AIM Text
- Visual separation is a means employed by ATC to separate aircraft in terminal areas and en route airspace in the NAS. There are two methods employed to effect this separation:
- The tower controller sees the aircraft involved and issues instructions, as necessary, to ensure that the aircraft avoid each other.
- A pilot sees the other aircraft involved and upon instructions from the controller provides separation by maneuvering the aircraft to avoid it. When pilots accept responsibility to maintain visual separation, they must maintain constant visual surveillance and not pass the other aircraft until it is no longer a factor.
- A pilot's acceptance of instructions to follow another aircraft or provide visual separation from it is an acknowledgment that the pilot will maneuver the aircraft as necessary to avoid the other aircraft or to maintain in-trail separation. In operations conducted behind heavy aircraft, or a small aircraft behind a B757 or other large aircraft, it is also an acknowledgment that the pilot accepts the responsibility for wake turbulence separation. Visual separation is prohibited behind super aircraft.
- Scanning the sky for other aircraft is a key factor in collision avoidance. Pilots and copilots (or the right seat passenger) should continuously scan to cover all areas of the sky visible from the cockpit. Pilots must develop an effective scanning technique which maximizes one's visual capabilities. Spotting a potential collision threat increases directly as more time is spent looking outside the aircraft. One must use timesharing techniques to effectively scan the surrounding airspace while monitoring instruments as well.
- Since the eye can focus only on a narrow viewing area, effective scanning is accomplished with a series of short, regularly spaced eye movements that bring successive areas of the sky into the central visual field. Each movement should not exceed ten degrees, and each area should be observed for at least one second to enable collision detection. Although many pilots seem to prefer the method of horizontal back-and-forth scanning every pilot should develop a scanning pattern that is not only comfortable but assures optimum effectiveness. Pilots should remember, however, that they have a regulatory responsibility (14 CFR section 91.113(a)) to see and avoid other aircraft when weather conditions permit.
Source: FAA Aeronautical Information Manual · current edition · paragraph 4-4-14.
The short answer
This AIM section is FAA advisory guidance on visual separation, a means ATC uses to separate aircraft in terminal and en route airspace. Either the tower controller sees both aircraft and issues instructions, or a pilot sees the other aircraft and maneuvers to avoid it. It supports the pilot's see-and-avoid duty under 14 CFR 91.113(a).
Research Notes
Common Questions
What do I accept when I take visual separation from another aircraft?
Accepting responsibility to maintain visual separation means maintaining constant visual surveillance and not passing the other aircraft until it is no longer a factor. Following a heavy aircraft, or a small aircraft behind a B757 or other large aircraft, it is also an acknowledgment that the pilot accepts responsibility for wake turbulence separation. Visual separation is prohibited behind super aircraft.
When is the other aircraft no longer a factor?
Per the AIM note, during the approach phase the other aircraft is no longer a factor when it is in the landing phase or executes a missed approach; during departure or en route, when the other aircraft turns away or is on a diverging course. If visual contact is lost or cannot be maintained, the pilot should promptly notify the controller.
What is an effective scanning technique?
The AIM recommends a series of short, regularly spaced eye movements, each not exceeding ten degrees, with each area observed for at least one second to enable collision detection. The eye can focus only on a narrow viewing area, so pilots should timeshare between scanning and instruments, remembering the regulatory duty under 14 CFR 91.113(a) to see and avoid when weather permits.