One popular tool for doing this is the airband scanner. It's a radio receiver which works in the frequency range assigned for aircraft radio transmissions. Ideally it can pick up both sides of the conversation. The VHF radio used in aircraft only works in line-of-sight, so if you're not close to a towered airport, you might only hear the aircraft's transmissions. On top of that, there's still shaky legal ground around scanners in this country. Ofcomm's position is that the radio spectrum is assigned for people's private business communications, so you shouldn't be listening in, even though it's an open transmission. This has left us with an odd position where listening is legal only so long as you don't act on or tell anyone what is said.
While you're listening to LiveATC, if you want a visual aid, you can use FlightRadar. They have a network of ADS-B receivers, which pick up the positions of most large aircraft from their radar transponders. Aircraft don't have to have ADS-B, so most light aircraft don't show up, but all airliners do. Having received the positions, they show them on a Google Maps overlay, online or in an app.
|FlightRadar24. Can you spot Heathrow?|
I've heard several experienced pilots recommend using LiveATC or similar to practise monitoring the radio, and to learn about how transmissions differ between different places. There's an international standard (ratified by ICAO, the International Civil Aviation Organization) that sets out standard forms of language to use on the radio, but even so there's a lot of variation. I was skeptical at first, but listening to a few places was a real eye-opener. It made me realise how formal and efficient Cambrige is.
You'd expect a small airport to be chattier, and perhaps a little lazy, but because Cambridge is often busy and has a wide variety of traffic (from students in Tiger Moths to military pilots in Hercules), they're very businesslike, with no small talk or pleasantries. If you take Dublin as an example, there's a big contrast. There's a lot of "hello" and "goodbye" messages. It also seems that lots of commercial pilots get lazy with their reports. In a nice quiet cockpit where they don't have to strain at every word, they tend to talk more informally, give information in the wrong order, and don't spell things out properly.
For example, when ATS wants an aircraft to change radio frequency to 123.45 MHz, he should spell that out, "one two tree decimal four fife", and the pilot should read it back. Tree, fife, and niner are all pronounced specially to make them easier to hear and harder to confuse, especially in languages that don't have the "th" sound. But some pilots will pronounce them the normal way, instead of the special way, say "point" instead of "decimal, or "oh" instead of "zero". In the US, it's common to hear the frequency read out as "twenty-three forty-five". (The "one hundred" is implied because all airband radio frequencies start with that.)
Hearing how chatty controllers are in some places isn't the only excitement, though. Sometimes you get to hear something that's less than routine. Recently the UK and Eire have been suffering unusually strong winds, so I got to hear some real gems like, "Company traffic landing ten minutes ago described the approach as 'sporty'," and a few exciting go-arounds because of wind shear and crosswinds. If you're ever annoyed by delays or diversions caused by crosswinds, just watch the following video and see how much worse it can be.