1. Low Pressure boost pump in wing tank, output is "constant"
2. Low Pressure - engine driven, output is direct relationship to engine rpm
3. High Pressure - engine driven, output is direct relationship to engine rpm
Low inlet pressure to the HP pumps is a focus of the investigation. There's a lot of cheese slices between the fuel tanks and HP pumps!
Harmonics? Perhaps.
Beyond FCOC and fuel tubing atheromata, I'm suspicious of excessive
Prerotation and Backflow of unusually cold & viscous fuel reducing output of all the low pressure pumps.
An increase of intake vortices at the wing tank boost pumps may have been exacerbated by relative fuel surface level changes in relation to the pickups due to aircraft pitch changes during approach.
http://caltechbook.library.caltech.e...igs/fig408.jpg
http://caltechbook.library.caltech.e...igs/fig406.gif
-=MachacA=-