AIM 

4/20/23 

has certain altitude crossing restrictions. Shortly after takeoff, the flight receives a new clearance changing the maintaining 
FL from 290 to 250. If the altitude restrictions are still applicable, the controller restates them. 

2. 

A departing aircraft is cleared to cross Fluky Intersection at or above 3,000 feet, Gordonville VOR at or above 12,000 

feet, maintain FL 200. Shortly after departure, the altitude to be maintained is changed to FL 240. If the altitude restrictions 
are still applicable, the controller issues an amended clearance as follows: “cross Fluky Intersection at or above three 
thousand, cross Gordonville V

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R at or above one two thousand, maintain Flight Level two four zero.” 

3. 

An arriving aircraft is cleared to the destination airport via V45 Delta VOR direct; the aircraft is cleared to cross Delta 

VOR at 10,000 feet, and then to maintain 6,000 feet. Prior to Delta VOR, the controller issues an amended clearance as 
follows: “turn right heading one eight zero for vector to runway three six I

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S approach, maintain six thousand.” 

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Because the altitude restriction “cross Delta V

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R at 10,000 feet” was omitted from the amended clearance, it is no longer 

in effect. 

h. 

Pilots of turbojet aircraft equipped with afterburner engines should advise ATC prior to takeoff if they 

intend to use afterburning during their climb to the en route altitude. Often, the controller may be able to plan 

traffic to accommodate a high performance climb and allow the aircraft to climb to the planned altitude without 

restriction. 

i. 

If an “expedite” climb or descent clearance is issued by ATC, and the altitude to maintain is subsequently 

changed or restated without an expedite instruction, the expedite instruction is canceled. Expedite climb/descent 

normally indicates to the pilot that the approximate best rate of climb/descent should be used without requiring 

an exceptional change in aircraft handling characteristics. Normally controllers will inform pilots of the reason 

for an instruction to expedite. 

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11.  IFR Separation Standards 

a. 

ATC effects separation of aircraft vertically by assigning different altitudes; longitudinally by providing 

an interval expressed in time or distance between aircraft on the same, converging, or crossing courses, and 

laterally by assigning different flight paths. 

b. 

Separation will be provided between all aircraft operating on IFR flight plans except during that part of the 

flight (outside Class B airspace or a TRSA) being conducted on a VFR

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on

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top/VFR conditions clearance. Under 

these conditions, ATC may issue traffic advisories, but it is the sole responsibility of the pilot to be vigilant so 

as to see and avoid other aircraft. 

c. 

When radar is employed in the separation of aircraft at the same altitude, a minimum of 3 miles separation 

is provided between aircraft operating within 40 miles of the radar antenna site, and 5 miles between aircraft 

operating beyond 40 miles from the antenna site. These minima may be increased or decreased in certain specific 

situations. 

NOTE

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Certain separation standards may be increased in the terminal environment due to radar outages or other technical reasons. 

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12.  Speed Adjustments 

a. 

ATC will issue speed adjustments to pilots of radar

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controlled aircraft to achieve or maintain appropriate 

spacing. If necessary, ATC will assign a speed when approving deviations or radar vectoring off procedures that 

include published speed restrictions. If no speed is assigned, speed becomes pilot’s discretion. However, when 

the aircraft reaches the end of the STAR, the last published speed on the STAR must be maintained until ATC 

deletes it, assigns a new speed, issues a vector, assigns a direct route, or issues an approach clearance. 

b. 

ATC will express all speed adjustments in terms of knots based on indicated airspeed (IAS) in 5 or 10 knot 

increments except that at or above FL 240 speeds may be expressed in terms of Mach numbers in 

0.01 increments. The use of Mach numbers is restricted to turbojet aircraft with Mach meters. 

c. 

Pilots complying with speed adjustments (published or assigned) are expected to maintain a speed within 

plus or minus 10 knots or 0.02 Mach number of the specified speed. 

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ATC Clearances and Aircraft Separation