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AIM

10/12/17

3−2−1

Controlled Airspace

Section 2. Controlled Airspace

3−2−1. General

a. Controlled Airspace. A generic term that

covers the different classification of airspace

(Class A, Class B, Class C, Class D, and Class E

airspace) and defined dimensions within which air

traffic control service is provided to IFR flights and

to VFR flights in accordance with the airspace

classification. (See FIG 3−2−1.)

b. IFR Requirements. IFR operations in any

class of controlled airspace requires that a pilot must

file an IFR flight plan and receive an appropriate ATC

clearance.

c. IFR Separation. Standard IFR separation is

provided to all aircraft operating under IFR in

controlled airspace.

d. VFR Requirements. It is the responsibility of

the pilot to ensure that ATC clearance or radio

communication requirements are met prior to entry

into Class B, Class C, or Class D airspace. The pilot

retains this responsibility when receiving ATC radar

advisories.  (See 14 CFR Part 91.)

e. Traffic Advisories. Traffic advisories will be

provided to all aircraft as the controller’s work

situation permits.

f. Safety Alerts. Safety Alerts are mandatory

services and are provided to ALL aircraft. There are

two types of Safety Alerts:

1. Terrain/Obstruction Alert. A Terrain/

Obstruction Alert is issued when, in the controller’s

judgment, an aircraft’s altitude places it in unsafe

proximity to terrain and/or obstructions; and

2. Aircraft Conflict/Mode C Intruder Alert.

 An Aircraft Conflict/Mode C Intruder Alert is issued

if the controller observes another aircraft which

places it in an unsafe proximity. When feasible, the

controller will offer the pilot an alternative course of

action.

FIG 3−2−1

Airspace Classes

MSL - mean sea level
AGL - above ground level
FL - flight level

CLASS B

CLASS B

CLASS C

CLASS C

CLASS E

CLASS E

CLASS D

CLASS D

CLASS G

CLASS G

CLASS G

CLASS G

CLASS G

CLASS G

Nontowered

Airport

Nontowered

Airport

FL 600

18,000 MSL

FL 600

18,000 MSL

14,500 MSL

14,500 MSL

1,200 AGL

700 AGL

CLASS A

CLASS A