Flashing "B"

I don't why but I always see a Flashing B in the HUD right side of the altimeter, what si that?

Did you select the radar altimeter as primary source?

The flashing B means that the radar altimeter is unavailable and therefore the barometric altimeter is used. This can be because you are flying to high or your bank angle is to large.

RADALT only works up to 5,000 feet. Once above that it will switch to Barometric which is the flashing B.

to add to the above which is all correct, if you don't set the radar alt on it will just be barometric all the time and you won't see the flashing B. So if it becomes annoying during a long high flight just turn the Radar ALT switch under the HUD to Baro instead of Radar, just don't forget to turn it back on if you are close to engagement zones/plan on going low especially in IFR conditions.

thanks guys I will check

thanks guys I will check

The only reason it should be flashing B is that you have the HUD setting for radar altitude enabled and you either A aren't belly to the ground or B above 5000 feet AGL. It's under the UFC panel and above the color display labeled "ALT". It's a switch that turns it on and off. So either turn it off(baro only) and never get your radar ALT reading on the HUD or get used to the flashing B or do what I said earlier and cycle based on need. :D :D

That or you have some weird bug that hasn't been reported. Also this isn't the bug reporting section if you need to report it you will need to go here https://forums.eagle.ru/forumdisplay.php?f=594 for reporting f18c bugs. That said I would check the switch I mentioned, before you report it as a bug.