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Chart your course

Need answers? Check out this guide for chart meanings

Q: I always thought that military training routes (MTR) were identified by either three or four numbers, depending on altitude. How can you explain IR20, IR50, IR51, and IR56 on the Miami sectional?

A: Good question. For review, military training routes at or below 1,500 feet agl (with no segment above 1,500 feet) are identified by four-digit numbers such as VR1007. These routes are generally developed for flight under visual flight rules (VFR). Routes above 1,500 feet agl (some segments of these routes may be below 1,500 feet) are identified by three or fewer digit numbers such as IR21 or IR302. These routes are developed for flight under instrument flight rules (IFR).

Routes numbered from 1 to 99 are actually 001 to 099, and are shown as IR1 or IR99, eliminating the initial zeros. MTRs can vary in width from four to 16 miles; however, detailed width information is not depicted on the navigation charts.

Most important is the real lesson to be learned here: The AOPA Pilot Information Center regularly receives calls from members who see an unfamiliar symbol on a navigation chart and, upon reviewing the chart legend, still cannot find the answer. My go-to resource for all these questions is the free FAA book Aeronautical Chart Users’ Guide, which can be downloaded from

This guide describes every single mark, line, symbol, and detail you will find on sectional charts, IFR en route charts, and instrument approach procedures. When you cannot find what you are looking for elsewhere, open this guide and you will absolutely find the answer. If it’s on a chart, it’s in this guide. Use it to your advantage.

Craig Brown is a senior aviation technical specialist in the AOPA Pilot Information Center. [email protected]

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