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Q&A

Stumped trying to decipher an FAA reg? Need help with a technical project? Drop an e-mail to Experimenter@eaa.org, and help will be on its way.

Questions About Replicas

Q: In a previous Q&A you talked about special rules for marking the N number on certain homebuilts. I have a few follow-up questions. First, you mentioned that a homebuilt aircraft that is at least 30 years old, or a replica of an aircraft that is at least 30 years old, can use 2 inch N numbers and can use “NX” instead of just “N.” Is the 30-year time frame a rolling one, or is it 30 years from a particular date?

A: The 30 years is a rolling target. This year an aircraft built in 1979 or earlier would be eligible to display the 2-inch N numbers. Next year, aircraft built in 1980 or before will be eligible, and so on.

Q: How does the FAA define “replica”? Does the aircraft have to be identical in every detail, or just have to basically look like the aircraft being replicated?

A: The FAA considers a replica to be an aircraft that has the “same external configuration.” So it must have the same look as the original, including same length, span, etc. (Scaled-down replicas do not count.) But it does not have to be an exact part-for-part replica in structure or equipment. There would be no problem with updated controls, different horsepower, etc. So long as it has the “same external configuration” your aircraft will qualify as a replica.

Q: Are there any restrictions as far as the old 1930s-style large N numbers on the top and bottom of the wings on a replica from that time period?

A: Wing numbers are no problem. They are not addressed in the current regulations at all, so they don’t “count” toward the display of the N number. In other words, you still need the number on the tail or fuselage in order to be legal. But you are perfectly welcome to display the big numbers on the wings if you want.

Q: I am building a homebuilt that when completed will meet the definition of a light-sport aircraft. Some of my fellow EAA chapter members have suggested that I may want to register and certificate the aircraft as an experimental light-sport aircraft (E-LSA) instead of experimental amateur-built. Can I do this? And if so, what would be the benefit?

A: At this time there is no regulation that would allow you to certificate your aircraft as E-LSA. Under current regulations the only aircraft that are eligible for certification as E-LSA are specific kits offered by manufacturers that have certificated at least one aircraft in the light-sport aircraft category (commonly referred to as “special LSA” or “S-LSA”). Manufacturers are allowed to market kits based on their S-LSA prototypes for certification as E-LSA. The only other way to certificate an E-LSA today is to convert an aircraft that was originally certificated as S-LSA.

During the period when the FAA was allowing two-seat ultralight trainers and other “fat ultralights” to be converted to E-LSA, the regulation actually was broad enough to allow any aircraft that had not been previously certificated to be brought into the E-LSA category, so some builders of LSA-compliant aircraft (such as the Sonex and some Zenith 601 models) decided to certificate their aircraft as E-LSA rather than amateur-built. They did this thinking that it would be a selling point down the road because future owners would be eligible for a repairman certificate for the aircraft under the LSA repairman regulations.

Unfortunately this opportunity ended on January 31, 2008, when the “grandfather” period for ultralight trainers closed. There is a limited opportunity for aircraft that had been registered as E-LSA before that date to be inspected and certificated through January 31, 2010, by using an EAA exemption. But since your aircraft was not registered as E-LSA before the January 2008 deadline you are not able to certificate it as E-LSA. You’ll have to certificate it as amateur-built.

Remember that a sport pilot is allowed to fly any aircraft that meets the LSA definition, regardless of what type of airworthiness certificate it holds, so you’ll still be able to fly your aircraft under sport pilot rules even though it’s certificated as amateur-built. The only difference is that a future owner of your aircraft will not be eligible for a repairman certificate authorizing him or her to perform the condition inspection each year. You, as the original primary builder of the aircraft, are the only person eligible for the repairman certificate for your amateur-built aircraft.

Q: I’ve seen some homebuilts with N numbers that start with “NX” and some vintage aircraft with N numbers that start with “NC.” How does one go about getting an NX or NC number?

