889 

Federal Aviation Administration, DOT 

§ 171.319 

must not deviate from the true ele-
vation angle at that point by more 
than 

±

0.04 degree for elevation angles 

from 2.5

° 

to 3.5

°

. Above 3.5

° 

these errors 

may linearly increase to 

±

0.1 degree at 

7.5

°

. Multipath and drift effects are ex-

cluded from this requirement. 

(3) 

Antenna alignment. 

The antenna 

must be equipped with suitable optical, 
electrical, or mechanical means or any 
combination of the three, to align the 
lowest operationally required glidepath 
to the true glidepath angle with a max-
imum error of 0.01 degree. Addition-
ally, the elevation antenna bias adjust-
ment must be electronically steerable 
at least to the monitor limits in steps 
not greater than 0.005 degrees. 

(4) 

Antenna far field patterns in the 

plane of scan. 

On the lowest operation-

ally required glidepath, the antenna 
mainlobe pattern must conform to Fig-
ure 10, and the beamwidth must be 
such that in the installed environment, 
no significant ground reflections of the 
mainlobe exist. In any case, the beam-
width must not exceed 2 degrees. The 
antenna mainlobe may be allowed to 
broaden from the value at boresight by 
a factor of 1/cos

q

, where 

q 

is the angle 

of boresight. Anywhere within cov-
erage, the 

¥

3 dB width of the antenna 

mainlobe, while scanning normally, 
must not be less than 25 microseconds 
(0.5 degrees) or greater than 250 micro-
seconds (5 degrees). The sidelobe levels 
must be as follows: 

(i) 

Dynamic sidelobe levels. 

With the 

antenna scanning normally, the dy-
namic sidelobe level that is detected by 
a receiver at any point within the pro-
portional coverage sector must be 
down at least 10 dB from the peak of 
the mainlobe. Outside the proportional 
coverage sector, the radiation from the 
scanning beam antenna must be of 
such a nature that receiver warnings 
will not be removed or a suitable OCI 
signal must be provided. 

(ii) 

Effective sidelobe levels. 

With the 

antenna scanning normally, the 
sidelobe levels in the plane of scan 
must be such that, when reflected from 
the ground, the resultant PFE along 
any glidepath does not exceed 0.083 de-
grees. 

(5) 

Antenna far field pattern in the hor-

izontal plane. 

The horizontal pattern of 

the antenna must gradually de-empha-

size the signal away from antenna 
boresight. Typically, the horizontal 
pattern should be reduced by at least 3 
dB at 20 degrees off boresight and by at 
least 6 dB at 40 degrees off boresight. 
Depending on the actual multipath 
conditions, the horizontal radiation 
patterns may require more or less de- 
emphasis. 

(6) 

Data antenna. 

The data antenna 

must have horizontal and vertical pat-
terns as required for its function. 

(f) 

False guidance. 

False courses 

which can be acquired and tracked by 
an aircraft shall not exist anywhere ei-
ther inside or outside of the MLS cov-
erage sector. False courses which exist 
outside of the minimum coverage sec-
tor may be suppressed by the use of 
OCI. 

N

OTE

: False courses may be due to (but not 

limited to) MLS airborne receiver acquisi-
tion of the following types of false guidance: 
reflections of the scanning beam and scan-
ning beam antenna sidelobes and grating 
lobes. 

§ 171.319 Approach elevation monitor 

system requirements. 

(a) The monitor system must act to 

ensure that any of the following condi-
tions do not persist for longer than the 
periods specified when: 

(1) There is a change in the ground 

component contribution to the mean 
glidepath error component such that 
the path following error on any glide-
path exceeds the limits specified in 
§ 171.317(d) for a period of more than 
one second. 

N

OTE

: The above requirement and the re-

quirement to limit the ground equipment 
mean error to 

±

0.067 degree can be satisfied 

by the following procedure. The integral 
monitor alarm limit should be set to 

±

0.067 

degree. This will limit the electrical compo-
nent of mean glidepath error to 

±

0.067 degree. 

The field monitor alarm limit should be set 
such that with the mean glidepath error at 
the alarm limit the total allowed PFE is not 
exceeded on any commissioned glidepath 
from the limit of coverage to an altitude of 
100 feet. 

