FAA Flight Instructor Airplane (FIA)Aircraft Systems and InstrumentsMedium
A pilot notices that the fuel quantity gauge does not exactly match the readings from a digital fuel totalizer during cruise flight. According to 14 CFR part 23 certification standards, at what fuel quantity is the gauge required to indicate accurately?
- AHalf tank capacity
- BEmpty (zero usable fuel remaining)
- CFull tank capacity
- DAny indicated level within 5% of actual quantity
Show answer & explanationAnswer & explanation
Correct answer: B. Empty (zero usable fuel remaining)
Under 14 CFR 23.1337, fuel quantity indicators are only required to be accurate when they read "zero" (empty), corresponding to the point at which no usable fuel remains. At other fuel levels, gauges may be inaccurate, so pilots should verify fuel state using time, fuel flow, and visual checks rather than relying solely on the gauge.
Why the other options are wrong
- A. Half-tank accuracy is not a certification requirement.
- C. There is no regulatory requirement for the gauge to be precisely accurate at full.
- D. No blanket percentage accuracy requirement exists across all fuel levels.
Fuel Quantity Indicating System
A float-type sender in each fuel tank moves a variable resistor connected to a cockpit gauge; by regulation, the gauge is only required to be accurate at the empty (zero) reading.
- 14 CFR 23.1337 requires accuracy only at zero (empty)
- Gauges may be inaccurate at other fuel levels
- Pilots should cross-check fuel state using time and fuel flow calculations
Memory trick: Zero is the only guarantee — trust the gauge at empty, not in between.