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.