10  Aircraft information

Author

Xavier Olive

A number of flight information is usually not directly accessible from settings recording aircraft trajectories. Metadata usually refers to any additional information enriching a trajectory. Enriching trajectories with relevant information is usually a costly process, and access to such information can be complicated.

10.1 ICAO identifiers

The most common identifier for aircraft in radar based technologies would be the identifier of the transponder: a six-digit hexadecimal identifier, i.e. an integer written in its hexadecimal form, which classically identifies an aircraft uniquely. In the remaining of the book, it is commonly referred as the ICAO identifier, or icao24 in data records (24 standing for the number of bits encoding the integer).

Ranges of addresses are reserved per countries, who are free to assign addresses to aircraft registered by their authorities. All US registered aircraft get an address in the 0xa00000 to 0xafffff range; in Europe, France gets 0x380000 to 0x3bffff, Germany gets next interval from 0x3c0000 to 0x3fffff, then the UK gets 0x400000 to 0x43ffff, etc.

Are ICAO addresses unique?

Yes and no. In practice, for most short-term analyses, we can consider the answer is yes.

However, an aircraft may get a different transponder identifier when she gets a different registration. This may happen when the aircraft is sold to new owners who want to register their aircraft in a different country. Then, after the aircraft gets a new registration, her old identifier can be reassigned to new aircraft.

Also, most aircraft manufacturers keep a small set of transponders that they reuse across many newborn aircraft for test flights. Those usually correspond to temporary registration numbers.

To sum up, it is safer to keep in mind that:

  • the same aircraft can have different ICAO identifiers throughout her life;
  • the same identifier can refer to different aircraft depending on the day we get data from her.

10.2 Tail numbers

The tail number is the number usually written on the back side of the aircraft, like the license plate number of cars, but for aircraft. Tail numbers also follow a pattern per country: F- for France, D- for Germany, G- for the UK, with some recognised patterns for specific categories of aircraft. Every country is free to decide how to assign registrations to aircraft within their range, and to give them a tail number accordingly. In some countries, like the US, Japan or Korea, there is a direct correspondence between tail numbers and ICAO identifiers, but that’s not the case in every country.

In the US, tail registrations start with the N letter (they are also called N-numbers) and are followed by up to 5 numbers, or up to 4 numbers and 1 letter, or 3 numbers and 2 letters. Letters I and O are excluded. Then there is a “direct” correspondence with transponder addresses: 0xa00001 for N1, 0xa00002 for N1A, 0xa00003 for N1AA then 0xa00004 for N1AB until 0xadf7c7 fort N99999.

What is the PIA program?

To address privacy concerns, FAA has initiated the Privacy ICAO aircraft address (PIA) program to improve the privacy of the eligible US-registered aircraft, ADS-B equipped and flying in the domestic US airspace. Recent research [1] have shown this attempt is vain as it is very easy to break the anonymization and find which PIA address (between N41000 0xa4d691 and N42 0xa4f946) is associated to which aircraft.

Table 10.1 illustrates some examples of patterns in registrations numbers assigned by countries. In the Netherlands, KLM matches the two first letters after the country code to aircraft types.

Table 10.1: Some countries reserve registration patterns to specific categories of aircraft.
country range pattern category
France 380000 3bffff F-
F-A Historic aircraft
F-C Gliders
F-J Ultralights
F-W Test and Delivery
F-Z State owned
Switzerland 4b0000 4b7fff HB-
HB-B Balloons
HB-F Produced in Switzerland
HB-X or Z Helicopters
The Netherlands 480000 487ffff PH-
PH-AO KLM Airbus A330
PH-BH KLM Boeing 787-9
PH-BK KLM Boeing 787-10
PH-BQ KLM Boeing 777-200

10.3 Aircraft type designators

DOC 8643 - Aircraft Type Designators by ICAO contains designators for aircraft types which are most commonly provided with air traffic service (ATS).

Each designator consists of a 4-letter code associated with a manufacturer and an aircraft type, e.g., A320 for Airbus A320, B78X for Boeing 787-10 or E190 for Embraer 190. More specific designators can be used for balloons BALL or gliders GLID.

This designator is often referred as typecode in aircraft databases and helps associating an aircraft type to an ICAO identifier.

10.4 Data sources

Maintaining a data base of transponder identifiers, aircraft tail numbers, type designators, owners and/or operators is a very cumbersome process. New aircraft are manufactured every month, which generates new transponder identifiers [2]. Some countries keep a database of their registered aircraft public (e.g. FAA (US), France, Switzerland or The Netherlands), but this is not a systematic practice in every country, and those do not always contain the transponder identifier.

There have also been some crowdsourcing effort to constitute and maintain aircraft databases based on various open records and entries on social networks. Such databases raise some privacy concerns among some aircraft owners, who may be tempted to vandalise those databases [3].

Some public aircraft databases: