Meteorological conditions expressed in terms of visibility, distance from clouds, and ceiling less than the minimums specified for visual meteorological conditions. Flight without visual reference to the horizon. 

Interference drag.  Type of drag produced by placing two objects adjacent to one another. Combines the effects of form drag and skin friction. 

International Civil Aviation Organization (ICAO).  The United Nations agency for developing the principles and techniques of international air navigation, and fostering planning and development of international civil air transport. 

International standard atmosphere (IAS).  A model of standard variation of pressure and temperature. 

Inversion. An increase in temperature with altitude. 

Isobars.  Lines which connect points of equal barometric pressure. 

Jet stream. A high-velocity narrow stream of winds, usually found near the upper limit of the troposphere, which flows generally from west to east. 

Keel. See wing keel and carriage keel. 

Judgment. The mental process of recognizing and analyzing all pertinent information in a particular situation, a rational evaluation of alternative actions in response to it, and a timely decision on which action to take. 

KIAS. Knots indicated airspeed. 

Kinesthesia.  The sensing of movements by feel. 

King post.  The post on top of the wing which is attached to the keel that holds used for the ground wires which hold up the wings on the ground and during negative loads during flight. 

Knowledge exam. See FAA Knowledge Exam. 

Lateral axis. An imaginary line passing through the center of gravity of a WSC and extending across the WSC from one side of the aircraft to the other side. 

Leading edge.  The part of an airfoil that meets the airflow first. This as a structural tube on the WSC airfoil. 

Lift. One of the four main forces acting on an aircraft. On a WSC, an upward force created by the effect of airflow as it passes over and under the wing. 

Lift coefficient.  A coefficient representing the lift of a given airfoil. Lift coefficient is obtained by dividing the lift by the free-stream dynamic pressure and the representative area under consideration. 

Lift/drag ratio.  The efficiency of an airfoil section. It is the ratio of the coefficient of lift to the coefficient of drag for any given angle of attack. 

Lift-off. The act of becoming airborne as a result of the wings lifting the airplane off the ground, or the pilot rotating the nose up, increasing the angle of attack to start a climb. 

Light-Sport Aircraft (LSA).  An aircraft that meets the requirements defined in 14 CFR section 1.1, regardless of airworthiness certification. 

Limit load factor. Amount of stress, or load factor, that an aircraft can withstand before structural damage or failure occurs. 

Load factor. The ratio of a specified load to the total weight of the aircraft. The specified load is expressed in terms of any of the following: aerodynamic forces, inertial forces, or ground or water reactions. Also referred to as G-loading. 

Logbook.  A record of activities: flight, instruction, inspection and maintenance. Reference 14 CFR part 43, 14 CFR section 61.51, and 14 CFR section 91.417. 

Longitude. Measurement east or west of the Prime Meridian in degrees, minutes, and seconds. The Prime Meridian is 0° longitude and runs through Greenwich, England. Lines of longitude are also referred to as meridians. 

Longitudinal axis. An imaginary line through an aircraft from nose to tail, passing through its center of gravity about which the aircraft rolls in flight. The longitudinal axis is also called the roll axis of the aircraft. 

Longitudinal stability (pitching).  Stability about the lateral axis. A desirable characteristic of an airplane whereby it tends to return to its trimmed angle of attack after displacement. 

LSA.  See Light-Sport Aircraft. 

MAC. See mean aerodynamic chord. 

