PS Engineering PAC45J Pilot's Manual And Operation Manual page 8

If the observer personnel would like to CABIN CALL the crew intercom
stations. On the observer control head (CTL45-X), pressing "ACK" button
will activate an ICS call light and a chime in the crew headsets and crew
control head.
PAC45J Intercom State Rules
The following charts show the intercom mode state rules with a four
CTL45J control heads, for pilot, copilot, OBS1 & OBS2.
At the top of each section, it states these button presses below. For explana-
tion we will use "Pilot ICS States"
1. On initial power up, all control heads in ALL mode.
2. Pilot presses ICS button, all control heads to CRW mode.
3. Pilot presses ICS button, Pilot to ISO, while all other control heads to
ALL mode.
4. Pilot pressed ICS button, all control heads to CRW mode
This is consistent on the CTL45J control heads, so the pilot (and any other
control head) can select all steps 1 thru 4 as above.
Additional Notes:
1. Pilot & Copilot can force all control heads to ALL mode, regardless of
ICS selections are on the OBS1 & OBS2 control head.
2. When all control heads are in the ALL mode, any control head can
force all locations to CRW mode.
Page 8 202-045-2200 Oct. 2021 PAC45J Pilot Guide