Aerotech -
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Regarding the engine fire warning light - if you have an engine fire, when the light goes "out" - maybe the light bulb "failed" - or the fire detection loop got burned-out by the fire itself, and the warning light would no longer test. Note that on some airplanes - such as the 747, you have double fire detection loops and double temperature gages which permit perfect monitoring.
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As far as fire protection equipment - freon bottle - some 747 have 2 bottles only per wing (selectable to any of the engines on that wing) or the option of 2 bottles per engine (4 per wing). It is an option. Most 747 have the 2 bottles per engine (and also for the APU in the tail). For education and statistics - most engine fire warnings are bleed air related (overheat) and often "stop" when power is reduced. Other fires are electrical accessories on the engine, such as generator wiring. Some airlines have the policy "engine fire warning, continue engine fire procedure in any and all cases". Some other airlines permit to stop the procedure if the warning goes out (power reduction or power to idle = bleed air).
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There is a "constant fire" inside operating engines...! - And a "tailpipe" engine fire (often on engine starts) cannot be extinguished by discharging a freon bottle. The only thing that you can do in a tailpipe fire situation is to continue to operate the starter motor. If you would operate the fire handle, it would stop bleed air to the starter, and make a tailpipe a worse situation if unable to crank the engine.
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I hope that some "nerds" will have acquired some "system knowledge" here.
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In a 3 or 4 engine airplane, should you have an engine fire, or engine failed, you can continue to your destination. I would, as per company policy, more than aircraft performance capability, recommend landing ASAP after an engine fire. Engine failure... well, that is ok. A BA 747s crossed the Atlantic with an engine out. Since it is BA, nobody will critique their decision. Would it be a US airline, most here would say "bunch of idiots, these Yanks"...!
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Happy contrails