Aircraft Fuel Tester; What is it and Do I need it? 

An aircraft fuel tester is the unknown hero of aircraft reliability; when used correctly they could save money and lives. In this article, we look at aircraft fuel testers.

The aerodynamic component of flying has been thoroughly discussed, as have engines, and systems. An often-forgotten component of flying is the actual fuel. Having good quality fuel in your aircraft is important for the long-term safe use of aircraft. We will be looking at fuel testing – the reason for it, the aircraft fuel testers available and techniques for testing fuel. Whether you are a brand new or experienced pilot, increasing your understanding of fuel testing will increase your overall skill and ultimately make you a safer pilot.  

small plane in flight
Fuel testing is an essential step to ensure safe flying

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What is the purpose of aircraft fuel testing?

Fuel, heat and air combine to provide a flame, and flames are harnessed by engines to provide thrust. Having contaminated fuel can negatively influence the quality of the flame produced. And when we investigate the aircraft power units (engines) a bit we find that the statement is true for both piston and turbine engines.

Piston engines use a mixture of air and fuel under compression (in the piston), which is then ignited. This creates an explosion, forcing the piston down and thus providing torque to the rest of the engine and eventually the prop.

Turbine engines ignite a mixture of air and fuel under high pressure to supply hot air to a series of rotating discs (turbines) that provide torque to drive the engine and provide thrust.

The short engine descriptions above should remind the reader about the importance of the fuel/air/pressure ratios. If the ratios are wrong, then a flame might not ignite, and thus, the engine cannot sustain itself, nor provide thrust.

Fuel is a susceptible component of the flame to imperfections. Fuel contamination (rust particles/dust), water-mixed fuel, and wrong-grade fuel have all led to accidents, as can be seen in this crash back in 2020.

By testing the fuel before flight, a pilot minimizes the risk of having fuel cause a loss of power or in less severe cases long-term damage to an aircraft engine. Unfortunately, it is also a check that is often omitted by pilots.

“It is of critical importance that the fuel taken onboard at uplift is not contaminated in any way since the effects of any such contamination are likely to affect all engines and this may not be evident until after an aircraft has become airborne.”

Fuel Contamination | SKYbrary Aviation Safety

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Where is aircraft fuel stored? 

Aircraft fuel follows an elaborate path to the engine spanning multiple forms of transport and rigorous testing. Pilots’ responsibilities start at the second-from-last point, the “fuel container” before it gets transferred to the aircraft’s tanks. These containers can be any of a couple of things – a truck, a drum, or a bowser.  

Fuel at an airport is usually stored in a secure area, often in big stainless steel containers containing thousands of liters. The fuel is then pumped to trucks/bowsers. Before accepting fuel from a truck or bowser, ensure they are in good condition. Things to look out for are rust, leaks, dirt and cavities. The drivers of the trucks must regularly test the fuel onboard their trucks and are usually of a high standard, however as a pilot do not hesitate to ask for proof of testing. It is easier to screen fuel before it is pumped into the airplanes.

Most aircraft use their wings to store fuel, although modern, light aircraft might have fuel containers inside the fuselage. Most aircraft have small fuel reservoirs inside the fuselage.

The last point to note, at quiet/small airfields, fuel could be stored inside drums. These fuel containers are most prone to contaminants and need to be well inspected before use.

aviation fuel tank
It’s essential to check the condition of the fuel tanks and browsers to avoid contamination (Source Fuel Proof)

How do you check fuel in an aircraft?

Most aircraft have a fuel tester as part of the standard equipment however, pilots are encouraged to always carry their own. In smaller planes, a fuel sample is drained off specially designed drain points along the aircraft.

The sample is tested for water and other foreign particles. Australian Civil Aviation Safety Authority released a very good, and comprehensive study into water in fuel and issued an airworthiness directive.

Depending on the standard operating procedures (SOPs) of the owners of the aircraft, some aircraft need to have fuel tested on each flight, other than after each refuel, and some once a day.

Water is denser than fuel, and as such, should sink to the lowest point in the wing. This is also where the drain points usually sit.

For AvGas aircraft, water can usually be seen in the aircraft fuel tester, as the colors are different.

Jet A1 fuel looks nearly the same as water, and as such a special water indicator will need to be used. Many different types exist and the operator of an aircraft will have a preferred method. This YouTube video shows how much fuel and water look alike, but how you can tell when it may be contaminated.

Fuel testing can consist of having a good look at it, smelling the fuel, or using some sort of reactant.

Small plane on tarmac fueling
It’s essential to test fuel whenever fuel contaminant could have entered the tanks, or as a standard pre-flight inspection.

What is an aircraft fuel tester?

A tongue-in-cheek reply would be a device to test fuel with. And that statement is not worth much in itself, but it does contain a certain truth. Aircraft Fuel testers do vary significantly and are thus hard to define.

The standard fuel tester is a container (usually cylindric) made of transparent material open on one end. A sharp protrusion often sits above the open end of the cylinder, this is used to activate the drain on the aircraft wing. The fuel is then collected in the cylinder for further testing. This video shows a comprehensive breakdown of fuel tester types.

How do you use an aircraft fuel tester?

The best way to learn is to have someone show you how it is done, alternatively one can reference the pilot operating handbook (POH) of the applicable aircraft.

