Aeronautical Information Manual (AIM), page 235

Index   234 -- Page 235 -- 236

routing and an alternative clearance if VFR-on-top
is not reached by a specified altitude.

c. A pilot on an IFR flight plan, operating in VFR
conditions, may request to climb/descend in VFR

d. ATC may not authorize VFR-on-top/VFR
conditions operations unless the pilot requests the
VFR operation or a clearance to operate in VFR
conditions will result in noise abatement benefits
where part of the IFR departure route does not
conform to an FAA approved noise abatement route
or altitude.
e. When operating in VFR conditions with an ATC
authorization to "maintain VFR-on-top/maintain
VFR conditions" pilots on IFR flight plans must:

1. Fly at the appropriate VFR altitude as

prescribed in 14 CFR Section 91.159.
2. Comply with the VFR visibility and distance
from cloud criteria in 14 CFR Section 91.155 (Basic

VFR Weather Minimums).
3. Comply with instrument flight rules that are
applicable to this flight; i.e., minimum IFR altitudes,
position reporting, radio communications, course to
be flown, adherence to ATC clearance, etc.

Pilots should advise ATC prior to any altitude change to
ensure the exchange of accurate traffic information.
f. ATC authorization to "maintain VFR-on-top"
is not intended to restrict pilots so that they must
operate only above an obscuring meteorological
formation (layer). Instead, it permits operation above,
below, between layers, or in areas where there is no
meteorological obscuration. It is imperative, howev-
er, that pilots understand that clearance to operate
"VFR-on-top/VFR conditions" does not imply
cancellation of the IFR flight plan.

g. Pilots operating VFR-on-top/VFR conditions
may receive traffic information from ATC on other
pertinent IFR or VFR aircraft. However, aircraft
operating in Class B airspace/TRSAs must be
separated as required by FAA Order JO 7110.65,
Air Traffic Control.

When operating in VFR weather conditions, it is the pilot's
responsibility to be vigilant so as to see-and-avoid other

h. ATC will not authorize VFR or VFR-on-top
operations in Class A airspace.
AIM, Paragraph 3-2-2 , Class A Airspace

4-4-9. 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 clear-
ance 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.

OROCA is an off-route altitude which provides obstruc-
tion clearance with a 1,000 foot buffer in nonmountainous
terrain areas and a 2,000 foot buffer in designated
mountainous areas within the U.S. This altitude may not
provide signal coverage from ground-based navigational
aids, air traffic control radar, or communications

4-4-10. 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.

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,

ATC Clearances and Aircraft Separation 4-4-5

Page 235 of the Aeronautical Information Manual (AIM.pdf)
AIM: Official Guide to Basic Flight Information and ATC Procedures

Index   234 -- Page 235 -- 236