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853 

Federal Aviation Administration, DOT 

§ 171.309 

inspect the facility and its operation 
whenever necessary. 

(5) The owner must assure the FAA 

that he will not withdraw the MLS fa-
cility from service without the permis-
sion of the FAA. 

(6) The owner must bear all costs of 

meeting the requirements of this sec-
tion and of any flight or ground inspec-
tion made before the MLS facility is 
commissioned. 

(b) [Reserved] 

§ 171.309 General requirements. 

The MLS is a precision approach and 

landing guidance system which pro-
vides position information and various 
ground-to-air data. The position infor-
mation is provided in a wide coverage 
sector and is determined by an azimuth 
angle measurement, an elevation angle 
measurement and a range (distance) 
measurement. 

(a) An MLS constructed to meet the 

requirements of this subpart must in-
clude: 

(1) Approach azimuth equipment, as-

sociated monitor, remote control and 
indicator equipment. 

(2) Approach elevation equipment, as-

sociated monitor, remote control and 
indicator equipment. 

(3) A means for the encoding and 

transmission of essential data words, 
associated monitor, remote control and 
indicator equipment. Essential data 
are basic data words 1, 2, 3, 4, and 6 and 
auxiliary data words A1, A2 and A3. 

(4) Distance measuring equipment 

(DME), associated monitor, remote 
control and indicator equipment. 

(5) Remote controls for paragraphs 

(a) (1), (2), (3), and (4) of this section 
must include as a minimum on/off and 
reset capabilities and may be inte-
grated in the same equipment. 

(6) At locations where a VHF marker 

beacon (75 MHz) is already installed, it 
may be used in lieu of the DME equip-
ment. 

(b) In addition to the equipment re-

quired in paragraph (a) of this section 
the MLS may include: 

(1) Back azimuth equipment, associ-

ated monitor, remote control and indi-
cator equipment. When Back Azimuth 
is provided, a means for transmission 
of Basic Data Word 5 and Auxiliary 
Data Word A4 shall also be provided. 

(2) A wider proportional guidance 

sector which exceeds the minimum 
specified in §§ 171.313 and 171.317. 

(3) Precision DME, associated mon-

itor, remote control and indicator 
equipment. 

(4) VHF marker beacon (75 MHz), as-

sociated monitor, remote control and 
indicator equipment. 

(5) The MLS signal format will ac-

commodate additional functions (e.g., 
flare elevation) which may be included 
as desired. Remote controls for para-
graphs (b) (1), (3) and (4) of this section 
must include as a minimum on/off and 
reset capabilities, and may be inte-
grated in the same equipment. 

(6) Provisions for the encoding and 

transmission of additional auxiliary 
data words, associated monitor, remote 
control and indicator equipment. 

(c) MLS ground equipment must be 

designed to operate on a nominal 120/ 
240 volt, 60 Hz, 3-wire single phase AC 
power source and must meet the fol-
lowing service conditions: 

(1) AC line parameters, DC voltage, 

elevation and duty: 

120 VAC nominal value—102 V to 138 V (

±

V)* 

240 VAC nominal value—204 V to 276 V (

±

V)* 

60 Hz AC line frequency—57 Hz to 63 Hz (

±

0.2 

Hz)* 

*N

OTE

: Where discrete values of the above 

frequency or voltages are specified for test-
ing purposes, the tolerances given in paren-
theses indicated by an asterisk apply to the 
test instruments used to measure these pa-
rameters. 

Elevation—0 to 3000 meters (10,000 feet) 

above sea level 

Duty—Continuous, unattended 

(2) Ambient conditions within the 

shelter for electronic equipment in-
stalled in shelters are: 

Temperature, 

¥

10 

°

C to + 50 

°

Relative humidity, 5% to 90% 

(3) Ambient conditions for electronic 

equipment and all other equipment in-
stalled outdoors (for example, antenna, 
field detectors, and shelters): 

Temperature, 

¥

50 

°

C to + 70 

°

Relative humidity, 5% to 100% 

(4) All equipment installed outdoors 

must operate satisfactorily under the 
following conditions: 

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854 

14 CFR Ch. I (1–1–24 Edition) 

§ 171.311 

Wind Velocity: The ground equipment shall 

remain within monitor limits with wind 
velocities of up to 70 knots from such di-
rections that the velocity component 
perpendicular to runway centerline does 
not exceed 35 knots. The ground equip-
ment shall withstand winds up to 100 
knots from any direction without dam-
age. 

