Part 1: The Origin of Airspace
Part 2: Class A Airspace
Part 3: Class B Airspace
Part 4: Class C Airspace
Airspace exists on an alphabetical sliding scale—from Alpha to Golf. With each step down the airspace is less regulated and less controlled. Class Alpha Airspace stands as the most highly regulated of the airspace classes. In contrast, Class Golf Airspace is completely uncontrolled.
We begin our discussion at the top of the airspace ladder. Class Alpha Airspace is an exclusive members-only club. It is highly regulated. Most of the three-quarters of a billion airline passengers that traverse the sky each year cruise in Class Alpha Airspace. It’s regulated for a reason.
Remember, ask yourself these three questions when you are learning airspace:
- Where is it?
- What equipment do I need?
- What are the weather minimums?
Where is it?
Class Alpha Airspace begins at Flight Level 180 [18,000 feet] and extends to Flight Level 600. Alpha blankets the continental United States and Alaska extending twelve miles from the coasts—it does not exist over Hawaii. Incidentally, the twelve mile extension corresponds with our international waters. Above the vertical limit of Class Alpha the airspace reverts back to Class Echo.
Aren’t FL180 and 18,000 feet the same thing? Sort of. Flight levels refer to pressure altitudes. When at or above 18,000 feet, all pilots reset their altimeters to a standard pressure setting—29.92 in Hg. You’ll remember that to find pressure altitude we set the altimeter to 29.92 in Hg. The airplanes in Alpha airspace are cruising on a “theoretical” altitude. What is 18,000 feet today may not be 18,000 feet tomorrow. In fact, When the air pressure is below 29.92 in Hg, FL180 becomes unusable due to possible conflicts with VFR traffic cruising at 17,500 feet. Flying at standard pressure altitudes ensures proper vertical separation for high-speed jet aircraft. A jet zips between levels of pressure so quickly it is impractical if not impossible to maintain a correct altimeter setting.
What equipment do I need?
Technically, you need to be on an instrument flight plan, have a clearance, and a working Mode C Transponder. You need all those things to legally fly IFR anyway. You must be on an IFR flight plan. NO VFR operations are allowed in Alpha airspace. Additionally, above Flight Level 240 distance measuring equipment [DME] or GPS equivalent is required.
Cruising between FL290 and FL410? You will need to ensure the crew and plane meet Reduced Vertical Separation Minima. This is commonly referred to as “RVSM Airspace” — Historically, IFR airplanes are separated by 1000 feet until FL290, then 2000 ft until FL410, and 4000 feet above this. Why the larger separation the higher you get? The accuracy of an airplane’s pressure altimeter decreases with height. The introduction of Air Data Computers [ADC] combined with more precise altimeters meant the 2000 foot separation requirement was a bit excessive. Now, all airplanes within RVSM airspace are separated vertically by 1,000 feet. RVSM airplanes must have specifically certified altimeters and the autopilot must be operational and in use by the crew. Critics charge that reducing separation standards is a bad idea – but in the ten years since RVSM was first implemented there have been no incidents attributable to it.
What are the weather minimums?
There is no VFR flying so no VFR weather minimums to remember! That was easy.
Next, we visit the big, busy, and blue Class Bravo Airspace.
Wings of Eagles Assistant Chief Instructor Chris Carnett holds a CFI, CFII, and MEI. He is a former regional airline pilot and currently an adjunct professor at his alma mater, MTSU—where he earned his B.S. and M.Ed. in Aerospace.
