Bjorn’s Corner: The challenges of airliner development. Part 5. Developing to Cert rules

By Bjorn Fehrm, Henry Tam, and Andrew Telesca

May 28, 2021, ©. Leeham News: After an overview of different certification rules and discussions about why there are different rule sets, we now exemplify the rules by looking at specific aircraft projects and how the certification rules affect the design.

We start this week with the idea to certify a 9-seat mini-airliner like the Tecnam P2012 Traveller. It’s a recent development with US-based Cape Air as the launch customer.


Figure 1. Passengers boarding the 9-seat Tecnam P2012. Source: Tecnam.

Developing a Product Suitable for Operating Rules

There are many aviation startups exploring opportunities in the air taxi or commuter market these days.  Let’s examine some of the rules related to operations and product certification in this segment.

In the United States, commercial air transport operations are governed by either FAA 14 CFR Part 121 – Operating Requirements: Domestic, Flag and Supplemental Operations or Part 135 – Operating Requirements: Commuter and On Demand Operations and Rules Governing Persons on Board Such Aircraft. Examples of Part 121 operators include American, Delta, and United.  Even their regional operators, such as Envoy (American Eagle), Endeavor (Delta Connection), and Air Wisconsin (United Express), operate under Part 121.  These are very well-known brands and many of us travel with these airlines.

Part 135 operators are less well-known.  They, such as Cape Air and Kenmore Air, provide either commuter (more than five scheduled round trips a week with some equipment restrictions) or on-demand services. While both types of operations are safe and heavily regulated, Part 121 operations come with additional regulatory overhead, crew requirements, and additional required airplane equipment.

Other countries structure their rules a bit differently.  For example, the Canadian Aviation Regulations (CARs) divide similar types of operations into Air Taxi (703), Commuter (704), and Airline Operations (705).  EASA, on the other hand, groups all commercial air transport operations into Part-CAT in the Commission Regulation (EU) No 965/2012.

From a product certification standpoint, the main rule for commuter aircraft is FAA 14 CFR Part 23 – Airworthiness Standards: Normal Category Airplanes.  It covers aircraft with a maximum certified takeoff weight of 19,000 lb (8 618 kg) or less, with 19 passenger seats or less.  There are four airplane certification levels within it:

  • Level 1—for airplanes with a maximum seating configuration of 0 to 1 passenger.
  • Level 2—for airplanes with a maximum seating configuration of 2 to 6 passengers.
  • Level 3—for airplanes with a maximum seating configuration of 7 to 9 passengers.
  • Level 4—for airplanes with a maximum seating configuration of 10 to 19 passengers.

Notable examples of Part 23 aircraft include Cessna 172, PC-12, Twin Otter, and HondaJet. With each certification level come shifting requirements. This distinction in Part 23, combined with the operator rules in Part 121/135 results in the need for a careful trade study if a designer wants to add extra seats (such as going above nine seats for operating economics). 

Larger aircraft are certified based on FAA 14 CFR Part 25 – Airworthiness Standards: Transport Category Airplanes.  It is the basis for many recognized aircraft ranging from E-145 to A380.  Turboprops such as Dash 8 and ATR are Part 25 aircraft as well.  Many purpose-built business jets, ranging from G650 to LearJet 45, are also in this category even though they typically have 19 passenger seats or less.

The Part 23 example

Now, let’s take a look at a real-life example.  The Tecnam P2012 Traveller is Part 23 aircraft that was type certified by EASA in 2018 (Figure 1 and 2).  It is a twin-engine, piston-powered, propeller-driven aircraft. 

Figure 2. Tecnam P2012 Traveller, designed to FAA 14 CFR Part 23. Source: Tecnam.

It has a maximum passenger seating capacity of nine and a maximum certified takeoff weight of 3 680 kg (8,113 lb).  Would this product work as a “commuter” in the US, EU, and Canada?

FAA EASA Transport Canada
Operating Rule Part 135 COMMISSION REGULATION (EU) No 965/2012, Part-CAT CARs 703
Aircraft Limitation Airplanes, other than turbojet-powered airplanes, having a maximum passenger-seat configuration of 9 seats or less, excluding each crewmember seat, and a maximum payload capacity of 7,500 pounds or less. CAT covers all commercial operations.  “Commuter” is not defined in Part-CAT. A single-engined aircraft; a multi-engined aircraft, other than a turbo-jet-powered aeroplane, that has a MTOW of 8 618 kg (19,000 pounds) or less and a seating configuration, excluding pilot seats, of nine or less;

Under Canadian Aviation Regulations, there is a clear set of rules (CARs 703) permitting the use of aircraft with nine passenger seats or less.  This set of rules, as an example, allows operators to use an aircraft without a cabin attendant resulting in lower crew cost per trip compared to that of an airline operation.

