In the prediction of takeoff distance from the AFM/POH  data, the following primary considerations must be given:  excessive AOA may not allow the aircraft to climb out of  ground effect. On the other hand, an excessive airspeed at  takeoff may improve the initial ROC and “feel” of the aircraft  but produces an undesirable increase in takeoff distance.  Assuming that the acceleration is essentially unaffected, the  takeoff distance varies with the square of the takeoff velocity.  Thus, ten percent excess airspeed would increase the takeoff  distance 21 percent. In most critical takeoff conditions, such  an increase in takeoff distance would be prohibitive, and the  pilot must adhere to the recommended takeoff speeds.  The effect of pressure altitude and ambient temperature  is to define the density altitude and its effect on takeoff  performance. While subsequent corrections are appropriate  for the effect of temperature on certain items of powerplant  performance, density altitude defines specific effects on  takeoff performance. An increase in density altitude can  produce a twofold effect on takeoff performance:  In many cases, the landing distance of an aircraft defines the  runway requirements for flight operations. The minimum  landing distance is obtained by landing at some minimum safe  speed, that allows sufficient margin above stall and provides  satisfactory control and capability for a go-around. Generally,  the landing speed is some fixed percentage of the stall speed  or minimum control speed for the aircraft in the landing  configuration. As such, the landing is accomplished at some  particular value of lift coefficient and AOA. The exact values  depend on the aircraft characteristics but, once defined, the  values are independent of weight, altitude, and wind.  To obtain minimum landing distance at the specified landing  speed, the forces that act on the aircraft must provide  maximum deceleration during the landing roll. The forces  acting on the aircraft during the landing roll may require  various procedures to maintain landing deceleration at the  peak value.  If an aircraft of given weight and configuration is operated at  greater heights above standard sea level, the aircraft requires  the same dynamic pressure to become airborne at the takeoff  lift coefficient. Thus, the aircraft at altitude takes off at the  same indicated airspeed (IAS) as at sea level, but because of  the reduced air density, the TAS is greater.  The effect of density altitude on powerplant thrust depends  much on the type of powerplant. An increase in altitude  above standard sea level brings an immediate decrease in  power output for the unsupercharged reciprocating engine.  However, an increase in altitude above standard sea level does  not cause a decrease in power output for the supercharged  reciprocating engine until the altitude exceeds the critical  operating altitude. For those powerplants that 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 aircraft with high thrust-to-weight ratios.  A distinction should be made between the procedures for  minimum landing distance and an ordinary landing roll  with considerable excess runway available. Minimum  landing distance is obtained by creating a continuous peak  deceleration of the aircraft; that is, extensive use of the brakes  for maximum deceleration. On the other hand, an ordinary  landing roll with considerable excess runway may allow  extensive use of aerodynamic drag to minimize wear and tear  on the tires and brakes. If aerodynamic drag is sufficient to  cause deceleration, it can be used in deference to the brakes  in the early stages of the landing roll (i.e., brakes and tires  suffer from continuous hard use, but aircraft aerodynamic  drag is free and does not wear out with use). The use of  aerodynamic drag is applicable only for deceleration to 60  or 70 percent of the touchdown speed. At speeds less than  60 to 70 percent of the touchdown speed, aerodynamic drag  is so slight as to be of little use, and braking must be utilized  to produce continued deceleration. Since the objective during  the landing roll is to decelerate, the powerplant thrust should  be the smallest possible positive value (or largest possible  negative value in the case of thrust reversers).  Proper accounting of pressure altitude and temperature is  mandatory for accurate prediction of takeoff roll distance.  The most critical conditions of takeoff performance are the  result of some combination of high gross weight, altitude,  temperature, and unfavorable wind. In all cases, the pilot  must make an accurate prediction of takeoff distance from  the performance data of the AFM/POH, regardless of the  runway available, and strive for a polished, professional  takeoff procedure.  1.  Greater takeoff speed  2.  Decreased thrust and reduced net accelerating force  • Runway slope and condition—the effect of an incline  and retarding effect of factors such as snow or ice  • Wind—a large effect due to the wind or wind  component along the runway  • Gross weight—a large effect on distance  • Pressure altitude and temperature—to define the effect  of density altitude on distance  Landing Performance  11-16 