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The Pilots Desk
US-FAA14 CFR 91.123

Compliance with ATC clearances and instructions

Read the official rule

In plain English

You must comply with an ATC clearance or instruction in controlled airspace. You may deviate only in an emergency or if an amended clearance is obtained; if you deviate due to an emergency, notify ATC as soon as possible and, if asked, file a written report.

Key points

  • Comply with clearances and instructions when operating under ATC.
  • Read back hold-short and runway instructions.
  • Emergency authority lets you deviate — then tell ATC.

Common pitfalls

  • "Climbing via" or "descend via" mistakes — verify altitude and route.
  • Accepting a clearance you can’t comply with instead of saying "unable".

*This is a plain-English summary for study only. The official 14 CFR text on this page is controlling — always read the current regulation.*

This is an original plain-English explanation for training and reference, not legal advice and not for navigation. Always rely on the current official rule linked above. Last reviewed June 7, 2026.