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System specifications development

Branches of activities/Production functions/System specifications development/

On-board equipment (OBE) development process must meet certain requirements and standards in accordance with global trends. On-board equipment development in accordance with P-4754 (Russia) and ARP-4754A (USA) consists of three interrelated procedures: requirements capture, SW and HW development, integration and testing.

Specification of the requirements is a top-down on-board equipment design process, because the distribution of requirements is held from the top level (requirements to the AC) to the lowest level (requirements to SW and hardware). It allows connecting all levels of requirements — the AC, systems, SW and hardware.

Special attention is paid to safety requirements. Functional hazard assessment of an aircraft and its systems, preliminary aircraft and systems safety assessment and SW and HW failure tree analysis are held to meet these requirements. The reliability and fail-safe assessment must be implemented in accordance with P-4761/ARP-4761.

The regulatory documents (in which the most common requirements to the developed aircraft and on-board equipment are stated: aviation rules, common requirements to on-board equipment development, and requirements to suppliers) form the basis of developed functional and technical requirements. Basing on these requirements the aircraft Developer (the aircraft Manufacturer) forms the common requirements (specifications) to aircraft OBE, which are the source data for specifications capture on structural and component parts of OBE.

Basing on these requirements, Integrator of on-board equipment with the Suppliers active participation formulates the functional requirements, requirements to the architecture, design and OBE interfaces, and then determines the detailed specifications on functions and equipment.

The concept of a function is a key concept of the end-to-end design. The function of an aircraft means the functional capabilities which can be provided by hardware and software systems installed on an aircraft, such as aircraft navigation management, communication, display etc. >>>
>>>  Technical and functional requirements compilation on integrated on-board equipment and its components (systems and equipment) includes the following main documents:
  1. Aircraft certification basis that includes:

    • the compilation of requirements on the airworthiness (including requirements on aircraft systems and equipment) and protection of the environment related to the certain type of an aircraft (for instance, AR-25);

    • project specific technical specifications (PSTS) developed by taking into account the foreign airworthiness standards (CS-25, FAR-25, CAR 525 and others), the requirements of which are absent in the AR-25 or set a higher level of airworthiness, ICAO, RTCA, ARINC, SAE requirements to CNS/ATM systems functions.

  2. General technical specification (for instance, requirements specifications on the complex), which states the source, basic requirements on the on-board equipment. These requirements are created by the aircraft Developer in such way to describe the minimum mandatory requirements to OBE.

  3. Specification on the on-board equipment (functional requirements on OBE), which is developed basing on the analysis of requirements specifications and regulatory documents on the on-board equipment. It must determine the following requirements to the developing on-board equipment:

    • functional requirements;

    • safety requirements;

    • requirements on reliability;

    • requirements on installation and environment conditions;

    • other requirements. >>>
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  1. The on-board equipment design and architecture specification, which shall contain a description of the on-board equipment architecture and include the following sections:

    • the distribution (segmentation) description of all requirements, described in the requirements specification for on-board equipment set and specifications on the aircraft functions on separate components — application software functions and/or the separate systems;

    • a description of information flows between systems and/or application software functions at the an integrated OBE;

    • a preliminary functional hazard assessment of OBE functions, a critical level of the systems determination;

    • a description of all the inputs/outputs interaction for each certain system up to the line replaceable unit, each data channel connecting replaceable units.

  2. Interface specification, which involves a description of the information exchange protocols and includes specifications on design and architecture of the n-board equipment, description of the dataflow for each component (unit) and application software functions. There shall be represented all the descriptions of interactions between replaceable units and/or application software functions in the specification.

  3. Functional hazard assessment of OBE functions.

  4. Preliminary OBE architecture safety assessment, which is held by aircraft Developer in the boundaries of preliminary aircraft safety assessment. >>>

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  1. System level requirements specifications on aircraft and/or certain system functions, which have to determine in more details the functional requirements listed in the specification on the on-board equipment set and to supplement these requirements in terms of operational aspects of the aircraft specific function. These requirements include:

    • detailed functional requirements;

    • safety requirements on the architecture and the structure;

    • requirements on the interaction of aircraft and/or certain system function with the operator (flight crew, technical staff);

    • requirements on the interaction of aircraft and/or certain system with the external for OBE systems and services (Air Traffic Management, other control services);

    • other requirements.
Technical specifications on the equipment and its components are developed by the Developer together with Suppliers and include the following types of technical specifications on the equipment and/or its components:
  • technical specifications on the commercially available equipment;

  • technical specifications for new/modernized equipment or its components (for instance, application software, IMA hardware line replaceable units).
FSUE «GosNIIAS» develops the basic version of the specifications system for the OBE and its components. To date, for the selected advanced OBE architecture — which is similar to the architectural principles of B-787 aircraft and optimizes the technical level of the OBE (weight, volume, cost of development, cost of operation) — the basic versions of requirements specifications for the SSJ-100 and MC-21 projects are developed.
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