The Nimrod Review - Official Documents

The Nimrod Review
Conclusion on Hazard H73
11.122 In my view, the Mech Systems Pro-Forma for Hazard H73 was a hurried, sloppy and muddled piece of work,
carried out by a junior individual, under time pressure, without sufficient guidance or management oversight.
Some of the mistakes in this Pro-Forma were very basic indeed, in particular the mistake in relation to the Cross-
Feed/SCP duct only being pressurised “during engine start” which displayed a startling lack of knowledge by
BAE Systems about its own aircraft. Anybody who knew anything about Nimrods would have known that this
was plainly wrong. If a proper, considered and careful job had been done on the Pro-Forma for Hazard H73, and
the MRA4 generic data had not been used as a ‘cure-all’ panacea, the outcome would have been different and
the catastrophic risk dormant in Zones 514/614 would have been revealed.
XV227
11.123 It is unfortunate that thought was not given to the earlier 1980s duct failure history when drawing up the Hazard
H73 Pro-Forma which stated “From in-service experience the potential for bleed air duct leakage is Improbable”.
As stated above, this ignored both the early BAe reports of the 1980s and the evidence presented to the Review
which clearly shows that there was a history of such hot air duct failures. As described earlier, BAe had provided
a synopsis of the potential hazards which eventually faced XV227 some 20 years previously. The transformation
of this prediction into fact seems not to have provoked any deep thought within the Nimrod IPT.
11.124 BAE Systems used MRA4 generic data which gave a standard failure probability rating for a number of common
failure types. A failure of a “ECS pipe with 2* (V-band clamp/ bolted type flange)” was ascribed a failure
probability of 2E-7, namely:
292
Failure Type
…
Failure Probability
Hydraulic pipe and associated coupling 1E-6
Fuel pipe and associated coupling 1 E-6
ECS pipe with 2* (V-band clamp/ bolted type flange). 2E-7
ECS pipe seal 1.5E-7
11.125 It is most difficult to see how a categorisation of “Improbable” could ever have been, appropriate in the light of
the BAe reports of the 1980s and XV227 incident and the large number of Rib 2 hot air leaks which occurred
in the late 1980s and early 1990s (see Chapter 7). It is impossible, in my view, to see how it could be at all
appropriate following XV227 and the subsequent failure on XV229. It is highly unfortunate to say the least
that this question was not properly re-visited when the XV227 incident should have brought sharp focus to it.
Instead, all those involved appear to have been content that the NSC “recognised” the sort of bleed-air duct
failure that occurred on XV227.
(18) The general standard of BAE Systems’ analysis, assessment and categorisation of
the hazards was lamentable: the Pro-Formas: (1) lacked consistency; (2) contained
numerous significant factual errors; (3) contained numerous examples of poor or
inefficacious mitigation; (4) demonstrated generally low levels of analysis; and (5)
showed the increasing effects of time constraints.
11.126 In my judgment, the very poor quality of the Hazard H73 Pro-Forma was symptomatic of the generally lamentable
standard of the NSC Pro-Formas prepared by BAE Systems. BAE Systems’ NSC work was riddled with errors of
fact and analysis. This was a direct result of the failures of attitude, approach, planning, management and
execution outlined above.