EASA, as previously mentioned, structures its commercial operating rules differently.  It does not specifically define “commuter operations”.  Instead, it uses combinations of propulsion types, seating capacity, or maximum certified takeoff mass as thresholds for requirements.  For instance:

ORO.FC.200 Composition of flight crew  

(c) Specific requirements for aeroplane operations under instrument flight rules (IFR) or at night. 

(1) The minimum flight crew shall be two pilots for all turbo-propeller aeroplanes with a maximum operational passenger seating configuration (MOPSC) of more than nine and all turbojet aeroplanes. 

(2) Aeroplanes other than those covered by (c)(1) shall be operated with a minimum crew of two pilots, unless the requirements of ORO.FC.202 are complied with, in which case they may be operated by a single pilot”, 

Since there are many thresholds associated with nine passenger seats, the P2012 could bring benefits to EASA operators similar to those to Canadian operators.

The aircraft is also suitable for FAA 14 CFR Part 135 commuter operations.  It is a non-turbojet-powered aircraft with nine passengers or less.  This contributed to US Cape Air as the launch customer of the P2012.

We can see, from the analysis above, the importance of understanding both product certification and operating rules when developing an aircraft.  In the next Corners, we will examine the pros and cons when adding a few seats.

20 Comments on “Bjorn’s Corner: The challenges of airliner development. Part 5. Developing to Cert rules

  1. Very nice text!

    A little thought came to mind, which is on a higher philosophical level than the matter discussed in the text, that we should all support every effort toward so-called regulatory harmonization.

    Regulatory harmonization is when countries and regulatory frameworks make efforts, in a coordinated fashion, to find opportunities to slightly modify regulatory statues so that the respective regulatory frameworks to the greatest extent possible come into alignment. In that way, it will greatly simplify for those who need to comply with regulatory statues in multiple countries/jurisdictions, and thus promote innovation!

    If we as tax-payers invest one unit of currency in efforts toword regulatory harmonization, I’m confident we get at least ten units of currency in return, so I believe it is a financially very sound proposition. The benefits are quite overwhelming, really.

    • Unfortunately although the FAA and EASA are fairly well harmonised (and the Canadian and Australian ones etc) the standards are sometimes used within political blocks to create trade barriers or even conduct politically motivated trade embargos by default. You can see Russian/CIS alignment with FAA and by default EASA “25 series” regulations here.
      The Irkut MC21 is expected to receive Domestic CIS/Russian certification in mid 2021 and EASA certification in mid 2022. It’s been a struggle with US bans on export of carbon fibres and composite resins forcing the development of domestic fibres and resins. The potential threat to PW geared turbofans has ensured the development of the PD-14 as an alternative. Likewise with indigenous FBW and APU. I have no idea if EASA under pressure is throwing road blocks in the way. This would eventually lead to a sino-russian block that may find acceptance in Africa, Sth America and Asia.

      • William:

        I am confused as to the point.

        After innumerable election hacks and infrastructure attacks, EU and USA are supposed to not impose sanctions on Russia?

        Equally both are withing their rights to revoke the so called harmonized agreements.

        Neither entity sees this as anything other than an attack and the EU is seeing the light on dealing with China as a normal relationship.

        • Where is the confusion Sir? Regulatory trade barriers are an natural outcome of different sovereignties, the harmonization of regulations is driven by the desire to trade and the deliberate deharmonisation of standards by a desire to create trade barriers for political or trade war reasons. Embargos, such as the ones placed on technology items for the MC-21 are a facts, the US imposed laws and stopped exports. That’s why i regards my self on topic for raising them. I think we should stay on topic but the “Russians hacked our election economy” is in my view narrative spin.

          • William:

            I don’t get the point still.

            Reality is going to over come any agreement. You can’t divorce what is going on as they are intertwined. It does not take place in a vaccuum.

            EASA did exactly that with the MAX review (and rightfully so). The US realized they could do nothing so did not squawk about it (again the right move).

            So, the point is? The Earth continues to orbit the sun and I am not sure stating that offers anything up in regards to a discussion.

