Virtual Skies

air speed

miles-in-trail spacing

coordination with approach control and center control and local control

ATM regulations

flow control center of operations

air speed

miles-in-trail spacing

coordination with approach control

ATM regulations

re-routing traffic en route to slow air flow

miles-in-trail spacing

call for release

coordination with approach contro

ATM regulations

ground stop operations

coordination with approach control and center controllers

ATM regulations

weather conditions throughout the United States

flow control center of operations

cost effectiveness for airline operations

coordination with approach control and other nearby local controllers

ATM regulations

Weather at the airport has deteriorated because of thunderstorm activity.

Your airport is presently receiving aircraft at a rate of 60 per hour. The 60 per hour rate is the amount of aircraft the approach control is receiving from the center over 3 to 4 arrival routes.

You are requested by the approach control and tower to reduce the arrival rate to 30 per hour.

Separation regulations: Laterally -- 5 miles; Vertically -- 1,000 feet (if the aircraft is below 29,000 feet) 2,000 feet (if the aircraft is at 29,000 feet or above)

The controllers can accomplish this separation by issuing instructions to the pilots of the aircraft involved. Altitude assignments, speed adjustments, and radar vectors are examples of instructions that might be issued to aircraft.

circling maneuvers, holding patterns and "S" flight maneuvers

Is re-routing to a different destination airport a top consideration?

ATM Tutorial

FAA web site

Safe Separation Standards

ATM Tutorial

FAA web site

miles-in-trail spacing

ATM Tutorial

FAA web site

call for release

ATM Tutorial

FAA web site

ground stop operations

ATM Tutorial

FAA web site

A variety of options are used to change the flow of air traffic without completely disrupting the system:1) increase spacing between aircraft by slowing the speed of each aircraft; 2) request that aircraft perform an "S" maneuver (a curved zigzag) that will serve to elongate their flight route and slow their arrival time to the detsination airport; 3) make an alternation in their course by having each aircraft follow a certain vector for awhile before resuming course toward airport; 4) Hold all aircraft that are scheduled for the affected destination airport that have yet to take off until inclement weather has passed or until traffic line has been reduced and regulated. 5) Have aircraft in the arrival phase assume a holding pattern high above the destination airport and the inclement weather until the arrrival rate has been appropriately adjusted and they can be placed in line to descend for approach.

During inclement weather aircraft are spaced farther apart.

Flow Control monitors the "big picture" for weather changes and "high traffic times" at all airports. Because they can make fairly accurate predictions of weather changes, they can look ahead and re-route traffic around "bad" weather spots and with some accuracy forecast an appropriate airport closure time thus allowing time and consideration for re-routing traffic to another airport. Traffic flow procedures are used dynamically and are approved by the Air Traffic Control System Command Center (Central Flow), located in Herndon, VA.

No, it is preferred that all other measures be implemented first before simply re-routing to a different airport. Re-routing an aircraft to a completely different airport costs the airlines too much revenue as these airplane passengers will usually have to be bussed to their intended destination or have to have major changes made in their ticketing and itineraries, which is costly in personnel time to make these changes.

First, the center will impose Miles-in-Trail (MIT) spacing on all arrival routes. Controllers will start vectoring aircraft under their control to increase spacing. Initial, MIT will be 7 to 10 miles and will be increased, as the aircraft numbers in the airspace are reduced, to 15 to 20 miles. When it is determined that Expanded Miles-in-Trail conditions are required, adjacent centers are asked to provide 20 MIT.

Slows air traffic farther out from airport and causes flight delays throughout the region. Increases fuel consumption.

Immediately begins to contain the situation at the affected airport and maintains a high level of safety for aircraft flying into the airport.

Second, in conjunction with MIT provisions, the center will have all aircraft entering the approach control airspace at reduced speeds. Normally, jets will enter approach control’s airspace at or above 250 knots, depending on the altitude the arrival is required to cross the arrival fix. When flow to the airport is reduced, jets will be required to enter the approach control airspace at speeds of less than 250 knots.

Slows air traffic farther out from airport and causes flight delays throughout the region.

Immediately begins to contain the situation at the affected airport and makes flying into the airport safer. Slower speeds reduce fuel consumption.

Third, all aircraft within the center’s airspace landing at the airport with the reduced rate would be placed in a Call for Release (CFR) category. This provides the center traffic management unit the ability to fit these flights in when spacing becomes available.

Increases the amount of delays per other airports, yet provides flexibility for controllers to fit in aircraft when appropriate to move air traffic flow along a certain route.

Provides flexibility for controllers to fit in aircraft when appropriate to move air traffic flow along a certain route.

Fourth, the center will initiate Re-Routes to have flights fly additional miles to increase spacing. Re-Routes are used to off load arrival routes with heavy traffic volume to other arrival routes not as busy.

Slows air traffic farther out from airport and causes flight delays throughout the region. Increases fuel consumption for the airlines.
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Immediately decreases air traffic flow to that area and evens out the air traffgic flow within and around that region, thus increasing safety.

Fifth, if the reduce rate continues for more than a certain amount of time based on the schedule for the airport, Ground Stop (GS) procedures are put into effect, which apply to the whole country.

Halts all aircraft before they takeoff from distant airports with this airport scheduled as their destination airport. Increases the amount of delayed flights immediately. Increases the amount of people, baggage and aircraft at the many departure airports, which could delay other incoming aircraft at the gates.

Cost effective measure for airlines in that they will not have aircraft burning fuel in elongated flight or holding patterns, instead the aircraft remain on the ground until they are able to fly directly and safely to that airport.

Note: All of the above traffic flow procedures are used dynamically and are approved by the Air Traffic Control System Command Center (Central Flow), located in Herndon, VA.