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Fuel Gauges. Can You Trust ‘Em? Probably no other airplane system is so universally discredited by pilots than the fuel quantity indicators. There’s a widespread misconception that fuel gauges are “only required to be accurate when there is no fuel in the tank.” Guess what – this is wrong. Where does that “only accurate when empty” misconception come from? It’s from a partial reading of 14 CFR 23.1337, the Federal regulation concerning certi- fication of fuel indicating systems. True, 23.1337(b)(1) says this: Each fuel quantity indicator must be calibrated to read “zero” during level flight when the quantity of fuel remaining in the tank is equal to the unusable fuel supply determined \[during aircraft certification\].” That’s the passage often quoted alone, out of context, when making the claim that fuel gauges are not accurate at any other time. Some airplane owners use this to conclude that it’s useless (and not necessary) to invest time and money into calibrating gauges that do not indicate properly. But as I said, this is quoted out of context. The Real Requirement The first part of 23.1337(b) tells us: There must be a means to indicate to the flight crew members the quantity of usable fuel in each tank during flight. An indicator calibrated in appropriate units and clearly marked to indicate those units must be used (emphasis added). The regulation stops short of saying the fuel gauges must be calibrated pre- cisely to their marked levels. However, conditions where gauges are noncompliant and must be repaired include: When a gauge does not indicate a steady reduction in fuel level as fuel is burned from the tank; A gauge indication stops at some point then shows an increase before again indicating a fuel level drop; Does not indicate approximately “Full”, “3/4”, “1/2”, “1/4”, or “E” when your calculations or a fuel totalizer say that they should. What about airplanes certificated to the old Civil Air Regulations Part 3, the body of regulations later superseded by FAR 23? Are these airplanes’ fuel gauges required to be accurate too? CAR 3.672 addressed fuel quantity indicator requirements, and read very much like the later Part 23 requirements: CAR 3.672 Fuel quantity indicator. Means shall be provided to indicate to the flight personnel the quantity of fuel in each tank during flight. Tanks, the outlets and air spaces of which are interconnected, may be considered as one tank and need not be provided with separate indicators. Exposed sight gauges shall be so installed and guarded as to preclude the possibility of breakage or damage. Fuel quantity indicators shall be calibrated to read zero during level flight when the quantity of fuel remaining in the tank is equal to the unusable fuel supply as defined by CAR 3.437. Like the first portion of 23.1337(b), the certification standard of CAR 3 airplanes requires that the fuel quantity indicators be accurate in flight as well as at the “zero usable fuel” level. Active general aviation pilot and retired TWA captain Tom Rosen, speaking at an American Bonanza Society convention a few years ago, had a great point: “It’s less important to know when your fuel tank is empty, than it is to know accurately when it is only one-fourth full. This gives you time to do something about fuel state before anything becomes critical.” If your airplane’s fuel gauges aren’t accurate and reliable, fix them. Not only is it required by the regulations, it’s also an important component of fuel monitoring that helps prevent all-too-frequent fuel management-related crashes. burn against anticipated. Recalculate fuel remaining at destination if your actual burn exceeds what you predicted to that point. As you did during climb, glance out at the fuel caps or fuel vents occasion- ally if they’re visible from the cockpit, and the wing or structure behind caps and ports to discover if fuel is siphoning overboard in the slipstream. Land if you note any leaks. Follow precise mixture leaning pro- cedures to get the best fuel flow for your mission, whether it be a fast trip, an endurance run or some compromise between the two. Compare fuel gauges and totalizers to your calculations and a clock in a regular fuel crosscheck. If the fuel gauges read lower than expected, land and reconfirm the fuel onboard. Recompute reserves often enough you can easily land early if needed. Use an alarm or timer to remind you when to switch fuel tanks, if the airplane requires. Reduce power and cruise slower for longer endurance, if needed. Don’t “hope” the ground speed will improve, or think you’ll “make it up in the descent.” Fuel exhaustion events often end up within a mile or two of the intended destination when the pilot thinks he/she has enough to make it. Make the decision early to land for fuel if you cannot determine the amount of fuel remaining, or if your computed reserve at destination slips below your minimums. “I might have been able to make it nonstop” is a much more desirable post-flight reflection than “I almost made it.” If you think you have enough fuel, you don’t have enough fuel. You need to know. The only way to know for sure is to enact a fuel strategy, then approach it tactically to meet your strategic goals. Thomas P. Turner is an ATP CFII/MEI, holds a master's Degree in Aviation Safety, and was the 2010 National FAA Safety Team Repre- sentative of the Year.Subscribe to Tom’s free FLYING LESSONS Weekly e-newsletter at www.mastery-flight- training.com. 16 • TWIN & TURBINE / October 2019