Ed Set 100 you said
And I say to you, DV, that you are going into areas you know little or nothing about
Clearly, from that statement and the points raised in your posting there is a strong indication that you are not as well informed as you make out to be. I hope you are not too senior in the chain of command.
I did not identify the hazard, nor did I set the severity. They were done by BAE Systems Chadderton Airworthiness Dept and the Nimrod IPT. The hazard in Maitenence Zone 413/443 was identified during the Zonal Hazard Analysis and the development of the Hazard log leading to the issue of the aircraft level baseline safety case in 2004. As a result hazard NM/H66 in the Nimrod Phase 2 Hazard log was raised to detail the potential for hot air leaks from LP & HP ducting on rib 2 to impinge on surrounding structure and systems (electrical wiring, CSDU oil pipes, fuel pipes and hydraulic pipes). As a result of this, the hazard was set at INCREDIBLE/CATASTROPHIC.
Following the second duct failure, which took place in this area, Chadderton recommended, in early 2006, that "the probability of failure should be reassessed to IMPROBABLE or more likely REMOTE" The IPT elected to settle for IMPROBABLE. Subsequently, during a reassessment of the Hazard log structure in 2008, QinetiQ recommended that because there had been a second failure the probalility level should be set at OCCASSIONAL. This has got nothing to do about understanding Nimrod, but about having specialist knowledge in system failure rates.
So at present we have a hazard set at IMPROBABLE/CATASTROPHIC (HRI "C") by the IPT, when QinetiQ believe it should be at OCCASSIONAL/CATASTROPHIC (HRI "A"). But in your posting you state that "I do not have an argument with the upgarde from 'remote' to 'occassional'. Your problem, it seems, is with the severity. Well that has been set at "CATASTROPHIC" from day one, not by me, but BAE and the IPT.
By the way, with regards to mitigation, a temperature sensor (S7) is located at Rib 2 (17 " away from the duct failure), and was unable to detect the failure. But there again, nothing detected the failure on XV227.
Ed, if you still believe there isn't a problem, ask yourself why has MoD finally decided to change some 37 hot air ducts in the engine bay areas, many of which were declared as being "life expired and in need of replacement" back in early 2005. Stop burying your head in the sand and look at the facts.
Not bad for someone out of his depth.
DV