Pilots and air traffic controllers use short, standard phrases so every instruction is clear the first time. "Roger" means I heard you, "wilco" means I will comply, "squawk" means set your transponder code, and "go around" means abort the landing and try again. Here are the terms you're most likely to hear, in plain English.
Radio phrases stay in English on purpose: English is the international language of aviation, so the terms below are the ones pilots and controllers actually say.
Radio basics
Roger
I received your last message. It doesn't mean yes, and it doesn't mean the pilot will do something.
Wilco
Short for "will comply": I understood and I will do it.
Affirmative / Negative
Yes and no. They are harder to miss than a short "yes" or "no" that can get clipped on the radio.
Unable
I can't do what you asked, often because of weather, aircraft performance or safety.
Say again
Please repeat that. Pilots and controllers use this instead of "repeat," which has a different meaning in military use.
Standby
Wait, I'll get back to you.
Readback
Repeating an instruction back to the controller so they can confirm it was heard correctly. Pilots must read back things like runway and altitude instructions.
Contact / Monitor
"Contact" means switch to a new frequency and check in. "Monitor" means switch and listen, without calling.
Heavy / Super
Added to the callsign of very large jets as a reminder of the strong wake turbulence behind them. "Super" is used for the Airbus A380. Airline callsigns →
Zulu time
Coordinated Universal Time (UTC). Aviation uses it everywhere so nobody has to convert time zones.
ATIS
Automatic Terminal Information Service: a recorded broadcast with the airport's weather, active runways and notices. Each update gets a letter, like "information Bravo." Phonetic alphabet →
Altimeter
The local air pressure setting, so every aircraft's altimeter reads the same altitude. "Altimeter two niner niner two."
On the ground
Clearance
The route, altitude and instructions a flight must follow, given before departure.
Cleared as filed
The flight may fly the route in its flight plan.
Pushback
A tug pushes the aircraft back from the gate.
Taxi
Moving on the ground under the aircraft's own power, following ground control's route along lettered taxiways.
Hold short
Stop before reaching a runway or taxiway. Pilots must read back every hold-short instruction.
Line up and wait
Taxi onto the runway and wait there for takeoff clearance.
Cleared for takeoff / Cleared to land
Permission to take off from or land on a specific runway, given by the tower.
Runway numbers
A runway's number is its compass direction divided by ten, so runway 27 points west (270 degrees). L, C and R mean left, center and right.
In the air
Climb and maintain / Descend and maintain
Change altitude and level off at the one given: "climb and maintain one zero thousand."
Flight level
In the U.S., altitudes from 18,000 feet up are said in hundreds of feet: flight level 350 is about 35,000 feet.
Vectors / Heading
Compass headings assigned by a controller to steer an aircraft, often to line it up for landing or to move it around traffic or weather.
Direct
Fly straight to a point, a welcome shortcut: "proceed direct ORLANDO."
Handoff
Passing an aircraft from one controller or facility to the next. Who handled my flight? →
Squawk
Set the transponder to a four-digit code so the aircraft can be identified on radar. Squawk codes →
Ident
Press the transponder's ident button so the aircraft's target briefly highlights on the controller's screen.
Radar contact
The controller sees and has identified the aircraft on radar.
Traffic
Another aircraft nearby, given by clock position, distance and altitude: "traffic, two o'clock, five miles, opposite direction."
Tally-ho / No joy
Informal terms borrowed from military pilots: "tally-ho" means I see the traffic, "no joy" means I don't.
Holding
Flying an oval racetrack pattern while waiting for space to land or for weather to improve. Why is my plane circling? →
Go around
Abort the landing, climb and come back around for another try. It is a normal, practiced maneuver.
ILS / Visual approach
An ILS (Instrument Landing System) uses radio beams to guide an aircraft to the runway in low clouds or fog. On a visual approach the pilot lands by looking at the runway in good weather.
Wake turbulence
Spinning air left behind an aircraft's wings. Controllers space aircraft further apart behind large jets.
VFR / IFR
Under Visual Flight Rules the pilot navigates by looking outside and sees and avoids other aircraft. Under Instrument Flight Rules the flight follows an ATC clearance and can fly through clouds. Airline flights fly IFR.
Flight following
Optional radar help for VFR pilots: controllers point out nearby traffic when workload allows.
Pattern
The rectangular path small planes fly around an airport to land: upwind, crosswind, downwind, base and final.
Delays and restrictions
Ground stop
Flights headed to an airport are held at their departure airports, usually because of weather or a runway problem. Why is my flight delayed? →
Ground delay program / EDCT
Flights to a busy airport get assigned takeoff times (Expect Departure Clearance Times) to spread out the arrivals.
Miles in trail
Required spacing between aircraft heading the same way, used to meter traffic into busy airspace.
Reroute
A new route around weather or congestion.
TFR
Temporary Flight Restriction: airspace closed to most flights for something like a presidential visit, a wildfire, a rocket launch or a stadium event.
NOTAM
Notice to Air Missions: an official notice about changes like a closed runway or a light that is out.
Emergencies
Mayday
The international distress call for a life-threatening emergency, said three times.
Pan-pan
An urgent situation that isn't immediately life-threatening, said three times.
Souls on board
The number of people on the aircraft, asked during an emergency so rescue crews know how many to expect.
Minimum fuel
The aircraft can accept little or no delay. It isn't an emergency yet, but controllers keep a close eye on it.
Every one of these phrases is a controller keeping someone safe. If they kept you safe, tell them.
Common questions
What does roger mean?
"I received your last message." It doesn't mean yes or that the pilot will comply. That's "wilco."
What does wilco mean?
It's short for "will comply": I understood your instruction and will do it.
What does squawk mean?
To set the aircraft's transponder to a four-digit code so controllers can identify it on radar.
What does heavy mean after a callsign?
It marks a large jet, like a Boeing 777, so others remember to leave extra space for its wake turbulence.
Why do pilots and controllers speak English?
English is the international language of aviation under ICAO rules, so crews and controllers from different countries can always understand each other. Local languages are also used in many countries.