On an instrument approach chart, which kind of altitude indicates the need to maintain a specific altitude?

• A. A singular underscore/overscore altitude.
• B. A double underscore altitude.
• C. An altitude to be avoided.
• D. An altitude to be ignored.

Answer: (A)

Maintaining a specific altitude on an instrument approach is communicated by an altitude shown with a single line (underscore) over or under the numbers. That formatting tells you to hold that exact altitude on the segment, leveling off there and staying at that altitude until you reach the next specified instruction or fix.

This symbol is used specifically to enforce a constant altitude for obstacle clearance and proper sequencing of the approach. Other notations aren’t used to indicate “maintain this altitude” on the approach segments, so they don’t convey the same instruction. If you see a single-line altitude, plan to stay at that level as published until you’re cleared to the next altitude.