How it listens

Keying the radio

Hold the on-screen microphone button while you talk and let go when you have finished. If you prefer, Settings can switch this to tap once to key and tap again to release. A single transmission can be up to 20 seconds long.

While you are keyed, the frequency is yours: any pilot talking is cut off, and that pilot repeats the whole reply once you release. On the phone speaker, the airport sound drops while you talk so your call comes through clean. With headphones it stays up. This setting is called "Quiet while talking" and can be set to auto, always, or never.

Your words appear on screen as you speak. The final text lands about a third of a second after you let go.

From your words to a clearance

The transcript is read by the game's own phraseology grammar. It is rules, not guesswork, and it reads the same call the same way every time. A call in full phraseology earns the score bonus, while looser wording is still flown without the bonus.

If a value is missing, the pilot asks for it. For example, if you say Seacliff four zero one, turn left heading and release the button without giving the numbers, the pilot answers say again heading, Seacliff four zero one. If the value cannot be flown, nothing is executed: the pilot answers negative, says why, and asks for that item again.

Only when the grammar cannot read the call at all does a language model step in. Its single job is to rewrite your words into standard phraseology. The grammar must then read that rewrite like any other call, and the rewrite may only use what you said. If what you said was not an instruction, it is not rewritten.

If the call still cannot be read, the pilot says say again. If no aircraft can be identified, you hear station calling, say again with your callsign. No transmission ends in silence.

What the pilots do

Readbacks are assembled from the instruction the game understood. They are not generated text, so the readback tells you exactly what the pilot will fly. Each pilot answers after a short pause of 0.2 to 0.6 seconds, the same for that aircraft all shift. The pilots' voices are your phone's own text-to-speech voices; several are drawn from the voices installed on it.

Pilots refuse a clearance onto a runway they can see is occupied. How often they catch it depends on the difficulty: at beginner level they catch it most of the time (80 percent), and at higher levels less often, so the safety is yours. Above beginner level, pilots also sometimes read back wrong. Catching it is part of the job. At beginner level they never do.

What the computer decides, and what it does not

Traffic, weather changes, and emergencies are set up by a director. Online it is a language model; offline it is a built-in director with fixed rules. Either way, the game's engine checks every event before it happens and drops anything that does not fit. Separation, runway rules, and approach procedures are written into the game's code. No language model flies an aircraft, decides whether a clearance is safe, or speaks for a pilot.

Where your voice goes

When playing online, while you are keyed, the audio is streamed to Codoha's server, passed to a speech-to-text service, and comes back as text. Neither the audio nor the text is stored, and the service is told not to use it to improve its models. The app keeps no history of what you said.

Offline mode in Settings uses your phone's own speech recogniser instead, and nothing leaves the device. This needs the phone's offline English speech pack installed; without it, use touch. See the privacy policy for the full detail.

English only

The radio is in English, the language of air traffic control. Recognition is set up for English.

Getting understood

• Start with the callsign.
• Say numbers the way controllers do. Headings, speeds, and flight levels can be spoken digit by digit (heading two seven zero) or in group form (heading two seventy).
• To change something you just said, say correction and the new value.
• Hold the button until you have finished speaking.
• A quiet room or a headset helps.
• Settings has a Radio check. In about a minute it tests the microphone, the input level, the recogniser, the grammar, and the readback, and tells you which step failed.
• If the microphone is not an option, tap an aircraft and build the call by touch, then press Transmit. Pilots answer a tapped call the same way.