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When may a pilot turn off an operating anti-collision light system?

Choices

Anytime during cruise to save the bulbs
It must operate in flight except when safety justifies turning it off.
✓ When the pilot determines that turning it off is in the interest of safetycorrect
The regulation allows it to be off when operation would be contrary to safety, such as in cloud.
Never; it must always remain on
There is an explicit safety exception.
Only on the ground
The safety exception applies in flight as well.

Why

An anti-collision light system must be operated in flight, but the pilot may turn it off when its operation would be in the interest of safety, for example when strobes cause disorientation in cloud.

FAA source: PHAK / 14 CFR 91.209browse the reference library →

This is taught in Aircraft Lights, Equipment and Preflight — study the lessons free, then practice with grading and mastery tracking.

Original study question written for this course — representative of FAA knowledge-test topics, not an actual current FAA exam question.