(2) There is a reduction in the radi-

ated power to a level not less than that 
specified in § 171.317(a)(4) for a period of 
more than one second. 

(3) There is an error in the preamble 

DPSK transmission which occurs more 
than once in any one second period. 

890 

14 CFR Ch. I (1–1–24 Edition) 

§ 171.321 

(4) There is an error in the time divi-

sion multiplex synchronization of a 
particular elevation function such that 
the requirement specified in § 171.311(e) 
is not satisfied and this condition per-
sists for more than one second. 

(5) A failure of the monitor is de-

tected. 

(b) The period during which erro-

neous guidance information is radiated 
must not exceed the periods specified 
in § 171.319(a). If the fault is not cleared 
within the time allowed, radiation 
shall cease. After shutdown, no at-
tempt must be made to restore service 
until a period of 20 seconds has elapsed. 

§ 171.321 DME and marker beacon per-

formance requirements. 

(a) The DME equipment must meet 

the performance requirements pre-
scribed in subpart G of the part. This 
subpart imposes requirements that per-
formance features must comply with 
International Standards and Rec-
ommended Practices, Aeronautical 
Telecommunications, Vol. I of Annex 
10 to ICAO. It is available from ICAO, 
Aviation Building, 1080 University 
Street, Montreal 101, Quebec, Canada, 
Attention: Distribution Officer and 
also available for inspection at the Na-
tional Archives and Records Adminis-
tration (NARA). For information on 
the availability of this material at 
NARA, call 202–741–6030, or go to: 

http:// 

www.archives.gov/federal

_

register/ 

code

_

of

_

federal

_

regulations/ibr

_

loca-

tions.html. 

(b) MLS marker beacon equipment 

must meet the performance require-
ments prescribed in subpart H of this 
part. This subpart imposes require-
ments that performance features must 
comply with International Standards 
and Recommended Practices, Aero-
nautical Telecommuncations, Vol. I of 
Annex 10 to ICAO. 

[Doc. No. 5034, 29 FR 11337, Aug. 6, 1964, as 
amended at 69 FR 18803, Apr. 9, 2004] 

§ 171.323 Fabrication and installation 

requirements. 

(a) The MLS facility must be perma-

nent and must be located, constructed, 
and installed in accordance with best 
commercial engineering practices, 
using applicable electric and safety 
codes and Federal Communications 

Commission (FCC) licensing require-
ments and siting requirements of 
§§ 171.313(b) and 171.317(b). 

(b) The MLS facility components 

must utilize solid state technology ex-
cept that traveling wave tube ampli-
fiers (TWTA) may be used. A maximum 
level of common modularity must be 
provided along with diagnostics to fa-
cilitate maintenance and trouble-
shooting. 

(c) An approved monitoring capa-

bility must be provided which indicates 
the status of the equipment at the site 
and at a remotely located maintenance 
area, with monitor capability that pro-
vides pre-alarm of impending system 
failures. This monitoring feature must 
be capable of transmitting the status 
and pre-alarm over standard phone 
lines to a remote section. In the event 
the sponsor requests the FAA to as-
sume ownership of the facility, the 
monitoring feature must also be capa-
ble of interfacing with FAA remote 
monitoring requirements. This require-
ment may be complied with by the ad-
dition of optional software and/or hard-
ware in space provided in the original 
equipment. 

(d) The mean corrective maintenance 

time of the MLS equipment must be 
equal to or less than 0.5 hours with a 
maximum corrective maintenance time 
not to exceed 1.5 hours. This measure 
applies to correction of unscheduled 
failures of the monitor, transmitter 
and associated antenna assemblies, 
limited to unscheduled outage and out 
of tolerance conditions. 

(e) The mean-time-between-failures 

of the MLS angle system must not be 
less than 1,500 hours. This measure ap-
plies to unscheduled outage, out-of-tol-
erance conditions, and failures of the 
monitor, transmitter, and associated 
antenna assemblies. 

(f) The MLS facility must have a reli-

able source of suitable primary power, 
either from a power distribution sys-
tem or locally generated. Adequate 
power capacity must be provided for 
the operation of the MLS as well as the 
test and working equipment of the 
MLS. 

(g) The MLS facility must have a 

continuously engaged or floating bat-
tery power source for the continued 
normal operation of the ground station