Air Traffic Management Concept Baseline Definition - The Boeing ...

ATC
Voice
Procedures
Waypoint
Reports
AOC
Voice
Procedures
ATIS
Broadcast
SELCAL
Voice
PTT
SATCOM HF VHF
VOR
Audio
Figure 5.2 Voice Communication
For those channels where the probability of receiving a call is sufficiently small (e.g., AOC
channels) or the normal channel noise is quite high (e.g., HF voice) a tone selective calling
(SELCAL) system is provided to indicate to the pilot that a call addressed to his aircraft
has been received. He can then turn up the receive audio and respond.
SATCOM does not use the PTT protocol. SATCOM provides a service which has more
in common with conventional or cellular telephone service. A telephone number is
entered into a control/display device in the aircraft or at the ground station. When a
‘send’ button is pressed a connection is established between the airplane and the ground
and an annunciator is activated at the other end. When the call is received a duplex voice
path is activated, allowing simultaneous talk in both directions. Since air time is relatively
expensive the connection is maintained only while active conversation is required, then the
call is terminated.
VHF radio is the preferred medium whenever the aircraft is within line-of-sight of a
ground station. When within range, VHF signal quality is generally good to excellent.
There are 760 channels to choose from, spaced 25 KHz apart. Some European countries
will soon activate VHF channels 8.33 KHz apart, allowing up to three times as many
channels to choose from, but the FAA has no plans to use this capability.
HF radio is the normal communication medium for oceanic and remote areas not covered
by VHF. Unlike VHF, HF communication is normally indirect, i.e., a radio operator
actually talks with the flight crew, then communicates with the ATC controller by text
(teletype). This is because of the unique skills required to communicate in the noise and
fading signal of HF and the need to choose communication frequency based on time of day
and ionospheric condition. A phone patch can be arranged if the controller and pilot need
to talk directly.
SATCOM service is generally available whenever at least one satellite is within line-ofsight
of the aircraft. The current satellite service, called Aeronautical Mobile Satellite
Service (AMSS) by ICAO, is currently provided by Inmarsat. Since the satellites are
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