Originally Posted by
jettison valve
Dear tdracer,
As was pointed out already, on A330/A340s (I think A380 is the same) the ENG master switch closes also the LP valve on the front spar. Unless... itīs assembled wrongly, as a hidden failure.
This lesson was learned when during a maintenance activity (for whatever reason!) an engine was to be shut down using just the ENG Fire P/B (which interestingly only moves the LP valve, but does not trigger the HMU or anything else in ATA 73). The engine kept on running for many minutes, when the engineers finally killed the engine with the ENG master switch.
Side facts: The incident took place on an A340 whose "operator" at that time was, well, a big aircraft manufacturer in Seattle. Secondly, we replicated the same scenario (eng shutdown via fire P/B) on a different airplane, and it took more than 60sec before the EGT started decreasing after P/B activation; I still wonder why it takes so long...
J. V.
It takes about a minute of idle operation for the engine to flame out after closing the spar valve or LP fuel valve only (not the HP valve in the engine HMU) because that's how long it takes to suck the remaining fuel out of the fuel line between the LP valve on the rear spar and the fuel pump to the point where LP stage of the fuel pump receives excessive vapor and sends vapor to the HP pump. It takes a similar amount of time on the Boeing airplanes.