How is a runway number determined from its magnetic direction?

2-3-3. Runway Markings
a. General. There are three types of markings for runways: visual, nonprecision instrument, and precision
instrument. TBL 2-3-1 identifies the marking elements for each type of runway and TBL 2 -3-2 identifies
runway threshold markings.
TBL 2-3-1
Runway Marking Elements
Marking Element Visual Runway
Nonprecision
Instrument
Runway
Precision
Instrument
Runway
Designation X X X
Centerline X X X
Threshold X1 X X
Aiming Point X2 X X
Touchdown Zone X
Side Stripes X
1 On runways used, or intended to be used, by international commercial transports.
2 On runways 4,000 feet (1200 m) or longer used by jet aircraft.
Airport Marking Aids and Signs 2-3-1

AIM 2/20/25
FIG 2-3-1
Precision Instrument Runway Markings
b. Runway Designators. Runway numbers and letters are determined from the approach direction. The
runway number is the whole number nearest one-tenth the magnetic azimuth of the centerline of the runway,
measured clockwise from the magnetic north. The letters, differentiate between left (L), right (R), or center (C)
parallel runways, as applicable:
1. For two parallel runways "L" "R."
2. For three parallel runways "L" "C" "R."
c. Runway Centerline Marking. The runway centerline identifies the center of the runway and provides
alignment guidance during takeoff and landings. The centerline consists of a line of uniformly spaced stripes and
gaps.
d. Runway Aiming Point Marking. The aiming point marking serves as a visual aiming point for a landing
aircraft. These two rectangular markings consist of a broad white stripe located on each side of the runway
centerline and approximately 1,000 feet from the landing threshold, as shown in FIG 2-3-1, Precision
Instrument Runway Markings.
e. Runway Touchdown Zone Markers. The touchdown zone markings identify the touchdown zone for
landing operations and are coded to provide distance information in 500 feet (150m) increments. These markings
consist of groups of one, two, and three rectangular bars symmetrically arranged in pairs about the runway
centerline, as shown in FIG 2-3-1. For runways having touchdown zone markings on both ends, those pairs of
markings which extend to within 900 feet (270 m) of the midpoint between the thresholds are eliminated.
2-3-2 Airport Marking Aids and Signs

20
20

2/20/25 AIM
FIG 2-3-2
Nonprecision Instrument Runway and Visual Runway Markings
AIMING POINT
MARKING
THRESHOLD THRESHOLD
MARKINGS
DESIGNATION
MARKING
PAVEMENT EDGE
AIMING POINT
MARKING
PAVEMENT EDGE
DESIGNATION MARKING
THRESHOLD
NONPRECISION INSTRUMENT RUNWAY MARKINGS
VISUAL RUNWAY MARKINGS
f. Runway Side Stripe Marking. Runway side stripes delineate the edges of the runway. They provide a
visual contrast between runway and the abutting terrain or shoulders. Side stripes consist of continuous white
stripes located on each side of the runway as shown in FIG 2-3-4.
g. Runway Shoulder Markings. Runway shoulder stripes may be used to supplement runway side stripes
to identify pavement areas contiguous to the runway sides that are not intended for use by aircraft. Runway
shoulder stripes are yellow. (See FIG 2-3-5.)
h. Runway Threshold Markings. Runway threshold markings come in two configurations. They either
consist of eight longitudinal stripes of uniform dimensions disposed symmetrically about the runway centerline
(as shown in FIG 2-3-1) or the number of stripes is related to the runway width as indicated in TBL 2-3-2. A
threshold marking helps identify the beginning of the runway that is available for landing. In some instances,
the landing threshold may be relocated or displaced.
TBL 2-3-2
Number of Runway Threshold Stripes
Runway Width Number of Stripes
60 feet (18 m) 4
75 feet (23 m) 6
100 feet (30 m) 8
150 feet (45 m) 12
200 feet (60 m) 16
Airport Marking Aids and Signs 2-3-3

AIM 2/20/25
1. Relocation of a Threshold. Sometimes construction, maintenance, or other activities require the
threshold to be relocated towards the rollout end of the runway. (See FIG 2-3-3.) When a threshold is relocated,
it closes not only a set portion of the approach end of a runway, but also shortens the length of the opposite
direction runway. In these cases, a NOTAM should be issued by the airport operator identifying the portion of
the runway that is closed (for example, 10/28 W 900 CLSD). Because the duration of the relocation can vary from
a few hours to several months, methods identifying the new threshold may vary. One common practice is to use
a ten feet wide white threshold bar across the width of the runway. Although the runway lights in the area between
the old threshold and new threshold will not be illuminated, the runway markings in this area may or may not
be obliterated, removed, or covered.
2. Displaced Threshold. A displaced threshold is a threshold located at a point on the runway other than
the designated beginning of the runway. Displacement of a threshold reduces the length of runway available for
landings. The portion of runway behind a displaced threshold is available for takeoffs in either direction and
landings from the opposite direction. A ten feet wide white threshold bar is located across the width of the runway
at the displaced threshold. White arrows are located along the centerline in the area between the beginning of
the runway and displaced threshold. White arrow heads are located across the width of the runway just prior to
the threshold bar, as shown in FIG 2-3-4.
NOTE-
Airport operator. When reporting the relocation or displacement of a threshold, the airport operator should avoid language
which confuses the two.
i. Demarcation Bar. A demarcation bar delineates a runway with a displaced threshold from a blast pad,
stopway, or taxiway that precedes the runway. A demarcation bar is 3 feet (1m) wide and yellow, since it is not
located on the runway, as shown in FIG 2-3-6.
1. Chevrons. These markings are used to show pavement areas aligned with the runway that are unusable
for landing, takeoff, and taxiing. Chevrons are yellow. (See FIG 2-3-7.)
j. Runway Threshold Bar. A threshold bar delineates the beginning of the runway that is available for
landing when the threshold has been relocated or displaced. A threshold bar is 10 feet (3m) in width and extends
across the width of the runway, as shown in FIG 2-3-4.
2-3-4 Airport Marking Aids and Signs

2/20/25 AIM
FIG 2-3-3
Relocation of a Threshold with Markings for Taxiway Aligned with Runway
Airport Marking Aids and Signs 2-3-5

 AIM 2/20/25
FIG 2-3-4
Displaced Threshold Markings
2-3-6 Airport Marking Aids and Signs

2/20/25 AIM
FIG 2-3-5
Runway Shoulder Markings
RUNWAY THRESHOLD
MIDPOINT OF
RUNWAY
SHOULDER SHOULDERRUNWAY
45 deg 45 deg
45 deg 45 deg