newswatcher - "I was not aware that the monitors were not planned to activate until the fire had become "uncontained"."
Your statement is not quite correct and could be seen as being slightly alarmist! I'll explain. If there is a fire in the engine itself, this will cause the temperature on the engine casing to rise sufficiently to trigger the Detection System. The fire itself will be still be "contained" within the core. The Detection System, as well as the surrounding structure, is so designed that the Detection System will activate well before there is any structural damage - even if the fire were to start outside the core but in the pod. Yes, things might get slighly blackened but the structural integrity of the engine, pod, pylon etc is designed to remain uneffected.
The problem with fire Detection is that you have a great big fire in the engine when it is running, all be it well contained in the combustors. You have to make sure the Detection System goes off only when the fires appear in areas other than where the designers intended! As Tyrannosaurus says, individual engines do have additional measures where required/prudent. This is particularly true of the big fan engines. Smaller engines, for example on helicopters, stick with the more simple system as the engine is physically much more compact. In addition, there are other systems which are used to indicate that all may not be well with an engine; oil pressure, oil temperature, engine vibration etc. An engine can be shut down as a precaution when these other indications suggest that there is a problem - well before anything else happens.
I simply wanted to convey the overall principles to you so that, no matter what aircraft you see flying overhead or you are in (possibly of much more interest to you!!!), you will understand that the concept is to detect and extinguish the fire before it is a danger to the aircraft. You may see smoke and flames and the airport fire service running round having a great time but the structure itself is safe. An example of how things can look spectacular but not have much real effect? A chip pan fire! When that catches fire there is smoke and flame everywhere. Quickly move in and put your dishcloth over it to put it out (remove the Oxygen from the good old Fire Triangle) and all you have is some soot round the pan rim. The metal itself is structurally uneffected even though it looked like the whole world was about to end. And, no, I've not tried this one at home - touch wood!!!!!
Hope this has been of help.
Cheers, H 'n' H
[ 01 March 2002: Message edited by: Hot 'n' High ]</p>