The FAA invites interested people to take part in this rulemaking by sending written comments, data, or views. The most helpful comments reference a specific portion of the proposed special conditions, explain the reason for any recommended change, and include supporting data.

The FAA will consider all comments received by the closing date for comments and will consider comments filed late if it is possible to do so without incurring delay. The FAA may change these special conditions based on the comments received.

Except for Confidential Business Information (CBI) as described in the following paragraph, and other information as described in title 14, Code of Federal Regulations (14 CFR) 11.35, the FAA will post all comments received without change to www.regulations.gov, including any personal information you provide. The FAA will also post a report summarizing each substantive verbal contact received about these special conditions.

Confidential Business Information (CBI) is commercial or financial information that is both customarily and actually treated as private by its owner. Under the Freedom of Information Act (FOIA) (5 U.S.C. 552), CBI is exempt from public disclosure. If your comments responsive to these special conditions contain commercial or financial information that is customarily treated as private, that you actually treat as private, and that is relevant or responsive to these special conditions, it is important that you clearly designate the submitted comments as CBI. Please mark each page of your submission containing CBI as “PROPIN.” The FAA will treat such marked submissions as confidential under the FOIA, and the indicated comments will not be placed in the public docket of these proposed special conditions. Send submissions containing CBI to the individual listed in the For Further Information Contact section above. Comments the FAA receives, which are not specifically designated as CBI, will be placed in the public docket for these proposed special conditions.

On May 3, 2024, ZeroAvia, applied for a type certificate for its Model ZA601 electric engine. The electric engine consists of an electric motor, stator, inverters/controllers and will operate with low and high-voltage electrical systems. The ZeroAvia ZA601 electric engine will be used in airplanes certificated under 14 CFR part 23 in the normal category, level 4 and higher.

Under the provisions of 14 CFR 21.17, ZeroAvia must show that the Model ZA601 electrical engines meet the applicable provisions of part 33, as amended by amendments 33-1 through 33-36, in effect on the date of application for a type certificate.

If the FAA finds that the applicable airworthiness regulations ( e.g., 14 CFR part 33) do not contain adequate or appropriate safety standards for the ZeroAvia Model ZA601 engine because of a novel or unusual design feature, the FAA prescribes special conditions under the provisions of § 21.16.

Special conditions are initially applicable to the model for which they are issued. Should the type certificate for that model be amended later to include any other model that incorporates the same novel or unusual design feature, these special conditions would also apply to the other model under § 21.101.

In addition to the applicable airworthiness regulations and special conditions, the ZeroAvia Model ZA601 engine must comply with the noise-certification requirements of 14 CFR part 36.

The FAA issues special conditions, as defined in 14 CFR 11.19, in accordance with § 11.38, and they become part of the type certification basis under § 21.17(a)(2).

The ZeroAvia ZA601 electric engine will incorporate the following novel or unusual design feature:

An electric motor, motor controller, and high-voltage electrical system used as the primary source of propulsion for an airplane.

Aircraft engines make use of an energy source to drive mechanical systems that provide propulsion for the aircraft. The technology that the FAA anticipated in the development of 14 CFR part 33 converts oxygen and fuel to generate energy through an internal combustion system for turning shafts attached to propulsion devices such as propellers and ducted fans.

Electric propulsion technology is substantially different from the technology used in previously certificated turbine and reciprocating engines. Therefore, these engines introduce new safety concerns that need to be addressed in the certification basis.

A growing interest within the aviation industry involves electric propulsion technology. As a result, international agencies and industry stakeholders formed Committee F39 under ASTM International, formerly known as American Society for Testing and Materials, to identify the appropriate technical criteria for aircraft engines using electrical technology that has not been previously type certificated for aircraft propulsion systems. ASTM International is an international standards organization that develops and publishes voluntary consensus technical standards for a wide range of materials, products, systems, and services. ASTM International published ASTM F3338-18, “Standard Specification for Design of Electric Propulsion Units for General Aviation Aircraft,” in December 2018. 1 The FAA used the technical criteria from the ASTM F3338-18, the published Special Conditions No. 33-022-SC for the magniX USA, Inc. Model magni350 and magni650 engines, and information from the ZeroAvia Model ZA601 engine design to develop special conditions that establish an equivalent level of safety to that required by part 33.

Energy can be generated from various sources such as petroleum and natural gas. The turbine and reciprocating aircraft engines certificated under part 33 use aviation fuel for an energy source. The reciprocating and turbine engine technology that was anticipated in the development of part 33 converts oxygen and fuel to energy using an internal combustion system, which generates heat and mass flow of combustion products for turning shafts that are attached to propulsion devices such as propellers and ducted fans. Part 33 regulations set forth standards for these engines and mitigate potential hazards resulting from failures and malfunctions. The nature, progression, and severity of engine failures are tied closely to the technology that is used in the design and manufacture of aircraft engines. These technologies involve chemical, thermal, and mechanical systems. Therefore, the existing engine regulations in part 33 address certain chemical, thermal, and mechanically induced failures that are specific to air and fuel combustion systems operating with cyclically loaded, high speed, high-temperature, and highly stressed components.

The existing part 33 airworthiness standards for aircraft engines date back to 1965. As discussed in the previous paragraphs, these airworthiness standards are based on fuel-burning reciprocating and turbine engine technology. The ZeroAvia Model ZA601 engines are neither turbine nor reciprocating engines. These engines have a novel or unusual design feature, which is the use of electrical sources of energy instead of fuel to drive the mechanical systems that provide propulsion for aircraft. The ZeroAvia aircraft engine is subject to operating conditions produced by chemical, thermal, and mechanical components working together, but the operating conditions are unlike those observed in internal combustion engine systems. Therefore, part 33 does not contain adequate or appropriate safety standards for the ZeroAvia Model ZA601 engine's novel or unusual design feature.

ZeroAvia's proposed aircraft engines will operate using electrical power instead of air and fuel combustion to propel the aircraft. These electric engines will be designed, manufactured, and controlled differently than turbine or reciprocating aircraft engines. They will be built with an electric motor, motor controller, and high-voltage electrical systems that draw energy from electrical storage or electrical energy generating systems. The electric motor is a device that converts electrical energy into mechanical energy by electric current flowing through windings (wire coils) in the motor, producing a magnetic field that interacts with permanent magnets mounted on the engine's main rotor. The controller is a system that consists of two main functional elements: the motor controller and an electric power inverter to drive the motor. 2 The high-voltage electrical system is a combination of wires and connectors that integrate the motor and controller.

In addition, the technology comprising these high-voltage and high-current electronic components introduces potential hazards that do not exist in turbine and reciprocating aircraft engines. For example, high-voltage transmission lines, electromagnetic shields, magnetic materials, and high-speed electrical switches are necessary to use the physical properties of an electric engine for propelling an aircraft. However, this technology also exposes the aircraft to potential failures that are not common to gas-powered turbine and reciprocating engines, technological differences which could adversely affect safety if not addressed through these proposed special conditions.

Although the electric aircraft engines ZeroAvia proposes use a novel or unusual design feature that the FAA did not envisage during the development of its existing part 33 airworthiness standards, these engines share some basic similarities, in configuration and function, to engines that use the combustion of air and fuel, and therefore require similar provisions to prevent common hazards ( e.g., fire, uncontained high energy debris, and loss of thrust control). However, the primary failure concerns and the probability of exposure to these common hazards are different for the proposed ZeroAvia Model ZA601 electric engine. This creates a need to develop special conditions to ensure the engine's safety and reliability.

The requirements in part 33 ensure that the design and construction of aircraft engines, including the engine control systems, are proper for the type of aircraft engines considered for certification. However, part 33 does not fully address aircraft engines like the ZeroAvia Model ZA601, which operates using electrical technology as the primary means of propelling the aircraft. This necessitates the development of special conditions that provide adequate airworthiness standards for these aircraft engines.

The requirements in part 33, subpart B, are applicable to reciprocating and turbine aircraft engines. Subparts C and D are applicable to reciprocating aircraft engines. Subparts E through G are applicable to turbine aircraft engines. As such, subparts B through G do not adequately address the use of aircraft engines that operate using electrical technology. Special conditions are needed to ensure a level of safety for electric engines that is commensurate with these subparts, as those regulatory requirements do not contain adequate or appropriate safety standards for electric aircraft engines that are used to propel aircraft.

Applicability: Proposed special condition no. 1 would require ZeroAvia to comply with part 33, except for those airworthiness standards specifically and explicitly applicable only to reciprocating and turbine aircraft engines.

Engine Ratings and Operating Limitations: Proposed special condition no. 2 would, in addition to compliance with § 33.7(a), require ZeroAvia to establish engine operating limits related to the power, torque, speed, and duty cycles specific to ZeroAvia Model ZA601 electric engines. The duty or duty cycle is a statement of the load(s) to which the engine is subjected, including, if applicable, starting, no-load and rest, and de-energized periods, including their durations or cycles and sequence in time. This special condition also requires ZeroAvia to declare cooling fluid grade or specification, power supply requirements, and to establish any additional ratings that are necessary to define the ZeroAvia Model ZA601 electric engine capabilities required for safe operation of the engine.

Materials: Proposed special condition no. 3 would require ZeroAvia to comply with § 33.15, which sets requirements for the suitability and durability of materials used in the engine, and which would otherwise be applicable only to reciprocating and turbine aircraft engines.

Fire Protection: Proposed special condition no. 4 would require ZeroAvia to comply with § 33.17, which sets requirements to protect the engine and certain parts and components of the airplane against fire, and which would otherwise be applicable only to reciprocating and turbine aircraft engines. Additionally, this proposed special condition would require ZeroAvia to ensure that the high-voltage electrical wiring interconnect systems that connect the controller to the motor are protected against arc faults. An arc fault is a high-power discharge of electricity between two or more conductors. This discharge generates heat, which can break down the wire's insulation and trigger an electrical fire. Arc faults can range in power from a few amps up to thousands of amps and are highly variable in strength and duration.

Durability: Proposed special condition no. 5 would require the design and construction of ZeroAvia Model ZA601 electric engines to minimize the development of an unsafe condition between maintenance intervals, overhaul periods, and mandatory actions described in the Instructions for Continued Airworthiness (ICA).

Engine Cooling: Proposed special condition no. 6 would require ZeroAvia to comply with § 33.21, which requires the engine design and construction to provide necessary cooling, and which would otherwise be applicable only to reciprocating and turbine aircraft engines. Additionally, this proposed special condition would require ZeroAvia to document the cooling system monitoring features and usage in the engine installation manual (see § 33.5) if cooling is required to satisfy the safety analysis described in proposed special condition no. 17. Loss of cooling to an aircraft engine that operates using electrical technology can result in rapid overheating and abrupt engine failure, with critical consequences to safety.

