Nimrods had ‘critical fault’
Simon McGee
THE nine Nimrod aircraft cancelled amid a storm of condemnation and at a cost of £4 billion were designed with the same critical safety fault blamed for the downing of an RAF Nimrod in 2006 with the loss of 14 lives.
Liam Fox, the defence secretary, has been accused of leaving a “massive gap” in the nation’s security by scrapping the fleet of maritime patrol planes.
But classified documents seen by The Sunday Times reveal Ministry of Defence (MoD) safety tests conducted last year on the first Nimrod MRA4, built by BAE Systems, found “several hundred design non-compliances”. Non-compliances are a fact of life. They are either agreed, in which case they become part of the updated Design Baseline, or are fixed.
Among them were problems opening and closing the bomb bay doors, (the Bomb-bay Doors opened fine thank you) failures of the landing gear to deploy (the landing gear never failed to deploy/retract once in the 5 years I flew on the program – there were 2 instances of Nose wheel door indication failure due to incorrectly positioned nosewheel door microswitches – this was partly a result of the original part manufacturer going out of business and the replacement sensors being of a slightly different design, a fact that wasn’t picked up until the first occurrence at which point it was fixed), overheating engines (no recollection of any engine overheat during flight trials – there may have been one induced deliberately as part of flight test but I don’t think so – utter crap) and gaps in the engine walls (true – gaps were found between the engine bay fire wall and surrounding structure. Temporary fix employed to enable flight test to continue whilst reason identified and permanent fix embodied through production), limitations operating in icy conditions (because QQ hadn’t finished its final recommendations, that’s why it was called an Incremental Release to Service, as QQ provided wider clearances, the RTS expanded), and concerns that “a single bird-strike” could disable the aircraft’s controls (there was a theoretical possibility that a suicidal albatross could somehow fly directly into the Bomb bay – whilst the doors were open of course – miss the life rafts and everything else in there – and impact a specific area about 6ins long x 4ins wide that may have ultimately had an adverse effect on the aileron system. A cover guard was being designed).
However, the most serious problem discovered by Defence Equipment and Support (DE&S) inspectors at MoD Abbey Wood in Bristol involved a still unresolved design flaw. It concerns the proximity of a hot air pipe to an uninsulated fuel line, widely blamed for an explosion on board Nimrod XV230 on September 2, 2006, near Kandahar airport in Afghanistan. A three-page summary of the faults, labelled “restricted” and written on September 17, last year, stated: “The work being undertaken by the MoD to validate the BAE Systems aircraft’s safety case during the week of September 13, 2010, identified a potentially serious design defect: a small section of a hot air pipe was discovered to be uninsulated in an area that also contains fuel pipes, which is outside the design regulations.” (The fuel feed pipe from the No1 Tank exits the lower fuselage area and travels upwards and slightly forwards through the inter-space between the fuselage and the inboard engine fire wall, before disappearing off to join the fuel feed line. This occurs roughly mid-way along the wing chord at the wing root. In the same inter-space is the Engine intake Anti-icing take-off pipe that travels up and then forward approximately 8ft 6ins. This pipe was insulated, apart from the very last 4ins or so, where it went through a small bulkhead into the Intake Nacelle and the piccolo tube for the Anti-icing system. The Functional Failure Analysis looked at likely failure rates of the fuel pipe, the maximum likely temperature of the Engine Intake Anti-icing air off-take, the likely usage frequency and time of the Engine Anti-Icing System, the fact that the fuel had to travel both forwards (about 8 feet against the natural airflow used to ventilate the inter-space) and upwards (about 30ins) and came to the conclusion that this was approximately a 10-9 probability event (which was the probability level agreed as the target to achieve). The subsequent MoD/RAF Zonal Hazard Analysis used the SWIFT approach (So What If Technique), which does not really look at probabilities (that’s generally a good thing!), it just starts off with “So What If?”. At this point it became obvious that a design solution would be needed, this was in the process of being worked and agreed. The temporary workround was to isolate the No1 Tank, this would have resulted in a temporary restriction to RAF training flights of around 3 hours duration plus div fuel if only No4 Tanks fuel was carried).
Apologies if the font/formatting didn't carry over from Word.