Unless otherwise specified, Federal Airways include that Class E airspace extending upward from

• A. 1,200 feet above the surface up to and including 17,999 feet MSL
• B. 700 feet above the surface up to 18,000 feet MSL
• C. Surface to 17,999 feet MSL
• D. 3,000 feet above the surface to 20,000 feet MSL

Answer: (A)

Federal airways are controlled-enroute corridors designated as Class E airspace that IFR traffic uses. Their vertical extent is from 1,200 feet above the surface up to, and including, 17,999 feet MSL. The upper limit stops just below 18,000 feet MSL because that is where Class A airspace begins. So, by default, these airways exist below Class A to provide a defined routing from the surface-area of vactors up into the upper airspace, unless a specific segment states a different floor or ceiling.