Haddon-Cave, Ch 19.8
‘The ALARP rule is one of the fundamental tenets of safety and a basic concept; and yet there is confusion in some (senior) quarters [of the RAF and MOD] as to the relationship between ALARP and the ‘tolerability’ of risk, and also a lack of appreciation in others as to the temporal and financial flexibility inherent in the ‘R’ in ALARP.
While I never used the term "ALARP (Temporal)", I was certainly always aware of the legal obligation to reduce risk as
soon as reasonably practicable, because the clock ran on litigation as soon as a technical solution became available. Our airworthiness letters of delegation were changed in the early 90s to reflect this more forcibly, given the repeal of Section 10 of the Crown Proceedings Act. Training also changed, at Cranwell and in PE. I used the "clock running" argument many times to acquire funding.
Very often the technical solution is known, but not available due to (e.g.) space constraints in aircraft. For example, the LIDAR Wire Strike Avoidance system developed by RSRE Malvern in the 80s was physically too large for Tornado, although it exceeded the distance/wire diameter spec by a huge margin, so ALARP was achieved because no practical solution was available AT THAT TIME. However, there is an enduring obligation to maintain progress, not just forget the risk because it was, at one point, ALARP by default. In that case, MoD stopped funding LIDAR work some years ago and all staff were made redundant; including the inventor. The MAA doesn't mention that when tagging wire strike as a major risk.
While he doesn't explain himself (mainly because he couldn't publish any evidence that contradicted his decision to name and blame those he did) this is what H-C is getting at. The failure of senior staffs to meet this enduring obligation. Related to this, there is the policy that risks can be ignored until they actually manifest themselves. Again, Tornado offers a good example in ZG710 (2003 Patriot shootdown, the specific risk having been notified in 1998 and ignored).
Given the evidence uncovered by Distant Voice, the current risk is unlikely to be ALARP (Temporal) because, by any reasonable interpretation, MoD have not met this enduring obligation to continue unhindered development of CWS. I'd qualify that by saying the Duty Holder may have decided the original agreed mitigation (CWS in a generic sense) is no longer valid, but as the risk to life is obvious I'm sure he has made his obligatory written declaration to this effect and his Service and Political seniors have agreed, also in writing. And that his alternative mitigation is recorded and in hand.
Another factor here is that, fairly obviously, there must be an associated Operational Constraint and/or associated Limitations in the RTS. And the Whole Aircraft Safety Case will reflect all this. Lawyers would have to argue what timescale was reasonable, but given the successful trials were in the early 90s, it is for MoD to prove compliance, not for anyone else to prove the negative. Any gap in CWS/collision avoidance related development would be evidence of non-compliance.
As EAP86 says, the term should be unnecessary and its use indicates an acceptance of H-C's criticism; which in turn was notified to H-C in evidence thus demonstrating prior knowledge within MoD. This prior knowledge is a crucial aspect, so why did H-C present his report as revelations?