859 

Federal Aviation Administration, DOT 

§ 171.311 

T

ABLE

7c—A

UXILIARY

D

ATA

F

UNCTION

T

IMING

— 

(A

LPHANUMERIC

)—Continued 

Event 

Event time slot 

begins at: 

15.615 

kHz clock 

pulse 

(number) 

Time 

(milli-

sec-

onds) 

End guard time; (end function ground)

................

5 .900 

(i) 

Preamble. 

Must be in accordance 

with requirements of § 171.311(i)(1). 

(ii) 

Data transmissions. 

Basic data 

must be transmitted using DPSK mod-
ulation. The content and repetition 
rate of each basic data word must be in 
accordance with Table 8a. For data 
containing digital information, binary 
number 1 must represent the lower 
range limit with increments in binary 
steps to the upper range limit shown in 
Table 8a. Data containing digital infor-
mation shall be transmitted with the 
least significant bit first. 

(j) 

Basic Data word requirements. 

Basic 

Data shall consist of the items speci-
fied in Table 8a. Basic Data word con-
tents shall be defined as follows: 

(1) 

Approach azimuth to threshold dis-

tance 

shall represent the minimum dis-

tance between the Approach Azimuth 
antenna phase center and the vertical 
plane perpendicular to the centerline 
which contains the landing threshold. 

(2) 

Approach azimuth proportional cov-

erage limit 

shall represent the limit of 

the sector in which proportional ap-
proach azimuth guidance is trans-
mitted. 

(3) 

Clearance signal type 

shall rep-

resent the type of clearance when used. 
Pulse clearance is that which is in ac-
cordance with § 171.311 (i) (2) (iv). Scan-
ning Beam (SB) clearance indicates 
that the proportional guidance sector 
is limited by the proportional coverage 
limits set in basic data. 

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