Engine Mounting Attachments and Structure: Proposed special condition no. 7 would require ZeroAvia and the proposed design to comply with § 33.23, which requires the applicant to define, and the proposed design to withstand, certain load limits for the engine mounting attachments and related engine structure. These requirements would otherwise be applicable only to reciprocating and turbine aircraft engines.

Accessory Attachments: Proposed special condition no. 8 would require the proposed design to comply with § 33.25, which sets certain design, operational, and maintenance requirements for the engine's accessory drive and mounting attachments, and which would otherwise be applicable only to reciprocating and turbine aircraft engines.

Overspeed: Proposed special condition no. 9 would require ZeroAvia to establish by test, validated analysis, or a combination of both, that—

(1) the rotor overspeed must not result in a burst, rotor growth, or damage that results in a hazardous engine effect;

(2) rotors must possess sufficient strength margin to prevent burst; and

(3) operating limits must not be exceeded in service.

The proposed special condition associated with rotor overspeed is necessary because of the differences between turbine engine technology and the technology of these electric engines. Turbine rotor speed is driven by expanding gas and aerodynamic loads on rotor blades. Therefore, the rotor speed or overspeed results from interactions between thermodynamic and aerodynamic engine properties. The speed of an electric engine is directly controlled by electric current, and an electromagnetic field created by the controller. Consequently, electric engine rotor response to power demand and overspeed-protection systems is quicker and more precise. Also, the failure modes that can lead to overspeed between turbine engines and electric engines are vastly different, and therefore this special condition is necessary.

Engine Control Systems: Proposed special condition no. 10(b) would require ZeroAvia to ensure that these engines do not experience any unacceptable operating characteristics, such as unstable speed or torque control, or exceed any of their operating limitations.

The FAA originally issued § 33.28 at amendment 33-15 to address the evolution of the means of controlling the fuel supplied to the engine, from carburetors and hydro-mechanical controls to electronic control systems. These electronic control systems grew in complexity over the years, and as a result, the FAA amended § 33.28 at amendment 33-26 to address these increasing complexities. The controller that forms the controlling system for these electric engines is significantly simpler than the complex control systems used in modern turbine engines. The current regulations for engine control are inappropriate for electric engine control systems; therefore, the proposed special condition no. 10(b) associated with controlling these engines is necessary.

Proposed special condition no. 10(c) would require ZeroAvia to develop and verify the software and complex electronic hardware used in programmable logic devices, using proven methods that ensure that the devices can provide the accuracy, precision, functionality, and reliability commensurate with the hazard that is being mitigated by the logic. RTCA DO-254, “Design Assurance Guidance for Airborne Electronic Hardware,” dated April 19, 2000, 3 distinguishes between complex and simple electronic hardware.

Proposed special condition no. 10(d) would require data from assessments of all functional aspects of the control system to prevent errors that could exist in software programs that are not readily observable by inspection of the code. Also, ZeroAvia must use methods that will result in the expected quality that ensures the engine control system performs the intended functions throughout the declared operational envelope.

The environmental limits referred to in proposed special condition no. 10(e) include temperature, vibration, high-intensity radiated fields (HIRF), and others addressed in RTCA DO-160G, “Environmental Conditions and Test Procedures for Airborne Electronic/Electrical Equipment and Instruments” dated December 8, 2010, which includes “DO-160G Change 1—Environmental Conditions and Test Procedures for Airborne Equipment” dated December, 16, 2014, and “DO-357—User Guide: Supplement to DO-160G” dated December 16, 2014. 4 Proposed special condition 10(e) would require ZeroAvia to demonstrate by system or component tests in proposed special condition no. 27 any environmental limits that cannot be adequately substantiated by the endurance demonstration, validated analysis, or a combination thereof.

Proposed special condition no. 10(f) would require ZeroAvia to evaluate various control system failures to ensure-that such failures will not lead to unsafe engine conditions. The FAA issued Advisory Circular (AC) AC 33.28-3, “Guidance Material for 14 CFR 33.28, Engine Control Systems,” on May 23, 2014, for reciprocating and turbine engines. 5 Paragraph 6-2 of this AC provides guidance for defining an engine control system failure when showing compliance with the requirements of § 33.28. AC 33.28-3 also includes objectives for control system integrity requirements, criteria for a loss of thrust (or power) control (LOTC/LOPC) event, and an acceptable LOTC/LOPC rate. The electrical and electronic failures and failure rates did not account for electric engines when the FAA issued this AC, and therefore performance-based special conditions are proposed to allow fault accommodation criteria to be developed for electric engines.

The phrase “in the full-up configuration” used in proposed special condition no. 10(f)(2) refers to a system without any fault conditions present. The electronic control system must, when in the full-up configuration, be single-fault tolerant, as determined by the Administrator, for electrical, electrically detectable, and electronic failures involving LOPC events.

The term “local” in the context of “local events” used in proposed special condition no. 10(f)(4) means failures or malfunctions leading to events in the intended aircraft installation such as fire, overheat, or failures leading to damage to engine control system components. These local events must not result in a hazardous engine effect due to engine control system failures or malfunctions.

Proposed special condition no. 10(g) would require ZeroAvia to conduct a safety assessment of the control system to support the safety analysis in proposed special condition no. 17. This control system safety assessment provides engine response to failures, and rates of these failures that can be used at the aircraft-level safety assessment.

Proposed special condition no. 10(h) requires ZeroAvia to provide appropriate protection devices or systems to ensure that engine operating limits will not be exceeded in service.

Proposed special condition no. 10(i) is necessary to ensure that the controllers are self-sufficient and isolated from other aircraft systems. The aircraft-supplied data supports the analysis at the aircraft level to protect the aircraft from common mode failures that could lead to major propulsion power loss. The exception “other than power command signals from the aircraft,” noted in proposed special condition no. 10(i), is based on the FAA's determination that the engine controller has no reasonable means to determine the validity of any in-range signals from the electrical power system. In many cases, the engine control system can detect a faulty signal from the aircraft, but the engine control system typically accepts the power command signal as a valid value.

The term “independent” in the context of “fully independent engine systems” referenced in proposed special condition no. 10(i) means the controllers should be self-sufficient and isolated from other aircraft systems or provide redundancy that enables the engine control system to accommodate aircraft data system failures. In the case of loss, interruption, or corruption of aircraft-supplied data, the engine must continue to function in a safe and acceptable manner without hazardous engine effects.

The term “accommodated,” in the context of “detected and accommodated,” referenced in proposed special condition 10(i)(2) is to assure that, upon detecting a fault, the system continues to function safely.

Proposed special condition no. 10(j) would require ZeroAvia to show that the loss of electric power from the aircraft will not cause the electric engine to malfunction in a manner hazardous to the aircraft. The total loss of electric power to the electric engine may result in an engine shutdown.

Instrument Connection: Proposed special condition no. 11 would require ZeroAvia to comply with § 33.29(a), (e), and (g), which set certain requirements for the connection and installation of instruments to monitor engine performance. The remaining requirements in § 33.29 apply only to technologies used in reciprocating and turbine aircraft engines.

Instrument connections (wires, wire insulation, potting, grounding, connector designs, etc.) must not introduce unsafe features or characteristics to the aircraft. Proposed special condition no. 11 would require the safety analysis to include potential hazardous effects from failures of instrument connections to function properly. The outcome of this analysis might identify the need for design enhancements or additional ICA to ensure safety.

Stress Analysis: Section 33.62 requires applicants to perform a stress analysis on each turbine engine. This regulation is explicitly applicable only to turbine engines and turbine engine components, and it is not appropriate for the ZeroAvia Model ZA601 electric engines. However, the FAA proposes that a stress analysis particular to these electric engines is necessary to account for stresses resulting from electric technology used in the engine.

Proposed special condition no. 12 would require a mechanical, thermal, and electrical stress analysis to show that the engine has a sufficient design margin to prevent unacceptable operating characteristics. Also, the applicant must determine the maximum stresses in the engine by tests, validated analysis, or a combination thereof, and show that they do not exceed minimum material properties.

Critical and Life-Limited Parts: Proposed special condition no. 13 would require ZeroAvia to show whether rotating or moving components, bearings, shafts, static parts, and non-redundant mount components should be classified, designed, manufactured, and managed throughout their service life as critical or life-limited parts.

The term “low-cycle fatigue,” referenced in proposed special condition no. 13(a)(2), is a decline in material strength from exposure to cyclic stress at levels beyond the stress threshold the material can sustain indefinitely. This threshold is known as the “material endurance limit.” Low-cycle fatigue typically causes a part to sustain plastic or permanent deformation during the cyclic loading and can lead to cracks, crack growth, and fracture. Engine parts that operate at high temperatures and high mechanical stresses simultaneously can experience low-cycle fatigue coupled with creep. Creep is the tendency of a metallic material to permanently move or deform when it is exposed to the extreme thermal conditions created by hot combustion gasses, and substantial physical loads such as high rotational speeds and maximum thrust. Conversely, high-cycle fatigue is caused by elastic deformation, small strains caused by alternating stress, and a much higher number of load cycles compared to the number of cycles that cause low-cycle fatigue.

The engineering plan referenced in proposed special condition no. 13(b)(1) informs the manufacturing and service management processes of essential information that ensures the life limit of a part is valid. The engineering plan provides methods for verifying the characteristics and qualities assumed in the design data using methods that are suitable for the part criticality. The engineering plan informs the manufacturing process of the attributes that affect the life of the part. The engineering plan, manufacturing plan, and service management plan are related in that assumptions made in the engineering plan are linked to how a part is manufactured and how that part is maintained in service. For example, environmental effects on life limited electric engine parts, such as humidity, might not be consistent with the assumptions used to design the part. ZeroAvia must ensure that the engineering plan is complete, available, and acceptable to the Administrator.

The term “manufacturing plan,” referenced in proposed special condition no. 13(b)(2), is the collection of data required to translate documented engineering design criteria into physical parts, and to verify that the parts comply with the properties established by the design data. Because engines are not intentionally tested to failure during a certification program, documents and processes used to execute production and quality systems required by § 21.137 guarantee inherent expectations for performance and durability. These systems limit the potential manufacturing outcomes to parts that are consistently produced within design constraints.

The manufacturing plan and service management plan ensure that essential information from the engineering plan, such as the design characteristics that safeguard the integrity of critical and life-limited parts, is consistently produced and preserved over the lifetime of those parts. The manufacturing plan includes special processes and production controls to prevent inclusion of manufacturing-induced anomalies, which can degrade the part's structural integrity. Examples of manufacturing-induced anomalies are material contamination, unacceptable grain growth, heat-affected areas, and residual stresses.

The service-management plan ensures the method and assumptions used in the engineering plan to determine the part's life remain valid by enabling corrections identified from in-service experience, such as service-induced anomalies and unforeseen environmental effects, to be incorporated into the design process. The service-management plan also becomes the ICA for maintenance, overhaul, and repairs of the part.

