Standard Location Protocol ELTs Coded with the Aircraft Operator Designator and a Serial Number (bits 41 to 55 and 56 to 64)

For an ELT using the Standard Location Protocol coded with the aircraft operator designator and a beacon serial number:

The aircraft operator is identified with a 3 letter designation agreed by ICAO (see ICAO DOC 8585). These three letters are encoded into bits 41 - 55 using a shortened form of the modified-baudot code. The modified-baudot code is shortened by deleting the first bit (which is always equal to 1 for letters) for any letter. The result is that each letter is identified by a 5-bit code.
The beacon serial number identification is provided in bits 56 - 64 in binary notation with the least significant bit to the right. This allows for serial numbers ranging from 0001 to 511. The serial number is normally assigned by the aircraft operator, who must ensure that the resulting beacon identification (bits 26 - 85) is unique and that information on which beacon is installed on each aircraft in its fleet is made available to SAR services on a 24-basis.