Fuel loading at a commercial apron — what's going into that wing tank is one of the most tightly specified industrial fluids on the planet
Why Do Airplanes Use Kerosene? A Student Pilot Explains
The question nobody asks at the airport
I was out on the apron at Sambra in 38-degree heat — the kind where your checklist sheet goes limp and your pen starts sliding — watching a fuel bowser lumber across to one of the training aircraft. My instructor was doing something on his phone and mentioned without even looking up that the jets on the commercial side use a completely different fuel. I asked why not just use petrol.
He looked up, said "it burns too easily," and went back to his phone. That was the whole explanation. I wrote it down and didn't really follow it.
It clicked months later, grinding through fuel systems for the DGCA Technical General paper at midnight in my room in Belagavi, when I had to actually understand it — not just flag it in my notes. What I found is that the choice of kerosene isn't a legacy standard nobody got around to changing. It's a direct answer to what happens to fuel at 35,000 feet. And what happens is that petrol would be genuinely dangerous up there, not theoretically risky.
What jet fuel actually is
Jet fuel isn't the kerosene you'd find at a hardware store. It's a refined, tightly specified hydrocarbon derived from crude oil — heavier than petrol, lighter than diesel, sitting in the middle of the distillation range. Think of it as kerosene that went through an extremely fussy quality control process.
The international standard for commercial aviation is Jet-A1. The US domestic variant is Jet-A, which has a slightly higher freeze point but is otherwise similar. Military aircraft use JP-8 — basically Jet-A1 with added corrosion inhibitors.
Older piston trainers like the Cessna 152 run on Avgas 100LL — leaded aviation gasoline. Completely different product, completely different engine. Students who haven't done fuel systems yet sometimes assume these are interchangeable. They're not even in the same category.
| Fuel | Type | Used In | Standard |
|---|---|---|---|
| Jet-A1 | Kerosene | Commercial turbofan / turboprop | ASTM D1655 / DEF STAN 91-091 |
| Jet-A | Kerosene | US domestic commercial | ASTM D1655 |
| JP-8 | Kerosene | Military aircraft | MIL-DTL-83133 |
| Avgas 100LL | Gasoline | Piston-engine GA aircraft | ASTM D910 |
Why not petrol
Reasonable question. Petrol's energy-dense, it's everywhere, and we already burn it in cars. The problem is three specific things that become dangerous in flight — not edge cases, but predictable failure modes at conditions jet aircraft operate in every day.
Petrol evaporates too easily
Its flash point is around −43°C. At altitude, where outside air hits −55°C and fuel tanks are partially depressurised, petrol vaporises fast inside the tank. That vapour-air mixture is explosive. Jet-A1's flash point is at least +38°C — at normal operating tank temperatures, it won't produce enough vapour to ignite accidentally. Ground crews can work around Jet-A1 without the ignition risk petrol would create. It's not close.
Petrol freezes near cruising temperatures
At 35,000 feet, outside air averages around −56°C. Petrol's lighter hydrocarbons start gelling somewhere between −40°C and −50°C — right at the edge of where jets routinely fly. Jet-A1 has to stay liquid at −47°C or below. Fuel for polar routes gets tested even colder. There's no room for "close enough" when the fuel needs to pump through injectors at those temperatures.
Petrol doesn't combust cleanly in a turbine
Turbine engines burn fuel continuously in a sustained flame — not in explosive cycles like a piston engine. Petrol's combustion behaviour is built for spark ignition. Put it in a turbine and it burns erratically, causing flameouts and hot section damage. Wrong tool for the job.
Five properties that matter
Start with energy density — Jet-A1 delivers around 43.2 MJ/kg. On a long-haul 777-300ER carrying about 145,000 litres, that's what keeps 300+ passengers airborne for 15 hours. Petrol's energy density is almost identical. That's the frustrating part — it's everything else that disqualifies it.
The one that surprised me most in ground school: jet fuel doesn't just combust. It circulates through heat exchangers to cool hydraulic fluid, engine oil, and avionics before it ever reaches the combustion chamber. That dual role — fuel and coolant — is built into the design of every modern turbofan fuel system. Petrol would break down chemically under those heat loads long before it reached the burner.
Lubricity
Jet fuel lubricates pump internals and fuel control units as it moves through them. The spec includes a minimum lubricity requirement. Drop that lubrication and precision components wear out fast — the same problem that hit ultra-low sulfur diesel in road vehicles, which is why mandatory lubricity additives exist for that too.
Static dissipation
High-speed fuel flow during refuelling builds up static charge. Without static dissipator additives, a discharge into fuel vapour could cause a tank explosion. It's not optional, and it's not left to the refuelling operator — it's in the spec.
Microbial contamination
Water accumulates in jet fuel tanks through condensation and sits at the bottom. That layer breeds Hormoconis resinae — the "kerosene fungus" — which produces acids that corrode tank structure and clog fuel filters. Engineers check for it in routine maintenance. It shows up. Biocide additives are a spec requirement, not a suggestion.