Lubrication System: Proposed special condition no. 14 would require ZeroAvia to ensure that the lubrication system is designed to function properly between scheduled maintenance intervals and to prevent contamination of the engine bearings. This proposed special condition would also require ZeroAvia to demonstrate the unique lubrication attributes and functional capability of the ZeroAvia Model ZA601electric engine design.

The corresponding part 33 regulations include provisions for lubrication systems used in reciprocating and turbine engines. The part 33 requirements account for safety issues associated with specific reciprocating and turbine engine system configurations. These regulations are not appropriate for the ZeroAvia Model ZA601 electric engines. For example, electric engines do not have a crankcase or lubrication oil sump. Electric engine bearings are sealed, so they do not require an oil circulation system. The lubrication system in these engines is also independent of the propeller pitch control system. Therefore, proposed special condition no. 14 incorporates only certain requirements from the part 33 regulations.

Power Response: Proposed special condition no. 15 would require the design and construction of the ZeroAvia Model ZA601 electric engines to enable an increase from the minimum—

(1) power setting to the highest rated power without detrimental engine effects, and

(2) within a time interval appropriate for the intended aircraft application.

The engine control system governs the increase or decrease in power in combustion engines to prevent too much (or too little) fuel from being mixed with air before combustion. Due to the lag in rotor response time, improper fuel/air mixtures can result in engine surges, stalls, and exceedances above rated limits and durations. Failure of the combustion engine to provide thrust, maintain rotor speeds below rotor burst thresholds, and keep temperatures below limits can have engine effects detrimental to the aircraft. Similar detrimental effects are possible in the ZeroAvia Model ZA601 electric engines, but the causes are different. Electric engines with reduced power response time can experience insufficient thrust to the aircraft, shaft over-torque, and over-stressed rotating components, propellers, and critical propeller parts. Therefore, this proposed special condition is necessary.

Continued Rotation: Proposed special condition no. 16 would require ZeroAvia to design the Model ZA601 electric engines such that, if the main rotating systems continue to rotate after the engine is shut down while in-flight, this continued rotation will not result in any hazardous engine effects.

The main rotating system of the ZeroAvia Model ZA601 engines consists of the rotors, shafts, magnets, bearings, and wire windings that convert electrical energy to shaft torque. For the initial aircraft application, this rotating system must continue to rotate after the power source to the engine is shut down. The safety concerns associated with this proposed special condition are substantial asymmetric aerodynamic drag that can cause aircraft instability, loss of control, and reduced efficiency; and may result in a forced landing or inability to continue safe flight.

Safety Analysis: Proposed special condition no. 17 would require ZeroAvia to comply with § 33.75(a)(1) and (a)(2), which require the applicant to conduct a safety analysis of the engine, and which would otherwise be applicable only to turbine aircraft engines. Additionally, this proposed special condition would require ZeroAvia to assess its engine design to determine the likely consequences of failures that can reasonably be expected to occur. The failure of such elements, and associated prescribed integrity requirements, must be stated in the safety analysis.

A primary failure mode is the manner in which a part is most likely going to fail. Engine parts that have a primary failure mode, a predictable life to the failure, and a failure consequence that results in a hazardous effect, are life-limited or critical parts. Some life-limited or critical engine parts can fail suddenly in their primary failure mode, from prolonged exposure to normal engine environments such as temperature, vibration, and stress, if those engine parts are not removed from service before the damage mechanisms progress to a failure. Due to the consequence of failure, these parts are not allowed to be managed by on-condition or probabilistic means because the probability of failure cannot be sensibly estimated in numerical terms. Therefore, the parts are managed by compliance with integrity requirements, such as mandatory maintenance (life limits, inspections, inspection techniques), to ensure the qualities, features, and other attributes that prevent the part from failing in its primary failure mode are preserved throughout its service life. For example, if the number of engine cycles to failure are predictable and can be associated with specific design characteristics, such as material properties, then the applicant can manage the engine part with life limits.

Complete or total power loss is not assumed to be a minor engine event, as it is in the turbine engine regulation § 33.75, to account for experience data showing a potential for higher hazard levels from power loss events in single-engine general aviation aircraft. The criteria in these proposed special conditions apply to an engine that continues to operate at partial power after a single electrical or electronic fault or failure. Total loss of power is classified at the aircraft level using proposed special condition nos. 10(g) and 33(h).

Ingestion: Proposed special condition no. 18 would require ZeroAvia to ensure that these engines will not experience unacceptable power loss or hazardous engine effects from ingestion. The associated regulations for turbine engines, §§ 33.76, 33.77, and 33.78, are based on potential performance impacts and damage from birds, ice, rain, and hail being ingested into a turbine engine that has an inlet duct, which directs air into the engine for combustion, cooling, and thrust. By contrast, the ZeroAvia electric engines are not configured with inlet ducts.

An “unacceptable” power loss, as used in proposed special condition no. 18(b), is such that the power or thrust required for safe flight of the aircraft becomes unavailable to the pilot. The specific amount of power loss that is required for safe flight depends on the aircraft configuration, speed, altitude, attitude, atmospheric conditions, phase of flight, and other circumstances where the demand for thrust is critical to safe operation of the aircraft.

Liquid and Gas Systems: Proposed special condition no. 19 would require ZeroAvia to ensure that systems used for lubrication or cooling of engine components are designed and constructed to function properly. Also, if a system is not self-contained, the interfaces to that system would be required to be defined in the engine installation manual. Systems for the lubrication or cooling of engine components can include heat exchangers, pumps, fluids, tubing, connectors, electronic devices, temperature sensors and pressure switches, fasteners and brackets, bypass valves, and metallic chip detectors. These systems allow the electric engine to perform at extreme speeds and temperatures for durations up to the maintenance intervals without exceeding temperature limits or predicted deterioration rates.

Vibration Demonstration: Proposed special condition no. 20 would require ZeroAvia to ensure the engine—

(1) is designed and constructed to function throughout its normal operating range of rotor speeds and engine output power without inducing excessive stress caused by engine vibration, and

(2) design undergoes a vibration survey.

The vibration demonstration is a survey that characterizes the vibratory attributes of the engine. It verifies that the stresses from vibration do not impose excessive force or result in natural frequency responses on the aircraft structure. The vibration demonstration also ensures internal vibrations will not cause engine components to fail. Excessive vibration force occurs at magnitudes and forcing functions or frequencies, which may result in damage to the aircraft. Stress margins to failure add conservatism to the highest values predicted by analysis for additional protection from failure caused by influences beyond those quantified in the analysis. The result of the additional design margin is improved engine reliability that meets prescribed thresholds based on the failure classification. The amount of margin needed to achieve the prescribed reliability rates depends on an applicant's experience with a product. The FAA considers the reliability rates when deciding how much vibration is “excessive.”

Overtorque: Proposed special condition no. 21 would require ZeroAvia to demonstrate that the engine is capable of continued operation without the need for maintenance if it experiences a certain amount of overtorque.

ZeroAvia's proposed electric engine converts electrical energy to shaft torque, which is used for propulsion. The electric motor, controller, and high-voltage systems control the engine torque. When the pilot commands power or thrust, the engine responds to the command and adjusts the shaft torque to meet the demand. During the transition from one power or thrust setting to another, a small delay, or latency, occurs in the engine response time. While the engine dwells in this time interval, it can continue to apply torque until the command to change the torque is applied by the engine control. The allowable amount of overtorque during operation depends on the engine's response to changes in the torque command throughout its operating range.

Calibration Assurance: Proposed special condition no. 22 would require ZeroAvia to subject the engine to calibration tests to establish its power characteristics and the conditions both before and after the endurance and durability demonstrations specified in proposed special condition nos. 23 and 26. The calibration test requirements specified in § 33.85 only apply to the endurance test specified in § 33.87, which is applicable only to turbine engines. The FAA proposes that the methods used for accomplishing those tests for turbine engines are not the best approach for electric engines. The calibration tests in § 33.85 have provisions applicable to ratings that are not relevant to the ZeroAvia Model ZA601 engines. Proposed special condition no. 22 would allow ZeroAvia to demonstrate the endurance and durability of the electric engine either together or independently, whichever is most appropriate for the engine qualities being assessed. Consequently, the proposed special condition applies the calibration requirement to both the endurance and durability tests.

Endurance Demonstration: Proposed special condition no. 23 would require ZeroAvia to perform an endurance demonstration test that is acceptable to the Administrator. The Administrator will evaluate the extent to which the test exposes the engine to failures that could occur when the engine is operated at up to its rated values, and determine if the test is sufficient to show that the engine design will not exhibit unacceptable effects in service, such as significant performance deterioration, operability restrictions, and engine power loss or instability, when it is run repetitively at rated limits and durations in conditions that represent extreme operating environments.

Temperature Limit: Proposed special condition no. 24 would require ZeroAvia to ensure the engine can endure operation at its temperature limits plus an acceptable margin. An “acceptable margin,” as used in the proposed special condition, is the amount of temperature above that required to prevent the least capable engine allowed by the type design, as determined by § 33.8, from failing due to temperature-related causes when operating at the most extreme engine and environmental thermal conditions.

Operation Demonstration: Proposed special condition no. 25 would require the engine to demonstrate safe operating characteristics throughout its declared flight envelope and operating range. Engine operating characteristics define the range of functional and performance values the ZeroAvia Model ZA601 electric engines can achieve without incurring hazardous effects. The characteristics are requisite capabilities of the type design that qualify the engine for installation into aircraft and that determine aircraft installation requirements. The primary engine operating characteristics are assessed by the tests and demonstrations that would be required by these special conditions. Some of these characteristics are shaft output torque, rotor speed, power consumption, and engine thrust response. The engine performance data ZeroAvia will use to certify the engine must account for installation loads and effects. These are aircraft-level effects that could affect the engine characteristics that are measured when the engine is tested on a stand or in a test cell. These effects could result from elevated inlet cowl temperatures, aircraft maneuvers, flowstream distortion, and hard landings. For example, an engine that is run in a sea-level, static test facility could demonstrate more capability for some operating characteristics than it will have when operating on an aircraft in certain flight conditions. Discoveries like this during certification could affect proposed engine ratings and operating limits. Therefore, the installed performance defines the engine performance capabilities.

Durability Demonstration: Proposed special condition no. 26 would require ZeroAvia to subject the engine to a durability demonstration. The durability demonstration must show that the engine is designed and constructed to minimize the development of any unsafe condition between maintenance intervals or between engine replacement intervals if maintenance or overhaul is not defined. The durability demonstration also verifies that the ICA is adequate to ensure the engine, in its fully deteriorated state, continues to generate rated power or thrust, while retaining operating margins and sufficient efficiency, to support the aircraft safety objectives. The amount of deterioration an engine can experience is restricted by operating limitations and managed by the engine ICA. Section 33.90 specifies how maintenance intervals are established; it does not include provisions for an engine replacement. Electric engines and turbine engines deteriorate differently; therefore, ZeroAvia will use different test effects to develop maintenance, overhaul, or engine replacement information for their electric engine.

