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Approach and Methodology
Document Development Process
This document was developed in accordance with the guidelines for the definition of
operational, safety, performance, and interoperability requirements.
The approach used is top-down in nature with an initial focus on the operational
perspective. The gradual increase of the involvement of systems expertise (and decrease of
the relevance of operational aspects) occurs when the work advances to the SPR and
This work is iterative in nature as each phase of the process feeds back into the previous
work, to mature and refine the work and ensure completeness and consistency. As an
example, during initial Operational Safety Assessment (OSA), comments are fed back into
the OSED identifying required additions or needs for clarification.
While the process moves from a more operational perspective to a system oriented one, it
is critical that key operational and analytical people are involved throughout, to ensure
overall consistency and coherence of the work and material.
Requirements emerge for ETOS by developing an Operational Services and Environment
Definition (OSED), deriving Safety and Performance Requirements (SPR), allocating
those requirements to the relevant domains, and developing interoperability requirements
(INTEROP) which specify the exchange of data between the domains. Each of these areas
is described in the subsections below.
Operational Services and Environment Definition (OSED)
The OSED (Appendix A) describes the services, intended functions, and associated
procedure of the TBD application, and the assumptions about the environment in which
the application is specified to operate.
The OSED also defines the characteristics of the environmental conditions and procedures
envisioned for this application. These environmental conditions play a role in determining
the assumptions, requirements, and mitigations derived in the Operational Safety
Assessment (OSA) and Operational Performance Assessment (OPA).
Safety and Performance Requirements
The OSED focuses on procedural aspects of the application, in which a flight crew uses
the EFVS, out-the-window visual references and flight deck technologies, including but
not limited to synthetic, enhanced, and combined vision systems to help it determine
alignment and maintain that alignment with the correct runway center for departure through
brake release to 35 ft above ground level or successfully complete a rejected takeoff. The
OSED also contains descriptions of the natural vision conditions, the role of the Air
Navigation Services Providers (ANSP), and use of airport and runway lighting and other
airport infrastructure under which this operation is to be realized.
Two assessments were performed from this OSED to derive the requirements needed to
assure proper and safe execution of the ETOS application.
The two assessments and how they are used to derive final SPR requirements are as
The OPA derives requirements by examining all operational requirements
defined in the OSED. Compiling requirements from the OSED establishes the
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