Interpolation  Takeoff Charts  Density Altitude Charts  Figure 11-21.  Interpolating charts.  Not all of the information on the charts is easily extracted.  Some charts require interpolation to find the information for  specific flight conditions. Interpolating information means  that by taking the known information  a pilot can compute  intermediate information. However  pilots sometimes round  off values from charts to a more conservative figure.  and read the approximate density altitude. The approximate  density altitude in thousands of feet is 7 700 feet.  Takeoff charts are typically provided in several forms and  allow a pilot to compute the takeoff distance of the aircraft  with no flaps or with a specific flap configuration. A pilot can  also compute distances for a no flap takeoff over a 50 foot  obstacle scenario  as well as with flaps over a 50 foot obstacle.  The takeoff distance chart provides for various aircraft  weights  altitudes  temperatures  winds  and obstacle heights.  Using values that reflect slightly more adverse conditions  provides a reasonable estimate of performance information  and gives a slight margin of safety. The following illustration  is an example of interpolating information from a takeoff  distance chart.  [Figure 11-21]  Use a density altitude chart to figure the density altitude at the  departing airport. Using  Figure 11-22   determine the density  altitude based on the given information.  Refer to  Figure 11-23 . This chart is an example of a combined  takeoff distance graph. It takes into consideration pressure  altitude  temperature  weight  wind  and obstacles all on one  chart. First  find the correct temperature on the bottom left  side of the graph. Follow the line from 22 °C straight up until  it intersects the 2 000 foot altitude line. From that point  draw  a line straight across to the first dark reference line. Continue  to draw the line from the reference point in a diagonal  direction following the surrounding lines until it intersects  the corresponding weight line. From the intersection of 2 600  pounds  draw a line straight across until it reaches the second  reference line. Once again  follow the lines in a diagonal  manner until it reaches the six knot headwind mark. Follow  First  compute the pressure altitude conversion. Find 30.10  under the altimeter heading. Read across to the second  column. It reads “–165.” Therefore  it is necessary to subtract  165 from the airport elevation giving a pressure altitude of  5 718 feet. Next  locate the outside air temperature on the  scale along the bottom of the graph. From 70°  draw a line up  to the 5 718 feet pressure altitude line  which is about two- thirds of the way up between the 5 000 and 6 000 foot lines.  Draw a line straight across to the far left side of the graph  Sample Problem 1  Sample Problem 2  To find the takeoff distance for a pressure altitude of 2 500 feet  at 20 °C  average the ground roll for 2 000 feet and 3 000 feet.  1 115 + 1 230  = 1 173 feet  2  11-20  Pressure Altitude...............................................2 000 feet OAT..........................................................................22 °C Takeoff Weight.............................................2 600 pounds Headwind...............................................................6 knots Obstacle Height.......................................50 foot obstacle Airport Elevation...............................................5 883 feet OAT...........................................................................70 °F Altimeter...........................................................30.10 "Hg Flaps 10° ns  TAKEOFF DISTANCE  Full throttle prior to brake release itio MAXIMUM WEIGHT 2 400 LB Cond Paved level runway  Zero wind  Weight  (lb)  Lift  AT  Takeoff  speed KIAS  Press  ALT  (ft)  0 °C  10 °C  20 °C  30 °C  40 °C  Total feet  to clear  Grnd  roll  Total feet  to clear  Grnd  roll  Grnd  roll  Total feet  to clear  Grnd  roll  Total feet  to clear  Grnd  roll  Total feet  to clear  off  50 ft  50 ft OBS (ft)  50 ft OBS (ft)  (ft)  50 ft OBS  (ft)  50 ft OBS  (ft)  50 ft OBS  2 400  51  56  S.L.  795  1 460  860  1 570  925  1 685  995  1 810  1 945 1 065  1 000  875  1 605  940  1 725  1 015  1 860  1 090  2 000  2 155 1 170  2 000  3 000  960  1 055  1 770  1 960  1 035  1 140  1 910  2 120  1 115  1 230  2 060  2 295  1 200  1 325  2 220  2 480  2 395  2 685  1 290  1 425  4 000  1 165  2 185  1 260  2 365  1 355  2 570  1 465  2 790  3 030 1 575  5 000  6 000  1 285  1 425  2 445  2 755  1 390  1 540  2 660  3 015  1 500  1 665  2 895  3 300  1 620  1 800  3 160  3 620  3 455  3 990  1 745  1 940  7 000  1 580  3 140  1 710  3 450  1 850  3 805  2 000  4 220  - - - - - - 8 000  1 755  3 615  1 905  4 015  2 060  4 480  - - - - - ­