Observer Audio control panel

[B767300]

Why did some operators install a fourth ACP for the 2nd (left) observer, I believe this was standard on the classics. I can only think of maintenance and workload reduction during emergencies. But wouldn't this be redundant since you already have a 1st obs ACP?

Thank you all in advance.

[Jeroen Hoppenbrouwers]

Probably to allow the 2nd obs to also have a working headset. Intercom and listening in. Not transmit on radio (but they could).

[b744erf]

Actually, I'm more interested in a fascinating discovery: the layout of the center pedestal panels on KLM's 747-406 is quite different. They place all three RCPs in the first row, the radar panel is positioned as the third one on the left side, and most interestingly, they only have two ACPs. I'm really curious—where are the ACPs for the two observers seated behind?

[B767300]

Some OBS ACP configs I found in FCOM's and AMM's:
KLM
2 ACP's on pedestal, 1st OBS ACP (right obs) on main sidewall. No 2nd OBS ACP.
China Airlines
3 ACP's on pedestal incl. 1st OBS ACP + 2nd OBS ACP behind CAPT seat.
China Southern
3 ACP's on pedestal incl. 1st OBS ACP, no 2nd OBS ACP.

So all airlines have a 1st OBS ACP, that may be used by the CAPT or F/O in case their ACP fails (OBS audio sw OVHD panel). I suppose that this one would mainly be used by maintenance, as it may be a bit of a hassle to enter either the CAPT or F/O seat (and just redundancy). But why a 2nd OBS ACP?

KLM didn't install the 1st OBS ACP on the pedestal but on the main sidewall, out of reach for both pilots in case their ACP fails.... Again just guessing, but maybe they didn't want maintenance to interfere with printer ops during preflight?

EDIT: KLM went for a config similiar to China Southern on their ERF's.