System and Component Tests: Proposed special condition no. 27 would require ZeroAvia to show that the systems and components of the engine would perform their intended functions in all declared engine environments and operating conditions.

Sections 33.87 and 33.91, which are specifically applicable to turbine engines, have conditional criteria to decide if additional tests will be required after the engine tests. The criteria are not suitable for electric engines. Part 33 associates the need for additional testing with the outcome of the § 33.87 endurance test because it is designed to address safety concerns in combustion engines. For example, § 33.91(b) requires the establishment of temperature limits for components that require temperature-controlling provisions, and § 33.91(a) requires additional testing of engine systems and components where the endurance test does not fully expose internal systems and components to thermal conditions that verify the desired operating limits. Exceeding temperature limits is a safety concern for electric engines. The FAA proposes that the § 33.87 endurance test might not be the best way to achieve the highest thermal conditions for all the electronic components of electric engines because heat is generated differently in electronic systems than it is in turbine engines. Additional safety considerations also need to be addressed in the test. Therefore, proposed special condition no. 27 would be a performance-based requirement that allows ZeroAvia to determine when engine systems and component tests are necessary and to determine the appropriate limitations of those systems and components used in the ZeroAvia Model ZA601 electric engine.

Rotor Locking Demonstration: Proposed special condition no. 28 would require the engine to demonstrate reliable rotor locking performance and that no hazardous effects will occur if the engine uses a rotor locking device to prevent shaft rotation.

Some engine designs enable the pilot to prevent a propeller shaft or main rotor shaft from turning while the engine is running, or the aircraft is in-flight. This capability is needed for some installations that require the pilot to confirm functionality of certain flight systems before takeoff. The proposed ZeroAvia engine installations are not limited to aircraft that will not require rotor locking. Section 33.92 prescribes a test that may not include the appropriate criteria to demonstrate sufficient rotor locking capability for these engines. Therefore, this special condition is necessary.

The proposed special condition does not define “reliable” rotor locking but would allow ZeroAvia to classify the hazard as major or minor and assign the appropriate quantitative criteria that meet the safety objectives required by special condition no. 17 and the applicable portions of § 33.75.

Teardown Inspection: Proposed special condition no. 29 would require ZeroAvia to perform a teardown or non-teardown evaluation after the endurance, durability, and overtorque demonstrations, based on the criteria proposed in special condition no. 29(a) or (b).

Proposed special condition no. 29(b) includes restrictive criteria for “non-teardown evaluations” to account for electric engines, sub-assemblies, and components that cannot be disassembled without destroying them. Some electrical and electronic components like ZeroAvia's are constructed in an integrated fashion that precludes the possibility of tearing them down without destroying them. The proposed special condition indicates that, if a teardown cannot be performed in a non-destructive manner, then the inspection or replacement intervals must be established based on the endurance and durability demonstrations. The procedure for establishing maintenance should be agreed upon between the applicant and the FAA prior to running the relevant tests. Data from the endurance and durability tests may provide information that can be used to determine maintenance intervals and life limits for parts. However, if life limits are required, the lifing procedure is established by special condition no. 13, Critical and Life-Limited Parts, which corresponds to § 33.70. Therefore, the procedure used to determine which parts are life-limited, and how the life limits are established, requires FAA approval, as it does for § 33.70. Sections 33.55 and 33.93 do not contain similar requirements because reciprocating and turbine engines can be completely disassembled for inspection.

Containment: Proposed special condition no. 30 would require the engine to have containment features that protect against likely hazards from rotating components, unless ZeroAvia can show the margin to rotor burst does not justify the need for containment features. Rotating components in electric engines are typically disks, shafts, bearings, seals, orbiting magnetic components, and the assembled rotor core. However, if the margin to rotor burst does not unconditionally rule out the possibility of a rotor burst, then the proposed special condition would require ZeroAvia to assume a rotor burst could occur and design the stator case to contain the failed rotors, and any components attached to the rotor that are released during the failure. In addition, ZeroAvia must also determine the effects of subsequent damage precipitated by a main rotor failure and characterize any fragments that are released forward or aft of the containment features. Further, decisions about whether the ZeroAvia engine requires containment features, and the effects of any subsequent damage following a rotor burst, should be based on test or validated analysis. The fragment energy levels, trajectories, and size are typically documented in the installation manual because the aircraft will need to account for the effects of a rotor failure in the aircraft design. The intent of this proposed special condition is to prevent hazardous engine effects from structural failure of rotating components and parts that are built into the rotor assembly.

Engine and Propeller Systems Test: Proposed special condition no. 31 would require ZeroAvia to conduct functional demonstrations, including feathering, negative torque, negative thrust, and reverse thrust operations, as applicable, based on the propeller's or fan's variable pitch functions that are planned for use on these electric engines, using a representative propeller. The requirements of § 33.95 prescribe tests based on the operating characteristics of turbine engines equipped with variable pitch propellers, which include thrust response times, engine stall, propeller shaft overload, loss of thrust control, and hardware fatigue. The electric engines ZeroAvia proposes have different operating characteristics that substantially affect their susceptibility to these and other potential failures typical of turbine engines. Because ZeroAvia's proposed electric engines may be installed with a variable pitch propeller, the proposed special condition is necessary.

General Conduct of Tests: Proposed special condition no. 32 would require ZeroAvia to—

(1) include scheduled maintenance in the engine ICA;

(2) include any maintenance, in addition to the scheduled maintenance, that was needed during the test to satisfy the applicable test requirements; and

(3) conduct any additional tests that the Administrator finds necessary, as warranted by the test results.

For example, certification endurance test shortfalls might be caused by omitting some prescribed engine test conditions, or from accelerated deterioration of individual parts arising from the need to force the engine to operating conditions that drive the engine above the engine cycle values of the type design. If an engine part fails during a certification test, the entire engine might be subjected to penalty runs, with a replacement or newer part design installed on the engine, to meet the test requirements. Also, the maintenance performed to replace the part, so that the engine could complete the test, would be included in the engine ICA. In another example, if the applicant replaces a part before completing an engine certification test because of a test facility failure and can substantiate the part to the Administrator through bench testing, they might not need to substantiate the part design using penalty runs with the entire engine.

The term “excessive” is used to describe the frequency of unplanned engine maintenance, and the frequency of unplanned test stoppages, to address engine issues that prevent the engine from completing the tests in proposed special condition nos. 32(b)(1) and (2), respectively. Excessive frequency is an objective assessment from the FAA's analysis of the amount of unplanned maintenance needed for an engine to complete a certification test. The FAA's assessment may include the reasons for the unplanned maintenance, such as the effects test facility equipment may have on the engine, the inability to simulate a realistic engine operating environment, and the extent to which an engine requires modifications to complete a certification test. In some cases, the applicant may be able to show that unplanned maintenance has no effect on the certification test results, or they might be able to attribute the problem to the facility or test-enabling equipment that is not part of the type design. In these cases, the ICA will not be affected. However, if ZeroAvia cannot reconcile the amount of unplanned service, then the FAA may consider the unplanned maintenance required during the certification test to be “excessive,” prompting the need to add the unplanned maintenance to mandatory ICA to comply with the certification requirements.

Engine electrical systems: The current requirements in part 33 for electronic engine control systems were developed to maintain an equivalent level of safety demonstrated by engines that operate with hydromechanical engine control systems. At the time § 33.28 was codified, the only electrical systems used on turbine engines were low-voltage, electronic engine control systems (EEC) and high-energy spark-ignition systems. Electric aircraft engines use high-voltage, high-current electrical systems and components that are physically located in the motor and motor controller. Therefore, the existing part 33 control system requirements do not adequately address all the electrical systems used in electric aircraft engines. Proposed special condition no. 33 is established using the existing engine control systems requirement as a basis. It applies applicable airworthiness criteria from § 33.28 and incorporates airworthiness criteria that recognize and focus on the electrical power system used in the engine.

Proposed special condition no. 33(b) would ensure that all aspects of an electrical system, including generation, distribution, and usage, do not experience any unacceptable operating characteristics.

Proposed special condition no. 33(c) would require the electrical power distribution aspects of the electrical system to provide the safe transfer of electrical energy throughout the electric engine.

Proposed special condition no. 33(d) would require the engine electrical system to be designed such that the loss, malfunction, or interruption of the electrical power source, or power conditions that exceed design limits, will not result in a hazardous engine effect.

Proposed special condition no. 33(e) requires ZeroAvia to identify and declare, in the engine installation manual, the characteristics of any electrical power supplied from the aircraft to the engine, or electrical power supplied from the engine to the aircraft via energy regeneration, and any other characteristics necessary for safe operation of the engine.

Proposed special condition no. 33(f) requires ZeroAvia to demonstrate that systems and components will operate properly up to environmental limits, using special conditions, when such limits cannot be adequately substantiated by the endurance demonstration, validated analysis, or a combination thereof. The environmental limits referred to in this proposed special condition include temperature, vibration, HIRF, and others addressed in RTCA DO-160G, “Environmental Conditions and Test Procedures for Airborne Electronic/Electrical Equipment and Instruments.”

Proposed special condition 33(g) would require ZeroAvia to evaluate various electric engine system failures to ensure that these failures will not lead to unsafe engine conditions. The evaluation would include single-fault tolerance, would ensure no single electrical or electronic fault or failure would result in hazardous engine effects, and ensure that any failure or malfunction leading to local events in the intended aircraft application do not result in certain hazardous engine effects. The special condition would also implement integrity requirements, criteria for LOTC/LOPC events, and an acceptable LOTC/LOPC rate.

Proposed special condition 33(h) would require ZeroAvia to conduct a safety assessment of the engine electrical system to support the safety analysis in special condition no. 17. This safety assessment provides engine response to failures, and rates of these failures, that can be used at the aircraft safety assessment level.

The proposed special conditions contain the additional safety standards that the Administrator considers necessary to establish a level of safety equivalent to that established by the existing airworthiness standards.

As discussed above, these proposed special conditions are applicable to the model for which they are issued. Should the type certificate for that model be amended later to include any other model that incorporates the same novel or unusual design feature, these special conditions would apply to the other model as well.

This action affects only a certain novel or unusual design feature on one model of engine. It is not a rule of general applicability.

The authority citation for these special conditions is as follows:

Accordingly, the Federal Aviation Administration (FAA) proposes the following special conditions as part of the type certification basis for ZeroAvia's Model ZA601 engine. The applicant must also comply with the certification procedures set forth in title 14, Code of Federal Regulations (14 CFR) part 21.

1. Applicability:

(a) Unless otherwise noted in these special conditions, the engine design must comply with the airworthiness standards for aircraft engines set forth in 14 CFR part 33, except for those airworthiness standards that are specifically and explicitly applicable only to reciprocating and turbine aircraft engines or as specified herein.

