(4)  
Adjust captain's, first officer's and first observer's audio selector panels to the following conditions: (1) BOOM/MASKS switch to BOOM position (2) all volume controls off except FLT INT which should be on with volume at mid-point.

(5)  
Set ALT/NORM mode selector switch to NORM position on all audio selector panels.

C.  Test for normal operation
(1)  
At the captain's, first officer's and first observer's audio selector panels, select FLT INT mic selector switch.

(2)  
Establish voice communication between captain and first officer stations using boom mic/headsets and control wheel PTT switches. Verify undistorted audio. Verify captain's and first officer's overhead speakers mute when mikes are keyed with BOOM microphones selected.

(3)  
Establish voice communication between captain and first officer stations using boom mic/headsets and audio selector panel PTT switches. Verify undistorted audio.

(4)  
Establish voice communication between captain and first officer stations using hand mic's and headphones. Verify undistorted audio, and check that FLT INT volume control on audio selector panels varies volume level.

(5)  
Establish voice communication between captain and first observer stations using boom mic/headsets or hand microphone and headset and FLT INT switch on audio selector panel for captain, and for first observer. Verify undistorted audio.

(6)  
Establish voice communication between captain and first observer stations using hand mic's and headphones. Verify undistorted audio, and check that FLT INT volume control on audio selector panels varies volume level.

(7)  
Turn FLT INT audio control to off and SERV INT audio control to comfortable listening level on each audio selector panel in

(8)  
Verify that each position in step C (1) can communicate with each flight attendant position.

(9)  
Return SERV INT audio control to off.

5C8
Jun 20/88 23-52-02 Page 501
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.

D.  Test Cockpit Speaker
(1)  
Set SPKR control knob on captain audio selector panel to mid-point. Press SPKR control knob to on.

(2)  
Set BOOM/MASKS switch on captain's audio selector panel to MASKS.

(3)  
Adjust FLT INT audio control to comfortable listening level.

(4)  
Make flight interphone voice transmission from first observer's station and verify
undistorted audio through captain's cockpit speaker.

(5)  
Set SPKR control knob on captain audio selector panel to off And verify speaker is off.

(6)  
Set BOOM/MASKS switch on first officer's audio selector panel to MASKS.

(7)  
Set SPKR control knob on first officer audio selector panel to mid-point. Press speaker control knob to on.

(8)  
Make flight interphone voice transmission using first observer's oxygen mask from first observer's station and verify undistorted audio through the first officer's cockpit speaker.

(9)  
Set SPKR control knob on first officer audio selector panel to off and verify speaker is off.

E.  Test Oxygen Mask Microphone
(1)  
At the captain, first officer, and first observer audio selector panels, position
BOOM/MASKS switch to MASKS.

(2)  
Use captain's and first officer's oxygen mask microphones and headsets, and establish communication between these two stations. Verify undistorted audio. Verify captain's and first officer's overhead speakers do not mute when microphones are keyed with MASK microphones selected.

(3)  
Repeat step (2). Establish communication between captain's and first observer's station.

F.  Test for alternate operation
(1) 
 Captain

(a)  
On captain's audio selector panel, position ALT/NORM switch to ALT.

(b)  
Verify VHF-1 receiver audio at captain headphone; no overhead speaker audio; no navigation receiver audio; VHF-1 MIC SEL illuminated.

(c)  
Verify no changes with change in MIC SEL selection.

(d)  
Verify that PTT from captain's station keys VHF-1 and VHF-1 sidetone audio is present at captain's headphone.

(e)  
Return ALT/NORM mode selector switch to NORM position on captain's audio selector panel.

(2)  
Observer

(a)  Same as par. (1) Captain, except use observer audio selector panel.

(3)  
F/O

(a)  Same as par. (1) Captain, except use F/O audio selector panel and VHF-2 in place of VHF-1.

(4)  
Return audio selector panels to normal condition.

G.  Remove electrical power if no longer required.
　
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