737NG SYSTEM

Communication

Document author: Mostafa Hammad

 Introduction

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 Introduction…
 The communication system includes:
1. radio communication system
2. interphone communication system
3. cockpit voice recorder system
4. communication crew alerting system

 The communication systems are controlled using the:

1. audio control panels
2. radio tuning panels
3. radio communication panels
 Radio tuning panel
 Frequency Indicator (displays six digit frequency in 8.33
KHz spacing)
1. ACTIVE – displays the tuned frequency of the selected radio.
2. STANDBY – displays the preselected or previously tuned
frequency of the selected radio

 Offside Tuning Light Illuminated (white) –

1. the radio normally associated with this panel is being tuned
by another radio tuning panel, or
2. the radio tuning panel is being used to tune a radio not
normally associated with this radio tuning panel.

 VHF TEST Switch Push

1. removes automatic squelch feature, permitting reception of
background noise and thereby testing receiver operation.
2. improves reception of weak signal.
 Audio Systems and Audio Control Panels
 An ACP is installed at the Captain, First Officer, and Observer stations.
Each panel controls an independent crew station audio system and
allows the crewmember to select the desired radios, navigation aids,
interphones, and PA systems for monitoring and transmission.

 Transmitter selectors on each ACP select one radio or system for

transmission by that crewmember. Any microphone at that crew
station may then be keyed to transmit on the selected system.

 Receiver switches select the systems to be monitored. Any

combination of systems may be selected. Receiver switches also
control the volume for the headset and speaker at the related crew
stations. Audio from each ACP is monitored using a
headset/headphones or the related pilot’s speaker.

 Audio warnings for altitude alert, ground proximity warning, collision

avoidance, and windshear are also heard through the speakers and
headsets at preset volumes. They cannot be controlled or turned off by
Speakers and Headsets
 Each crew station has a headset or headphone
jack. The Captain and First Officer have speakers
on the ceiling above their seats. There is no
speaker at the observer station.

 Headset volume is controlled by the receiver

switches. Speaker volume is controlled by the
receiver switches and also the speaker switch.
 Microphones
 Hand microphones and boom microphones may be
plugged into the related jacks at the flight deck crew
stations. Each oxygen mask also has an integral
microphone.

 An oxygen mask microphone is enabled and the boom

microphone is disabled when the left oxygen mask panel
door is open. The oxygen mask microphone is disabled
and the boom microphone is enabled when the left
oxygen mask panel door is closed and the RESET/TEST
Switch is pushed.

 Each hand microphone has a PTT switch to key the

selected audio system. The PTT switches on the control
wheel or ACP are used to key the oxygen mask or boom
microphone, as selected by the R/T and I/C switch. The
R/T and I/C switch does not affect the operation of the
 Normal / Degraded Audio System

Operation
Normal Mode: The Captain, First Officer, and Observer audio systems
are located in a common remote electronics unit in the E/E compartment.
They function independently and have separate circuit breakers. The
audio systems are normally controlled by the related ACPs through digital
or computerized control circuits.

 Degraded mode: If the remote electronics unit or ACP malfunctions, the

ACP cannot control the remote electronics unit. Audio system operation
can be switched to a degraded mode by placing the ALT–NORM switch to
ALT. In this mode:

1. the ACP at that station is inoperative and the crewmember can only
communicate on one radio.
2. The ACP transmitter selectors are not functional. Any transmission from
that station must be from the radio shown on the chart below.
3. The transmitter selector for the usable radio illuminates when a station is
operating in the degraded mode. The receiver switches are not
functional, and only the usable radio is heard at a preset volume, through
the headset.
Service (Attendant) Interphone System
 The service interphone system provides
intercommunication between the flight deck, Flight
Attendants, and ground personnel.

 Flight deck crewmembers communicate using either a

separate handset (if installed) or their related ACP and any
standard microphone.

 The Flight Attendants communicate between flight

attendant stations or with the flight deck using any of the
attendant handsets. Anyone who picks up a
handset/microphone is automatically connected to the
system.

 External jacks for use by maintenance or service personnel

Passenger Address
System
 The passenger address (PA) system allows flight deck
crewmembers and flight attendants to make announcements to
the passengers. Announcements are heard through speakers
located in the cabin and in the lavatories.

 The flight deck crewmembers can make announcements using a

PA handset or by using any standard microphone and the related
ACP. Flight Attendants make announcements using PA handset
located at their stations. The attendants use the PA to play
recorded music for passenger entertainment.

