The effect of pressure altitude and ambient temperature is to define primarily the density altitude and its effect on takeoff performance. While subsequent corrections are appropriate for the effect of temperature on certain items of power plant performance, density altitude defines specific effects on takeoff performance. An increase in density altitude can produce a two-fold effect on takeoff performance: (l) greater takeoff speed and (2) decreased thrust and reduced net accelerating force. If an airplane of given weight and configuration is operated at greater heights above standard sea level, the airplane will still require the same dynamic pressure to become airborne at the takeoff lift coefficient. Thus, the airplane at altitude will take off at the same indicated airspeed as at sea level, but because of the reduced air density, the true airspeed will be greater.The effect of density altitude on power plant thrust depends much on the type of power plant. An increase in altitude above standard sea level will bring an immediate decrease in power output for the unsupercharged reciprocating engine. However, an increase in altitude above standard sea level will not cause a decrease in power output for the supercharged reciprocating engine until the altitude exceeds the critical operating altitude. For those power plants which experience a decay in thrust with an increase in altitude, the effect on the net accelerating force and acceleration rate can be approximated by assuming a direct variation with density. Actually, this assumed variation would closely approximate the effect on airplanes with high thrust-to-weight ratios.Proper accounting of pressure altitude and temperature is mandatory for accurate prediction of takeoff roll distance.3.The power output of unsupercharged reciprocating engine （ ） with increasing altitude.