Almost all King Airs with Aircraft Instruments, capacitance-type fuel quantity indicators have the zero to 265 pounds range painted in yellow. The POH states, “Do not takeoff if fuel quantity gauges indicate in the yellow arc or if fuel quantity is less than 265 pounds in each wing system.” I know that a lot of King Air pilots think this comes from concern about a tank “un-porting” under certain conditions, causing air, not fuel, to reach the engine and leading to an engine failure. No, that is not the concern here.
In fact, the concern has nothing whatsoever to do with the physical or the engineering aspects of the system. Instead, it comes from Beech’s legal team. The attorneys want to be able to tell the jury, “See?! We told the pilot not to take off with so little fuel! It’s his disregard of this limitation that caused the fuel exhaustion and crash, not our system!”
Whether we are talking about a C90 or a King Air 350 model, the same 265 pounds yellow arc is used, so the quantity does not relate to actual fuel consumption rates but instead is a general “catch-all” amount. It can and does equate to more than 30 minutes of flight at Maximum Cruise Power in a C90, but less than 30 minutes even at Maximum Range Power at low altitude in a 350.
By its very nature, the nacelle fuel tank – where the fuel that gets sent to an engine originates – is a fairly tall, slab-sided, tank that would be unlikely to experience fuel pick-up problems at various unusual attitudes. Yet it is even “safer” than we think, since the main wheel well intrudes onto the lower, aft, portion of this tank. This makes the bottom of the tank exceedingly narrow and steep-sided with the chance of fuel sloshing away from the sump very unlikely.
We can sometimes be totally legal for a day VFR flight, even though we allow the fuel quantity to drop into the yellow arc at the end of the flight since we have a reasonable 30-minute reserve.
On the models that do not have a “Total” reading on the fuel quantity gauges – where the pilot must add Main and Aux quantities together to reach the total – the yellow arc has yellow lettering nearby that reads “Main Tank Only.” These three words are telling us that it is okay if the Aux tank quantity reads in the yellow since we rarely have a significant amount of fuel in the Aux tanks unless the Main tanks are full or close to full. In other words, the yellow arc applies to the Main tank quantity only.
Since we are discussing low fuel quantity, I want to also present an item on my King Air “wish list:”
I wish all King Air models had some low-fuel-level advisory system that is independent of the normal fuel quantity gauges. Only the 300-series – the 300 and the 350 models – have this desirable backup. In those models, there is an optical sensor that illuminates a Caution annunciator when approximately 300 pounds remain in the main tank system. For all the other King Air models, unfortunately, the quantity gauges are the only indication we have. If and when they are malfunctioning, we are left with confusion as to the actual state of FOB (Fuel Onboard).
Do you remember how to convert pounds of Jet-A into gallons in your head? Like 265 pounds is the same as 40 gallons. Just add half the fuel to itself and divide by ten, so 265 + 132.5 = 397.5 and 397.5 ÷ 10 = 39.75 which equals about 40 gallons. Of course, it is really unnecessary to use this degree of precision. Instead, using just two significant digits is fine: 26 + 13 = 39 (the 26 from 265 and 13 from 132.5). For another example, are you burning 560 pph in cruise today? That is (56 + 28) 84 gph.
If you have a question you’d like Tom to answer, please send it to Editor Kim Blonigen at kblonigen@cox.net.
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