Highlights
- U.S. Department of Transportation Secretary Sean Duffy and Federal Aviation Administration (FAA) Deputy Administrator Chris Rocheleau recently announced the issuance of a final rule to the Modernization of Special Airworthiness Certification (MOSAIC) for light-sport aircraft.
- The rule has significant effects on aircraft certification processes and standards that apply to special airworthiness certificates, as it expands the eligibility criteria for aircraft qualifying for such certification by using a performance-based standard.
- The many changes in MOSAIC, combined with the revised Advisory Circular (AC) that applies to powered-lift aircraft, are expected to usher in a new era for certification of aircraft.
At the Experimental Aircraft Association's (EAA) annual EAA AirVenture Oshkosh, Wisconsin, on July 22, 2025, U.S. Department of Transportation Secretary Sean Duffy and Federal Aviation Administration (FAA) Deputy Administrator Chris Rocheleau, with House Committee on Transportation and Infrastructure Chairman Sam Graves (R-Mo.), announced the issuance of a final rule to the Modernization of Special Airworthiness Certification (MOSAIC) for light-sport aircraft.
The rule has significant effects on aircraft certification for special airworthiness certificates, as it expands the criteria for aircraft to become eligible for such certification by using a performance-based standard. The rule also:
- updates the privileges and limitations of holders of sport pilot certificates
- revises operating limitations that apply to eligible aircraft
- sets forth a new framework for establishing and complying with maintenance requirements that apply to such aircraft
- permits self-certification of applicable noise compliance standards
In addition to issuing the MOSAIC rule, the FAA also issued a final version of Advisory Circular 21.17-4 (AC), which applies to certification of powered-lift aircraft.1 The guidance document provides certification criteria for manufacturers to use when seeking to establish a certification basis for their aircraft.2 Collectively, the many changes in MOSAIC, combined with the revised AC that applies to certification of powered-lift aircraft, will usher in a new era for aircraft certification. Moreover, the FAA's use of performance-based standards and its provisions that permit equivalent levels of safety in both documents signal that the FAA will use a malleable approach and remain committed to increasing its efficiency of review of new designs.
Newfound Flexibility: FAA's Adoption of Performance-Based Approach
The MOSAIC rule uses a performance-based standard within eligibility criteria because the FAA will use the performance characteristics of an aircraft to define it. The rule will enable the development of entirely new types of light-sport aircraft – in it, the FAA encourages industry to establish standards for "new aircraft types and classes, such as electric vertical takeoff and landing (eVTOL) aircraft and powered-lift, including those for fly-by-wire control systems."3
In addition, the rule not only encourages the development of industry consensus standards, but assumes that such standards exist as a basis for certain requirements in the rule, such as maintenance protocol. This approach of both reliance on industry and promulgation of performance-based standards indicates that regulators are turning over a new leaf when it comes to the approach they will use for establishing provisions.
The MOSAIC rule contains provisions that indicate the FAA will use a performance-based approach for certification, maintenance, oversight mechanisms and even noise standards. The rule even adopts a performance-based approach in defining light-sport aircraft in the first place: It removes the weight criterion entirely and describes aircraft eligible for certification as light-sport are those that fulfill certain performance-based characteristics, based in part on consensus standards.4
Within 365 days of the date of publication of the MOSAIC rule in the Federal Register, aircraft eligible for such certification will be defined as those that have a maximum stalling speed or minimum steady flight speed at the aircraft's maximum takeoff weight and most critical center of gravity of 61 knots calibrated airspeed (CAS) VS0 for an airplane, 45 knots CAS VS0 for a glider or 45 knots CAS without the use of lift-enhancing devices, VS1, for a weight-shift-control aircraft.5 This focus on stall speed will enable novel designs, as designers and manufacturers will no longer be limited by the prescriptive weight measurement of the aircraft. Rather, the new definition enables creative designs based on performance of the aircraft.
The eligibility criteria also includes a maximum CAS of 250 knots in level flight with maximum continuous power (VH) under standard atmospheric conditions at sea level. In addition, if the aircraft is equipped with a cabin, the cabin must not be pressurized. Airplanes that meet the definition must not have more than four seats, while types of aircraft other than airplanes must not have more than two seats. The definition further contains a clear criterion based on consensus standards: Light-sport aircraft are those that fulfill the applicable "design, production, and airworthiness requirements using a means of compliance consisting of consensus standards accepted or approved by the FAA."6 The definition also states light-sport aircraft are those inspected by the FAA and found to be in a condition for safe operation.
