Class A Airspace

AIM ¶ 3-2-2 — Class A Airspace

AIM 3-2-2 explains Class A airspace: 18,000 ft MSL to FL600, IFR-only operations, equipment rules, and charting. Study guide for pilot students.

In Plain English

Class A airspace is the high-altitude IFR-only environment used by airliners and most turbine traffic. Per AIM 3-2-2, here's what you need to know:

Vertical limits: From 18,000 feet MSL up to and including FL 600.
Lateral limits: Over the 48 contiguous states and Alaska, including the airspace over coastal waters out to 12 NM, plus designated international airspace beyond 12 NM where U.S. radar/navaid coverage exists and domestic procedures apply.
Operating rules: Unless otherwise authorized, all flight must be conducted under IFR. That means an instrument-rated pilot, an IFR-capable aircraft, an IFR clearance, and an active flight plan.
Equipment: Driven by 14 CFR 91.215 (transponder), 91.225 (ADS-B Out), and the IFR equipment rules in 91.205(d) and 91.167–91.193.
Charting: Class A is not depicted on sectional or enroute charts — pilots are simply expected to know it begins at 18,000 ft MSL.

Operationally, this is why VFR-only pilots cap their cruise at 17,500 ft MSL and why an IFR clearance is mandatory before climbing into the flight levels. Above FL180, altitudes are also expressed in flight levels with altimeters set to 29.92.

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AIM Source Text

FAA AIM ¶ 3-2-2

Definition. Generally, that airspace from 18,000 feet MSL up to and including FL 600, including the airspace overlying the waters within 12 nautical miles off the coast of the 48 contiguous States and Alaska; and designated international airspace beyond 12 nautical miles off the coast of the 48 contiguous States and Alaska within areas of domestic radio navigational signal or ATC radar coverage, and within which domestic procedures are applied. Operating Rules and Pilot/Equipment Requirements. Unless otherwise authorized, all persons must operate their aircraft under IFR. (See 14 CFR section 71.33, sections 91.167 through 91.193, sections 91.215 through 91.217, and sections 91.225 through 91.227.) Charts. Class A airspace is not specifically charted.

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You are flying VFR in Class E airspace at 8,500 feet MSL during the day. What are your minimum visibility and cloud clearance requirements?

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Oral Exam Questions a DPE Might Ask

Q1What are the vertical and lateral limits of Class A airspace?

Per AIM 3-2-2, Class A generally extends from 18,000 feet MSL up to and including FL 600, over the 48 contiguous states and Alaska, including airspace over coastal waters within 12 NM, and designated international airspace beyond 12 NM where U.S. radio navigation or ATC radar coverage exists and domestic procedures are applied.

Q2What are the operating rules for flight in Class A airspace?

Per AIM 3-2-2, unless otherwise authorized, all persons must operate their aircraft under IFR. This references 14 CFR 71.33, 91.167–91.193, 91.215–91.217, and 91.225–91.227 for the associated flight plan, equipment, transponder, and ADS-B requirements.

Q3How is Class A airspace depicted on aeronautical charts?

Per AIM 3-2-2, Class A airspace is not specifically charted. Pilots are expected to know that it exists from 18,000 feet MSL up to and including FL 600 within the defined lateral boundaries.

Related Paragraphs in Chapter 3

¶ 3-2-1

Controlled Airspace General