Normal static source Airspeed Calibration FLAPS UP KIAS KCAS  60  80  100 120  59  78  98 119 A Indicated airspeed: 100 knots B Calibrated airspeed: 98 knots knots True airspeed 0 3 1 knots True airspeed 8 9 0 A Indicated airspeed: 100 knots B Calibrated airspeed: 98 knots RAM AIR 15,000 feet MSL RAM AIR Sea level STANDARD CONDITIONS A B Figure 4-9.  The three types of airspeed are IAS, CAS, and TAS. Figure 4-11.  IAS at which V$_{NE}$ is reached decreases with altitude.  Figure 4-10.  In steady wings-level flight, IAS does not vary with altitude.  Altitude center vertically  1,000 feet 10,000 feet 20,000 feet 30,000 feet 40,000 feet True airspeed (TAS) 41 knots 48 knots 56 knots 64 knots 72 knots IAS at which stall occurs in  steady wings-level flight 40 knots 40 knots 40 knots 40 knots 40 knots Up to 6,500  10,000  13,000  16,500  135 128 121 115 Altitude (in feet) V$_{NE}$ (IAS in knots) Airspeed Indicator Markings Aircraft weighing 12,500 pounds or less, manufactured after  1945 and certificated by the Federal Aviation Administration  (FAA), are required to have airspeed indicators that conform  to a standard color-coded marking system.  [Figure 4-4]  This  system enables the pilot to determine, at a glance, certain  airspeed limitations that are important to the safe operation  of the aircraft. For example, if during the execution of a  maneuver, the pilot notes that the airspeed needle is in the  yellow arc and is rapidly approaching the red line, immediate  corrective action to reduce the airspeed should be taken. It  is essential that the pilot use smooth control pressure at high  airspeeds to avoid severe stressors upon the glider structure.  The following is a description of what the standard color- code markings are on an airspeed indicator and how they  correspond to maneuvers and airspeeds. particularly convenient thing to do while trying to fly.  Figure 4-10 shows how steady, wings-level flight stall  speed is affected by different altitudes.  Figure 4-10  is only  an example, and the figures used in it do not pertain to all  gliders. For specific stall speeds, always refer to the POH  of the glider that is being flown. A pilot can find TAS by two methods. The first method,  which is more accurate, involves using a flight computer.  In this method, the CAS is corrected for temperature and  pressure variation by using the airspeed correction scale on  the computer. A second method, which is a rule of thumb,  can be used to compute the approximate TAS. This is done  by adding to the IAS 2 percent of the IAS for each 1,000  feet of altitude.  •  The white arc—flap operating range •  The lower limit of the white arc—stalling speed with  the wing flaps and landing gear in the landing position. •  The upper limit of the white arc—maximum flaps- extended speed. This is the highest airspeed at which  the pilot should extend full flaps. If flaps are operated  at higher airspeeds, severe strain or structural failure  could result.  •  The lower limit of the green arc—stalling speed with  the wing flaps and landing gear retracted.  •  The upper limit of the green arc—maximum structural  cruising speed. This is the maximum speed for normal  operations.  4-5