Section 171.311

14 CFR Ch. I (1-1-19 Edition)

beam transmissions must not exceed 10
microseconds. The rise time at the
edge of each clearance pulse must be
less than 10 microseconds. Within the
fly-right clearance guidance section,
the fly-right clearance guidance signal
shall exceed scanning beam antenna
sidelobes and other guidance and OCI
signals by at least 5 dB; within the flyleft clearance guidance sector, the fly
left clearance guidance signal shall exceed scanning beam antenna sidelobes
and all other guidance and OCI signals
by at least 5 dB; within the proportional guidance sector, the clearance
guidance signals shall be at least 5dB
below the proportional guidance signal.
Optionally, clearance guidance may be
provided by scanning throughout the
approach guidance sector. For angles
outside the approach azimuth proportional coverage limits as set in Basic
Data Word One (Basic Data Word 5 for
back azimuth), proper decode and display of clearance guidance must occur
to the limits of the guidance region.

Where used, clearance pulses shall be
transmitted adjacent to the scanning
beam signals at the edges of proportional coverage as shown in Figure 8.
The proportional coverage boundary
shall be established at one beamwidth
inside the scan start/stop angles, such
that the transition between scanning
beam and clearance signals occurs outside the proportional coverage sector.
When clearance pulses are provided in
conjunction with a narrow beamwidth
(e.g., one degree) scanning antenna, the
scanning beam antenna shall radiate
for 15 microseconds while stationary at
the scan start/stop angles.
(3) Data function format. Basic data
words provide equipment characteristics and certain siting information.
Basic data words must be transmitted
from an antenna located at the approach azimuth or back azimuth site
which provides coverage throughout
the appropriate sector. Data function
timing must be in accordance with
Table 7a.

TABLE 6 - ANGLE SCAN TIMING CONSTANTS
Function
Approach azimuth .....................................................................
High rate approach azimuth ......................................................
Approach elevation ...................................................................
Back azimuth .............................................................................

TABLE 7a - BASIC DATA FUNCTION TIMING

15.625
kHz clock
pulse
(number)

Preamble ...............................................
Data transmission (bits I13-I30) ..............
Parity transmission (bits I31-I32) ............
End function (airborne) ..........................
End guard time: end function (ground)
1 The

0
25
43
45
................

To(usec)

13,000
9,000
3,500
9,000

6,800
4,800
3,350
4,800

0
1.600
2.752
2.880
3.100

TABLE 7b - AUXILIARY DATA FUNCTION TIMING - 
(DIGITAL)

Preamble ...............................................
Address transmission (bits I13-I20) ........
Data transmission: (bits I21-I69) .............

0
25
33

7,972
5,972
2,518
5,972

Pause
time
(usec)
600
600
400
600

15.625
kHz clock
pulse
(number)

Parity transmission (bits I70-I76) ............
End function (airborne) ..........................
End guard time; end function (ground)

82
89
................

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13,128
9,128
N/A
9,128

0
1.600
2.112

Fmt 8010

5.248
5.696
5.900

Event time slot
begins at:
Event

Time
(milliseconds)

Time
(milliseconds)

TABLE 7c - AUXILIARY DATA FUNCTION TIMING - 
(ALPHANUMERIC)

15.615
kHz clock
pulse
(number)

Preamble ...............................................
Address transmission (bits I13-I20) ........
Data transmission: (bits I21-I76 ..............
End function (airborne) ..........................

0
25
33
89

858

VerDate Sep<11>2014

Tt (usec)

Event

Event time slot
begins at:
15.625
kHz clock
pulse
(number)

0.02
0.02
0.02
Section0.02

Tm
(usec)

Event time slot
begins at:

Time
(milliseconds)

previous event time slot ends at this time.

Event

V(deg/
usec)

TABLE 7b - AUXILIARY DATA FUNCTION TIMING - 
(DIGITAL) - Continued

Event time slot
begins at: 1
Event

Max
value of
t(usec)

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Time
(milliseconds)
0
1.600
2.112
5.696