Plane spotting glossary

Aviation has a word for everything, and most of them turn up within ten minutes of opening a live stream, either on the tower radio or in the chat. This page is the short version: what each term means and, where it helps, what it looks like on a camera.

It's grouped by where you're likely to meet the word. If you want the longer explanation of radio calls, read how to follow ATC first.

On the radio

Words and phrases from the tower and ground frequencies.

ATC: Air traffic control. On a stream it usually means the tower frequency, the controller who clears aircraft to land and take off. Bigger airports split the job between several people: delivery, ground, tower, departure and approach.
ATIS: A recorded loop of the airport's current weather, runways in use and notices. Each update gets a letter, which is why pilots check in saying 'with information Kilo'.
Callsign: The name an aircraft uses on the radio. For airlines it's a company word plus the flight number, and the word isn't always the airline's name. British Airways is Speedbird, China Airlines is Dynasty, Aer Lingus is Shamrock.
Cleared for takeoff: Permission to start the takeoff roll. The word takeoff is kept for this one instruction and its cancellation. Everywhere else controllers say departure, so nobody hears it by accident.
Cleared to land: The runway is yours. A controller only says this when the runway is, or will be, clear. In the US you'll often hear it while another aircraft is still ahead; in Europe it tends to come later, sometimes only seconds before touchdown.
Go-around: An abandoned landing. The pilot adds full power and climbs away to try again. It looks dramatic on camera and gets the chat excited, but it's a routine, practised manoeuvre. Common causes are a runway that isn't clear yet, a gust at the wrong moment or an approach that wasn't stable.
Heavy: Added to the callsign of large aircraft, roughly anything from a Boeing 767 upwards: 'Delta 40 heavy'. It warns everyone that this aircraft leaves strong wake turbulence. The A380 gets its own word, super.
Hold short: Stop before the runway or taxiway named and go no further. Pilots must repeat it back word for word, because crossing a runway by mistake is one of the most dangerous errors on an airfield.
Line up and wait: Taxi onto the runway and stop there. It gets the aircraft in position while the one ahead clears, and saves a good half minute per departure at busy airports.
Mayday: The distress call, said three times, for serious and immediate danger. It gives the aircraft priority over everything else. Pan-pan is the step below it: urgent, but no immediate danger.
Phonetic alphabet: Alfa, Bravo, Charlie and so on, used to spell letters clearly over a crackly radio. Numbers get the same treatment: nine becomes niner, three is tree and five is fife.
QNH: The local air pressure setting pilots dial into the altimeter so it shows height above sea level. You'll hear it constantly outside North America. American controllers say altimeter instead.
Readback: The pilot repeating an instruction to prove it was heard correctly. It's why every exchange on the radio sounds like an echo.
Roger: I received your message. That's all. It doesn't mean yes, and it doesn't mean the pilot will do it.
Squawk: A four-digit code the controller assigns and the pilot dials into the transponder, so radar can tell which blip is which. 'Squawk 4521' is all it takes. Three codes are reserved: 7500 for hijack, 7600 for radio failure and 7700 for a general emergency.
Unable: A polite, standard no. Pilots say it when they can't accept an instruction, such as a runway that's too short or a turn they can't make. Controllers then offer something else.
Wilco: Short for will comply. This is the one that means I understood and I'll do it.

On the runway

What's happening on the tarmac in front of the camera.

