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Requirements capture

Up-to-date design process of avionics/Development process/Requirements capture/

Fig. 2.1. Levels of requirements.
Fig. 2.1. Levels of requirements.
There are three levels of responsibility during the requirements capture stage for the on-board equipment (OBE) (fig. 2.1):

I.  Aircraft manufacturer level.

II.  IMA system and airborne avionics integrator level.

III.  System, components, IMA platform and Software (SW) developers level.

Fig. 2.2. Requirements refinement at the Aircraft Developer and IMA system and avionics systems integrator levels.
Fig. 2.2. Requirements refinement at the Aircraft Developer and IMA system and avionics systems integrator levels.



The detailed process of requirements capture at the aircraft manufacturer, IMA system and airborne avionics integrator levels is shown at fig. 2.2.

Regulatory documents base the developing functional and technical requirements. These documents contain the most common requirements for aircraft and on-board equipment suite development: aviation regulations, general requirements for on-board equipment development, and requirements to suppliers. Basing on these requirements the aircraft Developer (manufacturer) forms the generic technical requirements (specifications) for aircraft on-board equipment. They are the initial data for specifications development of structured and composed on-board equipment parts.

Considering these requirements, the on-board equipment's integrator with suppliers’ active involvement forms the functional requirements, requirements for the architecture, design and interfaces of on-board equipment, and then detailed specifications on functions and hardware. Since it’s advantageous to use ready-to-use components (mass produced COTS-components) to decrease the cost of on-board equipment suite’s lifecycle, the functional and technical capabilities analysis of the proposed COTS-components to be used at the on-board equipment shall be done in parallel with specification development for the suite. >>>
>>>  The variety of functional and technical requirements for integrated on-board equipment and its components (systems and equipment) includes the following generic documents:

1.  Aircraft’s certification basis, which contains:

  • the collection of the requirements to airworthiness (including the requirements to aircraft’s systems and equipment) and environment control, relating to the concrete type of an aircraft (for instance, AR-25);

  • special technical conditions (STC), designed considering the international airworthiness standards (CS-25, FAR-25, CAR 525, etc.), which requirements are absent in AR-25 or establishing higher level of airworthiness, and also considering ICAO, RTCA, ARINC, SAE requirements to CNS/ATM functions of on-board equipment's systems.

2.  Generic Technical Specification (for example, requirements specifications for the suite) which states the initial, basic requirements for on-board equipment. The aircraft's Developer compiles these requirements in such a manner to describe the entry-level mandatory requirements to the on-board equipment.

3.  Specification for the on-board equipment (functional requirements for the on-board equipment), which are developed basing on the analysis of requirements specifications and regulatory documents for the equipment suite. It shall determine the following requirements to the equipment suite that is being developed:

  • functional requirements;

  • safety requirements;

  • reliability requirements;

  • installation and the environmental conditions requirements;

  • other requirements. >>>

>>>  4.  OBE design and architecture specification, that shall consist of OBE architecture description and shall include the following sections:

  • description of all requirements' distribution (segmentation), which are stated at the specifications for the on-board equipment and at the specifications for the aircraft functions on the certain components — functions of application software and/or certain systems;

  • the data flow description between systems and/or functions of application software inside the integrated OBE;

  • preliminary assessment of the after-effect caused by OBE functions’ functional failure, determination of the systems’ critical level;

  • the interaction’s description of every input/output for the every single system up to the replaceable unit, every data highway, that connects the replaceable units.

5.  Interfaces specification, which proposes the description of the information interaction protocols and which includes OBE design and architecture specifications, the description of the data flow for the every single component (unit) and application software functions. There shall be all the descriptions of the interactions between replaceable units and/or application software functions at the specification.

6.  The assessment of the threats for on-board equipment functions, including the following information:

  • on-board equipment functions descriptions;

  • failure conditions;

  • exploitation phases;

  • severity of exposure, triggered by the failure condition, on the aircraft, the crew and passengers;

  • failure condition classification;

  • recitation of the supporting materials;

  • safety requirements’ implementation verification method (at the on-board architecture) >>>

>>>  7.  On-board equipment preliminary safety assessment, held by the Aircraft manufacturer, in the boundaries of the Preliminary Aircraft Safety Assessment (PASA). The results of the preliminary fail-safe assessment of on-board equipment architecture fail-safe include:

  • backup identification, which is important for the safety requirements performance;

  • impact assessment for the breakdown of three replicable components from any system of an avionics;

  • error or failure impact assessment for any application SW function;

  • Design Assurance Level for functions/ on-board equipment systems.

8.  System level requirements specifications for aircraft and/or certain systems, which shall more accurate define the functional requirements, listed at the specification for the on-board equipment, and complete these requirements from the view of the exploitation aspects of the concrete AC function. These requirements include:

  • detailed functional requirements;

  • architecture and design safety requirements;

  • interaction between AC functions and/or certain system with operator (crew, technical staff) requirements;

  • interaction between AC and/or certain system with external for the on-board equipment systems and services (Traffic Control Management, other flight services);

  • other requirements.
Technical specifications on the equipment and its components, developed by Aircraft Manufacturer together with suppliers include the following types of the specifications for the equipment and/or its components:
  • technical specifications for the series-produced equipment;

  • technical specifications for the new/modernized equipment or its components (for example, application SW, IMA line replicable units).
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