How Jet Engines Work, Keeping Us Safe From Start To Shutdown

Pilot in jet engine inlet picture
by Captain Les

Updated September 19, 2019. Did you ever wonder how jet engines thrust you safely from point A to B every time you fly?

The next time you are in the airplane between New York and Paris, flying across the vast Atlantic Ocean you will appreciate their reliability.

Modern jet engines typically provide near-perfect reliability, being maintained in top shape by the great master mechanics of major airlines at all times.

You’ll be surprised to find out how easy it is to understand the basics of how jet engines work.

The following describes a jet engine continuously running, from start to shut down. It works the same whether you are on the ground or in the air:

Suck, Squeeze, Bang, Blow –
The 4 phases of how a basic Jet Engine works

how a jet engine works
Photo: GE/Canva.

1. “Suck” is the first phase

The air enters (is sucked into) the engine through those metal fan blades in the front. 

After the air passes the fan blades in the front of the engine: fuel is also introduced and sucked in, where it is mixed with the air.

jet engine inlet fan blades impeller
Air sucks into the fan blades in the front. Photo © Captain Les

2. “Squeeze” is the second phase

The ingested air/fuel mixture is being “squeezed”, or compressed by a compressor.

The compressed air/fuel mixture is then approaching an electric spark, where it goes into the next phase: 

B757 Rolls Royce jet engine
The squeezed air is mixed with fuel and then ignited inside the engine. Here showing a B757 Rolls Royce engine. Photo © Captain Les.

3. “Bang” is the third phase

Combustion, the “bang”, occurs when the fuel and air mixture is ignited.

This action happens inside what’s called a combustion chamber, located inside the core of the engine. 

jet engine combustion
Source: Emoscopes

4. “Blow” is the fourth and final phase

The ignition of the air and fuel mixture create a fast-moving exhaust, “blow”, through the jet nozzle.

As the jets of gas shoot backward, the engine and the aircraft are thrust forward.

This is based on Newton’s Third Law of Motion:

“For every action, there is an equal and opposite reaction”.

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You can compare this to an air-filled  balloon: 

if you let the air escape from the balloon the balloon will thrust away.

Exhaust pipe on a B757
The back of the jet engine, where the burning gases cause thrust. Photo © Captain Les.

Did you know?

  • The basic principle of how a jet engine works is actually similar to that of a car engine.
  • The “gas pedal” on your jet, one for each engine, is called a throttle, or a thrust lever. In an airplane thrust levers are moved by the hand.
  • To go faster, or to apply more power: Move the throttles forward (in your car you press your gas pedal).
  • To go slower, or to apply less power: Move the throttles back (in your car you depress your gas pedal).
B757 airplane throttles
2 Boeing 757 jet airplane throttles (white knobs attached to brown-colored levers). One for each engine. Photo © Captain Les.
Jet display
A jet engine on display without cover plates. Photo: Aerohow.

Bonus info for those of you who are into a deeper understanding:

The above description of a jet engine is about the basics.

Modern fan jet engines use some of the energy created by the exhaust (“bang”) to drive an added shaft, which turns a fan near the engine’s intake. 

That fan pushes a proportion of the incoming air, known as the “bypass”, AROUND the engine’s hot core and out of the back (instead of directing the air INTO the engine), thus providing additional thrust. 

This fan air is creating “bypass thrust”.

Bypass thrust is more fuel-economical to use than core thrust alone.

Another way to look at bypass thrust is to think about it as fan air made into additional thrust.

Jet engine schematic
Jet engine schematic. Source: GE.

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