The FAA and 14 CFR

Rachel Oduya's first briefing for the Petrel 19 team is a map of the rulebook. Engineers who have spent their careers on aerodynamics or structures often meet the regulations only as a list of section numbers in a compliance report. Rachel wants them to understand how the system is organized, who wrote each part, and where to look when a question arises that the design standard does not answer. In the United States the authority is the Federal Aviation Administration (FAA), an agency of the Department of Transportation, and its rules are the Federal Aviation Regulations, published as Title 14 of the Code of Federal Regulations under the authority of Title 49 of the United States Code.

The structure of 14 CFR

Title 14 is divided into chapters and parts. Chapter I, the FAA's rules, runs from Part 1 to Part 199. Part 1 contains definitions. Part 21 covers certification procedures for products and articles: type certificates, supplemental type certificates, production certificates, parts manufacturer approvals and technical standard order authorizations. Parts 23, 25, 27, 29, 31, 33 and 35 are the airworthiness standards for normal category airplanes, transport category airplanes, rotorcraft, balloons, engines and propellers. Part 39 governs airworthiness directives and Part 43 maintenance. Part 61 licenses pilots and Part 65 mechanics. Part 91 contains the general operating rules, Part 121 airlines, Part 135 commuter and on-demand operators and Part 145 repair stations. Part 5 sets out safety management systems.

Some parts are rules of procedure and others are technical standards. Part 21 tells an applicant how to obtain a type certificate; Part 23 tells it what the design must achieve. The FAA updates the technical standards through amendments, each identified by a number, such as 23-64, the 2017 rewrite that converted Part 23 into performance-based requirements. The amendment level matters, because a design is certified to the rules in force when it applied, as Lesson 4 explains.

How rules are made and changed

New or amended rules go through public rulemaking under the Administrative Procedure Act. The FAA publishes a notice of proposed rulemaking (NPRM) in the Federal Register, takes public comments, and then publishes a final rule with a preamble that answers the comments and explains the rule. Industry often contributes through the Aviation Rulemaking Advisory Committee and its working groups. Advisory circulars, orders and policy statements are issued without full rulemaking because they guide rather than bind, although the FAA usually invites comment on significant ones.

For an applicant, the practical lesson is that the rule text alone is never enough. The preamble or the regulatory impact analysis explains what the rule intends, and the advisory material shows what the authority will accept. Arjun keeps a folder for each requirement with all three, and finds that half his questions are answered by reading why a rule was written.

Delegation

No authority has enough engineers to review every calculation and witness every test for every aircraft. The US system therefore delegates. The FAA appoints individual designees such as designated engineering representatives (DERs) and designated airworthiness representatives, and authorizes organizations through organization designation authorization (ODA) under 14 CFR Part 183. An ODA holder's unit members make findings on the FAA's behalf under an FAA-approved procedures manual. The delegate's finding is legally the FAA's finding, and the delegate must act independently of commercial pressure from the employer. Congress strengthened FAA oversight of delegation after the 2018 and 2019 Boeing 737 MAX accidents, through the Aircraft Certification, Safety, and Accountability Act of 2020.

Delegation does not mean the authority steps back. It retains the findings it judges most significant, typically new technology, novel design features and anything where the company's own engineers might be tempted to accept less. For the Petrel 19, the hybrid powertrain is new to everyone, so the FAA will keep most powerplant and systems findings for itself. The code below estimates the split.

# Who finds compliance? Splitting the Petrel 19 compliance findings between
# the authority's own engineers and delegated company engineers.
findings = {'structures': 96, 'flight': 58, 'powerplant': 71, 'systems': 88, 'crashworthiness': 24}
retained = {'structures': 0.15, 'flight': 0.40, 'powerplant': 0.60, 'systems': 0.45, 'crashworthiness': 0.20}
hours_each = 14  # average review effort per finding, hours (illustrative)
auth = deleg = 0
for k, n in findings.items():
    a = round(n * retained[k]); auth += a; deleg += n - a
    print(f"{k:16s} total {n:3d}  authority {a:3d}  delegate {n - a:3d}")
print(f"authority keeps {auth} findings ({auth/(auth+deleg):.0%}), about {auth*hours_each} review hours")
print(f"delegates make {deleg} findings ({deleg/(auth+deleg):.0%}), about {deleg*hours_each} hours inside the company")

structures       total  96  authority  14  delegate  82
flight           total  58  authority  23  delegate  35
powerplant       total  71  authority  43  delegate  28
systems          total  88  authority  40  delegate  48
crashworthiness  total  24  authority   5  delegate  19
authority keeps 125 findings (37%), about 1750 review hours
delegates make 212 findings (63%), about 2968 hours inside the company

The authority keeps a little over a third of the findings, but these are the ones that drive the schedule. Rachel uses the estimate to agree a resourcing plan with the authority's project manager: if the authority's engineers have only a few hundred hours for the project in a given quarter, the company must schedule its submissions so they do not all arrive at once.