A: Actually, you will not receive a number starting with “NX” or “NC” from the FAA. Aircraft registration numbers in the United States all start with “N,” which is the letter designating a U.S. registration. The aircraft registration certificate, airworthiness certificate, and all other paperwork will indicate that the aircraft’s registration number is “N****.” However, some aircraft are allowed by the regulations to display “NX” or “NC” (or other certification designators) when marking the registration number on the aircraft.

Part 45 of the regulations covers aircraft identification and registration marking. In this case, the applicable regulation is § 45.22, titled “Exhibition, antique, and other aircraft: Special rules.” Section (b) of this regulation allows an airplane that is at least 30 years old or a full-size replica of an airplane at least 30 years old to use numbers at least 2 inches in height. (Normally the minimum height would be 3 inches on most experimental aircraft and 12 inches for a new production aircraft.)

Section (b)(1)(ii) of § 45.22 allows “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.” The appropriate symbol for an amateur-built aircraft is “X” because it holds an experimental airworthiness certificate, and a vintage aircraft would use “C” because it holds a standard (or “civil” in the vintage vernacular) airworthiness certificate.

Thus, due to the allowances of § 45.22, a homebuilt aircraft of a design that is more than 30 years old, or a civil aircraft that is itself more than 30 years old, is allowed to display the “X” or “C” as a part of the registration mark (e.g., “NX*****”) rather than just showing the “N” followed by the number.

An added benefit of this regulation for homebuilts (and other aircraft with special airworthiness certificates) can be found in § 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 requires the “EXPERIMENTAL” placard to be placed on the side of most homebuilt and other experimental aircraft. But note that the regulation says that this is required when the aircraft displays only the N in the registration mark. So experimental aircraft that are allowed by § 45.22 to display the “NX” registration mark do not have to display “EXPERIMENTAL” when they use “NX” in the registration mark. If they only use “N” to display the registration mark, they must display the “EXPERIMENTAL” placard as well.

Q. I’ve seen some amateur-built aircraft with very detailed maintenance records, and some that are much less complete. Aren’t there regulations that govern recording of aircraft maintenance? What is required to be in the aircraft logs?

A. The regulations regarding aircraft maintenance and the recording of same are found in FAR Part 43. However, the first section of Part 43 talks about the applicability of the part. Taking a look at Part 43.1(b) we find the following verbiage:

This part does not apply to any aircraft for which the FAA has issued an experimental certificate, unless the FAA has previously issued a different kind of airworthiness certificate for that aircraft.

An amateur-built aircraft receives an experimental airworthiness certificate at the very beginning, so this section tells us that the regulations found in Part 43 do not apply. That being the case, none of the record-keeping requirements of Part 43 are applicable. The only entries that are strictly required are those found in the aircraft’s operating limitations, issued by the FAA as a part of its airworthiness certificate. Mainly this would be condition inspections each year and the flight test sign-off, along with transponder tests (if a transponder is installed) and pitot/static tests if the aircraft is to be flown under instrument flight rules. There is no strict guidance on what to put (or what not to put) in an amateur-built aircraft logbook other than what is required by the aircraft’s operating limitations.

At the time of the airworthiness inspection by the FAA, the owner of the aircraft, whether or not he/she is the builder, will be required to record that a condition inspection has been completed on the aircraft prior to the FAA inspection. This initial condition inspection is recorded using the same language as later condition inspections, as follows:

I certify that this aircraft has been inspected on [insert date] in accordance with the scope and detail of Appendix D to Part 43, and was found to be in a condition for safe operation. [signature], Owner

The FAA also likes to see at least one hour of ground testing recorded in the aircraft records. This is not a strict regulatory requirement, but is very common among airworthiness inspectors.

