Airworthiness & Airworthiness Certification

Airworthiness technical requirements and design considerations:

The complete set of Joint Service Specification Guides (JSSGs) and their respective handbooks establish a common framework to be used by Government-Industry program teams in the aviation Sector for developing program unique requirement documents for air systems, air vehicles, and major subsystems. Each JSSG contains a compilation of candidate references, generically stated requirements, verification criteria, and associated rationale, guidance, and lessons learned for program team considerations. The JSSGs identify typical requirements for a variety of aviation roles and missions. By design, the JSSG sample language for “requirements” and “verification criteria” are written as generic templates, with blanks that need to be completed in order to make the requirements meaningful. Program teams need to review the JSSG rationale, guidance, and lessons learned to:

1. determine which requirements are relevant to their application; and
2. fill in the blanks with appropriate, program-specific requirements.

These documents, used in conjunction with service specific policies and procedures, are intended to provide Government and industry program teams with templates of performance oriented requirements typical of aviation systems and subsystems. The JSSGs replace the traditional prescriptive method of describing aviation design and manufacturing requirements with functional requirements. The JSSGs capture the essential performance objectives needed from aviation systems that were often buried within the "how-to" detail specifications and military standards. To help program teams understand the basis for each requirement, the JSSGs define the rationale for requirements and guidance on how to apply or tailor them. In this way, program teams can more easily adapt or modify the JSSG sample requirement statements to meet the specific and needs of individual programs.

The documents have been developed through the close collaboration between Naval Air Systems Command (NAVAIR), the Air Force Aeronautical Systems Center, the Army Aviation and Missiles Command, and the Aerospace Industries Association's Chief Engineers Working Group.

Data Requirements to Support Airworthiness Determination:

MIL-HDBK-516 establishes the airworthiness certification criteria to be used in the determination of airworthiness of all manned and unmanned, fixed and rotary wing air vehicle systems. It is a foundational document to be used by the program manager, the chief/lead systems engineer, and contractors to define their air system’s airworthiness certification basis.

The MIL-HDBK-516 provides a detailed list of typical data requirements for DON, USAF, and USA approvals. Development of the engineering design requirements should be overseen by the lead systems engineer and the airworthiness certification authority/technical area expert representatives starting early in the acquisition/planning phase. These requirements will drive the formation of the Contract Data Requirements Lists (CDRLs) to support the airworthiness certification process. The lead systems engineer, as part of the airworthiness planning, should reach an agreement with airworthiness certification authority/technical area experts on data requirements to support the airworthiness review process and document these in an Engineering Data Requirements Agreement Plan or equivalent document.

Configuration and Envelope Changes requiring Airworthiness Certification:

• Changes that affect structural integrity, propulsion/drive system operation, aircraft performance, aerodynamic characteristics (including drag, control response, and stability), electromagnetic characteristics, navigational system effectiveness, flight control system power requirements and effectiveness, weight and balance of an air item, air crew station noise levels, restrict air crew vision or performance, or increase the danger to the crew in the event of an accident.
• Changes that energize emission of electromagnetic energy that can affect any aircraft, subsystem or allied equipment controls, indicators, displays, or the navigational and communication systems effectiveness.
• Changes that emit light or sound energy that can raise air crew station noise levels, or distract and degrade air crew performance.
• Changes that can be energized to emit any form of radiation, gases, liquids, or debris that may be hazardous, such as explosive ordnance, explosive or flammable fluids, laser energy, and so forth.
• Changes that with their intended use would be in lieu of a standard aircraft system, subsystem, or component function.
• Changes that affect the operating limits and/or emergency procedures prescribed by the military operator’s technical manual.
• Changes that affect the prescribed limits for continued airworthiness. These changes include additions, deletions, or reconfiguration of hardware and material substitutions, software revisions, and any repair or replacement not authorized in the technical manual.
• Changes that are not secured to structure to withstand the aircraft’s existing static, dynamic and crash loads, thereby increasing the danger to the operator and crew in the event of an accident.
• Operation of carry-on equipment with a mission requirement for operation in-flight will be assessed for airworthiness impact. Airworthiness impact occurs when operation of that equipment can measurably affect the airworthiness of the aircraft system, subsystem or allied equipment. These include operation of carry-on equipment that causes any impact as described above, or operation of carry-on equipment that cannot be secured with existing cargo restraints while in use, thereby increasing the danger to the operator and crew in the event of an accident.
• Commercial off the shelf equipment adopted for aviation use shall be assessed for airworthiness impact. The assessment will include—review of any existing airworthiness approval for potential adoption if applicable to the military system; and determination of the airworthiness qualification impact of the COTS equipment and its installation on the authorized configuration.
• Any issue that significantly degrades airworthiness, any identified hazard that has a significant residual risk, unresolved conflicts between airworthiness and performance requirements, or any event that indicates such issue or hazard probably exists will be recorded appropriately in airworthiness/flight clearance documentation.

