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AIM

10/12/17

2−3−7

Airport Marking Aids and Signs

FIG 2−3−5

Runway Shoulder Markings

RUNWAY THRESHOLD

MIDPOINT OF

RUNWAY

SHOULDER

SHOULDER

RUNWAY

45°

45°

45°

45°

2−3−4. Taxiway Markings

a. General. All taxiways should have centerline

markings and runway holding position markings

whenever they intersect a runway. Taxiway edge

markings are present whenever there is a need to

separate the taxiway from a pavement that is not

intended for aircraft use or to delineate the edge of the

taxiway. Taxiways may also have shoulder markings

and holding position markings for Instrument

Landing System (ILS) critical areas and taxiway/

taxiway intersection markings.

REFERENCE−

AIM Paragraph 2−3−5 , Holding Position Markings

b. Taxiway Centerline.

1. Normal Centerline. The taxiway centerline

is a single continuous yellow line, 6 inches (15 cm) to

12 inches (30 cm) in width. This provides a visual cue

to permit taxiing along a designated path.  Ideally, the

aircraft should be kept centered over this line during

taxi. However, being centered on the taxiway

centerline does not guarantee wingtip clearance with

other aircraft or other objects.

2. Enhanced Centerline. At some airports,

mostly the larger commercial service airports, an

enhanced taxiway centerline will be used. The

enhanced taxiway centerline marking consists of a

parallel line of yellow dashes on either side of the

normal taxiway centerline. The taxiway centerlines

are enhanced for a maximum of 150 feet prior to a

runway holding position marking. The purpose of

this enhancement is to warn the pilot that he/she is

approaching a runway holding position marking and

should prepare to stop unless he/she has been cleared

onto or across the runway by ATC.  (See FIG 2−3−8.)

c. Taxiway Edge Markings. Taxiway edge

markings are used to define the edge of the taxiway.

They are primarily used when the taxiway edge does

not correspond with the edge of the pavement. There

are two types of markings depending upon whether

the aircraft is supposed to cross the taxiway edge:

1. Continuous Markings. These consist of a

continuous double yellow line, with each line being

at least 6 inches (15 cm) in width spaced 6 inches

(15 cm) apart. They are used to define the taxiway

edge from the shoulder or some other abutting paved

surface not intended for use by aircraft.

2. Dashed Markings. These markings are

used when there is an operational need to define the

edge of a taxiway or taxilane on a paved surface

where the adjoining pavement to the taxiway edge is

intended for use by aircraft (for example, an apron).

Dashed taxiway edge markings consist of a broken

double yellow line, with each line being at least 6

inches (15 cm) in width, spaced 6 inches (15 cm)

apart (edge to edge). These lines are 15 feet (4.5 m)

in length with 25 foot (7.5 m) gaps. (See FIG 2−3−9.)

d. Taxi Shoulder Markings. Taxiways, holding

bays, and aprons are sometimes provided with paved

shoulders to prevent blast and water erosion.

Although shoulders may have the appearance of full

strength pavement, they are not intended for use by

aircraft and may be unable to support an aircraft.

Usually the taxiway edge marking will define this

area. Where conditions exist such as islands or

taxiway curves that may cause confusion as to which

side of the edge stripe is for use by aircraft, taxiway

shoulder markings may be used to indicate the

pavement is unusable. Taxiway shoulder markings

are yellow. (See FIG 2−3−10.)