Now that we understand the system we’ll be flying in and the instruments we’ll be using, let’s get our air traffic control clearance. The term clearance is worth taking a minute to clarify, since it has caused some confusion in the past. An air traffic control clearance is simply any authorization given by air traffic control, so you have to put it in context. In this context clearance refers to an authorization by air traffic control to proceed under IFR into controlled airspace. We’ll still have to call for a taxi and takeoff clearance if departing from a towered airport.

When you filed your IFR flight plan with the flight service station, it was forwarded to the center for processing. From there, your flight plan information was forwarded to radar appropriate radar, tower, and center positions. Flight plan information becomes available to the controller 30 minutes prior to the proposed departure time and remains available until 2 hours after the proposed departure time. If you call for your clearance outside this time frame, the controller may have to do a little digging to find your flight plan or may be unable to retrieve it.

The procedure for obtaining your IFR clearance varies with the air traffic control services available at your departure airport. If you are departing from the primary airport of a Class B or C airspace area, a dedicated clearance delivery frequency will be provided. For a departure from the primary airport of a Class D airspace area, you will normally use the ground frequency to get your clearance.

If your departure airport is non-towered, then a number of options may be available. At some airports, center may be called directly from the ground using the center frequency listed for the airport. At most airports, communications with the center will not be possible until climbing a few thousand feet above field elevation, however. To permit direct communications with the center at such an airport, a remote communications outlet, or RCO, may be placed on the field. The RCO expands center communications to the ground where deemed necessary. When no direct communications with the center are possible, you can get your clearance by calling the flight service station for a clearance relay. The FSS specialist will place you on hold and call the center for your clearance. When departing from a non-towered airport, your IFR clearance protects you from other IFR aircraft. VFR traffic may still be flying in the area.

When you obtain a clearance on the ground at a non-towered airport, air traffic control will likely give you a clearance void time. They will also tell you to advise them if you are not able to takeoff prior to the clearance void time. Make sure you keep the ATC advised if you can’t takeoff as planned. If enough time goes by, ATC will not assume you decided to get lunch before you take off or are waiting on a passenger who is running late. They don’t know what happened to you, and will worry. And, when they worry, they start doing things like calling out search and rescue. You told them you were taking off, so they know you were. Something bad must have happened to you. If you are delayed, it’s not a problem. Just make sure you communicate your status with ATC.

The air traffic controller may also assign you a release time. You must takeoff after the release time and before the void time. If the controller states, "hold for release", you may not takeoff under IFR until released to do so by air traffic control.