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AIM 

6/17/21 

FIG 2

1

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

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11). 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

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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 

2

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Airport Lighting Aids