Making Sense of Small Airplane Certification Rules

The C-47 (military version of the DC-3) straddles the 12,500-pound line much like the King Air 200. Both are said to be able to safely carry more than their civilian certified weights.

The FAA rules that govern certification of “small” airplanes are a mess. Finally, the FAA has begun the lengthy process of trying to change FAR Part 23 so that both the makers of basic piston singles, as well as those designing advanced turbine powered airplanes, can know what to expect when seeking certification.

Not long after the end of World War II, the fundamental airplane certification standards were established by the CAB, the forerunner of the FAA. Rules in CAR 3 set certification standards for airplanes with a maximum takeoff weight of 12,500 pounds or less, while CAR 4 rules governed the certification of heavier airplanes. CAR 3 was for “small” airplanes while CAR 4 covered “large” or “transport” airplanes. 

Why the certification standards were divided at 12,500 pounds takeoff weight is unclear. As far as I know, there was no landmark airplane at that weight that would have provided a historic reason to pick 12,500. I’ve often heard that the DC-3, which was certified before CAR 3 and 4 were established, had something to do with the weight break, but the DC-3 can weigh double the 12,500 pounds so that makes no sense.

Whatever the reason for picking 12,500 pounds as the point where small airplanes become large, that weight limit stuck as the rules were rewritten into FAR Part 23 and FAR Part 25 in the 1970s. In general, an airplane in the Part 25 category must have enough redundancy of thrust and systems that it can continue on to a safe landing at an airport after critical failures. Airplanes in Part 23 do not have the same restrictions.

These aircraft are light enough to park on the grass but not as heavy as other aircraft in its certification class, which are currently driving the standards. Piston single manufacturers are hoping that the FAA will soon give the “heavy metals” their own certification standard. Photo by: Jim Koepnick/EAA

The certification standards were working reasonably well until it became feasible to build light business jets. The earliest civil jets all weighed more than 12,500 pounds maximum, so they naturally went into the CAR 4 or Part 25 transport category. But then Bill Lear created the Learjet 23 and purposefully set the max weight right at 12,500 pounds to remain in the light airplane category.

Lear hoped for a simplified certification standard, but more importantly wanted approval for single-pilot operation of his little jet. It was an automatic that airplanes weighing more than 12,500 pounds needed a crew of at least two pilots. The Learjet 23 did receive certification under the small airplane rules but at the last minute the FAA imposed a special condition requiring two pilots. The follow on Model 24 Learjet, which looks nearly identical to the 23, was recertified in the transport category.

Cessna’s original Citation 500 weighed much less than 12,500 pounds but, because it was a jet, was lumped into Part 25 and also required two pilots. A few years later Cessna build the Citation I-SP that was certified for single-pilot flight because it was a Part 23 “small” airplane, even though the only changes were a transponder ident button on the yoke and requirement for the pilot to use a headset with a boom mic.

The Gulfstream G650 weighs almost 100,000 pounds, but many aircraft that are far lighter must conform to the same complex certification standards. Courtesy: Gulfstream

So now jets were in Part 23 if they weighed less than 12,500 pounds. But what if a regional turboprop airliner needed to grow to more than 12,500 but couldn’t meet all of the rules of Part 25? The FAA solution was the Commuter category of Part 23 that allowed the Beech 1900, Merlin Metro, and several other airplanes to weigh more than 12,500 pounds.

At first the Commuter category was reserved only for airplanes already certified and in production, not new development projects. New business jets such as the Beech Premier and Citation CJ2 were capped at 12,500 pounds to remain in Part 23. But the weight limit didn’t hold and now several new business jets weighing more than the 12,500-pound standard are certified under Part 23 in the Commuter category.

To certify high-performance jets such as the Citation CJ4 or the Embraer Phenom 300 under Part 23 the FAA creates a huge number of special conditions the airplanes must meet. For example, the jets must meet the same engine failure minimum climb takeoff profile of the large jets, but that is imposed as a special condition on those airplanes and not extended to all airplanes in Part 23.

But the special conditions and the rule tweaking necessary to fit high-performance jets into a certification standard originally designed for piston singles and twins have a way of creeping down into all Part 23 certification projects. It’s really tough for the same people to take the same Part 23 rule and apply it logically to a basic piston single and to a jet designed to cruise at 45,000 feet and 450 knots. What has been happening is that the complexity of the certification process that is necessary for jets has found its way down into the certification of piston airplanes.

I’m not predicting this is the path the FAA’s review of FAR 23 will follow, but I would like to see a third set of rules developed. I think FAR 23 should be overhauled and aimed at piston airplanes and light turboprops, which would satisfy the rule’s original mission. Then there should be a new category created to certify most business jets weighing up to 50,000 pounds or so. And then Part 25 can be the rule for true transport airplanes that are many times larger and more complex than the typical business jet.

