How big must your N numbers be?

How big must your N numbers be?
Question: I have a question about
Experimental/Amateur-Built aircraft
and N numbers. What are the rules
for size, placement, ornamentation
and so on? I often see small N numbers on homebuilts but not as many
on certified aircraft. What’s up with
Answer: This is actually an easy one.
It’s all explained in the FARs. No judgment here.
FAR Part 45 covers identification and
registration marking. Unfortunately,
this part is either unread or misunderstood by many people. Basically it says
that the N numbers must be 12 inches
high, with some exceptions, and on
either side of the fuselage or vertical tail
surface. If the numbers are placed on the
fuselage, which most are, they must be
between the trailing edge of the wing
and the leading edge of the horizontal
stabilizer. Placement under the horizontal stabilizer is not acceptable, though
we have all seen this approach.
More specifically, FAR 45.21 is the
general paragraph that states the numbers must be permanent, have no ornamentation, be contrasting in color with
the background and be legible. FAR
45.22 covers exhibition, antique and
KITPLANES April 2009
other aircraft special rules. This is the
often overlooked paragraph 45.22(b),
which states that an Experimental/
Amateur-Built aircraft that has the same
external configuration as an aircraft
design built at least 30 years ago may
display at least 2-inch-high numbers.
This is the same paragraph, by the way,
that allows us to use an X following the
N instead of displaying the “Experimental” placard called for in 45.23(b).
For example, let’s say you have an
RV-3. Because the design is more than 30
years old, you may display the number as
“NX168TY” and the “Experimental”
placard is not required. The X in the
number denotes the Experimental category. This X is not indicated anywhere
else except on the aircraft. It is not listed
in any paperwork. It simply replaces the
“Experimental” placard.
FAR 45.29 gives the requirements
for marking height, width, thickness,
spacing and uniformity. This para-
For most aircraft, N numbers must be 12 inches high and placed on either side of the
fuselage or the vertical tail. With some exceptions, Experimental/Amateur-Built aircraft
can also use 3-inch-high numbers.
graph allows Exhibition, Experimental/
Amateur-Built and Experimental/Light
Sport Aircraft to use 3-inch numbers, as
long as the maximum cruising speed of
the aircraft does not exceed 180 knots
CAS. If the maximum cruising speed
does exceed 180 knots CAS, then we’re
back to the 12-inch requirement. Note
also that this is CAS, not true airspeed.
This paragraph is one of the most abused
of all the FARs. I dare say if you go to
any fly-in and walk the line, you will
find numerous violations to this rule.
Twelve-inch numbers are also
required on all aircraft when operated
in an ADIZ or DEWIZ as described in
Part 99. In this case the larger numbers
may to be temporary.
Many times when a DAR certificates
an aircraft, it is not painted. Yet I have
to require that the markings are there,
and they conform to the rules. That
does not mean that when it gets painted,
FAR Part 45 does not apply. The rules
are still the same. If you chose to ignore
Part 45, you are subject to a violation by
the FAA. For example, don’t arrive at a
fly-in with 3-inch N numbers and start
bragging that your airplane cruises at
250 knots, or take the opportunity of
the paint-shop visit by “hiding” the N
number under the tail. Where Precision Yields Performance
BPE has provided
the highest quality
engine work for
many of the world’s
most successful pilots.
• New Lycoming and Superior
Experimental Engines
• Introducing the Lancair Reno Edition
IO-550 and TSIO-550 series
• All Overhauls to Factory New Limits
• Experimental High Performance Modifications
• Verifiable Test Cell Data on Every Engine
• Prop Strike Inspections
Call Today
(918) 835-1089 •
The Independent Voice for Homebuilt Aviation
Please send your questions for DAR
Asberry to with
“Ask the DAR” in the subject line.
Looking Ahead to
the New FAA Rules
As this is written, in early January
2009, the FAA still had not reconvened the rulemaking committee as
its first step toward another shot at
revisions to the “51% Rule” Advisory
Circulars. When the next round
arrives, we’ll have our resident DAR
pore over the documents and give
you his no-nonsense interpretation
of what the changes could mean to
you, the builder. Stick with us.
Photos: Mel Asberry, Susan Brunner
KITPLANES April 2009