CS 25 Considerations Related to Both Technical and Safety Requirements

Sofema Online (SOL) considers the relationship between Technical and Safety Requirements when designing aircraft system modifications.

Introduction

Regulations by their nature are prescriptive conversely when we consider the potential exposure by referencing safety cases as part of the assessment process, we are substantially dealing with what could be considered a subjective approach.

Safety Analysis should add value rather than be simply a “Desktop” exercise.

Potential Issues may concern:

>> The review process is either superficial or too generic.
>> Lacking in recognition of potential Human Factor Issues & Exposures.
>> Issues with Competence of Assessors.
>> Failure to consider SHELL Interactions (People Components & Systems)

Where possible outcomes should be orientated to goals where possible rather than prescriptive objectives with a focus on managing risk.

There will always be a degree of assumption behind any safety assessment models and it is typically not always possible to fully demonstrate beyond doubt the satisfaction of safety requirements (required by aerospace safety standards).

Safety cases should represent clearly the structure and relationships between safety requirements and supporting evidence and in this way, it is easier to consider the various arguments, as well as to be able to further question the evidence, as well as to challenge the adequacy of the presented rationale.

Building a Safety Case

The development of a safety case provides an opportunity to achieve a greater understanding of the current safety position as well as supporting the potential for making improvements to reduce the risk & exposure.

>> Safety cases should address the realities of everyday system operation.
>> Require sufficient manpower to fully engage with the task.
>> Should not related only minimally to the actual design or operating practice.
>> Should support the demonstration of safety and not the mitigation of liability.
>> Be produced by stakeholders who are subject matter experts.
>> Require adequate oversight to ensure effective delivery.

What is a Safety Case?

A Safety Case is a structured argument, fully supported by evidence, and which provides a compelling, comprehensible and valid case that a particular system is safe for a given application within a designated environment.

We are able to establish confidence in the validity of safety judgments by linking together the amount of data, together with the structure and strength of the safety argument.

>> The core of a ‘safety case’ becomes the safety argument.
>> A safety argument communicates how the overall objectives and claims of the safety case can be shown to be supported by the available evidence (such as the safety analysis results).
>> A safety argument is typically composed of a hierarchy of safety claims and evidence, fully described with the interface which connects the claims to the evidence.
>> Such an approach encourages rigorous thinking as well as questioning which is ideally suited to consider the outputs of novel products and novel methods

Note: To provide an argument without supporting evidence is an unfounded outcome and therefore of questionable value

Next Steps

Sofema Aviation Services (SAS) and Sofema Online (SOL) provide EASA Regulatory Compliant and Vocational training including more than 20 courses specifically related to Part 21 / CS 25 – for details please see www.sassofia.com www.sofemaonline.com or email team@sassofia.com