(b) The applicant must comply with this part using a means of compliance, which may include consensus standards, accepted by the Administrator.

(c) The applicant requesting acceptance of a means of compliance must provide the means of compliance to the FAA in a form and manner acceptable to the Administrator.

2. Engine Ratings and Operating Limits: In addition to § 33.7(a), the engine ratings and operating limits must be established and included in the type certificate data sheet based on:

(a) Shaft power, torque, rotational speed, temperature, and time for:

(1) Rated takeoff power;

(2) Rated maximum continuous power; and

(3) Rated maximum temporary power and associated time limit.

(b) Duty cycle and the rating at that duty cycle. The duty cycle must be declared in the engine type certificate data sheet.

(c) Cooling fluid grade or specification.

(d) Power-supply requirements.

(e) Any other ratings or limitations that are necessary for the safe operation of the engine.

(f) In determining the engine performance and operating limitations, the overall limits of accuracy of the engine control system, of the engine electrical systems, and of the necessary instrumentation as defined in § 33.5(a)(6) must be taken into account.

3. Materials: The engine design must comply with § 33.15.

4. Fire Protection: The engine design must comply with § 33.17(b) through (g). In addition—

(a) The design and construction of the engine and the materials used must minimize the probability of the occurrence and spread of fire during normal operation and failure conditions and must minimize the effect of such a fire.

(b) Electrical wiring interconnection systems must be protected against arc faults that can lead to a fire that could result in hazardous engine effects as defined in special condition no. 17(d)(2) of these special conditions. Any non-protected electrical wiring interconnects must be analyzed to show that arc faults that can lead to a fire do not cause a hazardous engine effect.

5. Durability: The engine design and construction must minimize the development of an unsafe condition of the engine between maintenance intervals, overhaul periods, or mandatory actions described in the applicable ICA. The engine design must also comply with § 33.19(b).

6. Engine Cooling: The engine design and construction must comply with § 33.21. In addition, if cooling is required to satisfy the safety analysis as described in special condition no. 17 of these special conditions, the cooling system monitoring features and usage must be documented in accordance with § 33.5.

7. Engine Mounting Attachments and Structure: The engine mounting attachments and related engine structures must comply with § 33.23.

8. Accessory Attachments: The engine must comply with § 33.25.

9. Overspeed:

(a) A rotor overspeed must not result in a burst, rotor growth, or damage that results in a hazardous engine effect, as defined in special condition no. 17(d)(2) of these special conditions. Compliance with this paragraph must be shown by test, validated analysis, or a combination of both. Applicable assumed rotor speeds must be declared and justified.

(b) Rotors must possess sufficient strength with a margin to burst above certified operating conditions and above failure conditions leading to rotor overspeed. The margin to burst must be shown by test, validated analysis, or a combination thereof.

(c) The engine must not exceed the rotor speed operational limitations that could affect rotor structural integrity.

10. Engine Control Systems:

(a) Applicability. The requirements of this special condition apply to any system or device that is part of the engine type design that controls, limits, monitors, or protects engine operation, and is necessary for the continued airworthiness of the engine.

(b) Engine control. The engine control system must ensure that the engine does not experience any unacceptable operating characteristics or exceed its operating limits, including in failure conditions where the fault or failure results in a change from one control mode to another, from one channel to another, or from the primary system to the back-up system, if applicable.

(c) Design Assurance. The software and complex electronic hardware, including programmable logic devices, must be:

(1) Designed and developed using a structured and systematic approach that provides a level of assurance for the encoded logic commensurate with the hazard associated with the failure or malfunction of the systems in which the devices are located; and

(2) Substantiated by a verification methodology acceptable to the Administrator.

(d) Validation. All functional aspects of the control system must be substantiated by test, analysis, or a combination thereof, to show that the engine control system performs the intended functions throughout the declared operational envelope.

(e) Environmental Limits. Environmental limits that cannot be adequately substantiated by endurance demonstration, validated analysis, or a combination thereof must be demonstrated by the system and component tests in special condition no. 27 of these special conditions.

(f) Engine control system failures. The engine control system must:

(1) Have a maximum rate of loss of power control (LOPC) that is suitable for the intended aircraft application. The estimated LOPC rate must be documented in accordance with § 33.5;

(2) When in the full-up configuration, be single-fault tolerant, as determined by the Administrator, for electrical, electrically detectable, and electronic failures involving LOPC events;

(3) Not have any single failure that results in hazardous engine effects as defined in special condition no. 17(d)(2) of these special conditions; and

(4) Ensure failures or malfunctions that lead to local events in the aircraft do not result in hazardous engine effects, as defined in special condition no. 17(d)(2) of these special conditions, due to engine control system failures or malfunctions.

(g) System safety assessment. The applicant must perform a system safety assessment. This assessment must identify faults or failures that affect normal operation, together with the predicted frequency of occurrence of these faults or failures. The intended aircraft application must be taken into account to assure that the assessment of the engine control system safety is valid. The rates of hazardous and major faults must be documented in accordance with § 33.5.

(h) Protection systems. The engine control devices and systems' design and function, together with engine instruments, operating instructions, and maintenance instructions, must ensure that engine operating limits that can lead to a hazard will not be exceeded in service.

(i) Aircraft supplied data. Any single failure leading to loss, interruption, or corruption of aircraft-supplied data (other than power-command signals from the aircraft), or aircraft-supplied data shared between engine systems within a single engine or between fully independent engine systems, must:

(1) Not result in a hazardous engine effect, as defined in special condition no. 17(d)(2) of these special conditions, for any engine installed on the aircraft; and

(2) Be able to be detected and accommodated by the control system.

(j) Engine control system electrical power.

(1) The engine control system must be designed such that the loss, malfunction, or interruption of the control system electrical power source will not result in a hazardous engine effect, unacceptable transmission of erroneous data, or continued engine operation in the absence of the control function. Hazardous engine effects are defined in special condition no. 17(d)(2) of these special conditions. The engine control system must be capable of resuming normal operation when aircraft-supplied power returns to within the declared limits.

(2) The applicant must identify, document, and provide to the installer as part of the requirements in § 33.5, the characteristics of any electrical power supplied from the aircraft to the engine control system, including transient and steady-state voltage limits, and any other characteristics necessary for safe operation of the engine.

11. Instrument Connection: The applicant must comply with § 33.29(a), (e), and (g).

(a) In addition, as part of the system safety assessment of special condition nos. 10(g) and 33(h) of these special conditions, the applicant must assess the possibility and subsequent effect of incorrect fit of instruments, sensors, or connectors. Where practicable, the applicant must take design precautions to prevent incorrect configuration of the system.

(b) The applicant must provide instrumentation enabling the flight crew to monitor the functioning of the engine cooling system unless evidence shows that:

(1) Other existing instrumentation provides adequate warning of failure or impending failure;

(2) Failure of the cooling system would not lead to hazardous engine effects before detection; or

(3) The probability of failure of the cooling system is extremely remote.

12. Stress Analysis:

(a) A mechanical and thermal stress analysis, as well as an analysis of the stress caused by electromagnetic forces, must show a sufficient design margin to prevent unacceptable operating characteristics and hazardous engine effects as defined in special condition no. 17(d)(2) of these special conditions.

(b) Maximum stresses in the engine must be determined by test, validated analysis, or a combination thereof, and must be shown not to exceed minimum material properties.

13. Critical and Life-Limited Parts:

(a) The applicant must show, by a safety analysis or means acceptable to the Administrator, whether rotating or moving components, bearings, shafts, static parts, and non-redundant mount components should be classified, designed, manufactured, and managed throughout their service life as critical or life-limited parts.

(1) Critical part means a part that must meet prescribed integrity specifications to avoid its primary failure, which is likely to result in a hazardous engine effect as defined in special condition no. 17(d)(2) of these special conditions.

(2) Life-limited parts may include but are not limited to a rotor or major structural static part, the failure of which can result in a hazardous engine effect, as defined in special condition no. 17(d)(2) of these special conditions, due to a low-cycle fatigue (LCF) mechanism. A life limit is an operational limitation that specifies the maximum allowable number of flight cycles that a part can endure before the applicant must remove it from the engine.

(b) In establishing the integrity of each critical part or life-limited part, the applicant must provide the Administrator the following three plans for approval:

(1) an engineering plan, as defined in § 33.70(a);

(2) a manufacturing plan, as defined in § 33.70(b); and

(3) a service-management plan, as defined in § 33.70(c).

14. Lubrication System:

(a) The lubrication system must be designed and constructed to function properly between scheduled maintenance intervals in all flight attitudes and atmospheric conditions in which the engine is expected to operate.

(b) The lubrication system must be designed to prevent contamination of the engine bearings and lubrication system components.

(c) The applicant must demonstrate by test, validated analysis, or a combination thereof, the unique lubrication attributes and functional capability of (a) and (b).

15. Power Response:

(a) The design and construction of the engine, including its control system, must enable an increase:

(1) From the minimum power setting to the highest rated power without detrimental engine effects;

(2) From the minimum obtainable power while in-flight and while on the ground to the highest rated power within a time interval determined to be appropriate for the intended aircraft application; and

(3) From the minimum torque to the highest rated torque without detrimental engine effects in the intended aircraft application.

(b) The results of (a)(1), (a)(2), and (a)(3) of this special condition must be documented in accordance with § 33.5.

16. Continued Rotation: If the design allows any of the engine main rotating systems to continue to rotate after the engine is shut down while in-flight, this continued rotation must not result in any hazardous engine effects, as defined in special condition no. 17(d)(2) of these special conditions.

17. Safety Analysis:

(a) The applicant must comply with § 33.75(a)(1) and (a)(2) using the failure definitions in special condition no. 17(d) of these special conditions.

(b) The primary failure of certain single elements cannot be sensibly estimated in numerical terms. If the failure of such elements is likely to result in hazardous engine effects, then compliance may be shown by reliance on the prescribed integrity requirements of § 33.15 and special condition nos. 9 and 13 of these special conditions, as applicable. These instances must be stated in the safety analysis.

(c) The applicant must comply with § 33.75(d) and (e) using the failure definitions in special condition no. 17(d) of these special conditions, and the ICA in § 33.4.

(d) Unless otherwise approved by the Administrator, the following definitions apply to the engine effects when showing compliance with this condition:

(1) A minor engine effect does not prohibit the engine from performing its intended functions in a manner consistent with § 33.28(b)(1)(i), (b)(1)(iii), and (b)(1)(iv), and the engine complies with the operability requirements of special condition no. 15, special condition no. 25 and special condition no. 31 of these special conditions, as appropriate.

(2) The engine effects in § 33.75(g)(2) are hazardous engine effects with the addition of:

(i) Electrocution of the crew, passengers, operators, maintainers, or others; and

(ii) Blockage of cooling systems that could cause the engine effects described in § 33.75(g)(2) and special condition 17(d)(2)(i) of these special conditions.

(3) Any other engine effect is a major engine effect.

