map data (same information that drives CCIP solutions). Maybe the radar altimeter info is also used but I'm not sure

I can call you Betty

And Betty when you call me

You can call me Al

 

(as for the original question ... no idea, sry)

If you'll be my bodyguard I can be your long lost pal.

I can call you Daddy, then Daddy when you call me you can call me AL.

Not sure if this is the answer though LOL.

according to page 138 in the Flight Manual,

2. Radar Altimeter. The two position switch labeled RDR ALTM allows you to enable or

disable the radar altimeter. If the switch is in the NRM (normal) position, the radar

altimeter is functioning and will provide data for GCAS functions. If however the switch is

in the DIS (disable) position, the radar altimeter is disabled as well as GCAS functions

page 136 states

Ground Collision Avoidance System (GCAS)

 GCAS provides you warning of a potential ground impact; however, it will not prevent the

impact. GCAS uses a combination of inputs from the radar altimeter, INS and LASTE

computer to judge such an event. A GCAS warning is indicated by a large, flashing break-X

on the HUD and a “PULL UP, PULL UP” audio message.

 GCAS can provide you with an “ALTITUDE, ALTITUDE” audio alert messages when the

aircraft is below a preset mean sea level (MSL) altitude and above ground level (AGL)

altitude. These altitudes are set on the Up Front Controller (UFC).

So the question remains valid.

according to page 138 in the Flight Manual,

GCAS functions should be disabled.

 

page 136 states

 

 

So the question remains valid.

That's what I thought.

When I disable the RDR Altimiter, I do get a warning on the Caution light panel about GCAS. But if I am about to collide with the ground, I still get the big green cross and Betty warning me to pull up.

So is this a bug that needs reporting?

"You must spread some Reputation around before giving it to Flagrum again."

Well done Sir.

It depends a bit on which warning you get. (ALTITUDE, or PULL UP)

GCAS has different modes.

Predictive GCAS (PGCAS) based on elevation database loaded in the DTC.

It will warn you when approaching elevated terrain higher then youre present altitude.

Part of this is also Obstacle warning (like towers and buildings) but I'm not sure this implemented in the DCS A-10c.

Turning off radar altitude will disable pgcas.

On the other hand, pointing the nose down to the ground (high descent rate) will also generate a warning which has nothing to do with PGCAS. In the F-16 this is called GAAF (Ground Avoidance Advisory Function).

This function is independent of radar altitude.

see also this post : http://forums.eagle.ru/showpost.php?p=1560057&postcount=11

I found this gem from 2011.

GCAS cross is driven by BOTH 'normal' GCAS (which uses radar altimeter), and by DTSAS (Digital Terrain System Application Software). GCAS light usually means that you have lost 'normal' GCAS capability, but the part controlled DTSAS may still be working unless DTSAS is turned off or damaged.

So, it seems that the cross over the hud and the PULL UP, PULL UP audial warning should work even when the rdr altm is off (or when it can't get a measurement due to attitude etc).

I found this gem from 2011.

 

 

 

So, it seems that the cross over the hud and the PULL UP, PULL UP audial warning should work even when the rdr altm is off (or when it can't get a measurement due to attitude etc).

That's good to know, but as a test how do I turn off DTSAS.

With the UFC. Press DATA (or select?) and right lower corner it says something about DTAS. Select other options and wait 3 sec or hit ok...