If pilots follow the method laid out below, fuel testing should be sufficient.

  • Time for the testing of the fuel is important and my advice would be to not test fuel more than 2 hours before the flight, and not within 3-5 minutes of adding fuel or moving the plane.
  • Work methodically around the airplane draining from all drains. Knowing beforehand where the drains are located will assist in this, as drains can be hard to get to in low-wing, low-to-the-ground aircraft like the Mooney M20.
  • Take enough fuel for a decent sample.
  • Test the fuel by means of looking, smelling and testing with a chemical reactant.
  • Dispose of the fuel in an environmentally friendly manner. Fuel can be returned to tanks if clean, but the benefit is minuscule.
  • If water or other particles are found, reference POH/Maintenance.
  • Make especially sure to test fuel after the plane was standing for a couple of hours, as water can seep in through the temperature variation across a day.
Aircraft fuel tester in use
An aircraft fuel tester is a simple to use device that can save a lot of hassle down the track (Source General Aviation News)

What can an aircraft fuel tester measure and detect? 

Most aircraft fuel testers can test for water and dirt particles. Some expensive fuel testers do have measurements on them for precise measuring, but most are primarily for detection purposes.

Interestingly, due to the long “down” time during COVID-19, a new type of fuel contaminant is being discovered microbial contamination. Maybe in the future, fuel testers will have a function to screen for more threats.

How much does an aircraft fuel tester cost? 

As with many things when discussing cost, fuel testers have quite a wide range. The cheapest I could find online was around $10, and the most expensive ones could sell for $100.

“Fit for purpose” is a good rule to use when looking to buy a fuel tester. Remember this check could be the difference between a safe flight and engine failure.

Where can you buy an aircraft fuel tester? 

Fuel testers can be found at many online aviation shops including Flight Store.

Many airports will have a flight store close by as well.

Secondhand websites like Ebay and Facebook MarketPlace could have a bargain.

Most airplane manufacturers will also have a fuel tester available for purchase.

You can also buy them directly from Amazon.

Aircraft Fuel Tester
Aircraft fuel tester that fits all quick-drain valves and has an adapter for recessed drains. Includes both Phillips and slotted screwdriver tips. (Source: The aviator store)

What is the best kind of aircraft fuel tester? 

The one that works. Testing fuel should be an easy-to-do exercise without having to make multiple trips to empty the tester. The more effort it is to test the fuel, the more likely pilots will be to skip it.

Anecdotally, I can tell you about an event not so long ago. A Cirrus pilot friend of mine bought a big, multi-sample fuel tester. It has a spring-loaded valve drainer to ensure a pilot does not damage a drain. It all looks very neat, and this friend of mine was quite proud of it, making quite a show the first time he used it. The problem was that once done with the testing, the tester was too big to be stored in any of the easy-to-reach pockets of the plane and as such the tester was soon forgotten in the baggage area of the Cirrus. The cheap skinny tester was used way more.

For those who want more guidance, refer to these different fuel tester options.

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FAQs about aircraft fuel testers: 

What kind of fuel do airplanes use? 

Aircraft use mainly one of two types of fuel. Jet fuel or Avgas, depending on what engine is installed.

Turbines use Jet fuel or a variant thereof (Jet A, Jet A1, etc) whereas most piston engines use AvGas. Rotax piston engines are designed to use Mogas (car fuel, usually 95 Octane or greater)

Can I test my own aircraft fuel? 

Yes, as a pilot you are the person responsible for testing fuel. This is usually stipulated in the law. In Australia, the reference is CASR 91.

How often is aircraft fuel tested? 

As mentioned earlier, each operator will have their own rules for fuel testing. A good rule to follow would be whenever fuel contaminant could have entered the tanks, or as a standard pre-flight inspection.

Is there anything else I should be checking with my fuel?

Yes, when it comes to aircraft fuel, ensuring an accurate measure of fuel levels is also important. While onboard electronic fuel gauges are the primary indicators, they can occasionally be faulty or inaccurate, especially in older aircraft or under certain conditions. This is where the importance of an aircraft fuel dip stick becomes evident. It serves as a manual backup to verify fuel quantities directly. By inserting this calibrated tool into the tank and checking the wet mark, one can determine the exact volume of fuel present, providing an added layer of confidence and safety.

Aircraft fuel gauge with fuel stop
Fuel gauge with a fuel stop that snaps onto a standard straw fuel gauge and prevents the gauge from ever slipping into the tank. (Source Pilot Gear Online)

Summary

The fuel system plays a critical role in flying and in the common pilot’s mind, quantity checks dominate quality checks. Making sure that the fuel in your aircraft tanks is as clean as possible could save your life. This article should help motivate all fliers to regularly test the fuel by means of the appropriate aircraft fuel testers. Check for water and non petroleum contaminants, and if unsure, investigate. It testifies of a professional pilot.

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One thought on “Aircraft Fuel Tester; What is it and Do I need it? 

  1. Nice Post here! Funny story… At an airport, I had the FBO fuel my aircraft with their personnel. I looked outside to see one of their newest employees pull the wrong-grade fuel truck to the plane. I frantically ran outside to the plane before they started pumping fuel.
    Keep up the great writing!

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