TSM, at the risk of turning this thread into a Nimrod OCU:
Can you tell us exactly what indications are there in the cockpit when a duct bursts, other than a slight loss of thrust,
A red warning light comes on.
which I assume the pilots might feel?
I very much doubt that they would feel a loss of thrust or even a swing towards the associated engine. A loss of HP air from a single engine does not significantly affect the handling of the Nimrod. A single engine flame-out is not hazardous, even if the pilot does nothing. There might be a drop in rpm, which might be observed.
And are you also saying that, if a slight decrease in thrust IS noticed, the actions for that are to shut the engine down?
No. I'm saying that if the red warning light comes on, the crew will shut off the air supply from that engine (best case) or in the worst case, reduce the power on that engine and it might have to be idled or shut down to put the light out. This all standard FRC stuff
Even if that were the case, and even if it was during your own 'worst case' scenario, surely there is a serious risk of fire/explosion immediately the duct fails or leaks, especially during the take off run?
No, it is only hot air coming out of a duct into a very secure area. There might be a bang. However, for obvious reasons there are no combustible materials in the engine compartment, except fuel/hyd liquids which are inside stainless steel pipes and routed well away from the hot air pipes. The electrical wire insulation will not burn. If the crew does not react immediately to the warning light, it is possible in the worst case that the firewire will activate and the engine will then be shutdown within seconds.
Wouldn't it all be a bit too late then?
You are assuming that a burst HP air duct means instant explosion and fire. If it did, no aircraft in the World would get an airworthiness certificate, because no aircraft is airworthy if a single failure could cause that effect. As I said, most jet aircraft have HP air ducts connected to the engines.
may I ask who you believe are the experts on this subject?
The experts are the designers who put the ducts in the engine compartments, made sure that the compartments contain nothing that is flammable, gave us the warning systems in case of duct failures, carried out flight testing and issued us with the drills, which we practise regularly.
I would agree that a HP duct failure outside the engine compartment could be very serious if not dealt with immediately. XV227 is an example of this. However, no HP air exists outside the engine compartments in flight. Therefore, we flight deck aircrew are not worried in the slightest about the slow progress in replacing the ducts. This is a non-story from DV.
Regards
Ed