EASA CS-25
EASA CS-25, formally known as the Certification Specifications for Large Aeroplanes, is a comprehensive set of airworthiness standards established by the European Union Aviation Safety Agency (EASA) to ensure the safe design, construction, and certification of turbine-powered large aeroplanes intended for the transport of passengers, cargo, or mail in air commerce.[1] These specifications apply specifically to large aeroplanes, defined as those with a maximum certificated take-off mass exceeding 5,700 kg (12,500 lb). CS-25 is structured into several subparts that address critical aspects of aeroplane certification, including general provisions (Subpart A), flight characteristics and performance (Subpart B), structural integrity under various loads and environmental conditions (Subpart C), design and construction requirements (Subpart D), powerplant installation and performance (Subpart E), equipment and systems functionality (Subpart F), and operating limitations with marking and placard information (Subpart G).[2] Additional subparts cover specialized areas such as electrical wiring interconnection systems (Subpart H) and auxiliary power unit installations (Subpart J).[2] The specifications emphasize safety through rigorous requirements for performance in takeoff, climb, cruise, landing, and emergency scenarios, including operations on contaminated runways, in icing conditions, and during engine failures.[2] Structural design must withstand limit and ultimate loads, gusts, turbulence, and damage tolerance, with safety factors ensuring no detrimental deformation or failure under foreseeable conditions.[2] Powerplant and equipment standards mandate fire protection, redundancy, and reliability to minimize failure risks, while human factors considerations ensure flight crew interfaces reduce workload and enhance controllability.[2] Originally derived from the Joint Aviation Requirements (JAR-25) and aligned with international standards, CS-25 has undergone regular amendments to incorporate technological advancements and safety enhancements, with the latest being Amendment 28 issued in December 2023, which updates performance requirements for air operations and integrates state-of-the-art compliance methods.[3] Compliance with CS-25 is mandatory for type certification of large aeroplanes in the European Union, serving as the primary regulatory framework equivalent to the FAA's FAR Part 25 in the United States.[2]Overview
Scope and Applicability
EASA CS-25 applies to large aeroplanes in the transport category, defined as turbine-powered aeroplanes with a maximum certificated take-off mass exceeding 5,700 kg (12,500 lb). This specification establishes the airworthiness standards for the design, construction, and performance of such aircraft intended for commercial air transport operations, ensuring they meet safety requirements for carrying passengers, cargo, or mail over extended ranges.[2] It excludes non-turbine powered aeroplanes, as well as smaller categories like gliders, single-engine aeroplanes, and very light aircraft, which fall under separate certification specifications such as CS-22 or CS-23.[1] Specific exclusions encompass experimental aeroplanes, which operate under special conditions without full type certification, and military aeroplanes, governed by defence-specific standards unless they pursue civil certification for dual use.[2] These limitations ensure CS-25 focuses on civil transport aeroplanes designed for scheduled or non-scheduled commercial services, promoting uniformity in safety for high-capacity operations.Purpose and Harmonization
The Certification Specifications for Large Aeroplanes (CS-25) primarily establish the minimum standards for airworthiness to ensure the safe design, construction, and operation of large aeroplanes used in transport categories.[4] These specifications cover essential aspects such as flight characteristics, structural integrity, powerplant performance, equipment functionality, and operational limitations, all aimed at mitigating risks during all phases of flight.[4] By setting these requirements, CS-25 emphasizes the prevention of accidents through rigorous criteria for structural strength to withstand loads, performance capabilities under various conditions, and the reliability of critical systems to maintain control and safety.[2] CS-25 is harmonized with the Federal Aviation Administration's (FAA) Federal Aviation Regulations (FAR) Part 25 to facilitate consistent certification processes across jurisdictions, reducing redundant testing and enhancing global safety standards.[5] This alignment is supported by the Bilateral Aviation Safety Agreement (BASA) between the European Union and the United States, signed on 30 June 2008 with Technical Implementation Procedures (TIP) for mutual recognition of airworthiness certifications.[6] Where differences exist, such as in specific standards for systems or structures, they are documented in Significant Standards Differences (SSDs) to guide applicants on compliance needs for dual certification.[5] As part of the European Union's regulatory framework, CS-25 implements the initial airworthiness requirements outlined in Regulation (EC) No 216/2008, which establishes common rules for civil aviation and empowers the European Union Aviation Safety Agency (EASA) to develop and enforce such specifications.[7] This regulation mandates uniform standards for product certification, ensuring that large aeroplanes certified under CS-25 meet EU-wide safety objectives before entering service.[7] Through ongoing amendments, CS-25 remains aligned with evolving EU legislation to address emerging safety and environmental concerns.[3]Historical Development