The HondaJet is one of those light jets that weighs far less than 12,500 pounds and is aiming for certification Part 23, which among other things allows it to be operated single pilot. Photo by: Brett W. Bock

The issue is that a 20,000-pound business jet is a very different type of airplane flying a very different mission than an 800,000-pound true transport jet, but they are lumped under the same Part 25 rules. If there were three certification rule categories then they could be appropriate for pistons, business jets, and true transport airplanes.

Who knows what will come from the FAA’s rewrite of Part 23, but if they don’t kick the business jets out of the top end of the rule, there is no hope for simplifying the certification standards for basic pistons at the bottom end of the rule.

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12 Responses to Making Sense of Small Airplane Certification Rules

  1. With held by request says:

    It is not just the regulations that have gone awry but the entire certification process is a mess. The FAA was so over-burdened trying to support OEM certification projects that a new process, the ODA (Organization Delegation Authority) was developed so allow FAA approved OEM representatives to act on behalf of the FAA certification authorities. This new ODA process has relieved part of the FAA’s burden. But rather than the FAA becoming faster and more efficient, this relief has allowed the FAA, fueled by NTSB authoritarianism, to become more meddlesome and micro-managing of every item in the certification process. The OEM is now more constrained than ever by regulation and bureaucratic red-tape so it is a wonder that any new airframes get certified at all. Unfortunately, for the flying public- owners, pilots, and passengers alike – this means more cost of acquisition, operation, and more time spent in the maintenance cycle to further deal with the added bureaucracy imbedded through the certification requirements. Sure the regualtions need a re-write, but what really needs fixed is the FAA and the bureaucratic system behind the regs.

  2. Mac,
    I remember an excellent article you wrote in Flying about the Eclipse 500 certification process and how the FAA waived all sorts of regulations (including takeoff minimums for turbine engines, if I recall correctly). I think we give the FAA credit for recognizing the technology and business needs have outpaced the regulations, but how does any new manufacturer figure out what the rules are?

    Also, while I am a big supporter of the self-certification ideas of the LSAs, I’m not convinced all these airplanes reach the same safety standards Part 23 planes do. I have flown quite a few LSAs (and some are terrific planes) but I would say there are gaps.


  3. Mac says:

    Hi Andrew,

    You’re right about new manufacturers–or even very experienced ones–not knowing for sure how the certification standards will be applied to any given airplane. Making certification more predictable is one of the objectives of the FAR Part 23 review.

    One would think that the certification rules are very specific, but they are not. FAR Part 23 and 25 are really pretty short with surprisingly little detail. I would compare the certification rules to the U.S. Constitution that is a framework but courts over the years build laws on the framework. The same thing happens in certification. When one FAA certification office–and there are many–approves something, than other makers point to that approval and demand the same.

    That was one of the surprises with the Eclipse. Before Eclipse multi-engine jets approved in FAR 23, such as the Cessna CJ, Beech Premier and others–all met the minimum engine failure takeoff performance requirements of larger jets. But the FAA ruled that because the Eclipse weighs less than 6,000 pounds maximum it did not have to meet the engine failure climb requirements. Propeller airplanes that weigh less than 6,000 pounds do not have an engine-out climb requirement so that concept was passed on to the Eclipse even though jets had always been held to a higher standard than propeller airplanes. There was no change in FAR 23 to do that, just a new application of the rule.

    Would the FAA approve another very light jet weighing less than 6,000 pounds that couldn’t continue the takeoff after engine failure? I don’t know, but I wouldn’t want to bet my company on it. Those kinds of questions add cost and delay to any program and I hope the FAA resolves most of them with a new Part 23, or maybe even an entirely new rule to separate light jets from pistons.

    And you’re right that the LSA rule is not the same as FAR 23. Even if an LSA manufacturer follows that rule to the letter it is not the same as Part 23, or even the old CAR 3.


    Mac Mc

  4. D Dever says:

    While I agree that the cerification process needs to be overhauled. I think GA’s problem goes much deeper. A Cessna 172 sold for $8,700 in 1956. Today it sells for 269k – 300k. It should sell for about 75k based on the CPI. There is no certification process in this price. Couple that with the fact that people make less today (in real dollars and you have a real problem. I do not have an answer. I don’t think anyone does, but revamping the cert. process is a start.

