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AIM

10/12/17

2−1−8

Airport Lighting Aids

FIG 2−1−9

Runway Status Light System

c. Takeoff Hold Lights (THL) : The THL system

is composed of flush mounted, in-pavement,

unidirectional light fixtures in a double longitudinal

row aligned either side of the runway centerline

lighting. Fixtures are focused toward the arrival end

of the runway at the “line up and wait” point. THLs

extend for 1,500 feet in front of the holding aircraft

starting at a point 375 feet from the departure

threshold (see FIG 2−1−13). Illuminated red lights

provide a signal, to an aircraft in position for takeoff

or rolling, that it is unsafe to takeoff because the

runway is occupied or about to be occupied by

another aircraft or ground vehicle. Two aircraft, or a

surface vehicle and an aircraft, are required for the

lights to illuminate. The departing aircraft must be in

position for takeoff or beginning takeoff roll. Another

aircraft or a surface vehicle must be on or about to

cross the runway.

1. THL Operating Characteristics − Departing

Aircraft:
THLs will illuminate for an aircraft in position for

departure or departing when there is another aircraft

or vehicle on the runway or about to enter the runway

(see FIG 2−1−9.) Once that aircraft or vehicle exits

the runway, the THLs extinguish. A pilot may notice

lights extinguish prior to the downfield aircraft or

vehicle being completely clear of the runway but still

moving. Like RELs, THLs have an “anticipated

separation” feature.

NOTE−

When the THLs extinguish, this is not clearance to begin a

takeoff roll. All takeoff clearances will be issued by ATC.

2. What a pilot would observe: A pilot in

position to depart from a runway, or has begun takeoff

roll, will observe THLs illuminate in reaction to an

aircraft or vehicle on the runway or entering or

crossing it. Lights will extinguish when the runway is

clear. A pilot may observe several cycles of

illumination and extinguishing depending on the

amount of crossing traffic.

3. When a pilot observes the red light of the

THLs, the pilot should safely stop if it’s feasible or

remain stopped. The pilot must contact ATC for

resolution if any clearance is in conflict with the

lights. Should pilots note illuminated lights while in

takeoff roll and under circumstances when stopping

is impractical for safety reasons, the crew should

proceed according to their best judgment while

understanding the illuminated lights indicate that