Origins in JAR-25
The Joint Aviation Authorities (JAA), originally established as the Joint Airworthiness Authorities in 1970, developed JAR-25 during the 1970s as a common European airworthiness code for the certification of large aeroplanes. This harmonized standard was primarily based on the U.S. Federal Aviation Regulations Part 25 (FAR-25), with adaptations to align with the International Civil Aviation Organization (ICAO) Annex 8 provisions for aircraft airworthiness. The initiative aimed to facilitate mutual recognition of type certificates among European member states, reducing duplication in certification processes for manufacturers operating across borders.[8][9][10] JAR-25's initial formal arrangements were signed in 1979, enabling the first joint certification of an aircraft in 1983, marking a shift from disparate national rules to unified requirements. Subsequent changes, such as Change 10 adopted in 1983, incorporated enhanced safety standards for aeroplane doors and other features, reflecting ongoing harmonization efforts with global practices. By 2003, JAR-25 had reached Amendment 16, integrating refinements from operational experience and bilateral agreements with authorities like the FAA to address evolving safety needs.[11][12][13] Key differences from early FAR-25 versions included the mandatory use of SI (metric) units for measurements, facilitating consistency in European engineering and manufacturing practices, as well as provisions tailored to regional environmental factors, such as noise abatement and emissions aligned with emerging European directives. These adaptations ensured JAR-25 not only met ICAO baselines but also supported Europe's integrated aviation market. Prior to the establishment of the European Aviation Safety Agency (EASA), JAR-25 effectively unified certification standards across up to 32 JAA member states, streamlining approvals for aircraft like the Airbus A320 family and promoting safer, more efficient cross-border operations.[9][14][8]Transition to EASA CS-25
The European Aviation Safety Agency (EASA) was established through Regulation (EC) No 1592/2002, adopted on 15 July 2002 and entering into force on 28 September 2002, to create a centralized European Union authority responsible for civil aviation safety, including type certification. This replaced the intergovernmental Joint Aviation Authorities (JAA) model, which had coordinated standards across member states but lacked direct legal enforcement powers under EU law.[15] The rationale for the transition was to enhance regulatory efficiency, uniformity, and accountability in aviation certification across the EU, aligning with broader integration goals while maintaining harmonization with international standards like the U.S. Federal Aviation Regulations (FAR) Part 25.[16] The initial version of Certification Specifications for Large Aeroplanes (CS-25) was issued by EASA on 17 October 2003, directly based on JAR-25 at Amendment 16 (published 1 May 2003).[17] This adaptation involved minimal substantive changes to the JAR-25 text, primarily editorial clarifications and adjustments to ensure compatibility with the EU's Basic Regulation (EC) No 1592/2002, such as rephrasing requirements to fit the new legal structure without altering technical content.[16] CS-25 took effect upon issuance, enabling EASA to assume full responsibility for large aeroplane certifications from the JAA as of 28 September 2003.[18] The transition ensured continuity for the aviation industry, with ongoing type certification projects initiated under JAR-25 seamlessly transferred to the CS-25 framework without requiring revalidation.[19] Aircraft types already approved under JAR-25 were grandfathered, retaining their validity under EASA oversight, which prevented disruptions to production, operations, and fleet approvals while allowing future changes to be assessed against CS-25.[20] This approach preserved 29 years of JAA-developed standards and international harmonization efforts.[16]Amendment Process and Timeline
