IR.III.A.K1FAA-S-ACS-8C · Nov 2023Knowledge
Elements and procedures related to ATC clearances and pilot/controller responsibilities...
Elements and procedures related to ATC clearances and pilot/controller responsibilities for departure, en route, and arrival phases of flight, including clearance void times.
Bottom line
When an ATC clearance has been obtained, no pilot in command may deviate from that clearance unless an amended clearance is obtained, an emergency exists, or the deviation is in response to a TCAS resolution advisory. When a pilot is uncertain of an ATC clearance, that pilot shall immediately request clarification from ATC. It is the pilot's responsibility to comply with clearance instructions as given and to notify ATC if unable to comply.
Key numbers
| Number | What it means |
|---|---|
| Within 30 minutes of the original void time, if you fail to depart | Void time contact |
| At least 30 minutes in advance, departing an airport without an operating control tower | Flight plan filing |
| 2 hours after the proposed departure time, if not opened | Flight plan timeout |
| Not more than 10 minutes before proposed taxi time | Taxi clearance |
FAA references
- 14 CFR 91.123 (Compliance with ATC clearances and instructions.) — eCFR current as of 2026-03-05
- IPH ch. 1 (pp. 1-43–1-44) — FAA-H-8083-16B
- IFH ch. 2 (p. 2-5) — FAA-H-8083-15B
- IPH ch. 2 (p. 2-7) — FAA-H-8083-16B
- 14 CFR 91.185 (IFR operations: Two-way radio communications failure.) — eCFR current as of 2026-03-05
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