What does the light gun signal of flashing red mean to an aircraft in flight?

4-3-13. Traffic Control Light Signals
a. The following procedures are used by ATCTs in the control of aircraft, ground vehicles, equipment, and
personnel not equipped with radio. These same procedures will be used to control aircraft, ground vehicles,
Airport Operations 4-3-19

AIM 2/20/25
equipment, and personnel equipped with radio if radio contact cannot be established. ATC personnel use a
directive traffic control signal which emits an intense narrow light beam of a selected color (either red, white,
or green) when controlling traffic by light signals.
b. Although the traffic signal light offers the advantage that some control may be exercised over nonradio
equipped aircraft, pilots should be cognizant of the disadvantages which are:
1. Pilots may not be looking at the control tower at the time a signal is directed toward their aircraft.
2. The directions transmitted by a light signal are very limited since only approval or disapproval of a pilot's
anticipated actions may be transmitted. No supplement or explanatory information may be transmitted except
by the use of the "General Warning Signal" which advises the pilot to be on the alert.
c. Between sunset and sunrise, a pilot wishing to attract the attention of the control tower should turn on a
landing light and taxi the aircraft into a position, clear of the active runway, so that light is visible to the tower.
The landing light should remain on until appropriate signals are received from the tower.
d. Airport Traffic Control Tower Light Gun Signals. (See TBL 4-3-1.)
e. During daylight hours, acknowledge tower transmissions or light signals by moving the ailerons or rudder.
At night, acknowledge by blinking the landing or navigation lights. If radio malfunction occurs after departing
the parking area, watch the tower for light signals or monitor tower frequency.
TBL 4-3-1
Airport Traffic Control Tower Light Gun Signals
Meaning
Color and Type of Signal Movement of Vehicles,
Equipment and Personnel Aircraft on the Ground Aircraft in Flight
Steady green Cleared to cross, proceed or go Cleared for takeoff Cleared to land
Flashing green Not applicable Cleared for taxi Return for landing (to be
followed by steady green at the
proper time)
Steady red STOP STOP Give way to other aircraft and
continue circling
Flashing red Clear the taxiway/runway Taxi clear of the runway in use Airport unsafe, do not land
Flashing white Return to starting point on airport Return to starting point on airport Not applicable
Alternating red and green Exercise extreme caution Exercise extreme caution Exercise extreme caution