The amendment process for EASA CS-25 follows the European Union's standardized rulemaking procedure for aviation safety standards, governed by Regulation (EU) No 748/2012 on initial airworthiness. The European Union Aviation Safety Agency (EASA) initiates updates by issuing a Notice of Proposed Amendment (NPA), which outlines proposed changes to the certification specifications, acceptable means of compliance (AMC), and guidance material (GM). This NPA is published for public consultation, typically lasting three months, allowing stakeholders such as aircraft manufacturers, operators, and national authorities to submit comments. EASA then reviews these inputs and publishes a Comment Response Document (CRD) addressing the feedback, leading to refinements. Finally, the Executive Director of EASA issues a Decision adopting the amendment, which enters into force on a specified date and applies to new type certification applications thereafter. This process ensures harmonization with international standards, such as those from the Federal Aviation Administration (FAA), and incorporates lessons from safety incidents, technological advancements, and operational needs, with amendments generally issued every 1-2 years.[21] Acceptable Means of Compliance (AMC) and Guidance Material (GM) are updated concurrently with CS-25 amendments through the same NPA and Decision process, providing non-mandatory methods for demonstrating compliance with the specifications. These materials evolve to reflect best practices; for instance, updates to AMC often include revised advisory circulars or special conditions for emerging technologies. The integrated approach ensures that certification applicants have clear, up-to-date guidance without requiring separate rulemaking cycles.[2] CS-25 has undergone 28 amendments since its initial issuance in October 2003, with each building on prior versions to enhance safety and adaptability. Early amendments focused on clarifications and harmonization; for example, Amendment 1, effective December 12, 2005, introduced minor editorial and technical clarifications to align with JAR-25 transitions. Subsequent updates addressed specific risks, such as Amendment 11 in 2011, which incorporated enhancements to stall warning systems and angle-of-attack protection following the 2009 Air France Flight 447 (AF447) incident, where unreliable airspeed indications and loss of control highlighted needs for improved flight envelope protection in icing conditions.[22][23][24] Later amendments emphasized emerging threats and performance standards. Amendment 17, effective July 16, 2015, strengthened requirements for high-intensity radiated fields (HIRF) protection to safeguard avionics from electromagnetic interference. Amendment 25, effective January 13, 2020, introduced CS 25.1319 to address aircraft cybersecurity, mandating protection against unauthorized access to systems and networks amid growing digital integration in aviation. The most recent, Amendment 28, effective December 19, 2023, reviewed performance requirements for air operations, updated controllability and maneuverability criteria, and refined AMC/GM for state-of-the-art compliance, including considerations for advanced materials and operational interfaces. As of November 2025, no further amendments have been adopted, though ongoing NPAs signal continued evolution. These milestones underscore CS-25's role in proactively mitigating risks identified through accident investigations and industry feedback.[25][26][27]Document Organization
Subpart Structure
The Certification Specifications for Large Aeroplanes (CS-25) are organized into nine subparts, designated A through G, H, and J, which collectively outline the airworthiness requirements for transport-category aeroplanes. Subpart A covers general provisions, Subpart B addresses flight characteristics, Subpart C details structural integrity, Subpart D specifies design and construction standards, Subpart E focuses on powerplant installations, Subpart F pertains to equipment and systems, Subpart G includes operating limitations and information, Subpart H covers electrical wiring interconnection systems, and Subpart J addresses auxiliary power unit installations.[2] The certification specifications, along with Acceptable Means of Compliance (AMC) and Guidance Material (GM), are compiled into the Easy Access Rules for Large Aeroplanes (CS-25), a consolidated publication available in online and PDF formats.[9] Paragraphs within CS-25 are cross-referenced using the notation CS 25.XXX, where XXX denotes the specific requirement number, facilitating precise navigation and citation across the document and related materials. Appendices are included to address special conditions, interpretations, and additional detailed requirements not covered in the main subparts.[2] Consolidated versions of CS-25, incorporating amendments, exceed 1,200 pages, reflecting the comprehensive nature of the standards; these versions are periodically updated through the amendment process to incorporate evolving safety and technological considerations.Acceptable Means of Compliance and Guidance
