The arrival of the flight plan (FPL)

At the birth of commercial aviation, aviators often flew wealthy people and charged them a fortune and didn’t worry about other aircraft.

Unfortunately, some aircraft failed to arrive at their destination and sadly the first mid-air collision involving commercial flights occurred as early as 1922. Therefore, as aeronautical activity increased, it became necessary to have more regulations and air routes were defined; the dawn of air traffic control (ATC) was upon us and with this came the inclusion of the flight plan (FPL).

These FPLs had to be transmitted efficiently. As you would expect, the FPL is now sent electronically but earlier FPLs were relayed over a fixed network of tele-printers knows as the AFTN. Prior to this, the information was sent between stations via morse code. Regardless of the technology, the FPL message remains largely unchanged.

The job of the FPL is to tell all interested parties everything they need to know about a flight. This information allows the ATC to regulate traffic flow and, where necessary, impose flow restrictions in order to ensure safety, where demand is too high in certain sections of airspace for the prevailing conditions. Additionally, the FPL enables the safe arrival of flights to be monitored, so should the worse happen and a flight becomes overdue then FPLs play a vital role in alerting the emergency services.

So, let’s look at the anatomy of a FPL between London Heathrow (EGLL) and Frankfurt (EDFF).

An example is below:

The first line (highlighted purple) tells us that this FPL is for a flight with the call-sign NATS145 (a made up flight operated by NATS, ATC would use a special callsign for each operator e.g. Speedbird for British Airways flights) which will be operated under Instrument Flight Rules (IFR) and is a Scheduled air transport flight (this is indicated by the I and S at the end of the line).

Next, is the detail about the aircraft (shown in yellow). In the illustration above, this is a Boeing 777, which has a wake vortex category of “Heavy” (depicted by the H) which is really important for ordering aircraft. The equipment is also detailed on this line. In this instance the aircraft carries: Standard radios (VHF voice, VOR & ILS), DME, data link pre-departure clearance (E3), ADF, GPS, INS, MLS (shown by K), RNAV (performance based navigation or PBN), it meets the requirements for using RVSM (shown by the W) airspace and it’s VHF voice radios use 8.33kHz channel spacing shown by the letter Y. Finally, it has a mode S equipped transponder, which relays certain flight parameters (speed, heading etc.) to ATC so they can check the aircraft is doing what it has been told to do.

The next block (in green) relates specifically to the flight. In this example the flight will depart EGLL (Heathrow) at 12:00 with a planned cruising true airspeed of kNots 450, at Flight level (F) 330. It will depart from EGLL on the MID4F standard instrument departure, joining the airway system at BIG (Biggin Hill VOR). It will then follow airway UL9 to KONAN (reporting point) and UL607 to KOKSY (another reporting point) where it will fly a AMASI standard arrival route depending on the runway in use for landing at Frankfurt.

The block below (in blue) shows that the destination is EDDF (Frankfurt) and the estimated flight time is 01 hour and 30 minutes. The planned alternate airfield in the event of diversion is Luxembourg (ELLX).

The final block (in red) contains supplementary information, where more detail is provided about the aircraft’s PBN capabilities, which determines the airspace and the type of instrument approaches that can be flown. The SURveillance transponder is also TCAS (Traffic Collision Avoidance System) enabled. The Date Of Flight (DOF) and aircraft REGistration are shown. Estimate Elapsed Times (EET) to the Dutch airspace boundary (EDDY) is 00 hours 20 minutes. The SELCAL identifier of the aircraft, in this example,  is NATS which is useful to know so air traffic control can contact the aircraft (like ringing a doorbell) without the crew constantly having to monitor their radios on longer flights. The OPeRator is NATS (NTS) and the minimum Runway Visual Range (RVR) in which the aircraft can operate is 075m, which is also very useful information for ATC. Finally, some other remarks (RMK) have been added for different users’ reference.

As you can see, a great deal of information is included in a very short message which, these days, can be transmitted in milliseconds but, even back in the days of morse code, would have only taken a minute or so.

Whilst the days of the majority of pilots manually completing and filing a FPL with ATC by trudging across a windy airfield to the control tower may have gone and the methods of transmission may have changed, the purpose of the FPL has not changed. The FPL ensures that any pilot, anywhere in the world, with whatever payload, can be sure that air traffic controllers are looking out for them and managing the orderly flow of air traffic.