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AIM 

4/20/23

 

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ATC Clearances and Aircraft Separation

h.

ATC will not authorize VFR or VFR

on

top operations in Class A airspace.

REFERENCE

AIM, Para 3

2

2, Class A Airspace.

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9. VFR/IFR Flights

A pilot departing VFR, either intending to or needing to obtain an IFR clearance en route, must be aware of the
position of the aircraft and the relative terrain/obstructions. When accepting a clearance below the
MEA/MIA/MVA/OROCA, pilots are responsible for their own terrain/obstruction clearance until reaching the
MEA/MIA/MVA/OROCA. If pilots are unable to maintain terrain/obstruction clearance, the controller should
be advised and pilots should state their intentions.

NOTE

OROCA is a published altitude which provides 1,000 feet of terrain and obstruction clearance in the US (2,000 feet of
clearance in designated mountainous areas). These altitudes are not assessed for NAVAID signal coverage, air traffic
control surveillance, or communications coverage, and are published for general situational awareness, flight planning and
in

flight contingency use.

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10. Adherence to Clearance

a.

When air traffic clearance has been obtained under either visual or instrument flight rules, the

pilot

in

command of the aircraft must not deviate from the provisions thereof unless an amended clearance is

obtained. When ATC issues a clearance or instruction, pilots are expected to execute its provisions upon receipt.
ATC, in certain situations, will include the word “IMMEDIATELY” in a clearance or instruction to impress
urgency of an imminent situation and expeditious compliance by the pilot is expected and necessary for safety.
The addition of a VFR or other restriction; i.e., climb or descent point or time, crossing altitude, etc., does not
authorize a pilot to deviate from the route of flight or any other provision of the ATC clearance.

b.

When a heading is assigned or a turn is requested by ATC, pilots are expected to promptly initiate the turn,

to complete the turn, and maintain the new heading unless issued additional instructions.

c.

The term “AT PILOT’S DISCRETION” included in the altitude information of an ATC clearance means

that ATC has offered the pilot the option to start climb or descent when the pilot wishes, is authorized to conduct
the climb or descent at any rate, and to temporarily level off at any intermediate altitude as desired. However,
once the aircraft has vacated an altitude, it may not return to that altitude.

d.

When ATC has not used the term “AT PILOT’S DISCRETION” nor imposed any climb or descent

restrictions, pilots should initiate climb or descent promptly on acknowledgement of the clearance. Descend or
climb at an optimum rate consistent with the operating characteristics of the aircraft to 1,000 feet above or below
the assigned altitude, and then attempt to descend or climb at a rate of between 500 and 1,500 fpm until the
assigned altitude is reached. If at anytime the pilot is unable to climb or descend at a rate of at least 500 feet a
minute, advise ATC. If it is necessary to level off at an intermediate altitude during climb or descent, advise ATC,
except when leveling off at 10,000 feet MSL on descent, or 2,500 feet above airport elevation (prior to entering
a Class C or Class D surface area), when required for speed reduction.

REFERENCE

14 CFR Section 91.117.

NOTE

Leveling off at 10,000 feet MSL on descent or 2,500 feet above airport elevation (prior to entering a Class C or Class D
surface area) to comply with 14 CFR Section 91.117 airspeed restrictions is commonplace. Controllers anticipate this action
and plan accordingly. Leveling off at any other time on climb or descent may seriously affect air traffic handling by ATC.
Consequently, it is imperative that pilots make every effort to fulfill the above expected actions to aid ATC in safely handling
and expediting traffic.

e.

If the altitude information of an ATC DESCENT clearance includes a provision to “CROSS (fix) AT” or

“AT OR ABOVE/BELOW (altitude),” the manner in which the descent is executed to comply with the crossing
altitude is at the pilot’s discretion. This authorization to descend at pilot’s discretion is only applicable to that