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852 

14 CFR Ch. I (1–1–24 Edition) 

§ 171.305 

Microwave Landing System (MLS) 

means the MLS selected by ICAO for 
international standardization. 

Minimum glidepath 

means the lowest 

angle of descent along the zero degree 
azimuth that is consistent with pub-
lished approach procedures and obsta-
cle clearance criteria. 

MLS Approach Reference Datum 

is a 

point at a specified height located 
vertically above the intersection of the 
runway centerline and the threshold. 

MLS back azimuth reference datum 

means a point 15 meters (50 feet) above 
the runway centerline at the runway 
midpoint. 

MLS datum point 

means a point de-

fined by the intersection of the runway 
centerline with a vertical plane perpen-
dicular to the centerline and passing 
through the elevation antenna phase 
center. 

Out of coverage indication (OCI) 

means 

a signal radiated into areas outside the 
intended coverage sector, where re-
quired, to specifically prevent invalid 
removal of an airborne warning indica-
tion in the presence of misleading guid-
ance information. 

Path Following Error (PFE) 

means the 

guidance perturbations which could 
cause aircraft displacement from the 
desired course or glidepath. It is com-
posed of the path following noise and of 
the mean course error in the case of 
azimuth functions, or the mean glide-
path error in the case of elevation 
functions. Path following errors are 
evaluated by filtering the flight error 
record with a second order low pass fil-
ter which has a corner frequency at 0.5 
radian/sec for azimuth data or 1.5 radi-
ans/sec for elevation data. 

Path following noise (PFN) 

means that 

portion of the guidance signal error 
which could cause displacement from 
the actual mean course line or mean 
glidepath as appropriate. 

Split-site ground station 

means the 

type of ground station in which the azi-
muth portion of the ground station is 
located near the stop end of the run-
way, and the elevation portion is lo-
cated near the approach end. 

Time division multiplex (TDM) 

means 

that each function is transmitted on 
the same frequency in time sequence, 
with a distinct preamble preceding 
each function transmission. 

§ 171.305 Requests for IFR procedure. 

(a) Each person who requests an IFR 

procedure based on an MLS facility 
which that person owns must submit 
the following information with that re-
quest: 

(1) A description of the facility and 

evidence that the equipment meets the 
performance requirements of §§ 171.309, 
171.311, 171.313, 171.315, 171.317, 171.319, 
and 171.321 and is fabricated and in-
stalled in accordance with § 171.323. 

(2) A proposed procedure for oper-

ating the facility. 

(3) A proposed maintenance organiza-

tion and a maintenance manual that 
meets the requirements of § 171.325. 

(4) A statement of intent to meet the 

requirements of this subpart. 

(5) A showing that the facility has an 

acceptable level of operational reli-
ability and an acceptable standard of 
performance. Previous equivalent oper-
ational experience with a facility with 
identical design and operational char-
acteristics will be considered in show-
ing compliance with this subparagraph. 

(b) FAA inspects and evaluates the 

MLS facility; it advises the owner of 
the results, and of any required 
changes in the MLS facility or in the 
maintenance manual or maintenance 
organization. The owner must then 
correct the deficiencies, if any, and op-
erate the MLS facility for an in-service 
evaluation by the FAA. 

§ 171.307 Minimum requirements for 

approval. 

(a) The following are the minimum 

requirements that must be met before 
the FAA approves an IFR procedure for 
a non-Federal MLS facility: 

(1) The performance of the MLS facil-

ity, as determined by flight and ground 
inspection conducted by the FAA, must 
meet the requirements of §§ 171.309, 
171.311, 171.313, 171.315, 171.317, 171.319, 
and 171.321. 

(2) The fabrication and installation of 

the equipment must meet the require-
ments of § 171.323. 

(3) The owner must agree to operate 

and maintain the MLS facility in ac-
cordance with § 171.325. 

(4) The owner must agree to furnish 

operational records as set forth in 
§ 171.327 and agree to allow the FAA to 

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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: