AIM Text
A safety alert will be issued to pilots of aircraft being controlled by ATC if the controller is aware the aircraft is at an altitude which, in the controller's judgment, places the aircraft in unsafe proximity to terrain, obstructions or other aircraft. The provision of this service is contingent upon the capability of the controller to have an awareness of a situation involving unsafe proximity to terrain, obstructions and uncontrolled aircraft. The issuance of a safety alert cannot be mandated, but it can be expected on a reasonable, though intermittent basis. Once the alert is issued, it is solely the pilot's prerogative to determine what course of action, if any, to take. This procedure is intended for use in time critical situations where aircraft safety is in question. Noncritical situations should be handled via the normal traffic alert procedures.
- Terrain or Obstruction Alert
- Controllers will immediately issue an alert to the pilot of an aircraft under their control when they recognize that the aircraft is at an altitude which, in their judgment, may be in an unsafe proximity to terrain/obstructions. The primary method of detecting unsafe proximity is through Mode C automatic altitude reports.
- Most En Route and Terminal radar facilities have an automated function which, if operating, alerts controllers when a tracked Mode C equipped aircraft under their control is below or is predicted to be below a predetermined minimum safe altitude. This function, called Minimum Safe Altitude Warning (MSAW), is designed solely as a controller aid in detecting potentially unsafe aircraft proximity to terrain/obstructions. The radar facility will, when MSAW is operating, provide MSAW monitoring for all aircraft with an operating Mode C altitude encoding transponder that are tracked by the system and are:
- Operating on an IFR flight plan; or
- Operating VFR and have requested MSAW monitoring.
- Due to the lack of terrain and obstacle clearance data, accurate automation databases may not be available for providing MSAW information to aircraft overflying Mexico and Canada. Air traffic facilities along the United States/Mexico/Canada borders may have MSAW computer processing inhibited where accurate terrain data is not available.
- Aircraft Conflict Alert.
- Controllers will immediately issue an alert to the pilot of an aircraft under their control if they are aware of another aircraft which is not under their control, at an altitude which, in the controller's judgment, places both aircraft in unsafe proximity to each other. With the alert, when feasible, the controller will offer the pilot the position of the traffic if time permits and an alternate course(s) of action. Any alternate course(s) of action the controller may recommend to the pilot will be predicated only on other traffic being worked by the controller.
Source: FAA Aeronautical Information Manual · current edition · paragraph 4-1-16.
Research Notes
AIM 4-1-16 — Safety Alerts — describes ATC's obligation to issue a safety alert when, in the controller's opinion, an aircraft is in a position or on a course that is unsafe.
Two types of safety alerts:
- Terrain/Obstruction Alert: Issued when a controller observes an aircraft at an altitude that, in the controller's judgment, places it in unsafe proximity to terrain or obstructions. Phraseology: "LOW ALTITUDE ALERT, Cessna Two-Three-Uniform, check your altitude immediately."
- Aircraft Conflict Alert: Issued when a controller observes a potential conflict between aircraft. Phraseology: "TRAFFIC ALERT, Cessna Two-Three-Uniform, [position/heading] for traffic."
The controller's authority: A safety alert is the controller's exercise of judgment to prevent an accident. It supersedes routine traffic management and ATC may issue avoidance instructions immediately.
The pilot's response: Take immediate corrective action — climb, turn, descend — and acknowledge. Don't wait to confirm; the alert exists because the controller already judged the situation unsafe.
The terrain alert system: Modern radar facilities have automated low-altitude alerting (MSAW — Minimum Safe Altitude Warning) that triggers when an aircraft descends below a published terrain-safe altitude. The controller receives an audible/visual alert and is required by FAA Order 7110.65 to issue the safety alert to the pilot.
Reference: FAA Order 7110.65 § 2-1-6 (Safety Alerts); AIM 4-1-16.