Aviation questions
Why do planes leave white trails?
Those white trails are contrails, short for condensation trails — clouds that form when water vapour in an aircraft's engine exhaust meets the cold air at altitude.
Jet engines produce water vapour as a normal by-product of burning fuel. At cruising altitude the outside air is extremely cold, often far below freezing, so as that hot, moist exhaust hits the cold air it condenses and quickly freezes into tiny ice crystals — the same basic process that turns your breath visible on a frosty morning, just at a much larger scale. Whether a contrail lingers and spreads or vanishes almost immediately depends mostly on how humid the air is at that altitude, which is also why some aircraft leave a long trail and others, on the same day, leave none at all.
It's a striking effect at any of the altitudes covered in how high planes fly, and it's exactly the kind of dramatic sky that suits a large, gallery-style aircraft canvas rather than a small framed print.
Written by Craig Fearn, Aviation Gift Co.