Working across the border

Kuskokwim Air Link is the launch customer, but operators in Canada's north have also shown interest, so the Petrel 19 must be validated by Transport Canada. The United States and Canada have a Bilateral Aviation Safety Agreement (BASA) with implementation procedures for airworthiness. Under it, Transport Canada validates an FAA type certificate rather than certifying the design again from the beginning. The depth of the validation review depends on how novel the design is and on Transport Canada's confidence in the FAA's findings. For a hybrid powertrain Transport Canada will want to understand the special conditions in detail, so Rachel invites its specialists to the early technical meetings, a practice the agreement encourages.

Validation also creates a practical rule for the design team: where the two countries' standards differ, design to the more demanding one from the start. Late discovery of a difference, such as a different interpretation of a cold-weather operation requirement, can mean redesign after certification, the most expensive time to change anything.

Enforcement

The FAA can suspend or revoke certificates and seek civil penalties. Pilots and mechanics can appeal certificate actions to the National Transportation Safety Board, and civil penalty cases follow procedures in 14 CFR Part 13. The FAA's compliance philosophy, adopted in 2015 and later called the compliance program, favors correcting unintentional deviations through training and process change, keeping enforcement for wilful or reckless conduct.

Advisory material and consensus standards

Below the regulations sits a large body of guidance. Advisory circulars explain acceptable means of compliance; FAA orders, such as Order 8110.4 on type certification, tell the FAA's own engineers and inspectors how to run a project, and are published so applicants can see what will be expected; policy statements record how the FAA interprets a rule on a specific question. The FAA also accepts some guidance from other authorities when it is shown to be equivalent. Rachel's rule is that every reliance on guidance outside the FAA's own advisory circulars is written into the certification plan and agreed with the FAA, not assumed.

The newest layer is industry consensus standards. When the normal category rules were rewritten as performance objectives, the detailed design methods were moved into standards written by committees of manufacturers, authorities and specialists, principally ASTM International Committee F44 on general aviation aircraft. An authority can accept a consensus standard as a means of compliance, in whole or with exceptions. The advantage is speed: a committee can update a method far faster than a regulation can be amended. The cost is that an applicant must check which revision of a standard has been accepted, and whether the authority listed any exceptions, before relying on it.

For the Petrel 19, which uses both conventional structure and a hybrid powertrain, the result is a layered compliance picture. Structural loads follow long-established methods that have barely changed in decades. The powertrain relies on special conditions written for this aircraft and on consensus standards that are still evolving. Rachel tells the team that the more novel a feature is, the more of its compliance story must be negotiated rather than looked up, and that negotiation needs to start early.

How the authority oversees the applicant

Oversight of a design organization does not end with individual findings. The FAA audits an ODA holder's processes, checks that unit members are working within their authorized areas, samples completed findings to verify them, and reviews the company's handling of problems found after certification. The ODA holder must keep its procedures manual current and obtain FAA approval for significant changes. When oversight finds weaknesses, the FAA can limit the authorization or require more direct FAA involvement until the company shows that the problem has been corrected. Since the 2020 legislation, the FAA must also approve the individuals who serve as ODA unit members on certain transport category programs, a measure intended to strengthen their independence.

From the company side, good oversight is an asset. Marcus Webb, who leads structures, argues that every audit finding the authority raises is a weakness the company would otherwise discover later at greater cost. He asks that audit reports be circulated to all engineering leads, not filed by the quality department alone, so that the lessons reach the people who design the aircraft.

A map for the Petrel 19 team

Rachel closes her briefing with a single page that maps the program onto the rules. Design approval runs under 14 CFR Part 21 against 14 CFR Part 23 at certification level 4, with special conditions for the hybrid powertrain. Production approval, covered in Lesson 5, is a separate certificate with its own rules. Once the aircraft enters service, the operator's maintenance program and the technicians who sign for work are governed by 14 CFR Part 43, the operator's rules and the licensing rules covered in Lesson 8. Airworthiness directives, safety management and accident investigation each sit in their own part of the system. The engineers who will spend the next four years on the Petrel 19 do not need to memorize the rulebook, but they need to know where each question belongs, because a question asked of the wrong rule gets the wrong answer.

Arjun asks the obvious question: what happens when the rules simply do not address something? Rachel's answer is that the system has a tool for that, the special condition, and that Lesson 4 is largely about how such gaps are handled. Until then, she asks the team to flag anything for which they cannot find a clear requirement, rather than deciding on their own what an acceptable answer would be.