The Acceptable Means of Compliance (AMC) and Guidance Material (GM) serve as supplementary documents to Certification Specifications for Large Aeroplanes (CS-25), providing non-mandatory support for applicants seeking to demonstrate compliance with the airworthiness requirements. AMC outlines specific, acceptable methods for meeting CS-25 provisions, while GM offers explanatory material to clarify regulatory intent without prescribing particular approaches. These materials are developed by the European Union Aviation Safety Agency (EASA) to facilitate consistent interpretation and application across certification projects.[2] AMC provides detailed, practical methods that applicants may use to establish compliance with CS-25 requirements, though they are not the sole options available. For instance, AMC 25.1309 addresses equipment, systems, and installations by recommending a system safety assessment process, including the use of fault tree analysis to classify failure conditions based on severity—such as minor, major, hazardous, or catastrophic—and to quantify probabilities for acceptable risk levels. This guidance emphasizes a structured approach to failure condition analysis, ensuring that systems do not reduce safety or aircraft performance below acceptable thresholds.[28][2] In contrast, GM focuses on interpretive guidance to aid understanding of CS-25 requirements without mandating specific compliance methods. An example is GM 25.571, which elucidates the damage-tolerance and fatigue evaluation of structures by explaining the need to consider residual strength after damage, crack propagation rates, and inspection intervals, thereby supporting the design of structures resilient to fatigue, corrosion, or accidental damage over the aeroplane's operational life. This material draws from industry experience to highlight key considerations, such as the integration of damage-tolerance principles for metallic and composite structures.[29][2] The development of AMC and GM occurs alongside or following amendments to CS-25, involving consultation with industry stakeholders and review through EASA Certification Review Items (CRI). CRIs are tools used to convey additional regulatory information or interpretations not fully covered in the base specifications, ensuring that evolving technologies and safety insights are incorporated into the guidance. These materials are typically published as part of EASA's Easy Access Rules compilations, with updates reflecting lessons from certification programs and harmonization efforts.[30][2] Legally, both AMC and GM hold non-binding status under EASA regulations, meaning compliance achieved through these means satisfies CS-25 requirements but does not preclude alternative methods if they equivalently demonstrate airworthiness and gain EASA approval. Applicants proposing deviations must justify them via equivalent level of safety arguments, often through formal certification plans or special conditions. This flexibility promotes innovation while maintaining rigorous safety standards.[31][32]Certification Requirements
General Provisions (Subpart A)
Subpart A of EASA CS-25 establishes the foundational requirements for certifying large aeroplanes, ensuring compliance with airworthiness standards through defined procedures, terminology, and handling of design modifications.[33] These provisions apply universally to type certification and supplemental type certificates, setting the basis for demonstrating that the aeroplane meets all applicable certification specifications under normal and foreseeable operating conditions.[2] CS 25.21 outlines the proof of compliance, requiring that each certification requirement be met across appropriate combinations of weight, centre of gravity, altitude, airspeed, and power settings expected in service.[33] Compliance must be demonstrated through tests on the aeroplane type, calculations equivalent in accuracy to test results, or systematic investigations of probable configurations where direct inference is not feasible.[33] For new type certifications, the basis is the effective date of the application under the latest CS-25 amendment, while amended types may elect earlier amendments if shown compliant, subject to Agency approval.[2] Additionally, under CS 25.21(g), aeroplanes certified for flight in icing conditions must demonstrate compliance with relevant specifications using ice accretions defined in Appendices C and O, assuming normal operations and anti-icing/de-icing systems as installed.[33] CS 25.3 provides definitions and abbreviations to ensure consistent interpretation throughout CS-25.[33] Key terms include "aeroplane," defined as a power-driven heavier-than-air aircraft deriving lift primarily from fixed aerodynamic surfaces under given flight conditions, distinguishing it from the American English "airplane" used in FAA equivalents.[33] Undefined terms adopt meanings from ICAO Annex 1 to the Chicago Convention.[33] Abbreviations encompass entities like EASA (European Union Aviation Safety Agency), ICAO (International Civil Aviation Organization), and performance metrics such as CAS (calibrated airspeed), IAS (indicated airspeed), and VMO (maximum operating limit speed).[33] CS 25.31 addresses general certification procedures for changes in type design, mandating that proposed modifications to an approved product comply with applicable CS-25 provisions without adversely affecting safety.[33] Applicants must substantiate compliance via tests, analyses, or other methods approved by EASA, accounting for the change's impacts on weight, balance, performance, and systems.[33] Major changes, which appreciably affect airworthiness characteristics, require classification and approval under Part 21 procedures, potentially invoking the original certification basis or later amendments as determined by the Agency.[2]Flight (Subpart B)
