Hi airborneforever
Checkboard is correct. The APU is wired for "OR" logic. The Engine is wired for "AND" logic. You don't want to shut an engine down unnecessarily just because one Fire wire develops a fault. If one fire wire develops a fault (fault light initially) and then sometime later the second fire wire senses a fire - then you get the full fire warning.
The APU is wired for belt and braces so it can be left unattended whilst running.
Last edited by rudderrudderrat; 25th Jan 2010 at 22:18.
Reason: correction to full fire warning