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AIM

10/12/17

4−4−10

ATC Clearances and Aircraft Separation

Information Region, in Class E airspace below

10,000 feet MSL. However, in airspace underlying a

Class B airspace area designated for an airport, or in

a VFR corridor designated through such as a Class B

airspace area, pilots are expected to comply with the

200 knot speed limit specified in 14 CFR

Section 91.117(c).

k. For operations in a Class C and Class D surface

area, ATC is authorized to request or approve a speed

greater than the maximum indicated airspeeds

prescribed for operation within that airspace (14 CFR

Section 91.117(b)).

NOTE−

Pilots are expected to comply with the maximum speed of

200 knots when operating beneath Class B airspace or in

a Class B VFR corridor (14 CFR Section 91.117(c)

and (d)).

l. When in communications with the ARTCC or

approach control facility, pilots should, as a good

operating practice, state any ATC assigned speed

restriction on initial radio contact associated with an

ATC communications frequency change.

4−4−13. Runway Separation

Tower controllers establish the sequence of arriving

and departing aircraft by requiring them to adjust

flight or ground operation as necessary to achieve

proper spacing. They may “HOLD” an aircraft short

of the runway to achieve spacing between it and an

arriving aircraft; the controller may instruct a pilot to

“EXTEND DOWNWIND” in order to establish

spacing from an arriving or departing aircraft. At

times a clearance may include the word “IMMEDI-

ATE.” For example: “CLEARED FOR

IMMEDIATE TAKEOFF.” In such cases “IMMEDI-

ATE” is used for purposes of air traffic separation. It

is up to the pilot to refuse the clearance if, in the pilot’s

opinion, compliance would adversely affect the

operation.

REFERENCE−

AIM, Paragraph 4−3−15 , Gate Holding due to Departure Delays

4−4−14. Visual Separation

a. 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:

1. The tower controller sees the aircraft

involved and issues instructions, as necessary, to

ensure that the aircraft avoid each other.

2. 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.

NOTE−

Traffic is no longer a factor when during approach phase

the other aircraft is in the landing phase of flight or

executes a missed approach; and during departure or

en route, when the other aircraft turns away or is on a

diverging course.

b. 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 responsi-

bility for wake turbulence separation. Visual

separation is prohibited behind super aircraft.

NOTE−

When a pilot has been told to follow another aircraft or to

provide visual separation from it, the pilot should promptly

notify the controller if visual contact with the other aircraft

is lost or cannot be maintained or if the pilot cannot accept

the responsibility for the separation for any reason.

c. 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.

d. 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.