Qatar Airways Boeing 777-2DZ(LR) Reg. A7-BBG as flight QR921 displays some truly amazing and very beautiful rainbow contrails as she transits over Brisbane, Australia. Contrails are composed primarily of water, in the form of ice crystals. The combination of water vapor in aircraft engine exhaust and the low ambient temperatures that exist at high altitudes allows the formation of the trails. Impurities in the engine exhaust from the fuel, including sulfur compounds (0.05% by weight in jet fuel) provide some of the particles that can serve as sites for water droplet growth in the exhaust and, if water droplets form, they might freeze to form ice particles that compose a contrail.
Rainbow Contrails by a Qatar Airways Boeing 777