Controller-Pilot Communications

From pre-flight to landing, all Instrument Flight Rule (IFR) flights are conducted with controller-pilot communications. An IFR flight over a long distance requires many communications with many different controllers.

After the flight plan is filed for a commercial jetliner and the aircraft preflight is completed, the pilot is ready to taxi. A call is made to Clearance Delivery in local control (the airport's control tower) for either verification of the "clearance filed" or to receive a "modified clearance." Pilots are encouraged to file for "preferred" routes, if there are any. Pilots always like to hear "cleared as filed" as this means their flight plan was received without requiring any changes. When pilots receive an amended clearance, they copy and read back to verify. The controllers will warn a flight crew if the new clearance is a long or complicated notation. A clearance delivery controller at Chicago's O'Hare (ORD) airport would warn a pilot of complicated changes with the statement, "Hope you have a sharp pencil handy." The crew receiving the clearance would recognize that they would have to listen carefully and write quickly. After the pilot has clearance, he/she is instructed to contact ground control in local control (the airport's control tower) on the frequency given by the clearance delivery controller. Next, the ground controller clears the pilot to taxi to the takeoff runway. At large airports this can take a considerable amount of time, involving many turns on many taxiways with many stops (for further clearance if the taxi path crosses runways along the way). All clearances have a "cleared to" phrase that gives further directions on how to proceed once the aircraft arrives at that point.Once the pilot is at the takeoff runway in the run-up area, he/she contacts the airport tower. When the tower controller clears the aircraft for takeoff, the controller also instructs the pilot as to the heading and altitude to climb to after takeoff. Clearance for many flights specifies a standard Departure Procedure (DP).

After takeoff and the initial climb out from the departure airport, the local controller hands off the flight to the departure controller located in the Terminal Radar Approach Control (TRACON). The "hand-off" consists of the local controller telling the pilot to contact departure control and giving the radio frequency to which the pilot must switch. This hand-off also takes place electronically as the aircraft's transponder code is received by the controller in the TRACON. The signal appears on the controller's radar screen as a "target" with its data block. The pilot then contacts the departure controller located in the TRACON who then provides necessary altitude or heading changes to position the aircraft for its next flight phase: en route. The departure controller then hands off the flight to a controller in an Air Route Traffic Control Center (ARTCC).

The ARTCC controller then monitors the aircraft along the en route portion of the flight. A coast-to-coast flight will fly through many different ARTCC sections before the flight is handed off to an approach controller. The original flight clearance that was given probably contained a Standard Terminal Arrival Route (STAR) for the arrival phase of the flight. If there are no delays or weather problems, the STAR will be routinely followed.

The Approach Controller gives the pilot descent altitudes and vectors (headings) to a final approach fix. When the aircraft arrives at the final approach fix, it will be cleared to fly a published approach. The flight will next be handed off to the destination airport's tower controller for landing instructions. The tower controller clears the flight to land. Upon landing, the tower controller directs the pilot to an exit taxiway. The pilot also receives the next radio frequency to which he/she must switch the radio in order to contact the ground controller.After exiting the runway, the pilot contacts the ground controller for taxi clearance and gate instructions. The pilot parks the aircraft at the gate, terminating the flight.

NASA Research

Modern aircraft cockpits and air traffic control centers are very complex, high-technology environments in which to work. Understanding and optimizing the ways in which humans and high-technology systems work together are critical to aviation safety and the development of new aviation systems.
The Crew-Vehicle Systems Research Facility at NASA's Ames Research Center was designed for the study of human factors in aviation safety. The facility is used to analyze performance characteristics of flight crews; help develop new designs for future aviation environments; evaluate new and contemporary air traffic control procedures; and develop new training and simulation techniques required by the continued technical evolution of flight systems.

The facility is home to a Boeing 747-400 flight simulator, the Advanced Concepts Flight Simulator, and an air traffic control system simulator. Together, these systems provide full mission flight simulation research capability. Visual systems provide out-the-window cues in both cockpits. The Air Traffic Control System simulator provides a realistic air traffic control environment, including communication with the cockpits allowing the study of air-to-ground communications systems as they impact crew performance. Dedicated experimenter labs for each simulator provide full monitoring and control capability for each simulation system.