It is not clear when the first formal flight plans were used. In 1920, the US Post Office took over airmail delivery and set up a series of radio stations along a nationwide route. Airmail pilots flew from station to station. They would call in as they passed overhead if they had a two-way radio. If not, they would flash lights or gun the engine to let the station operators know they were passing overhead.
Whether they flew using a formal flight plan is not clear, but the fact is that each station knew when the planes flew over and could call ahead to the next station on the route providing rudimentary flight following—the primary reason for a flight plan.
Originally, the primary reason for a flight plan was safety. If a pilot did not close his flight plan within 30 minutes of his scheduled arrival time at his destination, airway system operators would know to initiate a search and rescue mission. That is still true today, especially for Visual Flight Rule (VFR) flights.
As aviation expanded rapidly after World War II, flight plans became standard practice for commercial flights, and required for any flights operating under instrument flight rules (IFR). Commercial and other IFR flights flew under the watchful eye of air traffic controllers who used the flight plans to help maintain a safe separation between aircraft.
Flight plans are required for: (1) IFR flights, Defense VFR (DVFR) flights into an Air Defense Identification Zone (ADIZ), flight into terminal airspace around some larger airports, and through other designated airspace such as over Washington, D.C. Pilots on VFR cross-country flights are encouraged to file flight plans. Information required on the flight plan includes the information shown on the form in Figure 2.
Information required includes the type of flight (IFR, VFR, DVFR), Aircraft registration (the “N-number” or flight number for commercial flights) and type of aircraft. Most of the remaining blocks are self-explanatory. This information enables Air Traffic Control (ATC) to manage and maintain separation between aircraft. Pilots determine their estimated time en route based on their true airspeed (TAS) and the wind direction and speed at the cruising altitude. The flight plan defines the route of flight the pilot plans to fly or requests.
General aviation pilots usually file flight plans through the nearest Flight Service Station in person or by telephone, or online through the Direct User Access Terminal (DUAT or DUATS). Commercial airline flight plans will be filed from their dispatch or operations office.
Flight plans for IFR flights must be filed in advance with ATC, preferably at least 30 minutes prior to departure. ATC reviews the requested flight plan, including departure and arrival times and the route of the flight, aircraft speed, and altitude requested. Frequently, ATC will approve the flight plan as requested, but they may issue IFR flight plans with changes in routing and altitudes.
Enter Clearance Delivery
During preflight activities, the pilot will contact clearance delivery or the nearest FSS to obtain the clearance. Clearance Delivery will read the clearance to the pilot. For example, a typical clearance will proceed as follows:
“Citation 01RJ is cleared to Richmond International Airport via the Delta departure then as filed. Climb and maintain 5,000 feet, expect flight level 240 five minutes after departure. Departure frequency 124.30. Squawk 7831.”
This will usually be followed by the phrase “Read back.”
The pilot is expected to repeat the clearance as read to confirm that he understands the clearance.
This “read back” procedure was routine for all IFR flight operations for private, business, commercial, and military flights well into the early 2000s. It is time-consuming, especially at busy major airports. The time for clearance delivery and read-back became a factor on the number of flights busy airports could handle.
Before radar following of all flights became routine, radio failure/loss of communication was a key consideration of the clearance. If ATC lost communication with an aircraft, the pilot was expected to fly according to his cleared flight plan (if possible) to the destination airport, unless he could make a safe emergency landing sooner and close his flight plan.
With essentially nation-wide radar coverage and highly reliable radios with backups, lost communications are very rare, and ATC uses flight plans for optimizing the use of airspace to permit safe operations of increasing numbers of aircraft.
The Introduction of Controller-Pilot Data Link Communications (CPDLC)
CPDLC uses a data link between ATC clearance delivery and a discreetly coded datalink control and display unit (DCDU) unit in the aircraft. The screen displays all of the elements of the standard clearance. The pilot simply reads the clearance and, if it is correct, presses an “Accept” function on the display. Once this is done, the flight plan is activated. No radio communications for this process are required.
