The core words
- Roger: “I have received all of your last transmission.” Not a yes: the FAA says it “should not be used to answer a question requiring a yes or a no answer.”
- Wilco: short for “will comply.” “I have received your message, understand it, and will comply with it.”
- Affirmative / Affirm: yes. US radio says “affirmative”; the international (ICAO) word, used in Europe and the UK, is “affirm.”
- Negative: “No,” “permission not granted,” or “that is not correct.”
- Unable: “I cannot comply with your request, instruction, or clearance,” normally followed by a reason.
Why “roger wilco” is wrong
Wilco already includes “I received your message,” so “roger wilco” says the first half twice. And for some instructions neither is enough: the UK manual notes that roger and wilco are an “insufficient acknowledgement” of a hold-short instruction, which the pilot has to read back in full.
