Fuel pumps / fuel flow?

[Keith Maton]

I'm wondering how detailed the fuel flow system is simulated.  The FCOM says:

"When main tank fuel pump pressure is low, each engine can draw fuel from its corresponding main tank through a suction feed line that bypasses the pumps. As the airplane climbs, dissolved air is released from the fuel in the tank due to the decrease in air pressure. This air may collect in the suction feed line and restrict fuel flow. At high altitude, thrust deterioration or engine flameout may occur as a result of the fuel flow reduction.

The dissolved air in the fuel tank will eventually deplete after reaching cruise altitude. The depletion time is dependent upon airplane altitude, fuel temperature, and type of fuel. Once the dissolved air is depleted, the engine may be capable of suction feed operation at cruise power."

Is this sort of thing simulated?  If I were to try and take off with all the pumps and crossfeeds switched off, would the suction feed from the engines be enough for full power?

Thanks.

[Hardy Heinlin]

Suction feed is simulated. Just try it out. The engines keep running but you cannot get high thrust.

[Keith Maton]

Ahh yes, thank you.  I can only get about 96% N1

[Hardy Heinlin]

You can see the effect on the EICAS FUEL synoptics as well: The flow bars turn amber.

[John H Watson]

I think engine and airplane manufacturers may be overestimating the ability of their engine pumps to suck fuel from the tanks. Many years ago, a 767 pilot accidentally turned off his fuel pumps in early climb and the plane nearly fell out of the sky.

It's certainly a possibility in the Air India accident.

There was Jetstar 787-8 incident in which both engines (within a minute of each other) went below idle because of fuel contamination from biocide residues.... Biocide is the stuff engineers put in tanks to stop things like this happening. The biocide residues consisted of magnesium salts which gummed up the engine fuel valves. I don't know if they still use it, however.

[Hardy Heinlin]

As usual, by suction feed, maximum thrust cannot be achieved, but now the thrust of the outboard engines is even more reduced than that of the inboard engines – in PSX update 10.183:

https://aerowinx.com/board/index.php/topic,4191.0.html


|-|ardy