What is the floor of Class A airspace?
A12,500 feet MSL
B18,000 feet MSL✓
C10,000 feet MSL
Why →Class A airspace begins at 18,000 feet MSL and extends to FL600 (60,000 feet MSL). sUAS operations under Part 107 are subject to a 400 ft AGL ceiling, so Class A airspace is generally not a practical concern, but pilots must know the boundaries.
The trap →10,000 ft is a common speed limit threshold in manned aviation; 12,500 ft is where some transponder requirements kick in. Neither is the Class A floor.
Field note →You'll never reach Class A under Part 107's 400 ft AGL limit, but the exam tests whether you know where all the airspace classes live.
SOURCE → FAA Aeronautical Information Manual (AIM) Chapter 3CHECKED JUL 16ACS II.A.K1MED