Under Part 107, what is the maximum altitude for standard sUAS operations without a waiver?

Why →Under 14 CFR § 107.51(b), the maximum altitude is 400 feet AGL, or, when operating within a 400-foot radius of a structure, 400 feet above the structure's immediate uppermost limit. This exception allows inspection of tall towers, buildings, and bridges without a waiver for each flight.

The trap →The 400-foot limit is AGL (above ground level), not MSL. MSL altitude would vary with terrain and is not the regulatory measure. The structure exception is important: near a 200-foot tower, the effective ceiling is 600 feet AGL.

Field note →The structure exception is widely used for cell tower and wind turbine inspections. The drone can legally fly above 400 feet AGL as long as it's within 400 feet of the tower. Know this exception. It appears on the knowledge test.