Belgian aircraft registration and serials

The first use of aircraft registrations was based on the radio callsigns allocated at the London International Radiotelegraphic Conference in 1913. The format was a single letter prefix followed by four other letters (like A-BCDE).[1] The major nations operating aircraft were allocated a single letter prefix but minor countries had to share a single letter prefix but were allocated exclusive use of the first letter of the suffix.[1] Belgium was not considered a major operator of aircraft and was allocated the prefix and first letter suffix O-B. When the conference allocated the same prefix it made sure that they were in different parts of the world, the other user of the O prefix was Peru and they were allocated O-P.[1] The first allocation was O-BEBE to a Fokker D.VII on 1 March 1920.[1]

Following the allocation of radio callsigns to Belgium of ON, OO, OP, OQ, OR, OS and OT at the 1927 International Radio-Telegraph Conference.[1] The callsign allocation did not align with those allocated for aircraft registrations and in 1928 the International Convention of Air Navigation re-allocated the aircraft registration prefix to align with the callsigns.[1] Belgium could use all or any letter groups that had been allocated as radio callsigns and in 1929 the prefix OO was selected.[1] The first allocation was OO-AJT to a Stampe et Vertongen RSV 26 in March 1929 and the format was still in use in 2011.[1]

Some of the blocks of registrations have had a reserved usage and these include:

• OO-BAA to OO-BZZ used mainly for balloons
• OO-CAA to OO-CZZ used for the Belgian Congo 1934-1960
• OO-YAA to OO-ZZZ used mainly for gliders
• OO-01 to OO-499 used for homebuild aircraft

When the Belgian Air Force was re-formed in 1946 individual aircraft were allocated serial numbers in either a one or two letter prefix followed by a one or two digit number. The first allocations were mainly single letters (for example A-1 was an Auster AOP.6) but sometimes a second letter was used to distinguish variants, for example NA-1 was an Avro Anson I and NB-1 was an Anson II.[2]

In the 1950s the first letter started to be used as a role prefix, for example FX-01 was a Lockheed F-104G Starfighter classified as a Fighter.[2]

An Aero Commander 560F was operated for royal flights between 1961 and 1973 without a serial number but display its radio callsign OT-CWB instead.[2] Similarly, there have been Douglas C-47B transports "registered" OT-CWA, OT-CWG and OT-CNR, and a Sikorsky S-58 helicopter "registered" OT-ZKP.

In 1954 the Belgian Army formed its own aviation element and serial numbers were allocated in the form OL-A01, the OL for Observation Leger (light observation), the letter for the type and the number for each individual aircraft. In 1974 the OL prefix was dropped.[2]

The Belgian Navy have operated a number of shipborne helicopters which were allocated serials with single letter prefix although the radio callsigns were also painted on the aircraft in a similar format to registrations.[2]