Federal Aviation Administration, DOT

Section 171.271

achieved at an angle not less than 0.30q
above the horizontal. However, if it is
achieved at an angle above 0.45q, the
DDM value may not be less than 0.22 at
least down to an angle of 0.45q.
[Doc. No. 14120, 40 FR 36110, Aug. 19, 1975; 40
FR 41093, Sept. 5, 1975; 40 FR 43719, Sept. 23,
1975]

Section 171.267 Glide path automatic monitor system.
(a) The ISMLS glide path equipment
must provide an automatic monitor
system that transmits a warning to
designated local and remote control
points when any of the following occurs:
(1) A shift of the mean ISMLS glide
path angle equivalent to more than
0.075q.
(2) For glide paths 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.
(3) A change of the angle between the
glide path and the line below the glide
path (150 Hz predominating), at which a
DDM of 0.0875 is realized by more than
Section0.0375q.
(4) Lowering of the line beneath the
ISMLS glide path at which a DDM of
0.0875 is realized to less than 0.75q from
the horizontal.
(5) Failure of any part of the monitor
itself. Such failure must automatically
produce the same results as the malfunctioning of the element being monitored.
(b) At glide path facilities where the
selected nominal angular displacement
sensitivity corresponds to an angle
below the ISMLS glide path, which is
close to or at the maximum limits
specified, an adjustment to the monitor operating limits may be made to
protect against sector deviations below
0.75q from the horizontal.
(c) Within 10 seconds of the occurrence of any of the conditions prescribed in paragraph (a) of this section,
including periods of zero radiation,
glide path signal radiation must cease.
Section 171.269 Marker beacon performance
requirements.
ISMLS marker beacon equipment
must meet the performance requirements prescribed in subpart H of this
part.

Section 171.271 Installation requirements.
(a) The ISMLS facility must be permanent in nature, located, constructed, and installed according to accepted good engineering practices, applicable electric and safety codes, FCC
licensing requirements, and paragraphs
(a) and (c) of Section 171.261.
(b) The ISMLS facility must have a
reliable source of suitable primary
power, either from a power distribution
system or locally generated. Adequate
power capacity must be provided for
the operation of test and working
equipment of the ISMLS.
(c) The ISMLS facility must have a
continuously engaged or floating battery power source for the ground station for continued normal operation if
the primary power fails. A trickle
charge must be supplied to recharge
the batteries during the period of available primary power. Upon loss and subsequent restoration of power, the batteries must be restored to full charge
within 24 hours. When primary power is
applied, the state of the battery charge
may not affect the operation of the
ISMLS ground station. The battery
must permit continuation of normal
operation for at least two hours under
the normal operating conditions. The
equipment must meet all specification
requirements with or without batteries
installed.
(d) There must be a means for determining, from the ground, the performance of the equipment including antennae, both initially and periodically.
(e) The facility must have, or be supplemented by, ground-air or landline
communications services. At facilities
within or immediately adjacent to controlled airspace and that are intended
for use as instrument approach aids for
an airport, there must be ground-air
communications or reliable communications (at least a landline telephone) from the airport to the nearest
Federal Aviation Administration air
traffic control or communication facility. Compliance with this paragraph
need not be shown at airports where an
adjacent Federal Aviation Administration facility can communicate with
aircraft on the ground at the airport
and during the entire proposed instrument approach procedure. In addition,
at low traffic density airports within

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