With certain exceptions, Class E airspace extends upward from either 700 feet or 1,200 feet AGL to but does not include

• A. 18,000 feet MSL
• B. 10,000 feet MSL
• C. 25,000 feet MSL
• D. 5,000 feet MSL

Answer: (A)

Class E airspace is the controlled airspace that starts at a designated base height (either 700 feet AGL or 1,200 feet AGL) and extends upward until it reaches the next higher class. The next higher class begins at 18,000 feet MSL, so Class E ends just short of that altitude. That boundary at 18,000 feet MSL is what marks the transition to Class A, which requires IFR clearance and specific equipment and procedures. So the correct upper limit is 18,000 feet MSL, because above that point you’re in Class A. The other altitudes listed do not represent the transition to Class A.