It is very important that jet fuel be free from water contamination . During flight , the temperature of the fuel in the tanks decreases , due to the low temperatures in the upper atmosphere . This causes precipitation of the dissolved water from the fuel . The separated water then drops to the bottom of the tank , because it is more dense than the fuel . Since the water is no longer in solution , it can form droplets which can supercool to below 0 °C . If these supercooled droplets collide with a surface they can freeze and may result in blocked fuel inlet pipes . This was the cause of the British Airways Flight 38 accident . Removing all water from fuel is impractical ; therefore , fuel heaters are usually used on commercial aircraft to prevent water in fuel from freezing
British Airways Flight 38
British Airways Flight 38
Jet fuel