Vital safety features were left out of the design specification for Nimrod surveillance aircraft despite being requested by the Royal Air Force, an inquiry has revealed.

Fuel tank explosion protection and a ban on carrying fuel in the fuselage were both listed as “air staff requirements” (ASR) by the RAF. But they were among several items not included in the final design blueprint known as the “aircraft specification”. The RAF’s comments about the design criteria were rejected by the Ministry of Defence when it drew up the specifications for the aircraft.

The investigation was commissioned by the MoD after the death of 14 servicemen in a mid-air explosion on a Nimrod XV230 over southern Afghanistan in September 2006.

No fuel-protection system was fitted and the Nimrods were flown with fuel in the fuselage, according to the report drawn up by the defence research company QinetiQ.

The inquiry also discovered that the number of maintenance specialists at RAF Kinloss, where the aircraft is based, had been cut by nearly 24 per cent and that many workers were inexperienced on Nimrods. Meanwhile, operational demands were increasing.

“Low confidence in the safety of the Nimrod will have an impact on those who operate the aircraft. Occasions may arise when some operators may be reluctant to fly,” QinetiQ says.

The unpublished report, released to The Times under the Freedom of Information Act, makes 30 recommendations to improve safety, 21 of which are already being implemented. Six have been deferred because they relate to air-to-air refuelling and three others are still under consideration.

The report says that its investigators noted a number of differences between ASR and the final design. “The ASR required fuel tank explosion protection. This has not carried through to the aircraft specification,” it says. However, QinetiQ repeatedly highlights the dangers of a fire and explosion on the Nimrod.

The report says that no risk assessment had been undertaken concerning the presence of an explosive atmosphere in the fuel tanks “as the nature of this potential risk is not fully understood”. Further study should be instigated, QinetiQ says, adding: “The most significant risk presented by the fuel system is associated with fire/ explosion.”

MoD officials said that a fuel protection system consisting of explosive-suppressant foam around the tanks would not have prevented the Nimrod disaster in 2006. It has now been fitted to Hercules transport aircraft after a barrage of ground fire caused one to explode in Iraq in January 2005, killing ten military personnel. The Hercules was flying at low altitude, whereas Nimrods operate from high altitude, beyond the range of ground fire.

After a highly critical board of inquiry report into the Nimrod tragedy, published in December, the MoD said it had already ensured that the suspected cause — fuel leaking from a corroded coupling and igniting on contact with a hot-air pipe — had been addressed. The RAF’s top engineer announced that the Nimrods were safe.

However, the QinetiQ report highlights longstanding shortcomings that may have led to the Nimrod disaster, focusing particularly on the maintenance manpower shortages and huge pressure placed on the ageing aircraft.

A third inquiry into the Nimrod crash is still under way.

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