(e) The intended aircraft application must be taken into account when performing the safety analysis.

(f) The results of the safety analysis, and the assumptions about the aircraft application used in the safety analysis, must be documented in accordance with § 33.5(c).

18. Ingestion:

(a) Rain, ice, and hail ingestion must not result in an abnormal operation such as shutdown, power loss, erratic operation, or power oscillations throughout the engine operating range.

(b) Ingestion from other likely sources (birds, foreign objects—ice slabs) must not result in unacceptable power or thrust loss, or hazardous engine effects defined by special condition no. 17(d)(2) of these special conditions, or unacceptable power loss.

(c) If the design of the engine relies on features, attachments, or systems that the installer may supply, for the prevention of unacceptable power loss or hazardous engine effects, as defined in special condition no. 17(d)(2) of these special conditions, following potential ingestion, then the features, attachments, or systems must be documented in accordance with § 33.5.

19. Liquid and Gas Systems:

(a) Each system used for lubrication or cooling of engine components must be designed and constructed to function properly in all flight attitudes and atmospheric conditions in which the engine is expected to operate.

(b) If a system used for lubrication or cooling of engine components is not self-contained, the interfaces to that system must be defined and documented in accordance with § 33.5.

(c) The applicant must establish by test, validated analysis, or a combination of both that all static parts subject to significant pressure loads will not:

(1) Exhibit permanent distortion beyond serviceable limits, or exhibit leakage that could create a hazardous condition when subjected to normal and maximum working pressure with margin;

(2) Exhibit fracture or burst when subjected to the greater of maximum possible pressures with margin.

(d) Compliance with special condition no. 19(c) of these special conditions must take into account:

(1) The operating temperature of the part;

(2) Any other significant static loads in addition to pressure loads;

(3) Minimum properties representative of both the material and the processes used in the construction of the part; and

(4) Any adverse physical geometry conditions allowed by the type design, such as minimum material and minimum radii.

(e) Approved coolants and lubricants must be documented in accordance with § 33.5.

20. Vibration Demonstration:

(a) The engine must be designed and constructed to function throughout its operating range of rotational speeds and engine output power, including defined

The FAA invites you to send any written relevant data, views, or arguments about this proposal. Send your comments using a method listed under ADDRESSES . Include “Docket No. FAA-2026-0007; Project Identifier MCAI-2025-01183-R” at the beginning of your comments. The most helpful comments reference a specific portion of the proposal, explain the reason for any recommended change, and include supporting data. The FAA will consider all comments received by the closing date and may amend this proposal because of those comments.

Except for Confidential Business Information (CBI) as described in the following paragraph, and other information as described in 14 CFR 11.35, the FAA will post all comments received, without change, to regulations.gov, including any personal information you provide. The agency will also post a report summarizing each substantive verbal contact received about this NPRM.

CBI is commercial or financial information that is both customarily and actually treated as private by its owner. Under the Freedom of Information Act (FOIA) (5 U.S.C. 552), CBI is exempt from public disclosure. If your comments responsive to this NPRM contain commercial or financial information that is customarily treated as private, that you actually treat as private, and that is relevant or responsive to this NPRM, it is important that you clearly designate the submitted comments as CBI. Please mark each page of your submission containing CBI as “PROPIN.” The FAA will treat such marked submissions as confidential under the FOIA, and they will not be placed in the public docket of this NPRM. Submissions containing CBI should be sent to Matthew Williams, Aviation Safety Engineer, FAA, 1600 Stewart Avenue, Suite 410, Westbury, NY 11590. Any commentary that the FAA receives which is not specifically designated as CBI will be placed in the public docket for this rulemaking.

EASA, which is the Technical Agent for the Member States of the European Union, has issued EASA AD 2025-0137, dated June 27, 2025, and corrected October 29, 2025 (EASA AD 2025-0137) (also referred to as the MCAI), to correct an unsafe condition on Airbus Helicopters Model AS 350 B2, AS 350 B3, EC 130 B4, and EC 130 T2 helicopters. The MCAI states that new or more restrictive airworthiness limitations have been developed. Additionally, the MCAI advises that the airworthiness limitations are identified as mandatory for continued airworthiness and that AH [Airbus Helicopters] has issued applicable ALS revisions to specify new and more restrictive life limits and maintenance tasks. The FAA is issuing this proposed AD to prevent failure of critical parts and primary structural components, which if not addressed, could result in loss of control of the helicopter.

You may examine the MCAI in the AD docket at regulations.gov under Docket No. FAA-2026-0007.

The FAA reviewed EASA AD 2025-0137, which specifies replacing components before exceeding their life limits and accomplishing all applicable maintenance tasks within thresholds and intervals specified in the ALS as defined in EASA AD 2025-0137. Depending on the results of the maintenance tasks, EASA AD 2025-0137 specifies accomplishing corrective action(s) or contacting Airbus Helicopters for approved instructions and accomplishing those instructions.

Additionally, EASA AD 2025-0137 specifies revising the Aircraft Maintenance Programme (AMP) by incorporating the limitations, tasks, and associated thresholds and intervals described in the specified ALS, as applicable. Revising the AMP constitutes terminating action for the requirement to record accomplishment of the actions of replacing components before exceeding their life limits and accomplishing maintenance tasks within thresholds and intervals specified in the applicable ALS as specified in EASA AD 2025-0137 for demonstration of AD compliance on a continued basis.

This material is reasonably available because the interested parties have access to it through their normal course of business or by the means identified in the ADDRESSES section.

These products have been approved by the civil aviation authority (CAA) of another country and are approved for operation in the United States. Pursuant to the FAA's bilateral agreement with this State of Design Authority, that authority has notified the FAA of the unsafe condition described in the MCAI and material referenced above. The FAA is issuing this NPRM after determining that the unsafe condition described previously is likely to exist or develop on other products of the same type design.

This proposed AD would require the actions specified in EASA AD 2025-0137, described previously, as incorporated by reference, except for any differences identified as exceptions in the regulatory text of this proposed AD. See “Differences Between this Proposed AD and the MCAI” for a discussion of the general differences included in this AD.

Where EASA AD 2025-0137 specifies revising the approved AMP within 12 months after the effective date of EASA AD 2025-0137, this proposed AD would require revising the ALS of the existing approved maintenance or inspection program, as applicable, within 30 days after the effective date of this proposed AD.

In the FAA's ongoing efforts to improve the efficiency of the AD process, the FAA developed a process to use some CAA ADs as the primary source of information for compliance with requirements for corresponding FAA ADs. The FAA has been coordinating this process with manufacturers and CAAs. As a result, the FAA proposes to incorporate EASA AD 2025-0137 by reference in the FAA final rule. This proposed AD would, therefore, require compliance with EASA AD 2025-0137 in its entirety through that incorporation, except for any differences identified as exceptions in the regulatory text of this proposed AD. Using common terms that are the same as the heading of a particular section in EASA AD 2025-0137 does not mean that operators need comply only with that section. For example, where the AD requirement refers to “all required actions and compliance times,” compliance with this AD requirement is not limited to the section titled “Required Action(s) and Compliance Time(s)” in EASA AD 2025-0137. Material required in EASA AD 2025-0137 for compliance will be available at regulations.gov under Docket No. FAA-2026-0007 after the FAA final rule is published.

The FAA estimates that this AD, if adopted as proposed, would affect 1,163 helicopters of U.S. registry.

The FAA estimates the following costs to comply with this proposed AD.

Title 49 of the United States Code specifies the FAA's authority to issue rules on aviation safety. Subtitle I, section 106, describes the authority of the FAA Administrator. Subtitle VII: Aviation Programs, describes in more detail the scope of the Agency's authority.

The FAA is issuing this rulemaking under the authority described in Subtitle VII, Part A, Subpart III, Section 44701: General requirements. Under that section, Congress charges the FAA with promoting safe flight of civil aircraft in air commerce by prescribing regulations for practices, methods, and procedures the Administrator finds necessary for safety in air commerce. This regulation is within the scope of that authority because it addresses an unsafe condition that is likely to exist or develop on products identified in this rulemaking action.

The FAA determined that this proposed AD would not have federalism implications under Executive Order 13132. This proposed AD would not have a substantial direct effect on the States, on the relationship between the national government and the States, or on the distribution of power and responsibilities among the various levels of government.

For the reasons discussed above, I certify this proposed regulation:

(1) Is not a “significant regulatory action” under Executive Order 12866,

(2) Would not affect intrastate aviation in Alaska, and

(3) Would not have a significant economic impact, positive or negative, on a substantial number of small entities under the criteria of the Regulatory Flexibility Act.

Accordingly, under the authority delegated to me by the Administrator, the FAA proposes to amend 14 CFR part 39 as follows:

The FAA invites you to send any written relevant data, views, or arguments about this proposal. Send your comments using a method listed under ADDRESSES . Include “Docket No. FAA-2026-0006; Project Identifier MCAI-2024-00735-R” at the beginning of your comments. The most helpful comments reference a specific portion of the proposal, explain the reason for any recommended change, and include supporting data. The FAA will consider all comments received by the closing date and may amend the proposal because of those comments.

Except for Confidential Business Information (CBI) as described in the following paragraph, and other information as described in 14 CFR 11.35, the FAA will post all comments received, without change, to regulations.gov, including any personal information you provide. The agency will also post a report summarizing each substantive verbal contact received about this NPRM.

CBI is commercial or financial information that is both customarily and actually treated as private by its owner. Under the Freedom of Information Act (FOIA) (5 U.S.C. 552), CBI is exempt from public disclosure. If your comments responsive to this NPRM contain commercial or financial information that is customarily treated as private, that you actually treat as private, and that is relevant or responsive to this NPRM, it is important that you clearly designate the submitted comments as CBI. Please mark each page of your submission containing CBI as “PROPIN.” The FAA will treat such marked submissions as confidential under the FOIA, and they will not be placed in the public docket of this NPRM. Submissions containing CBI should be sent to Matthew Williams, Aviation Safety Engineer, FAA, 1600 Stewart Avenue, Suite 410, Westbury, NY 11590. Any commentary that the FAA receives which is not specifically designated as CBI will be placed in the public docket for this rulemaking.

The FAA issued AD 2022-11-08, Amendment 39-22058 (87 FR 33632, June 3, 2022) (AD 2022-11-08), for Airbus Helicopters Model AS350B, AS350BA, AS350B1, AS350B2, AS350B3, AS350D, EC130B4, and EC130T2 helicopters. AD 2022-11-08 was prompted by an MCAI originated by EASA, which is the Technical Agent for the Member States of the European Union. EASA issued AD 2021-0194R1, dated October 8, 2021 (EASA AD 2021-0194R1) to address the identification of certain parts needing maintenance actions, including life limits and maintenance tasks.

