User's Manual

SYSTEM DESCRIPTION AND INSTALLATION MANUAL
T
3
CAS/Part No.9005000
Transponder replies and squitters, however, are not disabled by the air/ground switch,
and aircraft status (on ground or airborne) is included in the Mode S reply data.
In a dual Mode S System, the pilot can choose either transponder from the control panel.
When an ATCRBS Transponder is installed, the pilot can choose between the embedded
Mode S and ATCRBS Transponders. In either case (dual Mode S or Mode S/ATCRBS)
only one transponder is enabled at a time. If a Mode S Transponder failure occurs, the
XPDR FAIL indicator on the control panel lights. However, the failed transponder must be
the one selected on the control panel for the indicator to light. Switching between the
transponders occurs without loss of system function.
An SPI is added to the ATCRBS and Mode S replies when the control panel IDENT
button is pushed. The SPI is enabled for approximately 18 seconds and supplies the
ground station with a more positive aircraft identification capability. This function is
typically activated upon verbal command from the ground station.
Dual altitude input ports are supplied for each transponder; the capability to switch
between the two is supplied by a switch on the control panel. This function lets the pilot
select a second altitude source if the first fails. It also lets the ground station verbally
verify one source against the other. Additionally, this switch lets the pilot disable altitude
reporting altogether if the ground station finds a discrepancy between reported and actual
altitude.
(1) Mode S/ATCRBS Interrogations and Replies
The Air Traffic Control Radar Beacon System (ATCRBS) has been in operation
for several decades. Its purpose is to ensure safe separation and operation of
aircraft, especially in busy terminal areas. ATCRBS Transponder-equipped
aircraft transmit replies to interrogations from ground-based sensors
(interrogators). Depending on the type of interrogation, the reply contains either
the identification code currently assigned to the aircraft by ATC (Mode A), or
uncorrected barometric altitude with 100-foot resolution (Mode C).
The ground station uses reply delay time to compute range to within
approximately 500 feet (152.4 meters). The current angle of the rotating ground
antenna determines azimuth. There is an 18 ±2 second duration SPI pulse to aid
in identifying specific aircraft. Thus, ATC is provided with the information required
to ensure safe separation of aircraft.
(a) Assigned Code Number
The digits of the assigned code number indicate the code groups to be
used and the pulse coding within each group. The assigned code is a
four-digit octal number (any of 4096) in which the first or left-most digit
designates the A group; the second digit designates the B group; the
third digit designates the C group; and the last or right-most digit
designates the D group. Typical information pulses present in assigned
reply codes are given in Table 1-23.
Pub. No. 8600200-001, Revision 004
34-45-29
1-110
04 Nov 2014
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