ShyT, one question. How often was the pump flow rate checked? Pump capacity can decrease over time. ?????
It was checked every time I confirmed the amount in the aircraft fuel tanks after refuelling by the "clock" method. I did always check the gauges; that's how I knew it worked!
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I see folks here are now getting concerned about relatively insignificant density differences in the fuel. Put it in perspective, chaps!
For example, an aircraft with a "500 Kg" fuel tank (for round figures) fills up with 0.8 SG fuel. It will have taken 625 litres.
Next time it is filled, the fuel is 0.81 SG. It will "only" have 617.3 litres on board. A difference of 7.7 litres / 1.7 gallons, or approx 6 Kgs difference @ 0.81 SG.
Obviously, the fuel gauges and fuel flow meters still work, irrespective of a small error in SG and such a small mass will have a very small effect on aircraft performance. When performance is most critical, at takeoff and landing, a small wind variation will probably have more of an effect.
I certainly don't lose any sleep over it because I would land before the gauges showed 6 kgs total, whatever the circumstances. My present aircraft's stated unusable fuel is 5 Kgs /5 Kgs (approx 12 litres total).
Thankfully, from what I've read here, the fuel system is far more straightforward than that of the EC135. It has one transverse main tank, connected by gravity to a pair of smaller tanks, one feeding each engine.