  5. Timothy Spear says:

    In the recertification for part 23; using power plant, weight or any other measure will eventually encourage the same mess we are in now with Cessna and other manufactures trying to squeeze a plane in Part 23 which really should be in Part 25. The best way to divide would be define what the purpose of the airplane and how it is to be utilized. I would actually make it be multiple categories with additional restrictions based on potential impact of an accident.
    I would break it down in the following way:
    1. Personal Category: Owner flown, flight school, wet/dry rental to individual pilot. Max passenger capacity 6.
    2. Small Charter: Adds part 135 requirements to the personal Category (twin alternators, additional batteries…). Still limited to passengers 6.
    3. Small Cargo: Adds part 135 requirements to the personal Category (twin alternators, additional batteries…). Limited to single engine aircraft (e.g. Cessna Caravan).
    4. Small Transport: Current Part 23/25 requirements for any airframe/power plant with twin engines and able to carry more 6 and less then 20.
    5. LargeTransport: Anything bigger than a small transport.

    The idea is that each level increases the safety and redundancy requirements for progressive levels of safety. In addition by adding stall/landing speeds and turning radius requirements to each tier. If you fail to meet it you are promoted to the next level of certification requirements with all the attendant additional requirements.


  6. John Patson says:

    Call me a cynic but I do not believe prices will go down, even if the certification process is made a simple as tying a shoelace.
    It would be nice if the certification process was more coherent but give it to a few lawyers in court and we will soon be back to square one.
    As for random weights, one you have not mentioned is the famous 1,999 kilogram MTOW rule in Europe. One kilo heavier and you pay at least €80 a day for the privilege of IFR and, in some countries, for VFR too.
    How it was decided is a mystery.

  7. Thomas Boyle says:


    I’m fairly sure that several Part 23 airplanes don’t meet the safety standards you attribute to Part 23 either. There are Part 23 airplanes with notoriously vicious stalls, high control forces, inadequate control authority at forward CG, highly-restricted pilot visibility, fuel selectors on the floor (dangerous in IMC), seats that slip in their tracks, poor rates of climb, minimal power-off glide capability, dangerous single-engine characteristics, no shoulder harnesses… and even suspiciously high rates of in-flight structural failures. One well-known example has 13 fuel sampling points, which rather makes me wonder about the fuel system design.

    Part 23 is an extremely conservative and, by virtue of its open-ended-ness, expensive certification process, and generally speaking the planes that get through it are fairly safe – but let’s not get carried away: it’s hardly a Gold Standard.

  8. Pete Kuhns says:

    This may seem out of left field, but I wonder if this review of part 23 will lead to a fresh, overdue clean-sheet recategorization for all single-engine aircraft.

    An overhaul that may include (finally) placing all single-engine planes under xxxx kilograms/hp into the S-LSA category or some variant…

  9. Nick Miller says:

    Mac, Good Article, Old Topic. We did this back in the ’90s. The FAA met with Industry groups including the EAA, with the result that in 1997, AC 23-15 “Small Airplane Certification Compliance Program” (at the time for the typical four passenger single engine, 3000 lb airplane – as I recall), was issued. In 2003 AC 23-15A included up to 6,000 lb airplanes, up to 200 HP and two of three listed complex features including retracable gear, flaps, or controllable pitch prop (but not all three), not to mention other limitations. At the time, everyone agreed that Part 23 had become difficult to interpert by industry and the FAA to the point where different Aircraft Certification Offices (ACOs) required vastly different requirements for the same regs for small airplanes. It should be interesting to see what comes out of this, if anything.

  10. Withhold please says:

    Such fine aircraft as the Pilatus PC-12, TBM 700 (et al), Piper Meridian and Extra 500 have very high performance, but because they are singles, they will never continue a take-off after engine failure. Single engine fanjets such as the D-Jet and Piper Altaire will have simpler propulsion systems, but Canada and EASA consider them Transport Category, whereas the turbo-props are not, greatly distorting safety, operation, and market decisions.
    “Would the FAA approve another very light jet weighing less than 6,000 pounds that couldn’t continue the takeoff after engine failure?” FAA will not outlaw all single-engine aircraft, and there is no logic in selectively restricting VLJ .

  11. Steve Skinner says:

    I’m wondering where to find the information you found on CAR Part 3 and 4. I’m doing a study on fire extinguishers and first aid kits for small aircraft. Which airplanes are fire extinguishers and first aid kits required equipment? Your comment about CAR3 being for light aircraft and CAR 4 for heavier aircraft goes against what I’m finding. A Taylorcraft BC12-D (pretty light) is certificated under CAR4. A Piper PA-11 (pretty light) is certificated under CAR4a. Look up the TCDSs for these small light aircraft and you’ll see what I’m talking about. Let me know what you find.

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