I agree with Safeware (& soddim) on the airworthiness vs. safety thing.
I have to admit I don't feel that confident that I understand airworthiness particularly well (unlike safety) but I reckon that's largely because it's so badly defined and documented. Whatever, most of what follows is imo ...
Chugalug2 gave us the (MoD) definition of airworthiness (from JSP 553 - others bits of 553 support Safeware's interpretation as he pointed out):
The ability of an aircraft or other airborne equipment or system to operate without significant hazard to aircrew, ground-crew, passengers (where relevant), or to the general public over which such airborne systems are flown.
The key word, to me, is "ability". If you have an airworthy aircraft then you have an aircraft that is safe if:
1. It is operated in a safe manor
2. It is maintained in a manner that enables safe operation
3. Other stuff, e.g. ATM
And competence of aircrew is clearly essential to safe operation, so aircrew competence is not part of airworthiness but is obviously part of safety.
To be safe, an aircraft must be airworthy. The converse is not true.
So when Chugalug2 writes:
You could have the most gold plated airworthy aircraft in the inventory, put an untrained pilot in the driving seat and it immediately falls foul of the definition of airworthy
I disagree. The fact that you've chosen to fly the aircraft (unsafely) with untrained crew does not affect the "ability of an aircraft or other airborne equipment or system to operate without significant hazard [...]". It's gold-plated so it still has that ability if you operate and maintain it properly.
Chugalug2 again:
Safeware makes the very valid point that it is the Military Airworthiness Authority
I don't think he did. In any case, it's not. It's a Military Aviation Authority (despite the letter of Haddon-Cave's recommendation). And if you look at its web page, you'll see it is concerned with safety as well as airworthiness. Admittedly, it's a bit buried but that, to me, is just a reflection of a general MoD unwarranted focus, possibly unintentional, on airworthiness rather than safety. Hopefully, we can get this changed.
Part of the reason I don't like the concept of "airworthiness" much, besides the fact that it's vaguely defined and there's lots of disagreement about what it means, is that, imo, it tends to detract from really counts ... safety. And that is Chugalug2's main concern, I think, and there we do agree.
On a slightly different subject, engineer(retard) writes:
I have never seen the safety case revisited post MAR to a significant level of scrutiny unless driven by a significant formal design change. [...]
The safety case of a design is often underpinned by various assumptions that change or may prove to be invalid in service, again I have never seen the assumptions re-visited or even considered ...
Totally agree with this. In my experience, MoD aircraft Safety Cases (SCs) do tend to get thrown in the filing cabinet and forgotten. Aircraft mods tend to be dealt with piecemeal rather than as part of a coherent whole aircraft Safety Case update. And even worse, imo, updating the SC in response to in-service experience invalidating assumptions ... well, it just doesn't happen on the platforms I know of. This includes the Nimrod where in-service experience totally and massively invalidated the estimates of (effectively assumptions about) fuel leak probabilities. From The Nimrod Review, 3.11.1 ...
The [Nimrod Safety Case] quoted the potential for fuel system leakage as ‘Improbable’, which is defined as ‘Remote likelihood of occurrence to just 1 or 2 aircraft during the operational life of a particular fleet’. The BOI’s analysis of fault data, however, indicated an average of 40 fuel leaks per annum for the Nimrod MR2 fleet between 2000 and 2005
I know the MoD are trying to address some of this, specifically the validation of assumptions, with Operational Safety Cases but progress seems painfully slow to me.