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Tales from the DAR Side

Locating the required EXPERIMENTAL lettering and the passenger warning placard

Joe Norris

We’ve talked about the identification plate and the registration marks, but there are other markings that are required as well. One of the most obvious ones is the “EXPERIMENTAL” marking near the entrance. The specific requirement is called out in 14 CFR 45.23(b), which states:

“When marks include only the Roman capital letter ‘N’ and the registration number is displayed on limited, restricted or light-sport category aircraft or experimental or provisionally certificated aircraft, the operator must also display on that aircraft near each entrance to the cabin, cockpit, or pilot station, in letters not less than 2 inches nor more than 6 inches high, the words ‘limited,’ ‘restricted,’ ‘light-sport,’ ‘experimental,’ or ‘provisional,’ as applicable.”

This regulation has some general guidance and some specifics. For example, it gives you specific size for the lettering – not less than 2 inches nor more than 6 inches high. Now, I’ve never seen anyone with the desire to put “experimental” on the aircraft in greater than 6-inch letters, but if he did harbor such wishes he would be out of luck. The fact is, virtually everyone sticks with the 2-inch minimum size. Note that there are no other requirements called out. Unlike registration marks, there are no requirements for font, spacing, or thickness. The builder is free to use whatever style of lettering he might desire, so long as the letters (all the letters, not just the “e”) are at least 2 inches tall.


Another thing to note is that seemingly cryptic mention of registration marks that include “only the Roman capital letter ‘N’…” The answer to that little mystery is found in our friend §45.22, the “special rules” that were talked about in our N number discussion. Contained in that regulation is the following relevant verbiage stating that the N must be followed by:

“(i) The U.S. registration number of the aircraft; or

(ii) The symbol appropriate to the airworthiness certificate of the aircraft (‘C,’ standard; ‘R,’ restricted; ‘L,’ limited; or ‘X,’ experimental) followed by the U.S. registration number of the aircraft”

So, for those homebuilts that are included in the special rules allowed by §45.22, you could display the N number as “NX” followed by the registration mark. When displaying “NX” in the registration mark, you aren’t required to display “experimental” near each entrance.


Those are the specifics. But I mentioned some generalities as well. Just what constitutes “near each entrance”? This is where the discussion gets more interesting (and sometimes more heated). The fact is, there’s no specific guidance on this point, so each builder and inspector will have his own opinion on what’s acceptable.

The first thing to note is the fact there’s no requirement that the “experimental” marking be on the outside of the aircraft. It just says “near” each entrance. This opens up some very appealing options for builders. Many times, it’s perfectly acceptable to put “experimental” inside the aircraft and still be near the entrance.

A very common example can be found in Cub replicas, where they put “experimental” on the inside of the lower portion of the clamshell door. It’s visible when the door is open for entry, but if the door is closed, you don’t see it unless you’re sitting in the airplane (at which time it appears upside down on the inside of the lower door). Another common example of this is found in side-by-side RV series airplanes, and also on the Sonex as pictured below, where “experimental” can be placed on the panel behind the seats. It’s visible as you enter the aircraft from either side, even though it’s on the inside of the airplane.


Even if you put “experimental” on the outside, you may only need it on one side of the aircraft. If you only enter from, say, the left side of the aircraft and there’s no way to enter from the right side, you only need to put “experimental” on the left side near the entrance. However, if you have doors on both sides and may enter from either side, you’ll need to mark “experimental” on both sides near each entrance.

Passenger Warning
The other common marking I want to discuss in this month’s column is the “passenger warning” placard. This item is required in any amateur-built aircraft that has more than one seat. There’s no specific font or size called out for this placard, so you’re free to decide how to display the verbiage:


You won’t find this verbiage called out in the regulations. It’s found in FAA Order 8130.2, in the section about amateur-built operating limitations. The requirement does have a basis in regulation, though. 14 CFR 91.319(d)(1) requires the operator of an experimental aircraft to notify each passenger of the experimental nature of the aircraft, and this “passenger warning” placard takes care of that requirement.


Over the course of the last few issues, we’ve covered quite a bit of info on identifying and marking your homebuilt, but we still have more to talk about! Next month, I’ll continue the discussion with general info on control, switch, and instrument markings.


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