How should you acknowledge a change in altitude from ATC?

• A. Respond with "Copy that" only.
• B. Just say "OK."
• C. Ignore until instructed again.
• D. Read back the new altitude exactly and respond with "Wilco" or "Roger" as appropriate.

Answer: (D)

When ATC assigns a new altitude, you should confirm clearly by repeating the exact instruction and the altitude, then indicate your intent to comply or acknowledge what you heard. Repeating the precise altitude back leaves no doubt about what you’ve been told and what you will do, which helps prevent altitude slips or miscommunication with other traffic.

For example, if ATC says to descend and maintain FL180, you would reply with that exact phrase and then Wilco to show you will comply. This combination—readback of the exact altitude and a Wilco or Roger—provides both confirmation of the instruction and your intent. Short responses like “Copy that” or “OK” don’t confirm the exact value or your compliance, and ignoring the instruction is unsafe. Using the proper readback plus Wilco/Roger keeps ATC and you on the same page and helps maintain safe separation.