Fuel Quantity Test Sets & Calibration

Large commercial long-range jet aircraft need a large fuel load. This fuel is carried in fuel tanks that are incorporated in the aircraft’s main wings The biggest passenger aircraft in service today has a maximum fuel capacity of over 85,000 gallons. During the flight, the pilot monitors the consumption of fuel very closely to ensure the safety of the flight, so that it reaches its destination with still sufficient fuel left for emergencies or diversions. It is essential for the pilot to accurately monitor the fuel consumption and record it in his log. He has to manage the plane’s weight and balance to ensure a smooth and safe flight.


How do the in-flight fuel measuring systems work?

The in-flight fuel monitoring systems are of critical importance. At present most in-flight fuel measurement systems use capacitance-based technology. This technology used on most modern aircraft to measure fuel capacity is accurate, proven, safe, and reliable. Its design incorporates a large bank of about 20 to 30 capacitance probes that are mounted vertically in the fuel tanks. These probes act like variable capacitors, changing their capacitance value depending on the level of fuel that acts as a dielectric. As the fuel level reaches near a probe and wets it, its capacitance changes. This lets the system measure the level of the fuel in the tanks. The data from the probes go to an electronic box outside the fuel tank, where calculations are made to determine the total amount of fuel in each tank. This data is then relayed to the pilot in the cockpit and other aircraft systems.

Although this system is quite reliable, the capacitance-based fuel measurement system is rather complex and requires extensive design and engineering.Typically, a total of 20 to 30 probes need to be installed throughout each of the wing tanks in most large commercial aircraft. Additionally, complex wiring is required to connect all the probes. The electrical wiring, and the increasing use of composite materials in wing design, mean that extra measures must be taken to ensure that lightning strikes do not affect the wiring causing fuel tank explosion.  A great deal of engineering and cost goes into mitigating these risks.


The Fuel Quantity Test Sets

The Fuel Quantity Test Sets are specifically designed to satisfy the need to check the serviceability and accuracy of the capacitance-type aircraft fuel quantity-measuring systems. Accuracy and reliability are optimized together with portability and convenience. The accuracy of the Test Set ensures that the manufacturer’s measurement and calibration requirements are met. The voltage potentials and currents the test sets introduce during the tests are limited to meet all safety precautions.

Each aircraft Fuel Quantity Test Set requires adapter cables and the specific procedures for each type of aircraft. Adapter cable configurations and interfaces vary widely to accommodate the variety of fuel systems and aircraft.



A standard Fuel Quantity Test Set can perform the following functions:



Fuel Quantity Test Set Calibration

Since the fuel monitoring system on an aircraft is so critical, the equipment used to test it must be very accurate and reliable. These test sets need to be routinely calibrated to ensure that the measurements and outputs are within the manufacturer’s design specifications.

The procedure for calibrating each Fuel Quantity Test Set may slightly differ as it depends on its design and manufacturer, however, the following procedure is necessary as a minimum.


  1. The test set is calibrated by measuring the current output with an accurate multimeter. The capacitance output is calibrated by comparing it with a highly accurate capacitance bridge.
  2. The insulation meter and capacitance bridge are calibrated by simulating various values by using high accuracy resistance and capacitance standards.


The calibration of Fuel Quantity Test Sets must be performed by an approved laboratory that is certified to perform such calibrations with its engineers and technicians properly and certified to do the job.


If you need to make sure that your Fuel Quantity Test Set is calibrated accurately and then choose e2b calibration. We perform calibration procedures in a certified shop to ensure that the Fuel Quantity Test Set meets the highest standards. e2b calibration is an ISO 17025: 2017 accredited facility. Our services are unmatched in the industry.  Please contact e2b calibration for all issues related to Fuel Quantity Test Sets.



Should aircraft tools be calibrated in an accredited calibration lab?