FAA Federal Aviation Regulations (FARS, 14 CFR)

ATC light signals have the meaning shown in the following table:

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Meaning with
respect to         Meaning with
Color and type of signal        aircraft on the       respect to
surface       aircraft in flight
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Steady green....................  Cleared for         Cleared to land.
takeoff.
Flashing green..................  Cleared to taxi...  Return for landing
(to be followed
by steady green
at proper time).
Steady red......................  Stop..............  Give way to other
aircraft and
continue
circling.
Flashing red....................  Taxi clear of       Airport unsafe_do
runway in use.      not land.
Flashing white..................  Return to starting  Not applicable.
point on airport.
Alternating red and green.......  Exercise extreme    Exercise extreme
caution.            caution.
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