The Nimrod Review - Official Documents

Nimrod 2000/MRA4
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Chapter 2 – History of the Nimrod Aircraft and Technical Description
In 1993, Air Staff Requirement (ASR) 420 called for a replacement for the MR2. On 25 July 1996, the contract
was awarded to BAE Systems who proposed using the existing MR2 airframes, fitting larger wings (127 feet),
Rolls-Royce BMW BR.710 engines, new radar and sensor systems and a new tactical computer system. In
February 1997, the first three stripped-down Nimrod fuselages were delivered to FR Aviation in Bournemouth,
who were contracted to refurbish them. By 1999, however, the programme was three years behind schedule
and the first prototype Nimrod MRA4 flight did not take place until 26 August 2004. In September 2004, the
planned order for Nimrod MRA4 was reduced from 18 to “about 12”.
The original planned in-service date for the MRA4 was April 2003, but was delayed five times and now stands
at 2010. This has meant that the out-of-service date of the existing MR2 fleet has had commensurately to be
put back several times and Nimrod MR2 aircraft have had to remain in service far longer than anticipated (see
Chapter 14).
Nimrod aircraft – technical description
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The Nimrod is of a conventional aluminium alloy, semi-monocoque pressurised fuselage construction. It has
a low, cantilevered monoplane wing which has a 20-degree swept-back all metal two-spar structure. It is
approximately 129 ft long, 30 ft high, with a wingspan of 115 ft and wing area of 2,121 sq ft. It weighs 96,000
lbs without fuel, and 184,000 lbs fully loaded with fuel and stores. It has a maximum speed of 360 kts, a service
ceiling of 42,000 ft and a maximum range of about 3,800 nautical miles without AAR. It has a typical maximum
flight time of eight hours on internal fuel and maximum endurance of about ten hours; this was achieved by
routinely shutting down two engines for fuel economy. Flight times can be further extended to 20 hours with
multiple AAR.
The aircraft is powered by four Rolls-Royce RB 168-20 Spey 250 engines embedded in pairs in the root of each
wing. The Spey 250 is a two-spool, low ratio, by-pass turbo-fan engine with a tubo-annular combustion system,
developing 12,160 lb of thrust. An Auxiliary Power Unit (APU) is used to supply air for engine starts on the
ground. The air supplied by the APU is ducted to a Cross-Feed duct running across the bomb bay between the
port and starboard engines.
The MR1 was designed and certified to MOD Specification No. MR 254 D&P dated 1965. MR 254 D&P accepted
that the basic Comet 4C aircraft design was certificated to British Civil Airworthiness Requirements (BCAR)
1956 Edition. 21 The MR2 was designed and certified to MOD Specification No MR286 D&P dated 6 May 1975.
Specification No MR286 D&P accepted the same general certification base as MR 254 D&P. The change in
design from a Comet 4C to a Nimrod MR1 was required to comply with AvP 970 1965 Edition (Re-issue).
Fatigue and Corrosion
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The flight profiles of the Nimrod MR2s and R1s have been very different. The maritime patrol work of the
Nimrod MR2 has required it to fly ‘in the weather’ and frequently at low level (200-300 feet) over the sea,
causing the structure to fatigue at a faster rate than for normal cruise flight profiles. By contrast, the R1 has
tended to fly only at high level and, therefore, in a structurally more benign environment. As a result, the fatigue
and corrosion levels of the MR2s have been greater than the R1s. The corrosion suffered is not only evident on
the structure but on some components, such as elements of the fuel system.
The number of sorties and hours flown by the Nimrod types has been relatively low compared with civilian
commercial aircraft. 22 This is not unusual for military aircraft.
21 Section D, Issue 3, dated 1 July 1956 and Section J. Issue 2, dated 1 June 1953.
22 BAE Systems in BAE Report MBU-DEF-R-NIM-SDC-076 Review of Nimrod In-Service Accident History dated September 2004 noted that the Nimrod
MR 2 and R 1 fleet collectively had accumulated approximately 400,000 flying hours. As at the present date, the aircraft in the fleet which have
accumulated the most flying hours have flown more than 18,000 flying hours.
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