A remote pilot is inspecting a 380-foot communications tower. The pilot flies the drone to 30 feet above the top of the tower to photograph the antenna array. Is this flight legal under Part 107?
AYes; § 107.51(b) allows operations up to 400 feet above a structure's immediate uppermost limit, within a 400-foot lateral distance of the structure✓
BNo; the drone is above 400 feet AGL, which violates the altitude limit
CYes, only if the pilot holds a § 107.51 altitude waiver
Why →Section § 107.51(b) permits operations above the 400-foot AGL limit when the sUAS is within a 400-foot lateral distance of a structure and does not fly more than 400 feet above the structure's immediate uppermost limit. For a 380-foot tower, the drone may legally fly up to 780 feet AGL as long as it stays within 400 feet laterally of the tower.
The trap →Calling the flight illegal applies the 400-foot AGL limit as if it were the only altitude rule, missing the structure exception that is specifically designed to enable tower and tall-structure inspection.
Field note →This is the rule that makes drone tower inspection a real commercial category. Without it, most inspection work would require a waiver on every flight.
SOURCE → 14 CFR § 107.51(b)CHECKED JUL 16ACS II.B.K1MED