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What is the FAA-recommended PERSONAL minimum for SUPPLEMENTAL OXYGEN at night?

Choices

10,000 ft MSL — same as daytime regulatory minimum.
10,000 ft daytime is regulation minimum, not night personal recommendation.
✓ 5,000 ft MSL.correct
even at modest altitudes, hypoxia degrades night vision before any cognitive symptoms appear, because the rod cells are highly sensitive to hypoxia. Regulatory: 14 CFR 91.211 requires O2 for flight crew above 12,500 ft (after 30 min) and at all times above 14,000 ft. PERSONAL minimum at night: many CFIs recommend supplemental O2 above 5,000 ft because rod cells (low-light vision) are very oxygen-sensitive. Night vision degrades 5-10% per 1,000 ft above 5,000 due to hypoxia, even before any cognitive impairment.
3,000 ft MSL.
3,000 is too low to be a useful threshold.
Oxygen is only required above 18,000 ft.
18,000 is regulation for PASSENGERS, not crew minimum.

Why

even at modest altitudes, hypoxia degrades night vision before any cognitive symptoms appear, because the rod cells are highly sensitive to hypoxia. Regulatory: 14 CFR 91.211 requires O2 for flight crew above 12,500 ft (after 30 min) and at all times above 14,000 ft. PERSONAL minimum at night: many CFIs recommend supplemental O2 above 5,000 ft because rod cells (low-light vision) are very oxygen-sensitive. Night vision degrades 5-10% per 1,000 ft above 5,000 due to hypoxia, even before any cognitive impairment.

FAA source: AIM 8-1-2, effects of altitude; 14 CFR §91.211 for legal supplemental oxygen requirementsbrowse the reference library →

Covered in Supplemental · I — Preflight Preparation — 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.