The other requirement is for the flight testing to be properly recorded. The aircraft’s operating limitations will contain the appropriate language to use for closing out the flight-test period, as shown here:

I certify that the prescribed flight test hours have been completed and the aircraft is controllable throughout its normal range of speeds and throughout all maneuvers to be executed, has no hazardous operating characteristics or design features, and is safe for operation. The following aircraft operating data has been demonstrated during the flight testing: speeds VSO ______, VX ______, and VY ______, and the weight ______ and CG location ______ at which they were obtained. [Aircraft total time], [signature], [type of pilot certificate and certificate number]

Other than this, the annual condition inspections, and documentation of major changes as directed by the aircraft’s operating limitations, there isn’t any regulatory requirement to log anything! Of course EAA recommends a “best practice” of proper logging of all maintenance in accordance with Part 43 even though it’s not strictly required. This not only promotes safety by having a record of what has been done to the aircraft, but also increases the value of the aircraft at the time of sale.

Q. I’m filling out registration papers for the FAA. The “Affidavit of Ownership” asks for the “type of engine installed (reciprocating, turboprop, etc.).” I’m installing a Mazda rotary engine, which is not reciprocating and certainly not turboprop or jet. What is the proper answer? Does the FAA recognize rotary as its own class, or would it be considered “reciprocating” for this purpose, as it seems to be with LSA?

A. The FAA does not recognize rotary (Wankel) engines as a separate type. Rotary engines are lumped in with reciprocating engines for the purpose of certificating amateur-built or light-sport aircraft (LSA). If your aircraft incorporates a rotary engine, choose “reciprocating” on all the FAA forms.

It would probably be more appropriate for the FAA to use the terms “turbine” and “non-turbine” on these forms, since this is the issue it is driving at. The operating limitations for an experimental aircraft that incorporates a turbine powerplant are different than for an aircraft that incorporates a non-turbine engine. If your engine is non-turbine, choose “reciprocating” regardless of whether it’s a piston or a rotary engine.

Q: I see the torque values in 14 CFR 43.13 for tubing fittings. The only way I can see to torque a tubing fitting is to put a crowfoot on the torque wrench. Wouldn’t this offset the center of rotation and give an inaccurate reading? If so, how would you do it?

A. You’re right, you do have to adjust the setting of your torque wrench when you use an adapter such as a crowfoot. To calculate the setting, you need to do a little math. First, measure the length of your torque wrench from the center of the square drive to the center of the handle. Then measure the length of your extension from the center of the torque wrench’s square drive to the center of the point where the nut or fitting will be in the crowfoot or box end. Now we’re ready to do the math.

Here’s the formula: Length of torque wrench multiplied by desired torque, divided by length of wrench plus length of extension, equals torque setting.

Let’s say your torque wrench is 18 inches long from the center of the square drive to the center of the handle. Your extension is 2 inches from the center of the square drive to the center of the wrench head. You’re going to be tightening a -6 fitting on a 3/8 inch aluminum line, so you’re desired torque is 110 to 130 pound inches (we’ll call it 120 pound inches). Multiply the standard length of your wrench by your desired torque, which in this case is 18 times 120, or 2,160. Now add the length of your wrench to the length of your extension, which in this case is 18 plus 2 for a sum of 20. Now simply divide the answer from your first calculation by the answer from your second calculation, in this case 2,160 divided by 20. The answer to this calculation is the setting you’ll use for your torque wrench with the 2-inch extension - 108 pound inches!

Q. I am planning on changing the propeller on my homebuilt airplane. What does the FAA require with respect to forms, notification, and procedures to change props?

A. Changing the propeller on a homebuilt aircraft is considered a “major change” by the FAA (except when the change is a direct replacement of the same make, model, and pitch). To document a major change on a homebuilt, you need to look at the aircraft’s operating limitations. These operating limitations were issued by the FAA as a part of the aircraft’s airworthiness certificate and must be carried in the aircraft at all times.

