At FlightAware, our software needs to gracefully handle all sorts of weird and wonderful situations. While we as engineers might hope for aviation data to be clean and well-standardized, the real world is messy.

There are a lot of assumptions one could make when designing data types and schemas for aviation data that turn out to be inaccurate. In the spirit of Patrick McKenzie’s classic piece on names, here are some false assumptions one might make about aviation. While many of these are simply common misconceptions, some of these assumptions have bitten our customers at various points, and others have caused issues in our own systems over the years.

Together they are illustrative of the situations that Hyperfeed, our flight tracking engine, is responsible for correctly interpreting in order to provide a clean and consistent data feed for our website, apps, and APIs.

Flights

• Flights depart from a gate
• Flights that depart from a gate only leave their gate once
• Flights depart within a few hours of the time they were scheduled to
• Flights depart within a day of the time they were scheduled to
• Flights have schedules
• Flights take off and land at airports
• Airplanes (excluding helicopters) take off and land at airports
• Flights are at most a dozen or so hours long
• Okay, they’re at most a few days long
• Flights are identified by a flight number consisting of an airline’s code plus some numbers, like UAL1234
• Flights are identified by either an airline flight number like UAL1234, or the aircraft’s registration like N12345, B6459, or FHUVL
• A flight identifier like B6459 is unambiguously either a registration (B–6459), an airline flight number (B6 459), or something else
• Flights don’t have multiple flight numbers
• Flights with multiple flight numbers unambiguously have one “main” flight number
• A particular trip’s flight number(s) never change
• The flight number shown on your ticket is what the pilots and air traffic control are using
• Flights don’t use the code of some entirely unrelated airline in their flight identifier
• No flights use the same flight number within a day
• Surely at least no flights use the same flight number at the same time?
• Okay fine, separate flights from the same major passenger airline that depart within a few minutes of each other would not both have the same flight number… right?

Airports

• Airports never move
• Terminal and gate numbers have a consistent naming scheme
• Each runway is only used by one airport
• Airports always have two unique identifiers: a 4-letter Civil Aviation Organization (ICAO) code and a 3-letter International Air Transport Association (IATA) code
• Airports always have three unique identifiers: an ICAO, an IATA, and a regionally-administered location code
• The U.S. Department of Transportation assigns one canonical code to each airport it oversees
• No airports have multiple IATA codes
• The ICAO code for airports in the U.S. always starts with the letter K
• For U.S. airports whose ICAO code starts with K, the last three letters are its IATA code
• You can tell which geographic region an airport is in from its ICAO code
• Everything that has an IATA code is an airport
• Everything that has an ICAO code is on Earth
• Airports have at least one well-known identifier of some sort

Airlines

• No two airlines share the same IATA code
• No airlines use multiple IATA or ICAO codes
• You can tell what airline is operating a flight by looking at the physical aircraft
• Airlines assign flight numbers to specific routes
• Airlines only assign flight numbers to flights they operate
• Airlines only assign flight numbers to flights

Navigation

• Waypoint names are unique
• There is one agreed-upon definition of altitude
• Flight information from Air Navigation Service Providers is accurate
• Okay, pretty accurate; they wouldn’t indicate that a flight had departed unless it really had
• If they indicate that a flight plan has been cancelled, then that flight definitely isn’t going to operate — it wouldn’t simply be due to someone editing the flight plan
• At least their radar data accurately identifies each aircraft
• Radars with overlapping coverage areas agree on the location of a target they can both see
• If they send us a flight plan with the ICAO identifier of a known airport as the destination, then there must have been some intention of arriving there
• If an aircraft diverts to another destination, it won’t divert again

Transponders and ADS-B

• ADS-B messages only come from aircraft
• ADS-B messages only come from aircraft and airport service vehicles
• ADS-B messages only come from vehicles of some kind
• The GPS position in ADS-B messages is accurate
• The GPS position in ADS-B messages is accurate within some known uncertainty radius
• ADS-B messages always include the correct flight identification
• Transponders are correctly programmed to indicate the aircraft type (helicopter, airplane, balloon, etc)
• You can always determine a aircraft’s registration number from its ADS-B messages
• Transponders are programmed with the correct Mode S address
• All of the transponders on a single aircraft are programmed with the same Mode S address
• Nobody will ever set their flight identification to weird things like NULL
• People will remember to update the transponder when the aircraft’s registration changes
• ADS-B messages are always received exactly as they were transmitted
• No one ever transmits false ADS-B messages
• Transponders never break and rodents never chew through cables

Thanks to my colleagues who contributed to or reviewed this collection of falsehoods: Mark Duell, Paul Durandt, Karina Elizondo, Matt Higgins, Thomas Kyanko, Nathan Reed, and Amy Szczepanski.