What causes ignition of fuel in aircraft accidents?

A temperature at or above the flash point at the appropriate mixture of oxygen and fuel. Could be heat from friction or a thermally active device or could be electrical spark.

I read your question the same way some people on here did at first, they have assumed that you want to know about crashes caused by the fuel igniting. Like the official report into the TWA800 crash.

What your question actually asks is why does it ignite during a crash, correct me if i'm wrong there.

It can be caused, but is not exclusively caused by, the compressive forces of an impact.

Jet fuel in its liquid form is actually not easily ignited, but if you mix it with air it becomes highly flammable and ignites with explosive force.

The fuel pouring from a rupture in the airframe can be ignited by the engines, see the Concorde crash.

aircraft accidents don't always involve the fuel igniting. and when they do its more to do with the fuel vapour being ignited through a spark, a hot components or an engine fire.

if you look on this website it will go through all aircraft accidents that have happened in the uk airspace and will list there causes. you will find very few that have actually caught fire.

http://www.aaib.gov.uk/publications/index.cfm

bare in mind whilst searching that recent air crashes will not be on there as it takes years to fully understand what and how it happened

False. The fuel doesn't ignite in most aircraft accidents.

A fuel tank near empty might be more dangerous than a full tank -

Because of fuel vapors igniting (or exploding) more easily than fuel itself -

Jet fuel is more difficult to ignite than gasoline (petrol) -

Ignition source is generally sparks -

Long ago, I was a smoker and had a Zippo lighter -

As a joke, one day, I filled it with jet fuel -

I could never get that Zippo to ignite again -

.

Doesn't always happen. If it does, it's released fuel vapour ignited by sparks from one source or another, contact with hot engine parts . . .

ever heard of fuel air bombs?

right mixture of fuel, air, and kinetic energy turning into heat, in combination of plenty of already hot parts flying in random directions and sparks from electrical circuits as well as sparks from friction of metals against concrete are the cause.

Air demo

well a most engines get hot and burn fuel it must be obvious.