The flight deck crewmembers can make announcements using a PA hand microphone or by using any standard microphone and the related ASP. Flight Attendants make announcements using PA hand microphones 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. The forward attendant has priority over the aft attendant.
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.
Call system chime signals are audible in the passenger cabin through the PA system speakers. The PA speakers also provide an alerting chime signal whenever the NO SMOKING or FASTEN SEAT BELT signs illuminate or extinguish.
Location of Call Originator Called Position Visual Signal at Called Position Aural Signal at Called Position
Flight deck Attendant station Pink master call light Two–tone chime
Flight deck Nose wheel well Horn in nose wheel well
Attendant station Flight deck Blue flight deck call light Single high–tone chime
Nose wheel well Flight deck Blue flight deck call light Single high–tone chime
Flight deck Passenger cabin NO SMOKING or FASTEN BELT signs illuminate/ extinguish Single low–tone chime
Copyright . The Boeing Company. See title page for details.
5.20.4 August 1, 2003
Communications -System Description 737 Operations Manual
Selective Calling (SELCAL)
A ground station desiring communication 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 identification code. When the system receives an incoming call from a ground station, a two–tone chime sounds, and the related SELCAL light illuminates.
VHF Communications
Primary short–range voice communication is provided in the VHF range by two or 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 ASP.
VHF–3 communication on airplanes equipped with three VHF transceivers is used in conjunction with ACARS. Frequency tuning for this radio is provided by the ACARS system.
VHF–1 is located on the left aft electronic panel, VHF–2 on the right. The VHF–1 antenna is located on the upper fuselage, VHF–2 and VHF–3 on the lower fuselage.
HF Communications
HF transmission and reception are controlled at the related ASP. When the 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: Keying HF transmitter on the ground may cause oil and fuel quantity indicators to fluctuate if one or more of the following conditions exist:
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cargo or passenger entry door open
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service interphone microphone plugged into service interphone jack
.
airplane grounding wire attached to airplane
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