Fuel Flowmeters: Volumetric vs Gravimetric Flow and Fuel-Used Integration

022-01-04Pablo Asensio Martínez2026-03-271 min

Fuel flowmeters provide pilots and onboard computers with real-time data on engine performance and fuel consumption.

Principles of Measurement

Fuel flowmeters measure the quantity of fuel delivered to the engines per unit of time. There are two main methods of measurement:

  • Volumetric: Outputs volume per unit of time (e.g., US gal/h, Liters/h). Susceptible to density errors from temperature changes.
  • Gravimetric: Outputs mass per unit of time (e.g., kg/h, lb/h). This is the standard for Commercial Air Transport as it provides a more consistent and accurate measure of energy content.

Total Fuel Consumption (Fuel Used)

To determine the total fuel consumed during a flight, the system uses integration.

  • Process: A computer mathematically integrates the rate of fuel consumption (flow) over time.
    • $\text{Total Consumption} = \int (\text{Fuel Flow}) dt$
  • Function: This calculation accounts for all variables affecting consumption (altitude changes, speed, weather).
  • Utility: The calculated "Fuel Used" is compared alongside the "Fuel On Board" (FOB) from the tank sensors. This cross-check allows the crew and the Flight Management System (FMS) to:
    1. Verify accurate fuel burning.
    2. Detect leaks (if Fuel Used + Remaining does not equal Initial FOB).
    3. Predict fuel at destination accurately.

An Integrated Flowmeter is an instrument that displays both the instantaneous Fuel Flow and the Total Fuel Used.