I'm quite bewildered about what happened here. Perhaps the MEL procedure was supposed to be done on ground power. What I really don't understand is why the #2 HOT bus was not powering the DC essential bus after the generators were taken offline. The report claims they had a TOTAL electrical failure (the FADEC units would be still powered by the main generators, which were otherwise disconnected from the electrical busses). From what I gather, the tailpipe fire was due to residual fuel in the lines after the fire handles shut the upstream fuel valves. But what exactly happened here?
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Memo to pilots: being indecisive about whether you want the engines running or not isn't a good thing!
It looks to me like what happened is when electrical power was lost, the left engine FADEC lost power too as that engine's generator was inop. And it looks like the design of the engine is such that when the FADEC loses power, the fuel flow to the engine's injectors remains at its last setting?
So power was lost, but the engine did not stop as fuel was still flowing. Pilot observes engine not stopping, pulls fire handle. Fuel flow stops (eventually) and engine starts to wind down. Pilot is impatient and decides engine is not stopping fast enough so resets the fire handle (because adding fuel to the engine will make it stop faster?). Fuel flow to the engine is restored, at the same rate as before. But since engine is turning more slowly, that amount of fuel is more than can be burned with the air flowing through the engine's core, thus it burns in the tailpipe.
Result is a situation that might have been viewed in a more positive light by the pax and crew had marshmallows been available.Be alert! America needs more lerts.
Eric Law
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Originally posted by elaw View PostIt looks to me like what happened is when electrical power was lost, the left engine FADEC lost power too as that engine's generator was inop. And it looks like the design of the engine is such that when the FADEC loses power, the fuel flow to the engine's injectors remains at its last setting?
The story says they were testing the 'integrity of the circuits'. What does that mean? I'm thinking it was to test the HOT (BAT) bus powered DC ESS bus in case the second main and the APU (and the RAT!) were lost in flight. Obviously something went south.
I wonder if the procedure was supposed to be done on FADEC ground power.
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