Cross-feed/SCP duct

The first notable design change was in 1979, when the MR2 variant entered service, it was fitted with a Supplementary Conditioning Pack (SCP) to provide cooling air to the Nimrod MR2 s improved electronic systems. This Supplementary Conditioning Pack was powered by hot air bled off the Cross-Feed Duct - now called the Cross-Feed/SCP Duct. The normal condition of this Cross-Feed/SCP duct when in flight was therefore that it would be hot and pressurized. 

In practice, the insulation of the hot Cross-Feed/SCP Duct was imperfect in service the glass fiber insulation got squashed causing the stainless steel sheath to get hot. Bellows units at bends in the duct were, in any case, less well insulated, or even... 

The fitting of the permanent Air-to-air refuelling (AAR) modification to MR2s (1982/1989) to enable refuelling in flight to take place. The addition of AAR capability further increased the fire hazard posed by the cross-feed/SCP duct. 

BAE Systems sought to share blame for these design mistakes by stating that the design modifications had been accepted by the Ministry of Defence in 1977-1978. Haddon-Cave did not consider that this absolved BAE Systems of its responsibility in respect of the poor design of the aircraft. The cross-feed/SCP duct represented a fundamental flaw in the design of the Nimrod aircraft and was the primary physical cause of the accident. 

The addition of the Supplementary Conditioning Pack (SCP) to MR2s (1978-1984) provided additional cooling for the extra electronic equipment when MRls were upgraded to MR2s. The SCP required bleed-air taken off the cross-feed duct. The fitting of the SCP take-off duct significantly exacerbated the fire hazard posed by the bleed-air system. 

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