None of the three channels generating NO LAND 3 logic.
Jetdoc... Why would they put in the line "• Triple channel arm - all three channels either engaged
or armed." if
"No Land 3 logic" could simply be a fault in any of the channels at any height.
The Boeing Maintenance Manual (22-21-00) simply says...
4) Bus isolation discrete is issued when at ground is generated at the FCC's A/L BUS ISOL inputs. The ground is generated when:
a) The approach (APP) mode is selected
b) (Effectivity XXX, etc) The A/P is single channel engaged, multi-channel armed (off line channels are automatically armed by the FCC's when APP is selected) in the CMD mode.
c) (Effectivity ZZZ, etc) the A/P is single channel engaged, multi-channel armed (off line channels are manually armed by pressing the CMD switch/lights) in the CMD mode.
d) Autoland Status Annunciator (ASA) is not displaying NO LAND 3."
Anyway, I don't think we're going to resolve this issue (to our level of satisfaction) without input from Rockwell-Collins or Boeing, but my original quiz has been answered: There will be no drain on the battery under normal circumstances, because (in a very roundabout way), the Right AC Bus provides two FCC's with power.... that is, until something breaks. Under normal circumstances, independent power sources for each FCC is an illusion
As far as the VHF glitch goes, I suspect that its the L VHF that has the power interuption when the main battery transfer relay drops out and the main battery relay kicks in.
I agree... but pilots are telling me this happens when they push APP... not at 1500'
Rgds.
NSEU