A330 single pack ops with APU = fuel saving?
Morning all
The company I work for has recently instituted a new fuel-saving SOP on the A330, requiring us to switch off either pack 1 or 2 when we are on ground with APU bleed running.
Now as we all know, the system design is such that pack flow is set to "high" when APU bleed is on, regardless of what pack flow selection is made. Surely this means that once you've switched APU bleed on, deselecting one pack isn't going to affect the fuel flow at the APU itself?
Furthermore I have watched the APU page on start and as I carry out the procedure. There's no APU fuel flow meter of course, but you can clearly see a large APU EGT rise when the APU is running for electrical generation only, and then you select bleed on. Once you've done that, then any further selection of one / two / or zero packs on, doesnt cause APU EGT to budge by even a single degree.
So, is it a fuel saving or not, and if it is, can someone please explain to me how and why?