EdSett
The MoD issue Def Stans, but Design Authorities must also issue their own internal Safety Case Policy document, which articulates in detail how they apply the MoD's standards to their products. Extracts from a typical Aircraft DA Safety Pase Policy (in no particular order);
The Safety Assessment shall, in particular, assess the design for vulnerability to;
- Common Cause Failures
- Cascade Failures
- Maintenance Errors
- Flight Crew Errors
- Hidden Faults
- Faults in related systems
- Environmental Effects
- Lightning Effects
Zonal Analysis facilitates assessment of Cascade Failures. (A consecutive sequence of individual failures where each successive failure is a result of the preceding failure).
If a Hazard is considered and discounted, the reason must be recorded. It is not acceptable to expunge it from the list.
Any Safety Case which treats a (sub system) in isolation, and ignores the system or system of systems as a whole, is likely to be rejected (by Boscombe Down).
The environments within which the system functions (must be assessed), particularly defining where is passes from one environment to another (e.g. the passage of a fuel line from a wet environment to a dry one).
Where a Failure Condition resulting from a Functional Failure of a system can be made worse by additional Functional Failures or adverse events, either from within the system under examination or externally from a separate system, then this combination must also be considered.
If you mean MoD itself does not look at such detail, then you are correct as they seldom have the detailed knowledge. But DAs are required to and must demonstrate they have complied. As this particular book says, there is no point in not complying as they would be snagged by Boscombe. Of course, this always assumes MoD has the DA (and now Boscombe) under suitable and continuous contract to maintain the build standard. While mandated in airworthiness regs, the requirement is not complemented with funding.
In short, MoD have rafts of people with, in one hand (a) a letter of Airworthiness delegation warning them of the dire consequences of not complying, and in the other (b) an e-mail from bean counters telling them they can't have the resources to comply with the legal requirement of (a).