In class A airspace, minimum altitude separation is 1000 ft between which flight levels?

• A. FL180 FL290
• B. FL100 FL200
• C. FL290 FL410
• D. FL200 FL300

Answer: (A)

In Class A airspace, the vertical separation for IFR traffic is 1,000 feet between two aircraft on adjacent flight levels. Flight levels are spaced at 1,000-foot intervals starting at the base of Class A (which is FL180) and continuing upward to FL600. That means the separation is maintained between FL180 and FL190, then FL190 and FL200, and so on. The key idea is the separation applies to consecutive flight levels, not wide gaps like FL180 to FL290. So the correct understanding is that 1,000-foot separation exists between neighboring flight levels (e.g., FL180/FL190), rather than between a distant pair such as FL180 and FL290. The given options don’t illustrate adjacent levels, so the concept to focus on is adjacent flight levels with 1,000 feet between them.