Hail Stones: 1.25 centimeters (

1

2

inch) diame-

ter. 

Rain: Provide required coverage with rain 

falling at a rate of 50 millimeters (2 
inches) per hour, through a distance of 9 
kilometers (5 nautical miles) and with 
rain falling at the rate of 25 millimeters 
(1 inch) per hour for the additional 28 kil-
ometers (15 nautical miles). 

Ice Loading: Encased in 1.25 centimeters (

1

2

 

inch) radial thickness of clear ice. 

Antenna Radome De-Icing: Down to 

¥

°

C (20 

°

F) and wind up to 35 knots. 

(d) The transmitter frequencies of an 

MLS must be in accordance with the 
frequency plan approved by the FAA. 

(e) The DME component listed in 

paragraph (a)(4) of this section must 
comply with the minimum standard 
performance requirements specified in 
subpart G of this part. 

(f) The marker beacon components 

listed in paragraph (b)(4) of this section 
must comply with the minimum stand-
ard performance requirements specified 
in subpart H of this part. 

§ 171.311 Signal format requirements. 

The signals radiated by the MLS 

must conform to the signal format in 
which angle guidance functions and 
data functions are transmitted sequen-
tially on the same C-band frequency. 
Each function is identified by a unique 
digital code which initializes the air-
borne receiver for proper processing. 

The signal format must meet the fol-
lowing minimum requirements: 

(a) 

Frequency assignment. 

The ground 

components (except DME/Marker Bea-
con) must operate on a single fre-
quency assignment or channel, using 
time division multiplexing. These com-
ponents must be capable of operating 
on any one of the 200 channels spaced 
300 KHz apart with center frequencies 
from 5031.0 MHz to 5090.7 MHz and with 
channel numbering as shown in Table 
1a. The operating radio frequencies of 
all ground components must not vary 
by more than 

±

10 KHz from the as-

signed frequency. Any one transmitter 
frequency must not vary more than 

±

50 

Hz in any one second period. The MLS 
angle/data and DME equipment must 
operate on one of the paired channels 
as shown in Table 1b. 

T

ABLE

1a—F

REQUENCY

C

HANNEL

P

LAN

 

Channel No. 

Fre-

quency 

(MHz) 

500 ...........................................................................

5031.0 

501 ...........................................................................

5031.3 

502 ...........................................................................

5031.6 

503 ...........................................................................

5031.9 

504 ...........................................................................

5032.2 

505 ...........................................................................

5032.5 

506 ...........................................................................

5032.8 

507 ...........................................................................

5033.1 

508 ...........................................................................

5033.4 

509 ...........................................................................

5033.7 

510 ...........................................................................

5034.0 

511 ...........................................................................

5034.3 

*

*

*

*

598 ...........................................................................

5060.4 

599 ...........................................................................

5060.7 

600 ...........................................................................

5061.0 

601 ...........................................................................

5061.3 

*

*

*

*

698 ...........................................................................

5090.4 

699 ...........................................................................

5090.7 

T

ABLE

1b—C

HANNELS

 

Channel pairing 

DME parameters 

DME No. 

VHF freq. 

MHz 

MLS angle 

freq. MHz 

MLS Ch. 

No. 

Interrogation 

Reply 

Freq. 

MHz 

Pulse codes 

Freq. 

MHz 

Pulse codes 

µ

DME/N 

µ

DME/P Mode 

IA 

µ

FA 

µ

* 1X ....................

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

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

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

1025 

12  ..............

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

962 

12 

** 1Y ..................

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

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

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

1025 

36  ..............

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

1088 

30 

* 2X ....................

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

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

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

1026 

12  ..............

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

963 

12 

** 2Y ..................

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

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

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

1026 

36  ..............

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

1089 

30 

* 3X ....................

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

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

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

1027 

12  ..............

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

964 

12 

** 3Y ..................

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

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

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

1027 

36  ..............

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

1090 

30 

* 4X ....................

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

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

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

1028 

12  ..............

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

965 

12 

** 4Y ..................

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

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

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

1028 

36  ..............

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

1091 

30 

* 5X ....................

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

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

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

1029 

12  ..............

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

966 

12