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The Lowly Flight Strip: How ATC Follows Your IFR Flight

Ever wonder about those flight strips that controllers use?Ever wonder about those flight strips that controllers use? (You know, the ones you see being slung around in those sliding frames, like in the movie 'Pushing Tin'.) We pilots have our flight plan forms, navigation logs, and kneeboards. Well, controllers use paper, too (though that may not always be so).

In times of old, controllers used 'shrimp boats' and handwritten flight strips to help them keep track of aircraft moving along the airways. The 1950s saw early use of equipment for printing flight strips and efforts at automation. However, controllers were still passing handwritten flight information, using teletypes, and they spent a large percentage of their time talking to other controllers. In 1961, President Kennedy's Project Beacon task force recommended a computerized system, first deployed as 'NAS Enroute Stage A' in the early 1970s, and subsequently upgraded. One aspect of this was the Flight Data Input/Output (FDIO) system, first fielded in the mid-1980s and now in use at most of the almost 500 control towers, all Terminal Radar Approach Control (TRACON) facilities, and Air Route Traffic Control Centers (ARTCCs) in operation today. Its primary objective was to standardize the flight data processing functions at all air traffic control facilities. It consists of displays, keyboards, interfaces to ARTCC computers, and printers. What do these printers print? Flight strips, of course!

Whenever you file an IFR flight plan, it winds up in one of the ARTCC, or simply 'Center' (a.k.a. 'HOST') computers. A half-hour before your proposed departure time, it assigns you a transponder code and a flight progress strip (or just 'flight strip'). The physical strip gets printed out on a FDIO printer at your departure airport -- or if it doesn't have one, at the appropriate ARTCC sector, and the flight data controller at the tower then phones the ARTCC for it. Whether computer printed or hand-written, paper flight progress strips are currently still used in the United States air traffic control system to document flight information. Although controllers are generally quite attached to them, impending automation will (probably) eventually replace these paper strips with electronic flight data entries containing the same information.

So what's on them? Flight Progress Strips (FPS) are still a significant visual aid used by an Air Traffic Controller to relay the critical information needed to separate and sequence aircraft. Each strip of paper carries all the information a controller needs to know about a flight, and as instructions and information are given to the pilot, these are also recorded on the FPS. These strips of paper are simple, easy to use, and not susceptible to computer or power failure. Flight progress strips contain only the necessary data to handle the flight, such as: aircraft ID, type, beacon code, proposed time, requested altitude, and route of flight. (They do not usually contain complete flight plan information.) The FDIO system as a whole does what it was designed to do: it provides automated flight data input, manipulation, and printed flight strips throughout the National Airspace System (another acronym: NAS), at all en route operations (including military and oceanic areas), being installed in ARTCCs, towers, and TRACONs.

What do they look like? Standardized formats are used. There are basically two different kinds of flight strips: those used by ARTCCs, and the ones used at control towers or TRACONs. They're basically strips of heavy paper, about an inch wide and seven or so inches long, with partitioned printed sections, each designed to hold a specific piece of information. Full information on the formats used for each is contained in the Air Traffic Control Handbook (a.k.a. FAA Order 7110.65), Chapter 2, Section 3. (A fairly recent version is available here) Formats differ depending on whether an aircraft is departing, arriving, or an overflight. As one example, a TRACON flight strip for a departing aircraft (the field numbers for which are shown below) might include:

1) Aircraft ID
2) Revision number (FDIO locations only)
2A) Strip request originator (sector or position which requested the printed strip)
3) Aircraft type: For example, 2/F16 (two F16 fighters); H/B747 (a “heavy” Boeing 747). The same equipment suffixes we use on our flight plans (FAA Form 7233-1, field 3) are also used. Another example would be (T/B737) meaning the aircraft is TCAS equipped.
4) Computer identification number (FDIO only), which can be used in place of the aircraft ID to obtain additional information
5) Assigned transponder code, assigned by the center (HOST) computer according to the National Beacon Code Allocation Plan
6) Proposed departure time (UTC)
7) Requested altitude (usually in hundreds of feet—though sometimes written in thousands)
8) Departure airport
8A) Required when voice recorders not operational, to record any “resolution advisory” actions (climb/descent action, and time in hhmm)
9) Route of flight, destination, airport/clearance unit, and remarks. The route could be bracketed by plus signs indicating a preferential route has been assigned by the HOST Computer. Remarks could contain full route clearance (FRC), indicating complete routes need to be relayed to the flight crew, due to changes in original route filed by the pilot/company. (This gets used by the clearance delivery controller.)
10-18) Departure time, take-off runway, and any other items specified by controller needs or facility directives. The use of these fields are not the same at all airports.

And what do they do with them? A flight strip is normally printed out in the tower 30 minutes before your proposed departure time. If you leave early or you request a change, the controller can send 'request' or 'amendment' messages through the FDIO. When you depart, a 'DM' or departure message gets sent to the Center, either manually or via FDIO. If the control tower has ARTS (Automated Radar Terminal System), the DM is automatically sent to the HOST. At that point, the HOST computer begins estimating your future position and prints a flight strip for every sector controller who will be responsible for separation on your aircraft, 20 to 30 minutes in advance. Any changes in route or altitude result in new strips being printed for all controllers downstream. If you cross over into another Center, your flight information is automatically carried over into the next Center. When you leave the ARTCC or land though, your flight information gets erased (and your transponder code can get reallocated to another aircraft in that Center).

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