Terminal Radar Arrival Techniques for Air Traffic Controllers

3 August 2010 82 Comments

Terminal Radar Arrival Techniques For Air Traffic Controllers

The favorite part of many, if not all, terminal radar approach controllers is working arriving aircraft. Nothing gives a boost to an air traffic controller’s ego any more than a nice tight string of pearls stretching out 15 or 20 miles on final.

Properly spaced aircraft ensure enough room on the arrival runway for preceding arrivals to clear the runway, and, if necessary, allow departures room to take off. Aircraft spaced erratically along the final can present a challenge to the local controller who is trying to space departures in the gaps between arrivals.

Having to wait an extra minute between departures throughout the day can contribute to over an hour of collective departure delays at busy airports. Therefore, it is critically important to ensure your arrivals are properly spaced to make the most efficient use of the airspace and airport’s runways.

The “A to C” Rule for ATC

At Chicago TRACON, air traffic controllers use the “A to C” rule when determining the spacing required between aircraft. Subsequently, the FAA academy is teaching this technique at RTF and ITR classes as well. We’ll get to the idea behind the A to C rule in the next post, but first it is imperative that the controller understands the basic wake turbulence minima when vectoring aircraft onto the final, as well as the rules which allow 2.5 miles on final (as opposed to 3).

Wake turbulence separation is a subject for another posting, so today we will simply review the minima when vectoring. These are the minima at touchdown (we are ignoring the few instances where you may run a mile closer until the first aircraft touches down. It’s always harder to gain a mile on final, so we won’t even talk about doing it here):

* Small behind Large: 4 miles
* Small behind B757: 5 miles
* Small behind Heavy: 6 miles
* Large behind B757: 4 miles
* Large behind heavy: 5 miles
* Heavy behind Heavy: 4 miles

Otherwise, aircraft must have basic radar separation at touchdown (usually 3 miles for IFR aircraft). Aircraft may compress to 2.5 miles at touchdown, but there must be procedures outlining that practice (generally runway occupancy studies must be completed showing 50 seconds or less for arrivals) and the reduced separation may only be used within 5 miles of the runway.

Visual Separation

For visual separation (whether provided by the tower or the aircraft), all bets are off with regard to spacing on final. We’ll talk about visual separation in another post, but I did want to acknowledge that it does exist and it could affect how you run traffic on your final. VFR aircraft being vectored to final have to have the same radar separation as IFRs, but again, the visual part could come in to play here and reduce the space needed at touchdown.

So, that was your overview on the A to C rule. Coming up: The actual rule itself explained, and some technique on its application.

Until next time, “put ‘em where they ain’t”

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