If you are flying a Cirrus Perspective aircraft and still thinking in litres it may be time to consider using USG for all of your planning and flying.  I can already hear the naysayers, “but I always think in litres, I get it at the bowser in litres, I pay in litres, my car uses litres, milk is in litres…”

True, but you also fly in KIAS/ KTAS and nautical miles and you don’t convert back and forth to km/hr and kilometres (unless a passenger asks).

Cirrus aircraft are certified by the FAA with fuel in United States Gallons (USG).  This includes the fuel gauges, Initial Usable Fuel, Fuel Added, Fuel Flow, Fuel Used, Fuel Remaining, Fuel Required, Fuel Over Destination (FOD), and Econ (NMPG).  All in USG!

So it makes no sense to plan and fly using litres when this requires you to convert the whole time, to achieve what exactly?

(If you are operating an Avidyne equipped aircraft there is the option to select Litres, which is fine).

There is already enough to think about in the air without converting USG to litres.  USGs are just another measure and whether it is pounds, litres, kilograms or tonnes you should always work in the units that the aircraft was certified with.

Of course at the fuel bowser you are filling with litres so converting to USG is required – but only on the ground when your head is clear.  Dividing litres by 3.79 is close enough (the actual is 3.78541). Once you have the USG quantity and set it on the Initial Usable Fuel page on the MFD you are done.  I promise that when you do this you will plan and fly more confidently.

I am bemused by the calibration of USG reading fuel gauges – placarded in litres!  Exactly how is one supposed to use this information in litres without first converting to USG for comparison?

Whenever conversions are done there is always the possibility of making errors.  So do your one and only conversion to USG on the ground at the bowser unless of course you are filling to TABS or FULL. Yes, you  should absolutely flight plan in USG.


Fly safely,

Charles Gunter

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