Although the MOSAIC rule indicates FAA will maintain oversight by ensuring the aircraft are available for FAA inspection to ensure they remain in a condition for safe operation, various other provisions of the MOSAIC rule indicate an unprecedented amount of flexibility for oversight. A section concerning quality assurance states the aircraft must have been designed, produced and tested under a documented quality assurance system that ensures each product and article conforms to its design and is in a condition for safe operation. Similarly, inpiduals who have been trained on determining compliance with consensus standards will be authorized to find aircraft compliant with applicable standards. This manufacturer-led approach to quality assurance and findings of compliance indicates aircraft designs and operations will be able to proceed in an efficient manner, as waiting for general FAA oversight or FAA approval of a finding of compliance or will not be necessary.7
Similarly, ground and flight testing required for obtaining the certificate under MOSAIC will consist of a concise framework that will also be developed with FAA-accepted consensus standards.8 Aircraft under MOSAIC will be tested under documented production acceptance test procedures to verify the aircraft's performance data to ensure it:
- does not have hazardous operating characteristics
- is in a condition for safe operation
- can safely conduct any towing or aerial work operation, as applicable, in accordance with the manufacturer's designation for such
The MOSAIC rule also sets forth a flexible approach for compliance with standards that limit aircraft noise. The rule adds new provisions to 14 CFR Part 36 to broadly enable applicability of consensus standards concerning noise, which the FAA will approve upon determining the use of such standards is appropriate. Manufacturers may demonstrate compliance with such standards by using a variety of different procedures, including a procedure that might have applied to a similar aircraft that has a type certificate. Compliance with the applicable standards and requirements will be self-declared: The rule will require manufacturers to state that the aircraft has demonstrated compliance with the applicable provisions and include the aircraft's noise levels, procedures, configurations, weights and other information employed for obtaining the demonstrated noise levels. Such use of consensus-based standards and self-certification regarding standards that limit noise enables an industry-driven approach.
The role of industry-developed, FAA-accepted consensus standards for ground and flight testing, noise standards and maintenance will increase the efficiency of obtaining a special airworthiness certificate. In addition, FAA oversight mechanisms under the MOSAIC rule will foster a collective approach, given the new provisions for inspections and quality assurance protocols. These updates indicate the FAA is engaging in collaboration to fulfill its critical role in ensuring the safety of aviation operations.
Advanced Air Mobility (AAM): MOSAIC and FAA AC 21.17-4
The MOSAIC rule's inclusion of powered-lift aircraft will also result in operations of novel types of aircraft designs. Many aircraft used in AAM operations may include powered-lift aircraft because they are "capable of vertical takeoff, vertical landing and low speed flight that depends principally on engine-driven lift devices or engine thrust for lift during these flight regimes and on nonrotating airfoil(s) for lift during horizontal flight."9 The previous definition of light-sport aircraft, which the MOSAIC rule removes, had excluded powered-lift aircraft entirely; with the amendments in the MOSAIC rule, powered-lift aircraft, including eVTOL aircraft, will now be eligible for special airworthiness certificates in the light-sport category.
Although the MOSAIC rule does not amend the definition of "powered-lift" aircraft, it does require such aircraft certified in the light-sport category to have a known minimum safe speed for each flight condition encountered in normal operations, including applicable sources of lift and phases of flight, to maintain controlled safe flight. During such normal operations, measurement of the minimum safe speed determination must be based on "the most adverse conditions for each configuration."10 The MOSAIC rule's consideration of some light-sport aircraft as powered-lift indicates that the FAA might assume operations of powered-lift aircraft are a step in furtherance of enabling AAM operations. Though using light-sport aircraft to conduct air carrier operations is not permissible, such aircraft can be used for flight testing, which will be necessary for stakeholders who seek to establish a certification basis for obtaining further airworthiness certification. Stakeholders should note, however, that pilots who operate a powered-lift aircraft may only do so if they meet the minimum pilot standards for powered-lift operations; pilots who hold only a sport pilot certificate lack such qualification.11 As such, conducting operations of an aircraft with a special airworthiness certificate in the light-sport category is a step toward eventually conducting air carrier operations with an eVTOL or powered-lift.
