Under 14 CFR § 107.51(b), a small unmanned aircraft may not fly higher than 400 feet above ground level unless —

Why: 14 CFR § 107.51(b) caps altitude at 400 feet AGL unless the aircraft is flown within a 400-foot radius of a structure and does not fly higher than 400 feet above that structure's immediate uppermost limit.

• Class G airspace does not exempt an operation from the 400-foot AGL limit; § 107.51(b)'s only stated exception is the structure-radius rule.
• Logged flight hours have no bearing on the altitude limit in § 107.51(b); this invents a requirement that does not exist in the rule.