846
14 CFR Ch. I (1–1–24 Edition)
§ 171.263
(2) Transmission of the identification
signal may not interfere in any way
with the basic localizer function.
(3) The signal must be produced by
pulse duration modulation of the radio
frequency carrier resulting in a de-
tected audio tone in the airborne VHF
receiver of 1020 Hz
±
50Hz.
(4) The depth of modulation must be
between the limits of 10 and 12 percent.
(5) The emissions carrying the identi-
fication signal must be vertically po-
larized.
(6) The identification signal must
employ the International Morse Code
and consist of three letters. It must be
preceded by the International Morse
Code signal of the letter ‘‘M’’ followed
by a short pause where it is necessary
to distinguish the ISMLS facility from
other navigational facilities in the im-
mediate area. At airports where both
an ISMLS and an ILS are in operation,
each facility must have a different
identification call sign.
(7) The signal must be transmitted at
a speed corresponding to approxi-
mately seven words per minute, and
must be repeated at approximately
equal intervals, not less than six times
per minute, during which time the lo-
calizer is available for operational use.
When the localizer is not available for
transmission, the identification signal
must be suppressed.
§ 171.263 Localizer automatic monitor
system.
(a) The ISMLS localizer equipment
must provide an automatic monitor
system that transmits a warning to
designated local and remote control
points when any of the following oc-
curs:
(1) A shift of the mean course line of
the localizer from the runway center-
line equivalent to more than 0.015 DDM
at the ISMLS reference datum.
(2) For localizers in which the basic
functions are provided by the use of a
single-frequency system, a reduction of
power output to less than 50 percent of
normal or a loss of ground station iden-
tification transmissions.
(3) Changes of displacement sensi-
tivity to a value differing by more than
17 percent from nominal value for the
localizer.
(4) Failure of any part of the monitor
itself. Such failure must automatically
produce the same results as the mal-
functioning of the element being mon-
itored.
(b) Within 10 seconds of the occur-
rence of any of the conditions pre-
scribed in paragraph (a) of this section,
including periods of zero radiation, lo-
calizer signal radiation must cease or
the navigation and identification com-
ponents must be removed.
§ 171.265 Glide path performance re-
quirements.
This section prescribes the perform-
ance requirements for glide path equip-
ment components of the ISMLS. These
requirements are based on the assump-
tion that the aircraft is heading di-
rectly toward the facility.
(a) The glide slope antenna system
must be located near the approach end
of the runway, and the equipment must
be adjusted so that the vertical path
line will be in a sloping horizontal
plane containing the centerline of the
runway being served, and satisfy the
coverage requirements prescribed in
paragraph (g) of this section. For the
purpose of obstacle clearance, location
of the glide slope antenna system must
be in accordance with the criteria spec-
ified in subpart C of part 97 of this
chapter.
(b) The radiation from the glide path
antenna system must produce a com-
posite field pattern which is pulse du-
ration modulated by a 90 Hz and a 150
Hz tone, which is the time average
equivalent to amplitude modulation.
The pattern must be arranged to pro-
vide a straight line descent path in the
vertical plane containing the center-
line of the runway, with the 150 Hz tone
predominating below the path and the
90 Hz tone predominating above the
path to at least an angle equal to
1.752
q
. As used in this section theta (
q
),
denotes the nominal glide path angle.
The glide path angle must be adjusted
and maintained within 0.075
q
.
(c) The glide path equipment must be
capable of producing a radiated glide
path from 3 to 9 degrees with respect to
the horizontal. However, ISMLS glide
path angles in excess of 3 degrees may
be used to satisfy instrument approach