AD 2022-11-08 requires incorporating into maintenance records required by 14 CFR 91.417(a)(2) or 135.439(a)(2), as applicable for the helicopter, the requirements (airworthiness limitations) specified in EASA AD 2021-0194R1. The FAA issued AD 2022-11-08 to address the failure of certain parts, which could result in the loss of control of the helicopter.

Since the FAA issued AD 2022-11-08, EASA superseded EASA AD 2021-0194R1, with EASA AD 2024-0133 dated July 10, 2024, which was then superseded by EASA AD 2024-0133R1, dated June 27, 2025 (EASA AD 2024-0133R1) (also referred to as the MCAI). The MCAI states that new or more restrictive airworthiness limitations have been developed. Additionally, the MCAI advises that the airworthiness limitations and certification maintenance instructions are identified as mandatory for continued airworthiness and that AH [Airbus Helicopters] has issued applicable ALS revisions to specify new and more restrictive life limits and maintenance tasks, which includes repetitive checks and inspection requirements. The FAA is issuing this proposed AD to prevent failure of critical parts and primary structural components, which if not addressed, could result in loss of control of the helicopter.

You may examine the MCAI in the AD docket at regulations.gov under Docket No. FAA-2026-0006.

EASA AD 2024-0133R1 specifies that the manufacturer revised the ALS, for Airbus Helicopters Model AS350B2, AS350B3, EC130B4, and EC130T2 helicopters as applicable. The revised ALS for each model now incorporates the new and more restrictive tasks and limitations. The FAA is evaluating this issue and may take further rulemaking action to accommodate these ALS amendments.

The FAA reviewed EASA AD 2024-0133R1, which specifies procedures for replacing components before exceeding their life limits and accomplishing all applicable maintenance tasks within thresholds and intervals specified in the ALS as defined in EASA AD 2024-0133R1. Depending on the results of the maintenance tasks, EASA AD 2024-0133R1 specifies accomplishing corrective action(s) or contacting Airbus Helicopters for approved instructions and accomplishing those instructions.

Additionally, EASA AD 2024-0133R1 specifies revising the Aircraft Maintenance Programme (AMP) by incorporating the limitations, tasks, and associated thresholds and intervals described in the specified ALS, as applicable. Revising the AMP constitutes terminating action for the requirement to record accomplishment of the actions of replacing components before exceeding their life limits and accomplishing maintenance tasks within thresholds and intervals specified in the applicable ALS as required by EASA AD 2024-0133R1 for demonstration of AD compliance on a continued basis.

This material is reasonably available because the interested parties have access to it through their normal course of business or by the means identified in the ADDRESSES section.

These products have been approved by the civil aviation authority (CAA) of another country and are approved for operation in the United States. Pursuant to the FAA's bilateral agreement with this State of Design Authority, it has notified the FAA of the unsafe condition described in the MCAI and material referenced above. The FAA is issuing this NPRM after determining that the unsafe condition described previously is likely to exist or develop on other products of the same type design.

This proposed AD would retain none of the requirements of AD 2022-11-08 and would require the actions specified in EASA AD 2024-0133R1, described previously, as incorporated by reference, except for any differences identified as exceptions in the regulatory text of this proposed AD. See “Differences Between this Proposed AD and the MCAI” for a discussion of the general differences included in this AD.

Where EASA AD 2024-0133R1 specifies revising the approved AMP within 12 months after the effective date of EASA AD 2024-0133R1, this proposed AD would require revising the ALS of the existing approved maintenance or inspection program, as applicable, within 30 days after the effective date of this proposed AD.

EASA AD 2024-0133R1 applies to Airbus Helicopters Model AS350BB, whereas this proposed AD would not because that model does not have an FAA type certificate.

In the FAA's ongoing efforts to improve the efficiency of the AD process, the FAA developed a process to use some civil CAA ADs as the primary source of information for compliance with requirements for corresponding FAA ADs. The FAA has been coordinating this process with manufacturers and CAAs. As a result, the FAA proposes to incorporate EASA AD 2024-0133R1 by reference in the FAA final rule. This proposed AD would, therefore, require compliance with EASA AD 2024-0133R1 in its entirety through that incorporation, except for any differences identified as exceptions in the regulatory text of this proposed AD. Using common terms that are the same as the heading of a particular section in EASA AD 2024-0133R1 does not mean that operators need comply only with that section. For example, where the AD requirement refers to “all required actions and compliance times,” compliance with this AD requirement is not limited to the section titled “Required Action(s) and Compliance Time(s)” in EASA AD 2024-0133. Material required in EASA AD 2024-0133R1 for compliance will be available at regulations.gov under Docket No. FAA-2026-0006 after the FAA final rule is published.

The FAA estimates that this AD, if adopted as proposed, would affect 963 helicopters of U.S. registry.

The FAA estimates the following costs to comply with this proposed AD.

Title 49 of the United States Code specifies the FAA's authority to issue rules on aviation safety. Subtitle I, section 106, describes the authority of the FAA Administrator. Subtitle VII, Aviation Programs, describes in more detail the scope of the Agency's authority.

The FAA is issuing this rulemaking under the authority described in Subtitle VII, Part A, Subpart III, Section 44701: General requirements. Under that section, Congress charges the FAA with promoting safe flight of civil aircraft in air commerce by prescribing regulations for practices, methods, and procedures the Administrator finds necessary for safety in air commerce. This regulation is within the scope of that authority because it addresses an unsafe condition that is likely to exist or develop on products identified in this rulemaking action.

The FAA determined that this proposed AD would not have federalism implications under Executive Order 13132. This proposed AD would not have a substantial direct effect on the States, on the relationship between the national Government and the States, or on the distribution of power and responsibilities among the various levels of government.

For the reasons discussed above, I certify that the proposed regulation:

(1) Is not a “significant regulatory action” under Executive Order 12866,

(2) Would not affect intrastate aviation in Alaska, and

(3) Would not have a significant economic impact, positive or negative, on a substantial number of small entities under the criteria of the Regulatory Flexibility Act.

Accordingly, under the authority delegated to me by the Administrator, the FAA proposes to amend 14 CFR part 39 as follows:

All submitted comments and attachments are part of the public record and subject to disclosure. Do not enclose any material in your comments that you consider to be confidential or inappropriate for public disclosure.

Currently, the Postal Service only requires mailers to include accurate parcel dimensions in a manifest (Shipping Services File (SSF) or other approved electronic documentation) when the dimensions exceed 1 cubic foot or 22 inches in length. Failure to comply with this requirement, would subject the parcel to the Dimension Noncompliance Fee.

The Postal Service is proposing to expand the current standard in the Domestic Mail Manual by requiring mailers to always include accurate dimensions (length, width, and height) for parcels included in a manifest. Dimensions would not be required for Flat Rate priced pieces or USPS Returns pieces. Failure to comply with the expanded requirement, would continue to subject the parcel to the Dimension Noncompliance Fee. This proposal would also continue to only apply to commercial Priority Mail Express, Priority Mail, USPS Ground Advantage, and Parcel Select, products.

The Postal Service is proposing to implement this change effective July 12, 2026,

Although exempt from the notice and comment requirements of the Administrative Procedure Act (5 U.S.C. 553(b), (c)) regarding proposed rulemaking by 39 U.S.C. 410(a), the Postal Service invites public comment on the proposed revisions to Mailing Standards of the United States Postal Service, Domestic Mail Manual (DMM), incorporated by reference in the Code of Federal Regulations.

We will publish an appropriate amendment to 39 CFR part 111 to reflect these changes.

Accordingly, the Postal Service proposes the following changes to Mailing Standards of the United States Postal Service, Domestic Mail Manual (DMM), incorporated by reference in the Code of Federal Regulations (see 39 CFR 111.1):

Throughout this document “we,” “us,” and “our” refer to the EPA.

Submit your comments, identified by Docket ID No. EPA-R07-OAR-2025-3161, at https://www.regulations.gov. Once submitted, comments cannot be edited or removed from Regulations.gov. The EPA may publish any comment received to its public docket. Do not submit electronically any information you consider to be Confidential Business Information (CBI) or other information whose disclosure is restricted by statute. Multimedia submissions (audio, video, etc.) must be accompanied by a written comment. The written comment is considered the official comment and should include discussion of all points you wish to make. The EPA will generally not consider comments or comment contents located outside of the primary submission ( i.e., on the web, cloud, or other file sharing system). For additional submission methods, the full EPA public comment policy, information about CBI or multimedia submissions, and general guidance on making effective comments, please visit https://www.epa.gov/dockets/commenting-epa-dockets.

The EPA is proposing to approve a SIP revision submitted by the State of Missouri on March 19, 2025. The revisions are to Title 10, Division 10 of the Code of State Regulations (CSR), 10 CSR 10-6.060 “Construction Permits Required”. The purpose of the state regulation is to define sources required to obtain permits to construct and establishes requirements to be met prior to construction or modification of any sources, including procedures for the permitting authority to issue general permits, fees, and public notice requirements. The March 19, 2025, revisions to this rule include updates to the fees for facilities applying for and receiving construction permits for air pollution sources, removal of subsection (1)(B) from the state rule that provided the ability for facilities to apply for and receive voluntary permits which was never approved in the SIP, and administrative wording changes. EPA proposes to find that these revisions meet the requirements of the CAA, do not impact the stringency of the SIP, and do not adversely impact air quality. The full text of the rule revisions can be found in the redline strikeout section of the Missouri submittal included in this docket.

The State submission has met the public notice requirements for SIP submissions in accordance with 40 CFR 51.102. The submission also satisfied the completeness criteria of 40 CFR part 51, appendix V. The State provided public notice on this SIP revision from July 15, 2024, to September 5, 2024, and held a public hearing on August 29, 2024. Missouri received one (1) supporting comment during the comment period on 10 CSR 10-6.060. As explained above the revision meets the substantive SIP requirements of the CAA, including section 110 and implementing regulations.

The EPA is proposing to amend the Missouri SIP by approving the State's request to revise 10 CSR 10-6.060 “Construction Permits Required.” We are processing this as a proposed action because we are soliciting comments on this proposed action. Final rulemaking will occur after consideration of any comments.

In this document, the EPA is proposing to include regulatory text in an EPA final rule that includes incorporation by reference. In accordance with requirements of 1 CFR 51.5, the EPA is proposing to finalize the incorporation by reference of the Missouri rule 10 CSR 10-6.060 discussed in section II. of this preamble and as set forth below in the proposed amendments to 40 CFR part 52. The purpose of the state regulation is to define sources required to obtain permits to construct and establish requirements to be met prior to construction or modification of any sources and establish procedures for the permitting authority to issue general permits, fees, and public notice requirements. The EPA has made, and will continue to make, these materials generally available through https://www.regulations.gov and at the EPA Region 7 Office (please contact the person identified in the FOR FURTHER INFORMATION CONTACT section of this preamble for more information).

