Decision altitude (DA).  A specified altitude in the precision  approach, charted in feet MSL, at which a missed approach  must be initiated if the required visual reference to continue  the approach has not been established.  Critical altitude.  The maximum altitude under standard  atmospheric conditions at which a turbocharged engine can  produce its rated horsepower.  Critical angle of attack.  The angle of attack at which a  wing stalls regardless of airspeed, flight attitude, or weight.  Decision height (DH).  A specified altitude in the precision  approach, charted in height above threshold elevation,  at which a decision must be made either to continue the  approach or to execute a missed approach.  Deice.  The act of removing ice accumulation from an  aircraft structure.  Critical areas.  Areas where disturbances to the ILS localizer  and glideslope courses may occur when surface vehicles or  aircraft operate near the localizer or glideslope antennas.  CRM.  See crew resource management.  Cross-check.  The first fundamental skill of instrument flight,  also known as “scan,” the continuous and logical observation  of instruments for attitude and performance information.  Delta.  A GrGLYPH<df00>GLYPH<df00>k lGLYPH<df00>ttGLYPH<df00>r GLYPH<df00>xprGLYPH<df00>ssGLYPH<df00>d by thGLYPH<df00> symbol Δ to indicatGLYPH<df00>  a changGLYPH<df00> of valuGLYPH<df00>s. As an GLYPH<df00>xamplGLYPH<df00>, ΔCG indicatGLYPH<df00>s a changGLYPH<df00>  (or movement) of the CG.  Density altitude.  Pressure altitude corrected for nonstandard  temperature. Density altitude is used in computing the  performance of an aircraft and its engines.  Cruise clearance.  An ATC clearance issued to allow a  pilot to conduct flight at any altitude from the minimum  IFR altitude up to and including the altitude specified in the  clearance. Also authorizes a pilot to proceed to and make an  approach at the destination airport.  Current induction.  An electrical current being induced into,  or generated in, any conductor that is crossed by lines of flux  from any magnet.  Departure procedure (DP).  Preplanned IFR ATC departure,  published for pilot use, in textual and graphic format.  Deposition.  The direct transformation of a gas to a solid  state, in which the liquid state is bypassed. Some sources use  sublimation to describe this process instead of deposition.  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.  Deviation.  A magnetic compass error caused by local  magnetic fields within the aircraft. Deviation error is different  on each heading.  Datum (Reference Datum).  An imaginary vertical plane  or line from which all measurements of arm are taken. The  datum is established by the manufacturer. Once the datum  has been selected, all moment arms and the location of CG  range are measured from this point.  Dark adaptation.  Physical and chemical adjustments of the  eye that make vision possible in relative darkness.  Dead reckoning.  Navigation of an airplane solely by means  of computations based on airspeed, course, heading, wind  direction and speed, groundspeed, and elapsed time.  Deceleration error.  A magnetic compass error that occurs  when the aircraft decelerates while flying on an easterly  or westerly heading, causing the compass card to rotate  toward South.  DH.  See decision height.  DGPS.  Differential global positioning system.  Dewpoint.  The temperature at which air reaches a state where  it can hold no more water.  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.  D.C.  Direct current.  DA.  See decision altitude.  D  G-9 