Active runway: The runway in use right now. Airports switch it when the wind changes, which is why a camera that showed landings all morning can show nothing in the afternoon.
Apron: The parking area by the terminal where aircraft are loaded, fuelled and boarded. Americans call it the ramp.
Crosswind: Wind blowing across the runway. Aircraft approach pointing slightly into it, so they seem to fly sideways, then straighten at the last second. That sideways angle is called crabbing.
De-icing: Spraying the aircraft with heated fluid to remove ice and stop more forming. In winter you'll see trucks with long booms working over the wings before departure.
Final approach: The last straight stretch before landing, lined up with the runway. Short final is the last mile or so, when the aircraft is seconds from touchdown.
Flare: The gentle nose-up in the last few metres that softens the touchdown.
Follow-me car: A marked car that leads an aircraft across the apron, usually when the pilots are new to the airport or the visibility is poor.
ILS: Instrument landing system. Radio beams that guide an aircraft down to the runway when the pilots can't see it, which is how planes keep appearing out of the fog on the Hiroshima cam.
Pushback: A tug pushing the aircraft backwards off the gate. Jets could reverse on their own power, but they'd blast the terminal, so they almost never do.
Reverse thrust: After touchdown the engines redirect their thrust forward to help slow down. It's the roar you hear a second or two after the wheels touch, and you can often see the engine cowls slide open.
Rotate: The moment in the takeoff roll when the pilot lifts the nose. On cockpit audio you'll hear the other pilot call it out.
Taxiway: The roads between the gates and the runways. They have letter names, so 'taxi via Alfa, Bravo, hold short runway two five right' is a set of driving directions.
Threshold: The start of the usable runway, marked by a row of white stripes that pilots call the piano keys.
Touch-and-go: Landing and taking off again without stopping. Training aircraft do it in circuits, so you'll see plenty at small airfields and at airports with a flight school, like Sendai.
Wake turbulence: The swirling air a wing leaves behind, strongest behind big, heavy, slow aircraft. It's the reason for the gaps between landings: a small jet has to stay further behind an A380 than behind another small jet.

The aircraft

Words for the planes themselves.

APU: Auxiliary power unit. A small jet engine in the tail that powers the aircraft on the ground. Its exhaust is the round hole at the very back of the fuselage.
Contrail: The white line behind a high-flying jet: water vapour from the engines freezing into ice crystals.
Freighter: A cargo aircraft. The giveaways are the missing windows and, on a 747 freighter, a nose that swings up for loading. The F in 747-8F stands for it.
Livery: An airline's paint scheme. A special livery is a one-off design, like ANA's Pokémon jets or the Hello Kitty aircraft EVA Air flies.
Narrowbody: An airliner with one aisle, such as the Boeing 737 and the Airbus A320 family. They make up most of what you see at any airport.
Registration: The aircraft's number plate, painted near the tail. The first letters give the country: N for the United States, G for the UK, JA for Japan, D for Germany. Type it into a tracking site to see where that exact aircraft has been.
Retro jet: An aircraft painted in one of the airline's old colour schemes. Popular with spotters because there's usually only one in the fleet.
Turboprop: A propeller aircraft driven by a jet engine. The ATR 72 and the Dash 8 are the common ones, and they fly most island and short regional routes.
Widebody: An airliner with two aisles: the 777, 787, A330, A350, A380 and 747. They fly the long routes, and they're what most viewers are waiting for.
Winglet: The upturned tip of a wing, there to cut drag and save fuel. The shape is one of the quickest ways to tell aircraft types apart. Airbus calls its version a sharklet.

Spotting and the chat

Slang from spotters and stream regulars.

Avgeek: Aviation geek. What plane spotters call themselves, proudly.
Blue hour: The half hour after sunset when the sky is deep blue and the runway lights are on. Many spotters think it's the best time of day to watch.
Butter: A very smooth landing. 'Buttered it' is high praise in any stream chat. The opposite is a firm one, which pilots will tell you is often deliberate on a wet or short runway.
Heavy metal: Spotter shorthand for the big widebodies.
Jet blast: The exhaust behind a jet at takeoff power. At Maho Beach it's strong enough to knock people off their feet and into the sea, which is why the fence there is covered in warning signs.
PTZ: Pan, tilt, zoom. A camera an operator can steer to follow an aircraft, as opposed to a fixed view. It's why some streams track each landing and others just watch one stretch of runway.
Queen of the Skies: The Boeing 747. Few passenger airlines still fly it, so one on a stream is an event. Freighter versions are still common at cargo airports like Narita and Hong Kong.
Tail number: Another word for the registration, used mostly in North America.