← All explained questions · Supplemental · III — Airport & Seaplane Base Operations
If you receive an ATC instruction you cannot safely comply with, the correct phrasing is
Choices
comply but file a NASA report.
Compliance with unsafe clearance is dangerous.
✓ 'Unable, [callsign]'.correct
followed by your alternative if appropriate. ATC will work with you. Don't accept clearance you cannot safely meet (terrain, fuel, weather, performance). 'Unable' is a complete sentence in aviation. Use it whenever a clearance can't be safely complied with — wrong altitude (terrain), wrong heading (weather), wrong speed (performance limit). ATC then provides an alternate. Do NOT accept and try to comply unsafely. PIC has final authority (91.3). 'Unable' is not a confrontation; it's a partnership.
ignore the instruction.
Silence after instruction = no readback = ATC doesn't know you got it.
comply silently and complain later.
Silent unsafe compliance is the pattern that leads to accidents.
Why
followed by your alternative if appropriate. ATC will work with you. Don't accept clearance you cannot safely meet (terrain, fuel, weather, performance). 'Unable' is a complete sentence in aviation. Use it whenever a clearance can't be safely complied with — wrong altitude (terrain), wrong heading (weather), wrong speed (performance limit). ATC then provides an alternate. Do NOT accept and try to comply unsafely. PIC has final authority (91.3). 'Unable' is not a confrontation; it's a partnership.
FAA source: AIM 4-4-1, 14 CFR 91.3; 14 CFR 91.3 Responsibility and authority of PICbrowse the reference library →
Original study question written for this course — representative of FAA knowledge-test topics, not an actual current FAA exam question.