767-300 Flight Director
On the 767 what does the FD on switch do?
I have two contradicting statements in a theory book the first says;
"At least one FD switch must be on for the various functions of the AP's to be operational. In other words the FD switches turn ON the AP"(p28)
and the second one says;
"The FD is always powered when power is supplied to the cockpit. The FD switch merely lets the pilot see the FD bars on the EADI"(p74)
These come from Rob Avery's "Flying Glass"
Obviously Ive never flown one, so I might be way off track here. ]
What exactly does the FD switch turn on and off? is it just the command bars or does the it control whether the FD is calculating the required pitch and roll changes as requested through the MCP or FMC ?