Subpart B of CS-25 outlines the certification requirements for the flight characteristics of large aeroplanes, ensuring safe performance, controllability, and stability across various operational conditions, including normal operations and engine failures.[9] These specifications apply to aeroplanes intended for transport category operations and must be demonstrated through analysis, simulation, or flight testing under conditions representative of service environments.[9] Compliance proof is required for each altitude up to the maximum certificated operating altitude, with particular emphasis on multi-engine aeroplanes handling one-engine-inoperative scenarios to maintain safe flight paths.[9] Performance standards in CS-25 focus on critical phases such as takeoff, climb, and landing, with distances and speeds calculated under standardised environmental conditions like sea level, standard atmosphere, and level runway.[9] For takeoff performance (CS 25.107 to 25.113), key speeds include V1 (decision speed), VR (rotation speed), and V2 (takeoff safety speed), where V2 must be at least 1.13 times the stall speed (VS1g) or 1.2 VS1g for two-engine aeroplanes, ensuring positive climb capability even with one engine inoperative.[9] Takeoff distances account for all-engines-operating and one-engine-inoperative cases, with the path cleared by at least 35 feet at the end of the runway for the former and 15 feet for the latter at V2.[9] Climb performance requirements (CS 25.117 to 25.123) mandate minimum gradients; for example, the all-engines-operating takeoff climb at V2 requires a 4% gradient for all multi-engine aeroplanes, while the one-engine-inoperative second segment climb demands 2.7%.[9] The landing climb (CS 25.119) specifies a 3.2% gradient with all engines operating in the landing configuration at V2L, using available takeoff power.[9] Landing distances (CS 25.125) are limited to those achievable with a 3.3% glide path and all engines operating, including a 50-foot screen height, with adjustments for one-engine-inoperative go-arounds.[9] Climb performance is quantified using the climb gradient formula, where the gradient equals the excess power divided by weight, expressed as: \text{Climb gradient} = \frac{T - D}{W} with T as thrust, D as drag, and W as weight; for CS 25.119, this ensures the one-engine-inoperative landing climb meets the minimum gradient under gear-up, flaps-extended conditions.[9] Flight controllability and stability requirements (CS 25.143) mandate that the aeroplane remains safely controllable and manoeuvrable during takeoff, climb, cruise, descent, and landing, including intentional one-engine-inoperative operations and high angles of attack up to stall.[9] Control forces must not exceed specified limits, such as 50 pounds for primary controls in normal flight, with positive stability ensuring trim within ±10% of maximum control deflection.[9] Stall characteristics (CS 25.201 to 25.207) require distinguishable warnings (e.g., via stick shaker or buffet) at speeds 5-10% above stall, with recovery achievable without exceeding 1.13 VS1g or losing more than 20% speed, and no unrecoverable roll-off at high angles of attack.[9] Ground handling and takeoff/landing speeds (CS 25.149 to 25.159) address minimum control speeds to prevent loss of directional or lateral control during critical phases.[9] The minimum control speed on the ground (VMCG, CS 25.149) is the lowest speed at which rudder and nose-wheel steering maintain control with the critical engine failed and takeoff power on the remaining engines, considering wind-up turns and unprepared surfaces.[9] Airborne minimum control speed (VMCA) ensures directional control with one engine inoperative at takeoff or landing configurations, not exceeding 1.2 VS1g.[9] Stall speed determination (CS 25.159) involves calibrated speeds in various configurations, with VS1g as the 1g stall speed used as a reference for margins in performance calculations.[9]Structure (Subpart C)
Subpart C of EASA CS-25 establishes the structural requirements for large aeroplanes to ensure the airframe withstands anticipated loads throughout its operational life without failure or excessive deformation. These standards define limit loads as the maximum expected in normal operations and ultimate loads as 1.5 times those limits, providing a safety margin against structural failure. Amendment 28 (2023) enhanced provisions for ditching survivability under CS 25.563.