Aeronautical Information Manual (AIM), page 103

Index   102 -- Page 103 -- 104

LAHSO is in effect. These lights will be off when
LAHSO is not in effect.
AIM, Paragraph 4-3-11 , Pilot Responsibilities When Conducting

and Hold Short Operations (LAHSO)

2-1-6. Runway Status Light (RWSL)


a. Introduction.

RWSL is a fully automated system that provides
runway status information to pilots and surface
vehicle operators to clearly indicate when it is unsafe
to enter, cross, takeoff from, or land on a runway. The
RWSL system processes information from surveil-
lance systems and activates Runway Entrance Lights
(REL), Takeoff Hold Lights (THL), Runway
Intersection Lights (RIL), and Final Approach
Runway Occupancy Signal (FAROS) in accordance
with the position and velocity of the detected surface
traffic and approach traffic. REL, THL, and RIL are
in-pavement light fixtures that are directly visible to
pilots and surface vehicle operators. FAROS alerts
arriving pilots that the approaching runway is
occupied by flashing the Precision Approach Path
Indicator (PAPI). FAROS may be implemented as an
add-on to the RWSL system or implemented as a
stand-alone system at airports without a RWSL
system. RWSL is an independent safety enhancement
that does not substitute for or convey an ATC
clearance. Clearance to enter, cross, takeoff from,
land on, or operate on a runway must still be received
from ATC. Although ATC has limited control over
the system, personnel do not directly use and may not
be able to view light fixture activations and
deactivations during the conduct of daily ATC

b. Runway Entrance Lights (REL): The REL
system is composed of flush mounted, in-pavement,
unidirectional light fixtures that are parallel to and
focused along the taxiway centerline and directed
toward the pilot at the hold line. An array of REL
lights include the first light at the hold line followed
by a series of evenly spaced lights to the runway edge;
one additional light at the runway centerline is in line
with the last two lights before the runway edge (see
FIG 2-1-9 and FIG 2-1-12). When activated, the
red lights indicate that there is high speed traffic on
the runway or there is an aircraft on final approach
within the activation area.

1. REL Operating Characteristics - Departing

When a departing aircraft reaches a site adaptable
speed of approximately 30 knots, all taxiway
intersections with REL arrays along the runway
ahead of the aircraft will illuminate (see FIG 2-1-9).

As the aircraft approaches an REL equipped taxiway

intersection, the lights at that intersection extinguish
approximately 3 to 4 seconds before the aircraft
reaches it. This allows controllers to apply
"anticipated separation" to permit ATC to move
traffic more expeditiously without compromising
safety. After the aircraft is declared "airborne" by the
system, all REL lights associated with this runway
will extinguish.

2. REL Operating Characteristics - Arriving
When an aircraft on final approach is approximately
1 mile from the runway threshold, all sets of taxiway
REL light arrays that intersect the runway illuminate.
The distance is adjustable and can be configured for
specific operations at particular airports. Lights
extinguish at each equipped taxiway intersection
approximately 3 to 4 seconds before the aircraft
reaches it to apply anticipated separation until the
aircraft has slowed to approximately 80 knots (site
adjustable parameter). Below 80 knots, all arrays that
are not within 30 seconds of the aircraft's forward
path are extinguished. Once the arriving aircraft
slows to approximately 34 knots (site adjustable
parameter), it is declared to be in a taxi state, and all
lights extinguish.

3. What a pilot would observe: A pilot at or
approaching the hold line to a runway will observe
RELs illuminate and extinguish in reaction to an
aircraft or vehicle operating on the runway, or an
arriving aircraft operating less than 1 mile from the
runway threshold.

4. When a pilot observes the red lights of the
REL, that pilot will stop at the hold line or remain
stopped. The pilot will then contact ATC for
resolution if the clearance is in conflict with the
lights. Should pilots note illuminated lights under
circumstances when remaining clear of the runway is
impractical for safety reasons (for example, aircraft
is already on the runway), the crew should proceed
according to their best judgment while understanding
the illuminated lights indicate the runway is unsafe to

Airport Lighting Aids 2-1-7

Page 103 of the Aeronautical Information Manual (AIM.pdf)
AIM: Official Guide to Basic Flight Information and ATC Procedures

Index   102 -- Page 103 -- 104