Figure 7-7 to Figure 7-9 illustrate a sequence of events that leads to reconfiguration in downgraded mode.
Figure 7-7: The AESS operates normally.

WXR TAWS AESU1  WXR TAWS AESU2 
XPDR TCAS  XPDR TCAS 
Figure 7-8: AESS in mixed mode

Figure 7-8: The first failure is the loss of WXR function of AESU1. Per procedure, the WXR/TAWS function is switched to AESU2.
Figure 7-9: The second failure is the loss of TAWS function of AESU2. As the TAWS function of AESU1 is still available, TAWS alerts remain available thanks to an interconnection between TAWS functions of AESU1 and 2.
Refer to your FCOM for more reconfiguration scenarios.
7.1.3. TAWS FUNCTION
The AESS TAWS function is equivalent to the reactive and predictive functions provided by the EGPWS (refer to 4.1 – Description of TAWS, see reactive modes, TCF, RFCF, TAD, envelope modulation, obstacle, peaks mode).
In addition to the EGPWS set of functions, the AESS TAWS function provides an enlarged ND range (up to 640 NM) and a vertical view of the terrain on VD.
7.1.3.1. TAWS RNP
The TAWS RNP is defined according to the flight phase.
Flight phase  Take-off  Terminal  En-route  Approach 
Conditions  Below 4000 ft AGL and GS > 60kt  Below 16000 ft and 50 NM from runway  Outside other phases  Below 3500 ft and 10 NM from runway 
TAWS RNP (NM)  1  1  2  0.5 or less* 

* According to the runway selected into the FMS.
AESS uses the TAWS RNP to select the position source (GPIRS or FMS), and to define the width of the vertical cuts for vertical terrain view (refer to 7.1.7.1 – Generation of Vertical Terrain View).

7.1.3.2. SELECTION OF LATERAL POSITION SOURCE
The TAWS module selects the position source with the highest accuracy and integrity in the following sequence (by order of priority):
1.
 GPS position, then

2.
GPS-corrected IR data, then

3.
FMS position, then

4.
 IR position.

When all these sources are not valid or not accurate enough:
-
If the automatic deactivation of predictive TAWS functions has been selected (pin-programming), AESS automatically deactivates predictive functions (basic TAWS functions remain active).

-
If the automatic deactivation of predictive TAWS functions has not been selected, the flight crew must manually switch predictive functions to OFF (TERR SYS to OFF on MFD SURV page, refer to 7.1.9.4.1 – CONTROLS Page).

7.1.3.3. TERRAIN DISPLAY IN POLAR AREAS
The terrain database is coded in latitudes/longitudes (spherical coordinates). The displays (ND and VD) are graduated in NM (plane coordinates). The TAWS function translates the latitudes/longitudes into distances (i.e. projection of a spherical image on a plan). Consequently, this translation implies two limitations for the display of terrain.
　
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