Unmanned Systems:

Unmanned Air Vehicles/Unmanned Air Systems (UAV/UAS) vary greatly in size, weight and complexity. Because they are unmanned, safety of flight risks associated with loss of aircrew may not apply. However, as with manned aircraft, safety of flight risks associated with personnel, damage to equipment, property, and/or environment must be considered. As such, the airworthiness review process may be tailored for this unique application. Tailoring may be appropriate when a UAV/UAS is designed to be "expendable," will conduct missions with "minimum life expectancy," or are limited to science and technology experimentation. Consideration needs to be given to the environment in which the UAV/UAS will be operated (controlled test range, national airspace, Fleet usage, including ship based applications), the airframe life the air vehicle is designed for, the "expendability" of the UAV/UAS (a cost issue for the Program Manager) and the risks associated with operating the UAV/UAS in close proximity to the ground control system, personnel, property or other equipment. In some cases where analysis indicated that the system is safe with respect to personnel and non-program property, but that based on the available data there are questions regarding the airworthiness of the system, then a clearance can be issued stating such. It should not be assumed that a UAV/UAS will have relaxed engineering requirements simply because the air vehicle is unmanned since safety of flight concerns and risks may necessitate thorough engineering design requirements. The lead systems engineer should address these issues early in the airworthiness process to ensure the design, application and mission of the UAV/UAS is understood by engineering and the airworthiness teams.

Aviation Critical Safety Items (CSIs):.

All aviation spare parts have a subset of parts that are called Critical Items (CIs). These CIs have special management requirements and consist of Critical Application Items (CAIs) and their subset, CSIs. CAIs are defined in Defense Logistics Agency Instruction 3200.1. The foundation for criticality determination is performance of a Failure Modes, Effects, and Criticality Analysis (FMECA). The Prime System Contractor or OEM should be required to accomplish the FMECA during the design phase of weapon system development. The FMECA is used to incorporate design changes or outline maintenance requirements to minimize risk of a functional failure or mishap. New weapon systems generally have a FMECA performed to the subsystem level. On older platforms, FMECA should have been accomplished as part of the Reliability Centered Maintenance or Maintainability Analyses. If a FMECA has not been performed, then an informal analysis such as a Hazard Risk Assessment, hazard analysis as performed in an Airworthiness Impact Statement (AWIS) or equivalent analysis, may be used for criticality determination.

CSIs are parts whose failure could cause loss of life, permanent disability or major injury, loss of a system, or significant equipment damage. Special attention has been placed on CSIs because of the potential catastrophic or critical consequences of failure and because DoD has experienced problems in the past, particularly when CSIs were purchased from suppliers with limited knowledge of the items' design intent, application, failure modes, failure affects, or failure implications. Public law 108-136, sec 802 was enacted to address aviation CSIs.

The public laws address three specific issues. First, they establish that the Design Control Activity (DCA) is responsible for processes concerning the management and identification of CSIs used in procurement, modification, repair, and overhaul of aviation and ship systems. The DCA is defined in law as the systems command of a military Service responsible for the airworthiness certification of the system in which a CSI is used. Second, the law requires that DoD only enter into contracts involving CSIs with sources approved by the DCA. Finally, the law requires that CSI deliveries and services performed meet all technical and quality requirements established by the DCA.

DCA engineers shall designate items under their cognizance as CSIs, CAIs, or non-critical items using the procedures outlined in the Aviation Critical Safety Item Management Handbook . The Prime Manufacturers for items (or other parties) may provide recommendations for categorization to the DCA, but the DCA cognizant engineer shall perform the formal item criticality determination.