Find the paragraph in the operating limitations that deals with major changes. This paragraph usually starts out with “After incorporating a major change…” and goes on to describe the procedure you need to follow. This procedure has changed and evolved over time, so you need to check your individual aircraft’s operating limitations. The procedure will probably require contacting your local FAA flight standards district office (FSDO) for approval of the area where you want to test your major change, but there are variations. Some older operating limitations even require that the aircraft be re-certificated, while other operating limitations don’t require contacting the FAA at all! You need to check your particular set of operating limitations and follow the procedure outlined therein.

If you find that you have lost your operating limitations, you’ll need to get a replacement copy. Operating limitations are a part of the aircraft’s permanent record, so you can get a copy from the FAA Aircraft Registration Branch in Oklahoma City, Oklahoma. You can call there toll-free at 866-762-9434. Give the N number, builder name, and serial number of your aircraft and the FAA will fax or mail you a copy of the operating limitations.

Q: I hold the repairman certificate for my RV8. I’ve been told that my logbook entries should include a phrase similar to, “I deem this aircraft safe to return to service,” for entries other than the annual condition inspection entry. I was told that it was a legal matter to protect myself should a mishap occur. Having it state that the aircraft “was safe” in the entry, is the issue.

Please clarify. If this is true, what can be done about the earlier entries that don't include this phrase?

A: Actually, the verbiage you're supposed to use to enter your condition inspections into the aircraft records is found right in your aircraft's operating limitations. The entry that's called out in the operating limitations will contain the phrase "condition for safe operation." Check your operating limitations to get the exact and complete entry. Also, remember that your operating limitations are a part of the airworthiness certificate and must be carried in the aircraft at all times. So when you pull them out to check the condition inspection entry, don't forget to put them back in the airplane.

Since every new condition inspection supersedes the previous one, you don't need to go back and change the old entries. Just make the appropriate entry now and go forward from there.

Q: I’m working with flared tubing and AN fittings. How do I properly tighten the AN-818 coupling when connecting a flare connection? I figure I’m currently halfway between finger-tight and stripping the threads (based on thread-stripping experience). Is there any official guidance on this subject?

A: Guidance for this and other related questions can be found in FAA Advisory Circular (AC) 43.13, Acceptable Methods, Techniques, and Practices - Aircraft Inspection and Repair. The current version is AC 43.13-1B. The info on tightening AN-818 fittings can be found in Table 9-2, on page 9-19 of the AC. Here’s the table:

Note that these tightening torques are in pound-inches (sometimes referred to as inch-pounds). There is a “rule of thumb” on these fittings that says to tighten the fitting to finger tight, then one quarter of a turn more, but using the tightening torques as shown on the table is the best method.

If you don’t have a copy of AC 43.13-1B, I strongly suggest you get one. This is truly the bible of aircraft maintenance and repair, and it includes guidance on all manner of aircraft construction and maintenance. Your FAA inspector would be pleased to see that you have a copy on hand when the time comes. It is the best $25 you can spend on your project. You can get your own copy by calling EAA membership services at 800-843-3612. Ask for catalog number F00191.

You can also find the AC online at www.FAA.gov. It’s a very large document presented in 14 separate PDF files. I find it easier to have the printed version right on my bench in the shop.

Q: I’ve just finished building my Pietenpol, which is an experimental amateur-built aircraft that meets the LSA definition. I’m ready to begin the phase-one flight testing. I’m a student pilot working toward my sport pilot certificate and I don’t hold a current medical. Is it legal for me to do the flight testing as a student pilot? Can a student pilot fly an experimental aircraft at all?

A: Let’s take the second part of your question first. There is no regulatory prohibition on a student pilot (sport pilot or otherwise) flying an experimental aircraft. Pilot requirements, privileges, and limitations are found in 14 CFR Part 61, and student pilot privileges and limitations are specifically found in subpart C. There is no specific limitation in that section prohibiting a student pilot from flying an aircraft with an experimental airworthiness certificate.

