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Regulatory question: Two tail position lights


Well-Known Member
Supporting Member
Feb 24, 2008
Kanab, UT
Hi folks, this is a regulatory question, in the form of "is there a document / clause / paragraph somewhere that would change my interpretation of the rules"?

23.1385 requires (para (c)) either one rear position light "as far aft as practicable" on the tail, or two rear position lights "on each wingtip." It is unclear if the "as far aft as practicable" clause applies to wingtip mounts as well, and AC 20-30B doesn't clear this up, because it's definition of "as far aft as practicable" in para 7a refers to "the rear position light", singular.

I am currently trying to decide between wing-mounted rear position lights for my design, and aft-mounted. The wing-mounted ones are well understood and would meet my needs, and are the default choice.

For an aft-mounted position light, "as far aft as possible" is about 8" short of the aft-most point, due to constraints on mounting surfaces. The obvious fix here, which would look quite good and would meet all the angular requirements of Part 23 and AC 20-30B, would be to have two aft position lights, separated by the ~6" width of the fuselage at this point, each covering a bit more than half the required viewing angle (there is some overlap directly behind the aircraft where both would be visible).

However, I can't find anything in the regulations that would actually permit this type of installation. The rules seem to be "one if by aft, two if by wing", with no allowance for dual aft-mounted.

Obviously I could just build this and ask for a variance, since it seems that dual aft lights meet the intent of the rule if not the letter, but I'd rather not design something where that kind of after-the-fact negotiation is needed, so… does anyone have a different reading of this than me? What's your interpretation? Two aft lights clearly banned, clearly permitted (why), or fuzzy?