Readback is the repetition of critical information back to ATC for verification. When you read back, you are confirming that you have heard and understood the clearance correctly. ATC listens to your readback and checks it against what they said. If there is a discrepancy, they will stop you and clarify.
What MUST be read back (always):
  1. Clearances /strong> – Any ATC clearance (takeoff clearance, landing clearance, approach clearance)
  2. Assigned altitudes – Flight levels, altitudes, or altitude constraints ("climb to flight level one one zero," "descend to three thousand five hundred feet")
  3. Assigned headings – Any heading instruction ("turn left heading two seven zero")
  4. Transponder codes – Squawk assignments ("squawk four one zero zero")
  5. QNH settings – The altimeter setting ("QNH niner niner five")
  6. Hold short instructions – Runway crossing clearances or instructions to hold short of a runway ("hold short of runway zero eight")
  7. Frequencies – New frequency assignments ("contact Approach on one two four decimal five")
  8. Speed restrictions – "Reduce speed to one one zero knots"
  9. Recleared procedures – If you are recleared to a different procedure, you must read it back
What does NOT need to be read back (typically):
  1. Routine acknowledgments – "Roger" or "Wilco" are sufficient when you are simply acknowledging that you have heard and will comply with a routine instruction
  2. Traffic information – "Traffic one o'clock, five miles, opposite direction" is information; you acknowledge it with "Traffic acknowledged" or simply "Negative contact"
  3. Weather information – ATIS information is acknowledged by callsign only
  4. Position reports – When ATC says "continue," your response "continue" is sufficient readback /li>