14 CFR § 91.125 - ATC light signals.
§ 91.125 ATC light signals.
ATC light signals have the meaning shown in the following table:
|Color and type of signal||Meaning with respect to aircraft on the surface||Meaning with respect to aircraft in flight|
|Steady green||Cleared for takeoff||Cleared to land.|
|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 runway in use||Airport unsafe - do not land.|
|Flashing white||Return to starting point on airport||Not applicable.|
|Alternating red and green||Exercise extreme caution||Exercise extreme caution.|