The Nimrod Review - Official Documents

Ageing Air Audits: Background
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Chapter 23 – Age Matters
AAAs have historically been purely structural inspections of fleet leaders to determine the structural integrity
of the aircraft and, thus, its airworthiness. These audits were intended to complement the full scale fatigue
specimen tests undertaken by the Design Authorities. As aircraft systems became more complex and softwarebased,
there began to be recognition that the systems on an aircraft were similarly affected by ageing and that
their condition had a bearing on an aircraft’s airworthiness. The AAA programme was therefore extended to
include an assessment of the ageing effects on propulsion and aircraft systems to determine the current and
future airworthiness of the aircraft/fleet. The analysis is also intended to provide a validation and update of the
aircraft’s maintenance policy.
Nimrod Aged Aircraft Audits
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AAAs were conducted on the Nimrod fleet in 1993. These were reviewed in 2003. In common with both civilian
and military practice at the time, however, the AAA focused solely on the structural integrity of the airframe and
not systems. 11 The AAA review of 2003 addressed the delay in the MR2 OSD to 2010 and made a number of
airframe recommendations in response to the delay. In 2005, as part of a life extension programme, a Nimrod
Fatigue Specimen Teardown was carried out by BAE Systems (for the Nimrod IPT) in relation to certain parts of
the airframe.
Nimrod XV236 teardown 2008
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Comment
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The first aircraft to undergo an Ageing Aircraft Systems Audit (AASyA), rather than a purely structural audit,
was Nimrod XV236, comprising a destructive ‘teardown’ undertaken by QinetiQ. Further QinetiQ (destructive)
AASyA activity has commenced on a VC10, and will soon start on a C130. Other platforms are at various stages
of maturity with respect to this requirement.
The Nimrod AASyA was called for in the XV230 BOI recommendations. As a result of which, XV236 has been
subject to a forensic teardown by QinetiQ comprising destructive dismantling in order to assess the airworthiness
of the aircraft’s systems, and the impact of age on the aircraft’s airworthiness. No fatigue analysis of the aircraft
structure has so far been undertaken.
The AASyA does not stipulate a requirement for forensic teardown, rather it is intended to provide a periodic
independent assessment of the aircraft’s airworthiness by examining maintenance data, components, and
aircraft systems. However, for the Nimrod AASyA, QinetiQ were contracted by the IPT to undertake a forensic,
destructive teardown of the aircraft, even though there was no requirement for such an undertaking in the JAP
100A-01or JSP553 regulations governing AASyA.
No maintenance data analysis was undertaken prior to the destructive teardown to determine ‘trends or
patterns’ that may indicate future integrity issues or to provide a focus for the audit. Given that a destructive
assessment undertaken by QinetiQ would not have identified the gradual increasing in fuel coupling leaks
identified by Squadron Leader Andrew Gransden during the BOI, this raises the question whether, the AASyA
should have begun with a comprehensive analysis of the maintenance data to determine other underlying
trends and patterns that might indicate a developing airworthiness risk.
The audit was benchmarked against the standard of a new aircraft and identified all deviations from the
benchmark standard. The assessment was then compared against the aircraft log book to determine what faults
had been accepted and corrective action deferred. What the team found was an extensive number of faults that
were not recorded in the aircraft ADF12 log or in the aircraft husbandry log. The RAF’s response was to review
QinetiQ’s findings to determine which of the faults identified by QinetiQ represented an airworthiness risk. A
visual audit (limited to those areas considered by QinetiQ) identified that most of the faults were minor in nature
and did not represent an airworthiness risk, although a small number were assessed as a potential airworthiness
risk requiring further investigation. The detailed investigation into these faults subsequently confirmed they did
11 AAAs were expanded to include aircraft systems in September 2006 (too late for Nimrod XV230). Formal guidance on implementation has yet to
be issued: see BOI Report, paragraph 31b [2-18] and Exhibit 25.
12 Acceptable Deferred Faults.
553