Rule 5b. Never use single quotation marks in sentences like the previous three. Incorrect: I had a visit from my 'friend' the tax man. The single quotation marks in the above sentence are intended to send a message to the reader that friend is being used in a special way: in this case, sarcastically. Avoid this invalid usage.
Why do jets leave a white trail in the sky? Jets leave white trails, or contrails, in their wakes for the same reason you can sometimes see your breath. The hot, humid exhaust from jet engines mixes with the atmosphere, which at high altitude is of much lower vapor pressure and temperature than the exhaust gas.
Importance of the Jet Stream. In terms of commercial usage, the jet stream is important for the airline industry. Its use began in 1952 with a Pan Am flight from Tokyo, Japan to Honolulu, Hawaii. By flying well within the jet stream at 25,000 feet (7,600 meters), the flight time was reduced from 18 hours to 11.5 hours. The reduced flight time and aid of the strong winds also allowed for a reduction in fuel consumption.