The altitude of my transponder transmission shows a red cross in the ACD-57

The alticoder in the VT-01 may be set incorrectly. If this is the case, a red cross will appear in the ACD-57 (FL display) instead of the transmitted altitude. 

In this case, please change the following: 

• PIN CODE 3000
• MENU > XPDR SYSTEM > INSTALLATION > XPDR CONFIG > ALT SOURCE please change to "DATA BUS".

After that the altitude will be displayed normally.