Under the CAA, the Administrator is required to approve a SIP submission that complies with the provisions of the CAA and applicable Federal regulations. 42 U.S.C. 7410(k); 40 CFR 52.02(a). Thus, in reviewing SIP submissions, EPA's role is to approve state choices, provided that they meet the criteria of the CAA. Accordingly, this action merely approves state law as meeting Federal requirements and does not impose additional requirements beyond those imposed by state law. For that reason, this action:

• Is not a significant regulatory action subject to review by the Office of Management and Budget under Executive Order 12866 (58 FR 51735, October 4, 1993);

• Is not subject to Executive Order 14192 (90 FR 9065, February 6, 2025) because SIP actions are exempt from review under Executive Order 12866:

• Does not impose an information collection burden under the provisions of the Paperwork Reduction Act (44 U.S.C. 3501 et seq. );

• Is certified as not having a significant economic impact on a substantial number of small entities under the Regulatory Flexibility Act (5 U.S.C. 601 et seq. );

• Does not contain any unfunded mandate or significantly or uniquely affect small governments, as described in the Unfunded Mandates Reform Act of 1995 (Pub. L. 104-4);

• Does not have federalism implications as specified in Executive Order 13132 (64 FR 43255, August 10, 1999);

• Is not subject to Executive Order 13045 (62 FR 19885, April 23, 1997) because it approves a state program;

• Is not a significant regulatory action subject to Executive Order 13211 (66 FR 28355, May 22, 2001); and

• Is not subject to requirements of section 12(d) of the National Technology Transfer and Advancement Act of 1995 (15 U.S.C. 272 note) because application of those requirements would be inconsistent with the CAA.

In addition, the SIP is not approved to apply on any Indian reservation land or in any other area where EPA or an Indian Tribe has demonstrated that a Tribe has jurisdiction. In those areas of Indian country, the rule does not have Tribal implications and will not impose substantial direct costs on Tribal governments or preempt Tribal law as specified by Executive Order 13175 (65 FR 67249, November 9, 2000).

For the reasons stated in the preamble, the EPA proposes to amend 40 CFR part 52 as set forth below:

The DC title V operating permit program is implemented through its “Operating Permits and Acid Rain Programs,” codified in 20 District of Columbia Municipal Regulations (DCMR) Chapter 3. The EPA initially granted full approval of the DC title V operating permit program effective on November 30, 2001. See 66 FR 52538 (October 16, 2001). However, in a notice of deficiency (NOD) published in the Federal Register on December 21, 2001 (66 FR 65947), the EPA notified the District of Columbia of EPA's finding that the District's provisions for providing public notification of permitting actions did not fully comply with the requirements of the CAA and its implementing regulations. On April 4, 2003, the District of Columbia submitted revisions to the public notification requirements of the operating permit program and adequately resolved the deficiency identified in the 2001 EPA NOD (December 21, 2001, 66 FR 65947). The EPA subsequently determined that the District of Columbia maintains final full approval of the Clean Air Act title V operating permit program. See 68 FR 18581(April 16, 2003).

On May 30, 2024, DOEE submitted a revision to 20 DCMR Chapter 3 for approval into the state's EPA-approved title V program. DOEE revised 20 DCMR Chapter 3 to update fees for 40 CFR part 70 operating permits (“major source” or title V permits). Additionally, the DOEE revision clarified and resolved errors in the existing regulations, including adding a definition for the term “relevant emission units.” The revision also reorganized some sections in Chapter 3 with no substantive change in content.

DOEE's updated fee collection schedule is designed to ensure sufficient funding for its title V program, in order to cover all reasonable costs required to implement and administer the DOEE Title V Operating Permit Program as required by 40 CFR 70.9(a) and (b). Title V program costs include those for activities such as reviewing and processing operating permits and preconstruction permits, conducting inspections, responding to complaints and pursuing enforcement actions, emissions and ambient air monitoring, preparing applicable regulations and guidance, modeling, analyses, demonstrations, emission inventories, and tracking emissions. Under 40 CFR 70.9(a), an approved state or local title V operating permits program must require that the owners or operators of 40 CFR part 70 sources pay annual fees, or the equivalent over some other period, that are sufficient to cover the permit program costs and ensure that any fee required under 40 CFR 70.9 is used solely for permit program costs. The fee schedule must result in the collection and retention of revenues sufficient to cover the permit program implementation and oversight costs. See 40 CFR 70.9(b).

Following the District of Columbia's municipal rulemaking process, DC revised its State Operating Permits Program under title V of the Clean Air Act through a rulemaking titled Air Quality Permit Fees and Synthetic Minor Permitting Program (effective June 5, 2020, 67 DCR 006789-006825). Through this rulemaking, DOEE revised fees for 40 CFR part 70 operating permits—major sources or title V permits—in 20 DCMR Chapter 3. Additionally, Chapter 3 was revised to clarify and resolve errors in the existing regulations, including adding a definition for the term “relevant emission units.” The District requests the EPA approval of Air Quality Permit Fees and Synthetic Minor Permitting Program as a revision to the District of Columbia's title V program, as required under 40 CFR 70.4(i). This submittal also satisfies one of the action items from DOEE's FY2023 Clean Air Act Title V Program Evaluation, dated September 6, 2023, which required DOEE to submit this regulation as a title V program revision within 12 months of the report date. 1 The DC submission indicates that it is necessary to update its fee collection schedule, otherwise DOEE would not be able to fully fund its title V program.

In its May 30, 2024 submittal, DC sought the EPA approval of its revisions to 20 DCMR Chapter 3 into its title V program. DC's revisions to 20 DCMR Chapter 3 revised fees (Section 305) for its title V operating permit program. The revision reorganized three sections in Chapter 3 with no substantive change in content, including section 300 on applicability, section 301 on permit applications, and section 303 on permit issuance, renewal, reopening, and revision. The revision also clarified and resolved errors in the existing regulations, including adding a definition for the term “relevant emission units.” DOEE's initial submission also included revisions in 20 DCMR Chapter 2 sections 200, 202, and 210 to create a synthetic minor permitting program, and added new section 211 to establish general construction and operating permit fees. However, in a May 28, 2025 supplemental letter which is included in the docket for this action, DOEE clarified its request so that only the revisions in 20 DCMR Chapter 3 found in Air Quality Permit Fees and Synthetic Minor Permitting Program will be incorporated as a revision to the District of Columbia's title V program, as required under 40 CFR 70.4(i). 2

In 20 DCMR Chapter 3 section 305, DOEE restructured 40 CFR part 70 sources permit application fee (section 305.1) and annual fees based on the total tons of actual emissions of each regulated pollutant (section 305.2, section 305.3). Section 305.5 requires that owners or operators of sources accepting federally enforceable emission limits pursuant to sections 200.6 and 300.3(c) shall pay a permit application fee (original and renewal applications) of five thousand dollars ($5,000). Section 305.6 stipulates that DOEE use the Consumer Price Index for annual increases of fees charged under sections 305.2 and 305.3. Other subsections of section 305 are related to when and where to pay and penalties for failure to pay on time. DOEE added a definition of “relevant emission units” in section 399 (Definitions and Abbreviations).

With this fee schedule change, DOEE indicates that it can ensure that fees will remain sufficient to cover the costs of administering the plan approval application and operating permit process as required by section 502(b) of the CAA. Without this fee update, DOEE's title V program is vulnerable and may not be able to sustain its title V operating permit program in a manner that is consistent with Federal requirements. If funds were to become insufficient to sustain an adequate title V program in DC, the EPA may determine that DOEE has not taken “significant action to assure adequate administration and enforcement of the Program” and take subsequent action as required under 40 CFR 70.10(b) and (c). This determination could lead to the EPA withdrawing approval of the DC title V operating permit program. Were that to occur, the EPA would have the authority and obligation to implement a Federal title V operating permit program in DC pursuant to 40 CFR part 71. The withdrawal of program approval could also lead to the imposition of mandatory and discretionary sanctions under the CAA. See 42 U.S.C. 7509(b).

The EPA reviewed DOEE's submittal for consistency with the presumptive minimum fee rate outlined in the September 17, 2024, EPA Office of Air Quality Planning and Standards memorandum, 3 as well as the requirements of 40 CFR 70.9(b)(2), and determined that DOEE met the requirements of CAA section 502. The EPA also determined the submittal is consistent with applicable EPA requirements in the title V operating permit program of the CAA and 40 CFR 70.9 for the collection of sufficient title V fees to cover permit program implementation and oversight costs. This rulemaking proposes to approve DC's revision of its title V fees in order to ensure the fees collected are sufficient to fund DC's title V program.

Pursuant to 40 CFR 70.4(i)(2), the EPA is proposing to approve as a revision to the District of Columbia title V operating permit program. DOEE's May 30, 2024 submittal revised DC's title V fee structure in order to ensure sufficient fees are collected each year adequately and continually fund DC's title V program. The revisions meet the relevant requirements of section 502 of the CAA and 40 CFR 70.4 and 70.9. The EPA is soliciting public comments on the issues discussed in this document. These comments will be considered before taking final action.

Under the CAA, the Administrator approves title V operating permit program revisions that comply with the Act and applicable Federal Regulations. See 42 U.S.C. 7661a(d). Thus, in reviewing title V operating permit program submissions, the EPA's role is to approve state choices, provided that they meet the criteria of the CAA. This action merely approves state law as meeting Federal requirements and does not impose additional requirements beyond those imposed by state law. For that reason, this action:

• Is not a significant regulatory action subject to review by the Office of Management and Budget under Executive Orders 12866 (58 FR 51735, October 4, 1993);

• Is not subject to Executive Order 14192 (90 FR 9065, February 6, 2025) because SIP actions are exempt from review under Executive Order 12866:

• Does not impose an information collection burden under the provisions of the Paperwork Reduction Act (44 U.S.C. 3501 et seq. );

• Is certified as not having a significant economic impact on a substantial number of small entities under the Regulatory Flexibility Act (5 U.S.C. 601 et seq. );

• Does not contain any unfunded mandate or significantly or uniquely affect small governments, as described in the Unfunded Mandates Reform Act of 1995 (Pub. L. 104-4);

• Does not have federalism implications as specified in Executive Order 13132 (64 FR 43255, August 10, 1999);

• Is not subject to Executive Order 13045 (62 FR 19885, April 23, 1997) because it approves a state program;

• Is not a significant regulatory action subject to Executive Order 13211 (66 FR 28355, May 22, 2001); and

• Is not subject to requirements of section 12(d) of the National Technology Transfer and Advancement Act of 1995 (15 U.S.C. 272 note) because application of those requirements would be inconsistent with the Clean Air Act.

In addition, the proposed rulemaking is not approved to apply on any Indian reservation land or in any other area where the EPA or an Indian Tribe has demonstrated that a Tribe has jurisdiction. In those areas of Indian country, the rule does not have Tribal implications and will not impose substantial direct costs on Tribal governments or preempt Tribal law as specified by Executive Order 13175 (65 FR 67249, November 9, 2000).