Recently I had to fly a very low houred CTSW so assumed everything would be 'hunky dory' (which it actually was) but was a little concerned about fuel flow in flight:

To explain..... I had a flightplanned route of 3hrs so assumed it was prudent to have at least 80 litres onboard, according to the CTSW Fuel dipstick there was 20litres per side (which related to site glass in wing roots) so 40 more litres were required.... being extra prudent I asked for 60 litres to be placed 30 litres in each tank to give me 50 litres a side.

Now after having added an extra 60 litres I was surprised to see that the combination of both tanks registered as 115 litres !!! still I will work on 100litres I thought..... now with a Dynon D180 telling me we were averaging in the region of 17.5 lph I estimated that my leg from Sittles to the Coastline of Dublin would use 35 litres and that both tanks will have at least 32.5 litres per side remaining :-)

At the 'Liffy' waypoint I noticed that the RH Tank was showing absolutely nothing in it, but sometimes bubbles would appear briefly in the sight tube with a smattering of fuel ( Liffy to coast is 22nm) so this tended to concern me as I hadn't expected to see what perceived to be a basically dry tank on the RH side and a Totally FULL Tank on the LH side !!

All kinds of calculated thoughts ranging from 'was the LH Tanks pipes blocked' to 'was I actually going to run out of gas ?' shot through my head... I wasn't even able to comprehend that even if I did only have the RH tank supplying fuel how 50 litres would have disappeared in the time I had calculated 35litres to the coastline and should have used 32litres by 'Liffy' BELLS WERE RINGING !!!

Strangely as I got over the coastline near Dublin the RH tank seemed to be showing 15 litres again !!! still I couldn't understand why two interlinked tanks could have such an imbalance between them ? I had decided to divert into Dowth Hall to check the fuel status, but on arrival over the Boyne Bridge....found Dowth lying under a bank of cloud at about 250ft. The options were divert into DUBLIN AIRPORT or continue onward to my destination of Tandragee.... Tandragee won the toss and surprisingly even after landing there I found we had 50 litres remaining (avg 16.67lph) for the 3hr flight completed.

I know there is some strange anomaly with CTSW tanks, but can anyone advise if there is a cure to this issue or what actually causes the fuel to drop quicker from one tank than the other ?


MTIA, Peter