You’re heading out for a road trip. You grab your coffee, settle into the car, and head down the highway. Bags packed, tunes on, and you’re enjoying the view. Thinking about all the fun things to do at your destination has you super giddy, when you look over and see your tank is getting low. You decide it’s probably best to pull over now. Get some gas, maybe some snacks, and the passengers get a bathroom break, too! You fill up the gas tank, and to avoid the unnecessary walk into the gas station office, you pay via card with a quick tap. Just like that you are back on the road, car showing another 500 km of range (300-ish miles for you ‘Mericans).
While fuelling up our cars is a skill that seems so simple, and such a basic part of our driving culture (Tesla fans ignored) , fuelling up airplanes is not the same kind of deal. For one thing, even though we fly the planes, we don’t quite fuel them ourselves… but more on that later. In this topic, we explore fuel, where it came from, how we look at fuel as a resource, and what the future of fuel in aviation looks like.
BURNING DINOSAURS, ALL THE SAME
Jet fuel is a type of liquid fossil fuel; fuel created by the process of transforming the energy found in organisms which lived in the past. The earliest original ideas of using jet fuel came from the 16th century, when Da Vinci drew up a device that would use hot gas to do mechanical work (the modern jet engine). Centuries later, World War II lent it’s high science time to the development of the first jet-powered aircraft. While World War II came to an end, the science did not, and all those discoveries were put to good use by the U.S. to develop kerosene based fuel. JP-1 being it’s designation, became the first edition of our modern jet fuel. The current (and most common) version we use is known as Jet A-1. Why kerosene? Chemistry my friends! Kerosene lends itself to lower freezing points, high energy content for mass, stability, amongst others. All these properties put together, we get a fuel that can burn hot and create tremendous energy to move something as heavy as an airplane at speed, in the cold, efficiently!
FUEL TO CARRY FUEL
For commercial passenger carrying jets, the fuelling is being done by a separate fuelling company. A good example of this is Esso Fuels for example, who signs contracts with other airlines to be their fuelling partner. The company will order the fuel for the aircraft when it is at the gate, and a truck will automatically show up to get fuelling done. Where I work, my company uses special software to design flight plans that calculate how much fuel is needed for a given trip. But unlike a car, where we generally just fill the car until the tank is full, airplanes are rarely ever full of gas. Instead, the amount of fuel is just enough to get to destination, plus any reserve for contingencies, and any additional that the crew may ask for, although that last point is also rare.
The reason for this is weight. Unlike a car, which travels over the ground, planes fly in the air. And while that fact sounds obvious, it comes with it’s own unique challenges, mainly weight. You see when an object flies through the air, it has to carry it's own weight with gravity acting down on it. When we fuel planes above what we need, we increase it’s weight more than we have to. When the weight increases, we end up needing more fuel to carry that weight itself to the destination, and this problem compounds upon itself; a positive feedback loop. In addition, the more the aircraft weighs, the more fuel is burned because the engines have to work harder to generate lift, increase speed, and overcome gravity. The third issue, is that the aircraft may not be able to climb to a cruise altitude that is economical for the company, detrimental to the profitability of the route. For example, on long routes you will notice the aircraft climbs higher as you get closer to destination. This is because the aircraft is getting lighter, by virtue of burning fuel thus reducing its’s weight. As the aircraft climbs up higher, a lower burn rate is required to maintain it’s speed at altitude. But as you can see, if we fuelled more than we needed to, we could not reach those higher, more economical altitudes. That being said, it is important to remember, we never fly the aircraft with less fuel than we need; we simply don’t fill it up more than we have to.
BREAKING DOWN FUEL
Now let’s breakdown how pilots look at fuel. Fuel is stored in the aircraft according to a volume of space in the tanks that is measured with pre-defined environmental standards (temperature, pressure, etc). But, our flight deck systems show fuel in terms of weight, not volume. Adding complexity, fuelling in different countries is done in different units, like U.S. where they fuel in U.S. gallons, whereas in Canada litres is the standard. Thankfully, our onboard fuel calculator saves us from having to do the complex math, but back in the day conversion charts were commonly used.