 PA system use is prioritized. Flight deck announcements have

first priority and override all others. Flight Attendant
announcements override the music system.
Call System
 The call system is used as a means for various crewmembers to gain the attention
of other crewmembers and to indicate that interphone communication is desired.

 Attention is gained through the use of lights and aural signals (chimes or horn).

 The system can be activated from the flight deck, either flight attendant station,
or from the external power receptacle.

 Passengers may also use the system to call an attendant, through the use of
individual call switches at each seat.

 The flight deck may be called from either flight attendant station or by the ground
crew. The ground crew may only be called from the flight deck. Flight Attendants
may be called from the flight deck, the other attendant station, or from any
passenger seat or lavatory.

 Master call lights in the passenger cabin identify the source of incoming calls to
the attendants also call system chime signals are audible in the passenger cabin
VHF
Communications
 Primary short–range voice communications is provided in the VHF range by
three independent radios.

 Each radio provides for selection of an active frequency and an inactive

(preselected) frequency. Voice transmission and reception are controlled at the
related ACP.

 VHF–1 control panel is located on the left side of the aft electronic panel and
VHF–2 control panel on the right.

 The VHF–2 antenna is located on the lower fuselage and VHF–1 antenna is on
the upper fuselage.

Note: VHF antennae located on the lower fuselage are susceptible to multipath
interference from nearby structures or vehicles. This may disrupt VHF
communications. VHF antennae located on the upper fuselage are not as
susceptible to this interference.
Note: When a localizer frequency is selected, VHF NAV radios automatically switch
 HF
Communications
 The HF radio communications control panel allows for
frequency selection and adjustment of radio sensitivity. The
audio control panels are used to control voice transmission
and receiver monitoring.

 When an HF transmitter is keyed after a frequency change,

the antenna tunes. A steady or intermittent tone may be
heard through the audio system. While tuning, the tone can
last as long as 7 seconds.

 If the system fails to tune, the tone will last more than 7
seconds, to a maximum of 15 seconds. The antenna is
located in the vertical stabilizer.

Note: Data for the last 100 tuned frequencies is stored in

memory. Tuning duration for these stored frequencies will be
very short and a tune tone may not be noticeable.
 Cockpit Voice Recorder
 The cockpit voice recorder uses four independent channels to record flight deck
audio for 120 minutes. Recordings older than 120 minutes are automatically erased.
One channel records flight deck area conversations using the area microphone. The
other channels record individual ACP output (headset) audio and transmissions for
the pilots and observer.

 ERASE Switch (red)

Push (2 seconds) –
1. all four channels are erased.
2. operative only when airplane is on ground and parking brake is set.

 TEST Light Illuminates (green) (Refer to the FCOM.SUPP.Communication)

when the TEST switch is depressed and either an engine is running or the Cockpit Voice
Recorder Switch is in the ON position.

 VOICE RECORDER Switch (AUTO)

1. powers the cockpit voice recorder from first engine start until 5 minutes after last
engine shutdown ON
 Selective Calling (SELCAL)

• A ground station desiring communications with the flight deck can

use the SELCAL system. SELCAL monitors selected frequencies on
VHF and HF radios. Each airplane is assigned a unique four–letter
SELCAL code. When the system receives an incoming call from a
ground station, a two–tone chime sounds and the respective
SELCAL light illuminates.
ACARS System
 The ARINC Communications Addressing and Reporting System (ACARS) is an
addressable digital data link system which permits exchange of data and
messages between an airplane and a ground-based operation center utilizing an
onboard VHF communications system.

 The ACARS airborne subsystem provides for the manual entry of routine data
such as departure/arrival information. Also possible is manual entry of addresses
(telephone codes) of parties on the ground for voice communications.

 The airborne system consists of a management unit in the E/E compartment,

either an interactive display unit or multipurpose control display unit (MCDU),
and frequently a printer. Data is entered and transmitted to the ground
operations center.

 (Refer to the AFM) The following applies to aircraft with ACARS operational that
do not have the optional VMP (Voice Mode Protection) feature or AOA (ACARS
Over AVLC (Aviation VHF Link Control): Do not use VHF-3 (if installed for voice
 Questions…

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 Question

sWhen does the ALTN position for the ACP panel is used?
 Which have the farthest range (VHF/HF) and why?

 What would you do in the event of a stuck microphone switch?

 Why sometimes on the ground the VHF1 has a better communication and transmission?

 Who has priority over the pa (the flightdeck or the flight attendants?

 When does the VHF nav radios switch from tail antenna to nose antenna?

 When does the tone of the HF frequency may not be noticed?

 What could disable the boom mike operation?

 How SELCA checks are performed?

Thank you…