in what ATC manual are you getting that supposed directive from?????
US Department of Transportation
Federal Aviation Administration
Order JO 7110.65W
Chapter 2. General Control
Section 1. General
2−1−1. ATC SERVICE
The primary purpose of the ATC system is to prevent a collision between aircraft operating in the system and to provide a safe, orderly and expeditiousflow of traffic, and to provide support for National Security and Homeland Defense.
Section 1. General
2−1−2. DUTY PRIORITY
a.
Give first priority to separating aircraft and issuing safety alerts as required in this order. Good judgment must be used in prioritizing all other provisions of this order
based on the requirements of the situation at hand.
Section 1. General
2−1−6. SAFETY ALERT
Issue a safety alert to an aircraft if you are aware the aircraft is in a position/altitude that, in your judgment,places it in unsafe proximity to terrain, obstructions,or other aircraft.
NOTE−1. The issuance of a safety alert is a first priority (see para 2−1−2, Duty Priority) once the controller observes and recognizes a situation of unsafe aircraft proximity to terrain, obstacles, or other aircraft.
Chapter 3. Airport Traffic Control− Terminal
Section 2. Visual Signals
3−2−2. WARNING SIGNAL
Direct a general warning signal, alternating red and green, to aircraft or vehicle operators, as appropriate,
when:
NOTE− The warning signal is not a prohibitive signal and can be followed by any other light signal, as circumstances
permit.
a. Aircraft are converging and a collision hazard exists.
Pilot/Controller Glossary
PCG A−1
A
AIR TRAFFIC CONTROL SERVICE [ICAO]− A service provided for the purpose of a preventing collisions: 1. Between aircraft; and 2. On the maneuvering area between aircraftand obstructions. b. Expediting and maintaining an orderly flow of air traffic.
RESOLUTION ADVISORY−A display indication given to the pilot by the traffic alert and collisionavoidance systems (TCAS II) recommending amaneuver to increase vertical separation relative to an intruding aircraft. Positive, negative, and verticalspeed limit (VSL) advisories constitute the resolutionadvisories. A resolution advisory is also classified as corrective or preventive
SAFETY LOGIC SYSTEM ALERTS−a. ALERT− An actual situation involving two real safety logic tracks (aircraft/aircraft, aircraft/vehicle, or aircraft/other tangible object) that safety logic has predicted will result in an imminent collision, based upon the current set of Safety Logic parameters.