Federal Aviation Administration, DOT

Section 25.1389

(c) There must be a means to indicate
to the pilots when the landing lights
are extended.
Section 25.1385 Position light system installation.
(a) General. Each part of each position light system must meet the applicable requirements of this section and
each system as a whole must meet the
requirements of SectionSection 25.1387 through
25.1397.
(b) Forward position lights. Forward
position lights must consist of a red
and a green light spaced laterally as
far apart as practicable and installed
forward on the airplane so that, with
the airplane in the normal flying position, the red light is on the left side
and the green light is on the right side.
Each light must be approved.
(c) Rear position light. The rear position light must be a white light mounted as far aft as practicable on the tail
or on each wing tip, and must be approved.
(d) Light covers and color filters. Each
light cover or color filter must be at
least flame resistant and may not
change color or shape or lose any appreciable light transmission during
normal use.

spaschal on DSK3GDR082PROD with CFR

[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Amdt. 25-38, 41 FR 55468, Dec. 20,
1976]

Section 25.1387 Position light system dihedral angles.
(a) Except as provided in paragraph
(e) of this section, each forward and
rear position light must, as installed,
show unbroken light within the dihedral angles described in this section.
(b) Dihedral angle L (left) is formed
by two intersecting vertical planes, the
first parallel to the longitudinal axis of
the airplane, and the other at 110 degrees to the left of the first, as viewed
when looking forward along the longitudinal axis.
(c) Dihedral angle R (right) is formed
by two intersecting vertical planes, the
first parallel to the longitudinal axis of
the airplane, and the other at 110 degrees to the right of the first, as viewed
when looking forward along the longitudinal axis.
(d) Dihedral angle A (aft) is formed
by two intersecting vertical planes

making angles of 70 degrees to the
right and to the left, respectively, to a
vertical plane passing through the longitudinal axis, as viewed when looking
aft along the longitudinal axis.
(e) If the rear position light, when
mounted as far aft as practicable in accordance with Section 25.1385(c), cannot show
unbroken light within dihedral angle A
(as defined in paragraph (d) of this section), a solid angle or angles of obstructed visibility totaling not more
than 0.04 steradians is allowable within
that dihedral angle, if such solid angle
is within a cone whose apex is at the
rear position light and whose elements
make an angle of 30Section with a vertical
line passing through the rear position
light.
[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Amdt. 25-30, 36 FR 21278, Nov. 5,
1971]

Section 25.1389 Position light distribution
and intensities.
(a) General. The intensities prescribed
in this section must be provided by new
equipment with light covers and color
filters in place. Intensities must be determined with the light source operating at a steady value equal to the average luminous output of the source at
the normal operating voltage of the
airplane. The light distribution and intensity of each position light must
meet the requirements of paragraph (b)
of this section.
(b) Forward and rear position lights.
The light distribution and intensities
of forward and rear position lights
must be expressed in terms of minimum intensities in the horizontal
plane, minimum intensities in any
vertical plane, and maximum intensities in overlapping beams, within dihedral angles L, R, and A, and must
meet the following requirements:
(1) Intensities in the horizontal plane.
Each intensity in the horizontal plane
(the plane containing the longitudinal
axis of the airplane and perpendicular
to the plane of symmetry of the airplane) must equal or exceed the values
in Section 25.1391.
(2) Intensities in any vertical plane.
Each intensity in any vertical plane
(the plane perpendicular to the horizontal plane) must equal or exceed the
appropriate value in Section 25.1393, where I is

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