The clearance will be available within 30 minutes of the planned departure time. To obtain the clearance, select “CLEARANCE” on the ATC page of the DCDU, followed by the command “SEND.”
Once a successful ATC Connection has been established, and the controller has approved the Departure Clearance, it will be available for display on the DCDU.
“CLEARED TO KMIA AIRPORT” indicates the clearance to the Destination Airport.
“CLARE2.EIC THEN AS FILED” indicates the departure procedure that will include a Transition Fix that will connect to the filed route.
“MAINTAIN 10000FT” is the initial cleared altitude.
“EXPECT FL340 10 MIN AFT DP. DPFREQ 126.250 ” indicates the cleared cruise flight level followed by the departure frequency. Note that in an unlikely total communications failure after takeoff, ATC will expect the pilot to fly the published departure, maintain 10,000 feet for ten minutes, then climb to FL240 and proceed along the cleared route.
“CONTINUED” indicates that there is an additional page to the clearance.
“SQUAWK” indicates the transponder setting for departure.
Flight crews should treat any CPDLC clearance sent to the aircraft just as they would a voice clearance.
Pilots should expect an automated ATC initiated disconnect within 5-10 minutes after takeoff.
These are the basics of CPDLC-delivered clearances. There are other capabilities, including the ability to deliver changes to the clearance up until takeoff.
The pilot should review the clearance as displayed, and if correct, press “ACCEPT.” The clearance is then loaded into the ATC system. The flight plan may also be loaded into the aircraft’s flight management system.
Use of the data link is expected to significantly speed up the clearance delivery and expedite aircraft movement to takeoff.
NextGen – the next generation of air traffic communication and airspace management.
NextGen is possibly the most ambitious upgrade to the United States air transportation system in history. Its goals are to further enhance safety, achieve more efficient use of airspace, reduce wait times for departures and arrivals, improve situational awareness in the cockpit, and develop more fuel-efficient engines and alternative fuels. Underlying objectives of the overall program are significant reductions in air and noise pollution, reduced fuel consumption, and overall improved predictability of American aviation system.
NextGen promises to provide Airlines, general aviation operators, pilots, and air traffic controllers vastly advanced communication systems and information and tools that help aircraft arrive at their destinations more quickly, while consuming less fuel and producing fewer emissions. intiateed in 2007 nextGen will be fully deployed and operational in 2025
|Table 1. Notable Dates in the History of Air Traffic Control|
|Aug 1920||US Post Office establishes airmail radio stations for transcontinental airmail (The first federal action to manage air traffic).|
|1926||Air Commerce Act of 1926, Dept. of Commerce assumes responsibility for airmail service. Operates rudimentary flight following services. (Operated by Department of Lighthouse Services)|
|1930||The first control tower to use ground-to-air and air-to-ground radio communication was built in 1930 at Cleveland Airport.|
|1935||First Air Route Traffic Control Center, Newark, NJ|
|1937||231 Airmail Airway Radios in service|
|1940||Civil Aeronautics Administration established: Converts airmail airway radios to airway communication stations, provides weather reports, assists lost pilots (will become Flight Service Stations).|
|1950s||Initial arrival/departure radar services established for terminal area traffic.|
|Mar 1960||Federal Aviation Administration established. 297 Flight Services Stations (FSS) in service|
|1978||Enroute Flight Advisory Services available through FSS network, weather reporting services improved.|
|1980||FAA establishes plan to automate FSS|
|1995||91 Automated FSS in operation|
|2005||Lockheed Martin awarded contract to manage privatized FSS operations|
|2007||FAA launches NextGen program with improvements planned through 2025|
|2010||Lockheed Martin consolidates most US FSS into 3 hubs and 3 satellite facilities|
|2017||NextGen Controller-Pilot Data Link Communications for clearance delivery introduced in US|