            If the Russians put up the MC-21 for certification agreement (per an agreement between FAA/EASA and Russia) that is going to be interesting as its separate from tech removal.

        • You are reproducing a rather partisan narrative.
          What you overlook is US
          – political influencing via NGOs and subversive forces like Mr. Navalny.
          – industrial sabotage and spying, excessive snooping in general.
          – conjured up fake press on alleged misdeeds in RU,CN, elsewhere

          The topmost (and effective) election manipulators in the US are native.

        • @TW, If we were to count “election hacks” & other attacks (should I list tem?), US would be on the top of the list.

    • Yeah.

      Born there, hauled off at age 2 but have visited over the years, best friend is from there.

      A state I wish all the best for.

  2. Interesting analysis, there could be a need for the smallest size to keep routes to remote destination in the Nordics. Question if aircraft like Tecnam would endure in winter conditions and what passenger acceptance you would get.

    • I was surprised they did not go with a small turbo prop.

      Bane of piston engine in aircraft is when you push them hard in an application they get many maint issues.

      I assume diesels just are not big enough yet and they still have the issue of cooling problems.

      • I reviewed this engine.

        While some of those piston engine are pushed to the extreme, this one has a very solid history and on some very good and reliable aircraft in vast numbers.

        Included on the Robinson R44 which is a bonus endorsement.

        At 375 hp on a 514 Cubic Inch engine, its not maxed out or hot rodded, its pretty conservative rating. I am old school and still use Cubic Inches as that is my default.

        Engines often get 1 hp or more per CI these days. They chose a mild power conservation variant.

        While I do think diesels are a way to go the weight aspect as well as the background and reliability for the new ones would push them into this. For a commercial operation looking for a reliable and well supported as well as well proven and known engine, it does not get any better.

        Not sure what they do about fuel long term as Av Gas is going way. It may be approved to run on regular gas (and the lower altitudes they operate at would lend to that as well as no turbo chargers which do add issue)

        • “While I do think diesels are a way to go “. Formula 1 is using HCCI & RCCI engines showing 45%-50% efficiency across the power range without the weight of diesel. Basically a minute amount of a special fluid is injected to initiate ignition instead of a spark plug. The sparking plug is there as a back up. It’s a system not dissimilar in principle to that developed by IG Farben with pilot ignition by Diglycol-diethly-ether (aka. “R300”) in the 1930s. (A few aero engines developed & tested by Daimler Benz and BMW) This allows stable and predictable running even at Lambda 2.5. This is ultra-lean territory. F1 fuel efficiency has increased by nearly 30% due to this. The DB/BMW engines were meant to be aero engines.

  3. Bjorn,
    Don’t you think the regulatory separation of aircraft that can carry 1, 6, 9 or 19 is administrative overkill?

    • I don’t think so. A 19 seat airliner is carrying regular passengers for sure. The 9 seater in which I have placed my personnel safety likewise or running reguar charter flights. I’ve taken a Antanov An-2 to a silver mine in Siberia and a Cessna Caravan to a gold mine in Guyana. These aircraft are carrying people to work on mines, doing medivac, taking a Siberian lady and her baby to her monthly shopping trip. The people forced to use them deserve a higher grade of safety. They’re huge inside. You could probably fit a small hatch back car in a Caravan and I’ve seen them deliver large fuel and water tanks. As aircraft get smaller using them is more of a voluntary matter.

      • I would put over 6 into the same category as 19.

        That really separates private ops from commercial though in AK there are a fair number of size 6 used for commercial.

        AK is different in that is fly or if you are lucky, water access, few highways to many places.

        Water access is often restricted to a single delivery shot via barge in the summer out of Anchorage or even Seattle .

    • If you look at the regs there is very little difference in Part 23 certification requirements between six and nine passengers. IMO these could be easily combined. Nineteen is quite a bit more demanding and one is quite a bit easier. Both of these distinctions make sense based on risk to passengers.

      • I think the point is that relatively few commercial operations have 6 passengers involved.

        Yes it happen and Alaska is an exception

        So is both a numbers aspect as well as frequency.

        Even 6 passenger capacity in private use is often 2 or 4 (throw in the luggage and the balance moves to no more than 4)

        While there are exceptions, the norm for 6 and under is far fewer flights.

        So, by the reality, 19 done 4 times a day vs 6 done once a week or less is a huge difference.

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