What I learned about this in ground school
Fuel systems caught me off guard in DGCA Technical General prep. I'd underestimated how much the paper wants you to reason through it — not just name the fuel type. I was sitting in my room in Belagavi working through past papers at midnight and kept getting the fuel temperature and density questions wrong. Not because I didn't know the values, but because I hadn't understood why those values exist. Once the physics made sense, the questions stopped feeling arbitrary.
When you know why the freeze point matters, the question about minimum fuel temperature before departure stops being something you memorise and becomes something you can work out. That's the difference between passing the exam and actually understanding what you're signing off on a fuel log.
When fuel goes wrong: real incidents
Every fuel-related accident I've looked at traces back to one of three things: wrong quantity, wrong type, or a system failure nobody caught before departure. These three cases cover all three.
A Tuninter ATR 72 ditched into the Mediterranean after both engines flamed out from fuel exhaustion. A technician had installed a fuel quantity indicator from an ATR 42 — a different aircraft type — into the ATR 72, making the crew's gauges read far higher than the actual fuel on board. They flew into empty tanks believing they had plenty of reserve. Sixteen of 39 people on board died. BEA and ANSV investigators still reference this case in fuel system safety training because it shows that knowing how much fuel you actually have is just as critical as knowing what type it is.
BEA accident investigation reports →A maintenance technician installed a hydraulic pump that didn't fit correctly — it wore through a fuel line and drained both tanks over the Atlantic. The crew lost both engines at 39,000 feet and glided roughly 120 km to Lajes Air Base in the Azores with no power at all. All 306 people survived. The accident rewrote requirements for fuel leak detection, cross-feed valve procedures, and overwater quantity monitoring. Once the fuel system gave out, they were flying a very heavy glider — and that's exactly the framing investigators used.
A dispatcher calculated fuel uplift for the wrong route. The crew didn't catch it. The Boeing 737 ran dry and crash-landed in the Amazon jungle. ICAO-compliant operations now require mandatory pre-departure fuel verification — both physical dip and calculated — partly because of this accident. One error in a planning document, caught by nobody in the chain, ended the flight in a jungle.
The chemistry of the fuel matters a lot less if the quantity check doesn't happen. Every case above comes down to something someone didn't verify before pushback. The pre-flight fuel check isn't box-ticking.
What ICAO, FAA and DGCA require
ICAO Annex 6 requires operators to verify fuel quality and quantity before every flight — contamination checks for water and particulate matter, and confirmation the fuel meets the approved spec for the aircraft type.
FAA regulations under 14 CFR Part 121 cover fuel reserve requirements, quality control for suppliers, and system design certification. The FAA issues Airworthiness Directives on fuel system components when safety issues emerge.
DGCA in India follows ICAO standards under CAR Series M Part VI. Indian Oil, Hindustan Petroleum, and Bharat Petroleum supply Jet-A1 at Indian airports, and DGCA oversight includes periodic inspection of fuel quality control processes at major airports.
- ASTM D1655 — Standard specification for aviation turbine fuels (international benchmark)
- DEF STAN 91-091 — UK/NATO standard for Jet-A1 (equivalent)
- ICAO Annex 6 — Operational fuel requirements for aircraft operators
- FAA 14 CFR Part 121 — US airline fuel rules and reserves
- DGCA CAR Series M Part VI — Indian airworthiness and fuel standards
External references: ICAO Annex 6 · DGCA CAR requirements · FAA 14 CFR regulations
SAF — the same fuel made differently
Sustainable Aviation Fuel comes from non-petroleum sources — waste oils, agricultural residue, municipal solid waste, CO₂ capture. Chemically it's close enough to Jet-A1 that it works in existing engines without modification, currently blended at up to 50% with conventional Jet-A1. Flights on 100% SAF are still in certification as of 2026.
Airlines including IndiGo, Air India, British Airways, and United have run SAF-powered commercial flights. ICAO's CORSIA framework is driving adoption as part of the industry's net-zero target by 2050.
SAF works for one reason: it hits the same Jet-A1 property specs — freeze point, flash point, energy density, combustion behaviour. The aircraft can't tell the difference. Neither can the fuel planning calculations. That's the whole point of matching the spec rather than matching the molecule.
When I was working through fuel planning for Air Navigation — required fuel, alternate fuel, contingency, final reserve — what struck me is how much those calculations depend on the fuel behaving predictably. SAF meeting the same spec means nothing in the planning framework changes. The numbers still work. That's what spec compliance actually means in practice.
Frequently asked questions
The next time you watch a fuel truck pull up to an aircraft, what's going into that wing tank is one of the most tightly controlled industrial fluids on the planet. Not because aviation is slow to change — though it is careful — but because the conditions up there would expose any weakness in a fuel fast.
Petrol would vaporise at altitude. It would freeze near cruise. It wouldn't burn right in a turbine. Kerosene doesn't do any of those things, which is probably why nothing has displaced it in 70 years of commercial jet aviation.
I still do a manual dip check before solo flights. Thirty seconds. But knowing why the fuel matters makes it feel less like a checklist item.
Disclaimer: AviationDesk is an independent aviation education blog. All content is for informational purposes only and does not constitute official aviation regulatory or operational advice. Always consult ICAO, FAA, EASA, or DGCA publications for regulatory guidance.