The Nimrod Review - Official Documents

Chapter 7 – Damage from Cross-Feed/SCP Duct Failure
CHAPTER 7 – DAMAGE FROM CROSS-FEED/SCP DUCT FAILURE
Contents
Chapter 7 covers the possibility of a Cross-Feed/Supplementary Conditioning Pack duct failure and answers the following
questions:
Summary
How and why did a Cross-Feed/Supplementary Conditioning Pack duct failure pose a risk to the
Nimrod?
Did this represent a breach of applicable design standards?
Was the maintenance policy for hot air ducts satisfactory?
Were there warnings of risks from hot air duct failures?
Did a hot air duct failure cause the loss of XV230?
1. A rupture of the Cross-Feed/Supplementary Conditioning Pack duct represented a potentially serious
hazard to the Nimrod because of the risk of hot air (400ºC+) damaging the numerous adjacent fuel
seals in the starboard No. 7 Tank Dry Bay, leading to the escape of fuel and an in-flight fire.
2. This scenario represented a “single point failure” and a breach of general “fire zone” safety
standards applicable to the original Nimrod MR1 and MR2 designs in 1969 and 1979, in particular
Aviation Publication (AvP) 970 Chapter 715 (see Chapter 4).
3. British Aerospace’s 1 advice in 1983 to the MOD on predicted duct life had proved pessimistic when
compared with the actual life of ducts in service; a policy of pressure testing was adopted which
worked successfully for the next 21 years.
4. In November 2004 corrosion caused the fracture of a duct within the Supplementary Conditioning
Pack system of Nimrod MR2 XV227, resulting in considerable damage and the near loss of the
aircraft.
5. The XV227 incident amply illustrates the catastrophic risk the Cross-Feed/ Supplementary Conditioning
Pack duct posed to the aircraft.
6. A second duct failure (albeit a different duct in the engine bay) occurred on XV229 on 8 August 2005
and was caused by fatigue, possibly provoked by physical damage. The incident was not adequately
analysed by the Integrated Project Team in considering the possibly increased threat to the aircraft
from such failures.
7. The damage occasioned to XV227’s airframe and systems by the hot air leak should have been a
‘wake up call’ to everyone. With the benefit of hindsight, the potential for interaction between
the fuel and hot air systems existing in close proximity within the No. 7 Tank Dry Bay represented
a significant risk to the aircraft and its crews. Simply looking at the list of damaged components
should at the very least have provoked a careful re-examination of the conclusions of the Nimrod
Safety Case.
8. The Nimrod Integrated Project Team’s decision to switch the Supplementary Conditioning Pack back
on in April 2005 was based on an imperfect understanding of the completeness of the hot air leak
detection system. The analysis carried out by the Integrated Project Team in support of this decision
was far from satisfactory.
1 BAE Systems.
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