In addition to the MOSAIC rule's potential applicability to certain powered-lift designs, the FAA also issued its final AC 21.17-4, which specifically applies to certification bases for powered-lift aircraft. Manufacturers and designers might seek to use 14 CFR Section 21.17(b) to establish the necessary certification bases for novel aircraft designs. The AC contains airworthiness criteria that apply to powered-lift aircraft proposed to be type-certificated as special class under Section 21.17(b) when such aircraft have a maximum gross weight of 12,500 pounds, passenger seating configuration of six or fewer, and battery-powered, electric engine-driven propellers for propulsion.12 (Please see Holland & Knight's previous blog post, "NAA Network Releases First Roadmap for Advanced Air Mobility Aircraft Type Certification" June 20, 2025.)
AC 21.17-4 will enable streamlined approvals of aircraft designs, as it establishes both an efficient procedure and sets forth airworthiness criteria, much of which is performance-based, that the FAA has already determined are acceptable. Regarding procedure, an applicant's compliance with the criteria in Appendix A of the AC will greatly increase the efficiency of obtaining a type certificate because the FAA will not publish the criteria in the Federal Register and seek public comment on it. If the FAA determines the airworthiness criteria in Appendix A is insufficient "due to an aircraft's unique, novel, or unusual design or design features," the FAA might set forth alternate or additional criteria.13 Applicants seeking approval of airworthiness criteria might also propose criteria in their certification plans other than those set forth in the AC. In such circumstances, the FAA will publish and request comments on such criteria in the Federal Register.
Footnotes
1. FAA Advisory Circular 21.17-4, Type Certification – Powered-lift (July 18, 2025).
2. When airworthiness standards do not exist under the subchapter that applies to aircraft design, 14 CFR Section 21.17(b) has long allowed those designing aircraft to apply a collection of various requirements from 14 CFR parts 23, 25, 27, 29, 31, 33 or 35, as long as such proposed requirements are appropriate for the aircraft and applicable to a specific type design or consist of airworthiness criteria that the FAA finds will provide a level of safety that is equivalent to the level of safety that compliance with existing standards would reach.
3. MOSAIC final rule, 90 Fed. Reg. 35034, 35069 (July 24, 2025). Aircraft described in the Roadmap for Advanced Air Mobility Type Certification might now be eligible for special airworthiness certification under MOSAIC; such aircraft include "eVTOL, hydrogen-based propulsion systems, and other AAM technologies." Roadmap for Advanced Air Mobility Type Certification at 8. Holland & Knight published an Aviation Law Blog post concerning the legal implications of the Roadmap.
4. Light-sport aircraft, since 2004, have been aircraft with a maximum takeoff weight of not more than 1,320 pounds (600 kilograms) for aircraft not intended for operation on water or 1,430 pounds (650 kilograms) for aircraft intended for operation on water. 14 CFR Section 1.1. The MOSAIC rule removes these prescriptive weight limitations.
5. VS1 refers to the stalling speed or the minimum steady flight speed obtained in a specific configuration. VS0 means the stalling speed or the minimum steady flight speed in the landing configuration.
6. MOSAIC final rule, 90 Fed. Reg. 35034, 35086 (July 24, 2025).
7. Id. at 35209-35210 (setting forth 14 CFR § 22.185 (Quality assurance system); 14 CFR § 22.190 (finding of compliance by trained compliance staff)).
8. Id. at 35082-35083.
9. 14 CFR Section 1.1.
10. MOSAIC final rule 35034, 35209 (July 24, 2025) (setting forth 14 CFR § 22.115).
11. Id. at 35128.
12. Such a certification basis is necessary for many types of operations of the aircraft because the certification basis leads to the type certificate for the aircraft. To receive a standard airworthiness certification under Section 21.183(a) or (b), an aircraft must have a type certificate. Powered-lift might also be issued special airworthiness certificates described in Section 21.175(b).
13. FAA Advisory Circular 21.17-4, Type Certification – Powered-lift at Section 7.2 (July 18, 2025).
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