[2][3] The flight loads section (CS 25.301 to 25.341) specifies criteria for maneuver and gust conditions to simulate realistic aerodynamic forces. Maneuver loads must account for pilot-induced actions, with the positive limit maneuvering load factor not less than 2.5g at speeds up to the design dive speed (VD), varying based on aeroplane weight and configuration to prevent excessive stress during turns or pulls-ups. Gust and turbulence loads (CS 25.341) consider both discrete sharp-edged gusts and continuous atmospheric turbulence models, requiring the structure to endure vertical and lateral gust velocities up to 50 feet per second in level flight, ensuring stability across the flight envelope. These loads form the basis for deriving distributed forces on wings, fuselage, and empennage, prioritizing safety during unexpected environmental disturbances.[2] Structural integrity requirements (CS 25.303) mandate proof of compliance through analysis, testing, or a combination, demonstrating that the structure can carry all specified loads without permanent deformation beyond yield strength under limit conditions or failure under ultimate loads. The factor of safety of 1.5 applied to limit loads ensures the airframe remains intact even if loads slightly exceed expectations, with deformation limits set to avoid impairing continued safe flight or landing. This proof extends to all principal load-carrying elements, including control surfaces and landing gear attachments.[2] Fatigue evaluation and damage tolerance (CS 25.571) require a comprehensive assessment of the airframe's durability over its design life, assuming initial flaws or damage may exist. Manufacturers must conduct crack growth analyses to establish inspection thresholds and intervals, considering multiple damage scenarios such as fatigue cracks, corrosion, or manufacturing defects in critical locations like fuselage splices and wing attachments. The evaluation ensures that any damage remains detectable and contained until residual strength exceeds ultimate loads, with provisions for safe continued operation post-damage detection; for example, crack propagation rates are modeled using fracture mechanics to predict growth under repeated flight cycles.[2] Flutter prevention measures (CS 25.629) address aeroelastic instabilities by requiring analysis and ground/vibration tests to confirm no flutter, divergence, or control reversal occurs up to 15% above the design dive speed or maximum speed, whichever is lower. This includes evaluating the entire aeroplane, including stores or engines, under all combinations of mass, stiffness, and aerodynamic configurations to maintain stability margins. Compliance typically involves modal analysis and wind tunnel testing to verify damping ratios exceed critical values, preventing self-sustaining oscillations that could lead to structural failure.[2] Emergency landing provisions (CS 25.561) prescribe dynamic conditions for survivability, requiring the structure to absorb impact energies from hard landings on rough terrain or water without compromising occupant safety. Limit load factors include a 9g forward inertia force at the aeroplane center of gravity, combined with vertical accelerations up to 4.5g for fuselage and 6g for seats, ensuring no debris penetration of occupied areas or fuel systems and minimal risk of fire or injury. These conditions simulate worst-case scenarios like gear collapse, with the fuselage designed as a survival cell to protect passengers during deceleration. Amendment 28 (2023) provides additional guidance on ditching survivability.[2][3]Design and Construction (Subpart D)
Subpart D of EASA CS-25 establishes requirements for the design and construction of large aeroplanes, emphasizing materials, fabrication methods, and protective features to ensure structural integrity, occupant safety, and operational reliability under various conditions.[2] The provisions focus on preventing defects that could compromise safe flight and landing, with specific criteria for material selection and performance validation.Materials and Processes
CS 25.601 mandates that aeroplane structures must be free from inherent defects and designed to withstand all anticipated loads, including those from flight maneuvers and environmental factors, with strength justified through analysis, testing, or a combination thereof.[2] This general requirement ensures durability and safety by requiring that design details and parts are validated for suitability, often via tests to confirm performance under operational stresses.[2] Under CS 25.603, materials and manufacturing processes must demonstrate suitability, durability, and reliability, particularly for components whose failure could prevent continued safe flight and landing.[2] For composite materials, certification involves establishing strength, stiffness, fatigue resistance, and environmental durability through rigorous testing protocols outlined in Acceptable Means of Compliance (AMC) 25.603, including static, fatigue, and damage tolerance assessments to account for manufacturing variability and in-service degradation.[4] These processes prioritize statistical data from material coupons and structural elements to derive design allowables, ensuring composites meet or exceed metallic equivalents in critical airframe applications like fuselages and wings.[4]Protection Features
