Q. Hello! I’m wondering if you can give me some guidance on flight numbers. Chicago doesn’t seem to mention them, but flights appear to be capitalized when they follow the airline’s name from what I can see online—for example, Pan Am Flight 103 (the one in the Lockerbie bombing). So I’m thinking a flight should be, say, “flight 900” when used alone (as in “I took flight 900 to Geneva”), or Big Airline Flight 900 when it appears after an airline’s name. Does that sound about right to you? Many thanks!

A. In strict Chicago style, flight numbers would be lowercased—like room numbers, page numbers, and other such identifiers. Accordingly, we’d write “Pan Am flight 103” and, for subsequent mentions, “flight 103.” That’s the style Britannica follows in its article on the tragedy. According to this usage, “Pan Am” is a proper noun, whereas “flight 103” is not.

But you’re right that many sources capitalize flight numbers. If you’re going to go that route, however, you should still treat the airline name and flight number as separate terms, which would require a capital F even when the flight number is used alone: Pan Am Flight 103; Flight 103 (but the flight).