554 

14 CFR Ch. I (1–1–24 Edition) 

§ 27.1387 

§ 27.1387

Position light system dihe-

dral 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 dihe-
dral 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 rotorcraft, and the other at 110 de-
grees to the left of the first, as viewed 
when looking forward along the longi-
tudinal axis. 

(c) Dihedral angle 

R (right) is formed 

by two intersecting vertical planes, the 
first parallel to the longitudinal axis of 
the rotorcraft, and the other at 110 de-
grees to the right of the first, as viewed 
when looking forward along the longi-
tudinal 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 lon-
gitudinal axis, as viewed when looking 
aft along the longitudinal axis. 

(e) If the rear position light, when 

mounted as far aft as practicable in ac-
cordance with § 25.1385(c), cannot show 
unbroken light within dihedral angle A 
(as defined in paragraph (d) of this sec-
tion), a solid angle or angles of ob-
structed 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 30

° 

with a vertical 

line passing through the rear position 
light. 

(49 U.S.C. 1655(c)) 

[Doc. No. 5074, 29 FR 15695, Nov. 24, 1964, as 
amended by Amdt. 27–7, 36 FR 21278, Nov. 5, 
1971] 

§ 27.1389

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 de-
termined with the light source oper-
ating at a steady value equal to the av-
erage luminous output of the source at 
the normal operating voltage of the 
rotorcraft. 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 min-
imum intensities in the horizontal 
plane, minimum intensities in any 
vertical plane, and maximum inten-
sities in overlapping beams, within di-
hedral 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 rotorcraft and perpendicular 
to the plane of symmetry of the rotor-
craft) must equal or exceed the values 
in § 27.1391. 

(2) 

Intensities in any vertical plane. 

Each intensity in any vertical plane 
(the plane perpendicular to the hori-
zontal plane) must equal or exceed the 
appropriate value in § 27.1393, where 

I is 

the minimum intensity prescribed in 
§ 27.1391 for the corresponding angles in 
the horizontal plane. 

(3) 

Intensities in overlaps between adja-

cent signals. No intensity in any over-
lap between adjacent signals may ex-
ceed the values in § 27.1395, except that 
higher intensities in overlaps may be 
used with main beam intensities sub-
stantially greater than the minima 
specified in §§ 27.1391 and 27.1393, if the 
overlap intensities in relation to the 
main beam intensities do not adversely 
affect signal clarity. When the peak in-
tensity of the forward position lights is 
greater than 100 candles, the maximum 
overlap intensities between them may 
exceed the values in § 27.1395 if the 
overlap intensity in Area A is not more 
than 10 percent of peak position light 
intensity and the overlap intensity in 
Area B is not more than 2.5 percent of 
peak position light intensity. 

§ 27.1391

Minimum intensities in the 

horizontal plane of forward and 
rear position lights. 

Each position light intensity must 

equal or exceed the applicable values in 
the following table: 

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555 

Federal Aviation Administration, DOT 

§ 27.1401 

Dihedral angle (light in-

cluded) 

Angle from right or left 

of longitudinal axis, 

measured from dead 

ahead 

Intensity 

(candles) 

L and R (forward red 

and green).

10

° 

to 10

°

...................

10

° 

to 20

°

...................

20

° 

to 110

°

.................

40 
30 

5 

A (rear white) ..............

110

° 

to 180

°

...............

20 

§ 27.1393

Minimum intensities in any 

vertical plane of forward and rear 
position lights. 

Each position light intensity must 

equal or exceed the applicable values in 
the following table: 

Angle above or below the horizontal plane 

Intensity, l 

0

°

.........................................................................

1.00 

0

° 

to 5

°

................................................................

0.90 

5

° 

to 10

°

..............................................................

0.80 

10

° 

to 15

°

............................................................

0.70 

15

° 

to 20

°

............................................................

0.50 

20

° 

to 30

°

............................................................

0.30 

30

° 

to 40

°

............................................................

0.10 

40

° 

to 90

°

............................................................

0.05 

§ 27.1395

Maximum intensities in over-

lapping beams of forward and rear 
position lights. 

No position light intensity may ex-

ceed the applicable values in the fol-
lowing table, except as provided in 
§ 27.1389(b)(3). 

Overlaps 

Maximum Intensity 

Area A 

(candles) 

Area B 

(candles) 

Green in dihedral angle L .............

10 1 

Red in dihedral angle R ................

10 1 

Green in dihedral angle A .............

5 1 

Red in dihedral angle A ................

5 1 

Rear white in dihedral angle L ......

5 1 

Rear white in dihedral angle R .....

5 1 

Where— 

(a) Area A includes all directions in 

the adjacent dihedral angle that pass 
through the light source and intersect 
the common boundary plane at more 
than 10 degrees but less than 20 de-
grees, and 

(b) Area B includes all directions in 

the adjacent dihedral angle that pass 
through the light source and intersect 
the common boundary plane at more 
than 20 degrees. 

§ 27.1397

Color specifications. 

Each position light color must have 

the applicable International Commis-
sion on Illumination chromaticity co-
ordinates as follows: 

(a) 

Aviation red— 

y is not greater than 0.335; and 
z is not greater than 0.002. 

(b) 

Aviation green— 

x is not greater than 0.440

¥

0.320

y; 

x is not greater than y

¥

0.170; and 

y is not less than 0.390

¥

0.170

x. 

(c) 

Aviation white— 

x is not less than 0.300 and not greater than 

0.540; 

y  is not less than x

¥

0.040’’ or 

y

c

¥

0.010, 

whichever is the smaller; and 

y  is not greater than x  + 0.020 nor 

0.636

¥

0.400

x; 

Where 

y

c

is the 

y coordinate of the Planck-

ian radiator for the value of 

x considered. 

[Doc. No. 5074, 29 FR 15695, Nov. 24, 1964, as 
amended by Amdt. 27–6, 36 FR 12972, July 10, 
1971] 

§ 27.1399

Riding light. 

(a) Each riding light required for 

water operation must be installed so 
that it can— 

(1) Show a white light for at least 

two nautical miles at night under clear 
atmospheric conditions; and 

(2) Show a maximum practicable un-

broken light with the rotorcraft on the 
water. 

(b) Externally hung lights may be 

used. 

[Doc. No. 5074, 29 FR 15695, Nov. 24, 1964, as 
amended by Amdt. 27–2, 33 FR 964, Jan. 26, 
1968] 

§ 27.1401

Anticollision light system. 

(a) 

General.  If certification for night 

operation is requested, the rotorcraft 
must have an anticollision light sys-
tem that— 

(1) Consists of one or more approved 

anticollision lights located so that 
their emitted light will not impair the 
crew’s vision or detract from the con-
spicuity of the position lights; and 

(2) Meets the requirements of para-

graphs (b) through (f) of this section. 

(b) 

Field of coverage. The system must 

consist of enough lights to illuminate 
the vital areas around the rotorcraft, 
considering the physical configuration 
and flight characteristics of the rotor-
craft. The field of coverage must ex-
tend in each direction within at least 
30 degrees below the horizontal plane of 
the rotorcraft, except that there may 

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