It may indeed be 94% new build, but many of the CofG issues are determined by retention of (I believe) most of the fuselage, so rather less of it is a new design (in the sense that the basic layout is pre-determined). For example, you must put the mainplanes in the same place (give or take the extravagant tolerances between tail numbers). The underlying configuration control issues are discussed in the other Nimrod thread, but I think someone said that just enough of the MR2 was retained to make it a modification, not new build. This gets round certain MAR regs, but creates other problems – one of which is that the MR2 design baseline must be known and maintained. (In simple terms, the MRA4 build standard could be “MR2 plus mods”). Also, if the airworthiness of the MR2 is now doubt (AVM Loader’s conclusion, accepted by Des Browne) then it follows that this is a major emerging risk to MRA4 achieving MAR. If this is the case, then a non-MoD committee recommending cancellation as a “savings measure” is the MoD’s big “out” to avoid further embarrassment.
BAeS aren’t daft and I’m sure they have an engineering solution. But whether that is sufficient for some multi-Stars to sign MAR and RTS remains to be seen. I’m equally sure these stars will have been reading AVM Loader’s comments, speaking to him privately (and perhaps even reading the warnings going back 20 years!) and keeping an eye on the Nimrod Review developments – which is probably being delayed by political machinations at this level and above.
What worries me is that if MRA4 is cancelled, the Review will be a one-liner – “We’ve cancelled the programme, the problems are in the past and won’t be repeated”. Which would completely ignore the fact that the regulations which were not implemented apply to all aircraft, and management oversight is (meant to be) by the same people.