Protection against environmental hazards is integral to design, with CS 25.853 requiring compartment interiors, including seats, walls, and partitions, to use self-extinguishing materials that limit flame spread and smoke production during fire events.[2] Materials must pass vertical burn tests (e.g., 15-second flame application with no after-flame exceeding 15 seconds) and smoke density limits to minimize toxicity and visibility obstruction, enhancing evacuation safety in passenger and cargo areas.[2] Amendments to this certification specification, such as those in Amendment 28 (2023), have refined testing for new materials like advanced polymers, incorporating radiant panel tests for heat release rates.[3] Lightning strike protection under CS 25.581 requires the airframe to be designed to prevent catastrophic damage or ignition from direct strikes, typically achieved through conductive meshes or foils integrated into composite skins to divert current and limit thermal effects.[2] This involves zone classification (e.g., Zone 1A for highly vulnerable areas) and testing to verify no penetration or fuel ignition risks, ensuring continued structural integrity post-strike.[2]Doors and Exits
Doors must provide unobstructed access for crew and passengers while withstanding prescribed loads, as specified in CS 25.783, including emergency operation from both inside and outside without tools, and resistance to decompression forces up to 9 psi.[2] Accessibility provisions ensure that all doors, including service and emergency types, incorporate fail-safe mechanisms like torque-limiting handles to prevent jamming under impact or pressure differentials.[2] Emergency evacuation requirements in CS 25.803 demand that the aeroplane configuration allows full occupancy evacuation in 90 seconds or less under simulated emergency conditions, using half the exits with lighting failures.[2] This is demonstrated through full-scale demonstrations, factoring in cabin layout and exit usability to validate design features like clear paths and slide deployment.[2] CS 25.807 to CS 25.809 further detail emergency exits, requiring at least two Type I or equivalent exits per side with minimum dimensions (e.g., 24 inches wide by 48 inches high for Type I), located to ensure even distribution and rapid access within 9 meters for all occupants.[2] These exits must open inward or outward without impeding flow, with provisions for ditching and remote operations in larger aircraft.[2]Ventilation and Drainage
CS 25.831 requires ventilation systems to supply 0.55 pounds of fresh air per minute per occupant or 15 cubic feet per minute, whichever is greater, while preventing accumulation of harmful gases, fumes, or odors from any source.[2] Designs must include recirculation filters with efficiency against particulates and recirculation limited to 50% of total airflow, ensuring cabin air quality equivalent to ground levels and avoiding concentrations above 0.5% CO2.[2] For pressurized cabins, CS 25.841 specifies that the pressurization system must maintain a cabin altitude of no more than 8,000 feet at the maximum operating altitude of 41,000 feet, with rapid decompression capability to 25,000 feet in seconds.[2] Drainage provisions integrate with this system to remove condensate and prevent water accumulation, using sealed ducts and traps to avoid corrosion or icing, while tests under CS 25.843 verify structural endurance against pressure cycles equivalent to 16,000 flight hours.[2]Powerplant (Subpart E)
Subpart E of EASA CS-25 establishes certification requirements for the powerplant installation in large aeroplanes, ensuring that engines, auxiliary power units, and associated systems operate reliably under all anticipated conditions to support safe flight and landing.[9] The provisions emphasize the integration of propulsion components with the airframe, focusing on structural integrity, fluid management, and environmental protections to mitigate risks such as vibration, fire propagation, and external hazards. These requirements apply to turbine and piston engines, mandating designs that account for operational loads, failures, and maintenance accessibility without compromising overall aircraft safety.[9] Engine control and mounting specifications, outlined in CS 25.901 through CS 25.937, require installations that function effectively across the full range of powerplant characteristics and environmental exposures. For instance, CS 25.901 mandates that the powerplant be constructed to ensure safe operation essential for continued flight, including isolation from excessive vibrations that could endanger the airframe or systems. Engine mounts must withstand maximum torque and other loads, as per CS 25.903, while incorporating vibration dampers to limit stresses. Fire isolation is addressed through materials and arrangements that contain potential fires, preventing spread to adjacent structures. Controls for fuel and engines, under CS 25.931, must enable safe starting and operation, with safeguards against malfunctions that could lead to hazardous conditions. Thrust-reversing systems in CS 25.933 and turbopropeller drag-limiting systems in CS 25.937 are designed to avoid unsafe outcomes during normal use or failure, ensuring controllability remains intact.