Coming to Terms: Airworthiness Certification
By Al Lawless, Aurora Flight Sciences, and VFS E-VTOL Flight Test Council Chair
Vertiflite, Sept/Oct 2023
This series addresses uses of vertical flight aviation terminology that are unclear or incomplete, and so at risk of being confusing, misleading, unfavorable, erroneous or prejudicial. The goal is to clarify, and suggest improved terms, expressions or idioms for improved communications. This installment addresses the misuse of terminology regarding FAA airworthiness certification.
Companies often like to generate buzz about their progress — something regularly witnessed via press releases about investments, partnerships, new executives, etc. In civil aviation, certification milestones are particularly meaningful because trusted regulators issue them using consistent standards. Unfortunately, too many announcements and articles lack the full, properly descriptive terminology and standards used by regulators. Journalists too often propagate incomplete declarations, thus misleading or leaving many people lost in the fog. Murkiness has especially spread with buzzy press releases about novel electric aircraft and other vertical flight aircraft other than rotorcraft (the term “VTOL” will be used here for these).
Clearing the air and informing the public begins with trusting that everyone and everything in a safety-critical role is vetted — often via government certification. For civil aviation in the US, this acknowledges that Federal Aviation Administration (FAA) regulatory requirements have been or will continue to be met. The FAA issues separate but interwoven kinds of certifications for aircraft production, aeronautical products, aircrew, mechanics, controllers, operators, etc.
A critical one is aircraft airworthiness certification. This is certainly newsworthy, but is often misrepresented or misread. Understanding the nuances comes by clarifying that to fly at all, FAA regulations require issuance of one of three airworthiness types for an aircraft.
• A Standard Airworthiness Certification is the goal for aircraft intended to operate broadly because it allows minimal flying restrictions within the national airspace system (NAS). Earning this involves first obtaining a Type Certificate (TC), which denotes full compliance with publicly vetted design requirements, such as the established 14 Code of Federal Regulations (CFR) Part 23 airplane or Part 27 rotorcraft rule sets. Retaining validity requires maintenance that complies with the applicable rules [CFR Parts 21, 43 and 91]. Issued per tail number, an airworthiness certificate can be revoked if the aircraft deviates from the approved design or if regulators consider it not airworthy. Most aircraft have a standard airworthiness certificate issued within a specific operational category (e.g., normal, utility, acrobatic, commuter, transport and manned free balloons). Other, Special Class aircraft like VTOL aircraft are outside the established rule sets but can use an equivalent process and be eligible upon earning a TC. This opens paths to volume production and extensive use, including revenue operations transporting people or goods (“common carriage”).
• An Export Airworthiness Certification shows an aircraft or article (e.g., engine, propeller or other equipment) meets a specific standard before allowing it to be exported to a foreign country.
• A Special Airworthiness Certification can be issued to aircraft that have not (yet) shown compliance with all the applicable design regulations needed for a standard airworthiness certification. To enable flying such aircraft while ensuring NAS efficiency, public safety is typically assured via operational restrictions. To accommodate the needs of various operators, the FAA offers different categories. Some (Primary, Light Sport Aircraft, Limited, Multiple, and Special Flight Permit and Authorization) are not particularly relevant or newsworthy for novel aircraft, but three other special airworthiness certifications might generate excitement.
o Restricted applies to aircraft specifically built or modified for a special, narrow purpose, such as agricultural spraying, external load operation, survey, etc.
o Provisional is available to an aircraft or engine manufacturer or air carrier in the TC process. This allows special operations, such as flight crew training, manufacturer demonstration flights and aircraft service testing.
o Experimental certificates can be issued to any aircraft and are a kind of catch-all for those not covered by the above. Within “Experimental,” regulators again accommodate by authorizing narrower purposes such as exhibition, air racing, market survey, crew training, and operating amateur-built, kit-built and light sport aircraft. Reflecting design progress are two other authorizations: showing compliance and conducting research and development (R&D).
• A Special Airworthiness Certificate for Showing Compliance with Regulations may be requested by a TC applicant that is confident their aircraft build conforms with the design drawings and will pass the required certification tests.
• A Special Airworthiness Certificate for Experimental R&D applies to any combination of pure research, development and pre-flying tests needed for TC. It is needed for testing new designs, equipment, operating techniques, certified aircraft with substantial design changes and certain military designs. Because regulators protect the public primarily by restricting flight operations, an R&D issuance has minimal criteria for aircraft design or build quality.
The required certification tests are reasonably clear and consistent for established classes like airplanes and rotorcraft. Things are cloudier for non-rotorcraft VTOL aircraft because all are novel and will be certified as special class. This allows applicants and regulators to negotiate the certification basis — the custom airworthiness and environmental standards to which compliance must be shown. They also parley on how to show compliance. The FAA tracks progress on both efforts through their G-1 (“Certification Basis”) and G-2 (“Means of Compliance”) issue paper process. G-1 stage 1 begins with general information and identifying any known issues, stage 2 presents the FAA’s initial position and aircraft-specific safety regulations, stage 3 is negotiation, and stage 4 signifies final agreement as published. Note that the G-1 and G-2 papers address only certification rules, not the quality of aircraft design or construction.
For aircraft on the path to broad operations in the NAS, aircraft developers can step through the preceding milestones in the sequence reverse from that presented here. Each step presents an opportunity to broadcast regulator-recognized progress. OEMs might initially announce launching the Project Specific Certification Plan and initiating or closing each G-1 and G-2 stage. Next may come the flight-related press releases about being issued a series of special airworthiness certificates: experimental R&D for flight testing, experimental compliance showing, and provisional to allow pilot training and demonstration. Also likely is a restricted certificate for limited operations under specially controlled circumstances. All are minor milestones towards the significant Type Certificate.
Beyond this airworthiness overview is what happens after a design obtains a TC. Coming into play next are certifications to produce the aircraft per the approved design, license pilots to fly per the approved flight manual and flight rules, to operate and maintain the aircraft, and (usually) a standard airworthiness certification. Each brings yet more opportunities to generate buzz.
Additional reference materials: