Wind Wind Current Current Figure 9-1.  Wind drift and wind correction angle (crab angle). within this moving body of air (wind), it moves or drifts with  the air in the same direction and speed, just like the boat  moved with the river current. headed downwind, the groundspeed is increased. Through  the crosswind portion of a turn, the aircraft must be turned  sufficiently into the wind to counteract drift. When flying straight and level and following a selected ground  track, the preferred method of correcting for wind drift is to  head the aircraft (wind correction angle) sufficiently into the  wind to cause the aircraft to move forward into the wind at the  same rate the wind is moving it sideways. Depending on the  wind velocity, this may require a large wind correction angle  or one of only a few degrees. This wind correction angle is also  commonly known as the crab angle. When the drift has been  neutralized, the aircraft follows the desired ground track. To follow a desired circular ground track, the wind correction  angle must be varied in a timely manner because of the  varying groundspeed as the turn progresses. The faster the  groundspeed, the faster the wind correction angle must be  established; the slower the groundspeed, the slower the wind  correction angle may be established. It can be seen then that  the steepest bank and fastest rate of turn should be made on  the downwind portion of the turn and the shallowest bank  and slowest rate of turn on the upwind portion. To understand the need for drift correction during fl ight,  consider a flight with a wind velocity of 20 knots from the  left and 90° to the direction the aircraft is headed. After  1 hour, the body of air in which the aircraft is fl ying has  moved 20 nautical miles (NM) to the right. Since the aircraft  is moving with this body of air, it too has drifted 20 NM to  the right. In relation to the air, the aircraft moved forward;  but in relation to the ground, it moved forward as well as 20  NM to the right. The principles and techniques of varying the angle of bank  to change the rate of turn and wind correction angle for  controlling wind drift during a turn are the same for all ground  track maneuvers involving changes in direction of fl ight. When there is no wind, it should be simple to fly along a  ground track with an arc of exactly 180° and a constant  radius because the flightpath and ground track would be  identical. This can be demonstrated by approaching a road  at a 90° angle and, when directly over the road, rolling into  a medium-banked turn. Then, maintaining the same angle of  bank throughout the 180° of turn.  [Figure 9-2] To complete the turn, the rollout should be started at a point  where the wings become level as the aircraft again reaches  the road at a 90° angle and is directly over the road just as the  There are times when the pilot needs to correct for drift  while in a turn.  [Figure 9-2]  Throughout the turn, the wind  is acting on the aircraft from constantly changing angles. The  relative wind angle and speed govern the time it takes for the  aircraft to progress through any part of a turn. This is due to  the constantly changing groundspeed. When the aircraft is  headed into the wind, the groundspeed is decreased; when  9-3