[9] Fuel system design requirements in CS 25.951 to CS 25.981 prioritize reliable supply, distribution, and protection against operational anomalies. Each system must deliver fuel at rates and pressures suitable for engine and auxiliary power unit needs under all conditions, including independence for multi-engine setups to isolate failures (CS 25.953). Fuel flow provisions in CS 25.955 account for established rates during normal and fault scenarios, while unusable fuel quantities are defined in CS 25.959 to prevent flameout. Tanks must endure vibration, inertia, and fluid loads without rupture (CS 25.963), featuring sumps for contaminant drainage (CS 25.971) and vents to manage pressure and prevent spillage (CS 25.975). Pressure fuelling incorporates overpressure relief and misfuelling prevention (CS 25.979), and all components are engineered to eliminate ignition sources, such as through conductive materials or inerting (CS 25.981). Anti-icing measures ensure vapour vents and lines remain operational in cold weather, maintaining distribution integrity.[9] Oil and coolant systems, covered in CS 25.1011 to CS 25.1023, support engine lubrication and thermal management with independent, robust designs. Each engine requires an oil system supplying adequate pressure and flow for all phases, including an expansion space in tanks comprising at least 10% of capacity (CS 25.1013). Lines and fittings must resist pressure, vibration, and rupture risks (CS 25.1017), while radiators maintain oil temperatures within limits and are shielded from foreign object damage (CS 25.1023). Coolant systems follow analogous principles, ensuring circulation without leaks or blockages that could impair cooling. These provisions collectively enable sustained engine performance and facilitate inspections.[9] Propulsion safety extends to protections against external threats, including bird ingestion and nacelle icing. Under CS 25.631, powerplants must tolerate ingestion of a 4-pound bird into the engine or nacelle without uncontained debris or loss of thrust that prevents safe flight and landing, demonstrated through analysis or testing. Ice protection for induction systems and nacelles, per CS 25.1093, requires designs that prevent hazardous ice accumulation on critical components, often via thermal or pneumatic de-icing, ensuring continued operation in icing conditions. These measures integrate with overall powerplant resilience, referencing broader design integration for airframe compatibility.[9]Equipment (Subpart F)
Subpart F of EASA CS-25 establishes certification requirements for equipment in large aeroplanes, emphasizing reliability, functionality, and safety to ensure safe operation under all foreseeable conditions. This includes provisions for system safety assessments, electrical protections, navigational aids, communication systems, oxygen dispensing, and emergency provisions. These requirements apply to installed equipment, instruments, and systems that support flight operations, crew awareness, and passenger safety, with compliance demonstrated through analysis, testing, and design verification. Amendment 28 (2023) revised requirements for flight crew systems (CS 25.1302) and electrical fire protection (CS 25.869).[2][3] Central to Subpart F is CS 25.1309, which mandates a comprehensive system safety analysis for all equipment, systems, and installations. The applicant must demonstrate that each system performs its intended function without introducing unacceptable risks, considering normal operations, failures, and environmental factors. Failure conditions are classified based on their severity and effects on the aeroplane, crew, and passengers, using methods such as functional hazard assessments (FHAs) and fault tree analyses (FTAs). Compliance involves identifying potential failure modes, their probabilities, and mitigation strategies to prevent hazardous outcomes.[2] Failure conditions under CS 25.1309 are categorized into five severity levels, guiding the required level of design assurance and probabilistic targets:| Severity Level | Description | Example Effects |
|---|---|---|
| No Safety Effect | No impact on safety, operations, or crew workload. | Minor data display discrepancy with no operational consequence. |
| Minor | Slight reduction in safety margins or aircraft functions; manageable by crew. | Increased crew monitoring without significant workload. |
| Major | Significant reduction in safety margins; higher crew workload or impairment. | Reduced aircraft controllability requiring substantial crew intervention. |
| Hazardous | Large reduction in safety margins; serious or fatal injuries to few occupants. | Loss of primary flight controls, potential for crew incapacitation. |
| Catastrophic | Failure resulting in multiple fatalities or loss of the aeroplane. | Total loss of control or structural failure. |
| Failure Condition Severity | Probability Target (per flight hour) |
|---|---|
| Catastrophic | ≤ 10^{-9} |
| Hazardous | ≤ 10^{-7} |
| Major | ≤ 10^{-5} |
| Minor | ≤ 10^{-3} (guidance, not strict) |
| No Safety Effect | > 10^{-3} |