Now let’s look at the first part of your question regarding a student pilot (sport pilot or otherwise) flying an experimental aircraft during flight testing. Certification requirements for the pilot in command of an experimental aircraft are not found in the FAA regulations themselves but rather in the operating limitations of the individual aircraft. These operating limitations are issued by the FAA as a part of the aircraft’s airworthiness certificate and will vary depending on exactly what type of airworthiness certificate the aircraft holds. For an amateur-built aircraft such as your Pietenpol, the operating limitations will contain the following statement:

“The pilot in command of this aircraft must hold a pilot certificate or an authorized instructor’s logbook endorsement. The pilot in command must meet the requirements of § 61.31(e), (f), (g), (h), (i), and (j) as appropriate.”

Note that the pilot may hold a pilot certificate (which would include sport pilot) or an authorized instructor’s endorsement. This would open the door for a properly endorsed student pilot (including a sport pilot student) to fly the aircraft. The limitation makes no distinction between phase-one flight testing and phase-two normal operations. This limitation is in place for all operations. The limitation does go on to require any appropriate endorsements called out by 14 CFR 61.31(e) though (j). The most common of these endorsements are for tailwheel aircraft, high-performance aircraft, and complex aircraft. The only endorsement applicable to the Pietenpol would be the tailwheel endorsement, so the instructor would have to endorse the student appropriately before allowing him or her to solo a tailwheel aircraft as well as give the standard solo endorsement in order to be in compliance with this operating limitation.

Remember that, if the student seeks to solo an aircraft that does not meet the definition of a light-sport aircraft he/she would also need to hold a 3rd class FAA medical certificate.  This would be the case whether the aircraft holds a standard or special (such as experimental) airworthiness certificate.

The question you did not ask, but one I will answer anyway, is whether it is smart for a student pilot to perform the flight testing on an experimental aircraft. This is the most important question, and the answer is, no, it is not a good idea for a student pilot to perform flight testing on a new amateur-built aircraft.

The purpose of flight testing is to verify the aircraft’s handling characteristics and make sure it does not have any issues that would affect the safety of flight. Flight testing a new aircraft should be left to experienced pilots who are familiar with the normal handling characteristics of the aircraft being tested and are prepared to handle possible emergency situations that might arise. A student pilot does not have the background and experience to identify abnormal handling characteristics and may not be prepared to handle an emergency situation if one should present itself. So while it may be technically legal for a student pilot (sport pilot or otherwise) to fly an aircraft during the initial flight-test period, I strongly discourage this. Find an appropriate test pilot to perform the flight tests on the aircraft, then find a qualified instructor to check you out in the aircraft after it has been tested.

Q. I can’t find information on how much radius is permitted with a 1/8-inch cable for various diameters of pulleys. Do you know where I can look for this info? I want to have a 1/8-inch cable change direction by 90 degrees. How large should the diameter of the pulley be?

A. There seems to be very little specific info available on your question, so it took a bit of digging to find a published reference. But one has been found.

As you mentioned, there was nothing specific in AC 43.13 nor in any other readily available “handbook.” Furthermore, there was no specific mention in CAR 3, CAR 4, or 14 CFR Part 23 for standard category aircraft. The only ready reference I found was in Tony Bingelis’ book The Sportplane Builder. However, I knew Tony had to have received guidance from somewhere, so the search continued.

I finally found a document published in 1974 by the Defense Technical Information Center, a unit of the Department of Defense at Fort Belvoir, Virginia (www.DTIC.mil/dtic). Its studies indicate that a pulley diameter ratio of at least 20-to-1 (that is, the pulley diameter is at least 20 times the diameter of the cable) is desirable to provide maximum cable endurance. This would lead us to determine that the minimum pulley diameter for a 1/8-inch cable would be 2.5 inches.

That said, I have seen instances on many aircraft, including standard category types, where a slight deflection (45 degrees or less) is handled by smaller pulleys. However, for direction changes approaching 90 degrees, I would stick with the 20-to-1 formula. For direction changes approaching 180 degrees, you might consider going to an even larger pulley.

Hope this helps! Let us know if you have further questions.

- Joe Norris
EAA Homebuilding Community Manager