A cloud that trails an aircraft and is formed by the ejected water from the exhaust of the aircraft engines. It mixes with and saturates, or slightly supersaturates, the air in the wake of the aircraft. The duration of the trails is dependent on the prevalent temperature and relative humidity. Exhaust trails are of a more common occurrence and a longer duration than aerodynamic trails. For the trails to form, the temperature ordinarily must be below the critical value as indicated by a line marked MINTRA on a tephigram. MINTRA is a flight level below which engine-exhaust trails cannot form. On the other hand, it is not certain that the trails will positively form above that level. See exhaust trail. See also tephigram.
An Illustrated Dictionary of Aviation Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved