Airspace Transponder and Communication Requirements

“You are cleared into the class Charlie”

Ever hear this? Ever say it? It’s easy to get into the habit of treating class C and class B airspace the same. They’re both marked in bold, impressive lines on the chart, and they both serve major airports with many jets. But there is a difference in the requirements a pilot needs to enter these airspaces.

Requirements to enter Airspace Classes

Class A

You need to have two-way communication, mode C, an ATC clearance, and be IFR. “Climb and maintain flight level 230″ is your ticket into the class A airspace.

Class B

You need to have two-way communication, mode C and an ATC clearance. “Cleared into the class Bravo” does the trick. A bravo clearance is good for just one entry into the bravo. If you leave the class B for any reason, you need another clearance to enter it.

Class C

You need to have two-way communication and mode C. There is no such thing as “Cleared into the class Charlie,” because just having two-way radio communication is your clearance. But what is two-way radio communication? It’s the controller saying your call-sign.

• “N123, approach” — That’s all you need to hear. The controller has used your call-sign. This is your class C clearance.
   
• “N123, approach, standby” — this is the one that blows people’s minds. Even though the controller has said “standby,” you can go right on into the class C. That’s because “standby” means “don’t talk now, I’ll get back to you,” but the controller saying your call-sign established two-way radio communications.
   
• “Aircraft calling, standby” — Two-way communication has not been established, so remain clear of the class C. And don’t answer, since standby, in radio parlance means “hush up for now.”
   
• “N123, remain clear of the class C airspace, give me a call in 10 minutes” — The use of your call-sign has established two-way communication, but the controller barred you from entry. You may not enter.

Class D

You need two-way comms, same as for class C, but you no longer need the mode-C transponder.

Class E and G

No radio or transponder requirements.

From whom do you need the clearance?

You need the clearance from the controller in charge of the airspace. In real life, that’s simple: every airspace has its own controller. But on VATSIM, that can lead to interesting situations. That’s because, most of the time, C and D airspace is not manned and the overlaying approach or center controller handles those airspaces. That can lead to the interesting situation where you are in two-way radio communication with a center or approach controller, squawking mode-C, and there is no other controller controlling any of the C or D airspaces along your route. In that situation, you are, without any magic words being said, cleared into those airspaces.

How cool is that?

When you get to the thick purple line for the Charlie airspace, don’t hyperventilate. Don’t key the microphone and ask for a clearance. Just keep on flying.

Things change on those days when there is a separate controller for that C or D airspace. Your two-way radio communications with center does not automatically transfer to that other controller. So, if you’re on center’s frequency and approaching a class C or D being controlled by a different controller, you may not enter until you are switched to that other controller’s frequency and establish two-way radio contact with them.