effective use of all available resources: human resources, hardware, and information. Human resource groups include but are not limited to pilots, dispatchers, cabin crewmembers, maintenance personnel, and air traffic controllers. 

Critical angle of attack.  The angle of attack at which a wing stalls regardless of airspeed, flight attitude, or weight. 

CRM.  See crew resource management. 

Crossbar.  The structural component of the WSC wing that holds the leading edges in place. 

Crosswind.  Wind blowing across rather than parallel to the direction of flight. In a traffic pattern, the crosswind leg is a flight path at right angles to the landing runway off its upwind end. 

Crosswind component.  The wind component, measured in knots, at 90° to the longitudinal axis of the runway. 

Crosswind correction. Correction applied in order to maintain a straight ground track during flight when a crosswind is present. 

Crosswind landing. Landing made with a wind that is blowing across rather than parallel to the landing direction. 

Crosswind takeoffs.  Takeoffs made during crosswind conditions. 

CTAF.  See Common Traffic Advisory Frequency. 

Datum.  An imaginary vertical plane or line from which all measurements of moment arm are taken. The datum is established by the manufacturer. 

DECIDE Model.  Model developed to help pilots remember the six-step decision-making process: Detect, Estimate, Choose, Identify, Do, Evaluate. 

Density altitude.  Pressure altitude corrected for variations from standard temperature. When conditions are standard, pressure altitude and density altitude are the same. If the temperature is above standard, the density altitude is higher than pressure altitude. If the temperature is below standard, the density altitude is lower than pressure altitude. This is an important altitude because it is directly related to the PPC’s performance. 

Departure leg. The leg of the rectangular traffic pattern that is a straight course aligned with, and leading from, the takeoff runway. 

Designated pilot examiner (DPE).  An individual designated by the FAA to administer practical tests to pilot applicants. 

Detonation.  The sudden release of heat energy from fuel in an aircraft engine caused by the fuel-air mixture reaching its critical pressure and temperature. Detonation occurs as a violent explosion rather than a smooth burning process. 

Dew.  Moisture that has condensed from water vapor. Usually found on cooler objects near the ground, such as grass, as the near-surface layer of air cools faster than the layers of air above it. 

Dewpoint. The temperature at which air reaches a state of water saturation. 

Dihedral. The positive acute angle between the lateral axis of an airplane and a line through the center of a wing or horizontal stabilizer. Dihedral contributes to the lateral stability of an aircraft. 

Directional stability.  Stability about the vertical axis of an aircraft, whereby an aircraft tends to return, on its own, to flight aligned with the relative wind when disturbed from that equilibrium state. The wing design is the primary contributor to directional stability, causing a WSC in flight to align with the relative wind. 

Ditching. Emergency landing in water. 

Double-surface wing. Two pieces of fabric for most of the WSC wing which enclose the crossbar; typically used for higher speed wings. 

Downwind leg. Leg of the traffic pattern flown parallel to the landing runway, but in a direction opposite to the intended landing direction. 

DPE.  See designated pilot examiner. 

Drag. An aerodynamic force on a body acting parallel and opposite to the relative wind. The resistance of the atmosphere to the relative motion of an aircraft. Drag opposes thrust and limits the speed of the aircraft. 

Drag coefficient (C$_{D}$).  A dimensionless number used to define the amount of total drag produced by an aircraft. 

Drift angle.  Angle between heading and track. 

Drift correction.  Correction that is applied to counter the affects of wind on an aircraft’s flight and ground track. 

