The Nimrod Review - Official Documents

The Nimrod Review
7.10
136
Following BAe’s May 1982 report, the RAF provided further information regarding the Nimrod’s operational
procedures to BAe in October 1982. In light of this further information, BAe re-calculated the fatigue lives
for the Cross-Feed bleed-air ducting and set out its calculations in a further report dated January 198413 . As
before, a copy of this report was provided to the MOD’s RTO. The report highlighted the potential damage that
could be caused by a fracture of an element of the hot air system, recognising that there “could be potential
damaging to structure (spar), aircraft control systems and bomb bay loads”. 14 It concluded that, from theoretical
calculations, the fatigue lives for the Cross-Feed ducting had either been exceeded (for the ducting mounted on
the outboard side of rib 2) or were low (for the ducting between the two Cross-Feed air valves up to the fiveway
duct) compared to the required life of the aircraft. It was nonetheless acknowledged that a “safe factor of
5” 15 had been applied and that “only one serious leak has occurred”. 16
7.11 In light of its findings in its January 1984 report, BAe recommended that “a programme of inspection and
replacement should be initiated immediately”. 17 Subsequent documents (see below) make clear the fact that
the policy of ‘replacement’ now simply referred to replacing ducts as they failed, not undertaking a structured
replacement programme. It recommended that inspections for leaks should be carried out at the earliest
opportunity and at every Minor maintenance thereafter, with defective ducting being replaced. The report also
recommended that “a programme is initiated to provision adequate spares to support the replacement of all the
hot air ducts in runs 1 and 2b18 at least once in the life of the aircraft”.
7.12
7.13
On 12 January 1984, the Nimrod Structural Integrity Working Party (NSIWP) was informed that the January 1984
BAe report “showed that many of the ducts on the aircraft had already survived for nearly twice the calculated
(factor 5) life”, thus the “previous philosophy of changing at 2nd major was therefore no longer relevant.” 19
To make it perfectly clear “BAe reiterated that pipes were no longer lifed but changed on condition.” 20 At a
subsequent meeting of the NSIWP, the Headquarters Strike Command (HQ STC) representative stated that,
while the short-term policy was to leak check, “in the longer term the policy would be to change the complete
system once in the aircraft lifetime”. 21
Following these reports and meetings, the MPs discussed above were introduced. These MPs appear to have
been successful, in that there have been no catastrophic failures of ducts in the areas which they addressed;
however, as was discovered after the XV227 incident, the only pressure test of the SCP system aft of the
PRSOV was conducted after Major maintenance. It would further appear that, in accordance with the BAe
recommendation on spares provision, in February 1984, HQ STC initiated urgent provisioning action for 20
aircraft sets of spare ducts.
7.14 The long-term aspiration to replace the ducts was still being advertised by HQ STC in October 1984: “the EA’s
long term policy is to replace all the ducts concerned at least once during the remaining in-Service life of the
Nimrod”. 22 However, whilst the ensuing years saw continued discussion of a proposed replacement programme
for the ducts, 23 it never in fact materialised. This may well have been at least in part due to the low number of
leaks detected during testing. For example, a report of the Nimrod Aircraft Engineering Defect Investigation
Team (NAEDIT) in 1989 noted that “It appears that the resources expended on applying [the leak checks of the
high pressure duct system] have yet to find faults consistent with the concern expressed by the DA [BAE] over
the fatigue life of the ducting.” 24 Given that this report was produced almost seven years after the initial BAe
report highlighting that many of the ducts had passed their fatigue lives, the MOD’s questioning approach to the
initial BAe recommendations is perhaps understandable, if not wholly justifiable. However, despite its apparent
13 BAe report 801/MAN/DES/277, dated January 1984.
14 Ibid, paragraph 3.2.
15 Ibid, paragraph 4.2.
16 Ibid, paragraph 4.3.
17 Ibid, paragraph 5.1.
18 The Cross-Feed system, from the engines to the 5-way duct.
19 Minutes of the NSIWP held on 12 January 1984 (DD Nimrod 16/19, dated 18 Jan 1984).
20 Ibid.
21 Minutes of the NSIWP held on 30 October 1984 (DD Nimrod 16/19, date indecipherable).
22 STC/13004/7/1/ Strike Eng 21a, dated 9 October 1984.
23 For example, in April 1988, the MOD was still stating that “a programme to replace [25 hot air ducts] will be implemented at Major servicing”:
STC/13004/7/1/Srt Eng 21a, dated 7 April 1988.
24 NAEDIT/1505/88/21/Task (Ao1124), dated 22 Mar 1989.