Codes and Call Signs

Voices on VHF radio sound clear and easy to understand, but HF radio has a lot of extra crackling and hissing noises called static. Static makes voices hard to hear. Hearing information correctly is important to air and space travel, so sys­tems have evolved to help with clarity. The international language of aviation is English. All pilots who fly interna­tionally and all air traffic controllers have to be able to communicate in English while engaged in aviation.

Some letters and words sound very similar over a noisy radio link, and pilots often use a spelling alphabet that can be heard more clearly. A word is used instead of each letter. The words are chosen so that they cannot be con­fused with each other. This alphabet is used to spell out important words.

THE INTERNATIONAL RADIOTELEPHONY SPELLING ALPHABET

The International Radiotelephony Spelling Alphabet (below) is used by many organizations, including the International Civil Aviation Organization (ICAO) and the Federal Aviation Administration (FAA).

ч_________________ /

There has to be a way of identifying each aircraft so that pilots and air traffic controllers know exactly who is talking to whom. Each plane has its own code, or call sign, that the pilot spells out using the spelling alphabet. In general aviation, small planes use their registra­tion number as their call sign.

Airliners use a call sign for the airline, plus the flight number. The airline part of the call sign is often the airline’s name. American Airlines flight 142 would be identified in radio messages as American 142. Pilots of big aircraft, such as jumbo jets, add the word heavy to the call sign. This tells everyone that

this aircraft is big enough to cause tur­bulence (strong air currents) that may affect planes following it.