What does the A in a black triangle mean in aviation?

The black triangle with the A is used for two purposes. If it is followed by NA, then the procedure is Not Authorized to be used for filing purposes of an alternate. If the A symbol is not displayed, then the approach may be used as an alternate using the standard alternate minimums.



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If there is a problem on-board and the crew is unsure about the condition of the aircraft, the triangle indicates what window should be used to inspect flaps, slats or engines or look out for icing. This saves important time in case of an emergency, as the crew doesn't has to search the right window to look out.

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There are six classifications of airspace in the United States; A, B, C, D, E, and G. Class A is the most restrictive and Class G the least restrictive. They can be categorized as: Class A – 18,000 feet and higher above mean sea level (MSL). Class B – Airspace around the 40 most congested airports in the country.

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