Take a look at a trip from Toronto to Seattle. We might require 10.2 kg of fuel (expressed as 1000’s, so that number is actually 10200 kg of fuel). So when the aircraft system indicates 10.2 kg, we know that we can reference our flight plan and make sure what we are suppose to have, is indeed what we have. Our flight plan has a breakdown of that fuel. Inside that total 10.2 kg’s, is fuel that we need to carry the weight of the plane to the destination. This is commonly known as BURN. Alongside that is another important category called ALTERNATE. Alternate fuel is that needed to get from our destination airport to an alternate (or secondary airport). Working our way deeper into the categories, we find RESERVE. Regulations require that even after reaching an alternate airport, we still need 30 minutes worth of fuel to be used while in a hold in standardized weather conditions (ISA conditions). Thus, the RESERVE category fulfills this requirement. There are several other categories of fuel that are more in-depth and beyond the scope of this post. The main thing to take away is that 10.2 kg of fuel is not just an arbitrary number; it is made up of many different fuel categories, all of which are important in the safe operation of an airline. Modern computer programs intelligently calculate fuel specific to each aircraft with regards to route, altitude, temperature, wind, and many other factors. Therefore sticking to our flight plan guarantees that we will have the required fuel we need. Naturally, changes made to route, altitude, or speed will change the fuel required, something pilots pay close attention to, which does periodically happen.
We make periodic checks along the course of the flight to make sure the fuel on board over a given waypoint, matches or exceeds our flight plan. On our arrival briefing, fuel turns into a time value. For example, the A220 engines burn 30 kg/ minute. Having to do an additional approach takes roughly 400kg. So while briefing, we discuss how much extra fuel we have on top of what we need as the bare minimum to get to our alternate airport. That extra fuel on top is converted to a time value, say roughly 30 mins of extra fuel. We then get a mental picture of how much extra time we can spend on say another approach, or a hold at the destination airport, before we are committed to going to our alternate. Once we land at destination and park at the gate, we record the fuel numbers in our aircraft logbooks. Our onboard system also sends a snapshot of the fuel to operations control, who closely monitor it to design future routes that are more efficient.
THE FUTURE OF FUEL
Now that we got a brief summary of aviation fuel, and how we observe fuel as a resource, I wanted to quickly touch on the future of fuels. Sustainable Aviation Fuels (SAF) initiative has been in steady development in the commercial aviation world. SAF fuels are essentially those liquid fuels that are created from sources such as waste oil, municipal waste, etc. The goal is simple, to reduce emissions. All the key players in the world are in the race to design such technologies. SAF is sustainable because it uses products that are generally considered as part of the waste cycle, in it’s own development. Furthermore, the chemistry in which they burn allows for significant reductions in CO2. For now, most solutions are known as “drop in” solutions, which means that they are added to the existing Jet A1 fuel source. The major advantages with this trend is that existing airport infrastructure can handle it, and there is strong compatibility with current engine technology. Some of the disadvantages of SAF however are cost, and limited production capability. As far as cost is concerned, the largest cost to any airline is the cost of fuel, which in recent years has seen major fluxes as geopolitical events unfold. SAF requires new manufacturing technologies and life cycle changes, whose cost has yet to be spread amongst key players. To top that off, limited production is the result of new manufacturing technologies that are yet to be common place, and wide acceptance of SAF. Until it can be done at scale, it will remain in “the future.”
In this post, I hope you got to learn something new about a relatively common concept. Even though the topic of fuels may seem mundane at first, the manner in which airplanes use it is certainly an interesting one. The next time you are staring out the terminal window, and see a fuel truck pumping fuel into the plane, you will have found a new appreciation, and understanding of what it means to pump her up!
Wwwwooooooowwwwww 👏👏👏👏👏👏👏 beautifully written!
Never knew fuel is such an important factor in aviation industry. Beautifully explained the technicalities of it👍