On an actual cross-country flight, a combination of dolphin  flight and classic climb and glide is frequently needed. In a  previous example, the two pilots who decided not to stop  and circle in the weaker thermals would still benefit from  dolphin flight techniques in the lift and sink until stopping  to climb in the strong lift. Deviations due to poor weather ahead should be undertaken  before the flight becomes unsafe. For instance, if cloud bases  are lowering and showers developing, always have the option  for a safe, clear landing area before conditions deteriorate  too much. Generally, glider pilots will encounter stable air  or sinking air which will put them on the ground before VFR  conditions disappear. If the sky becomes cloudy, thermaling  will cease. Ridge lift might remain but will be in the clouds  so either way the glider pilot must get on the ground. It is  better to land on your terms rather than be forced down by  total lack of lift. Thunderstorms along the course are a special  hazard, since storm outflow can affect surface winds for many  miles surrounding the storm. Do not count on landing at a  site within 10 miles of a strong thunderstorm—sites farther  removed are safer. Thunderstorms ahead often warrant large  course deviations of up to 180° (i.e., retreat to safety). Diversion on a soaring cross-country flight is the norm rather  than the exception. Some soaring days supply fair weather  cumulus evenly spaced across all quadrants, and it is still  beneficial to deviate toward stronger lift. Deviations of 10°  or less add little to the total distance and should be used  without hesitation to fly toward better lift. Even deviations  up to 30° are well worthwhile if they lead toward better lift  and/or avoid suspected sink ahead. The sooner the deviation is  started, the less total distance is covered during the deviation.  [Figure 11-16] Deviations of 45° or even 90° may be needed to avoid poor  conditions ahead. An example might be a large cloudless area  or a shaded area where cumulus have spread out into stratus  clouds. Sometimes deviations in excess of 90° are needed  to return to active thermals after venturing into potentially  stable air. NOTE: Cloud development can and does shade the earth,  decreasing the heating, and hence decreasing lift. Be aware  of cloud shadowing. Navigation has become far easier with the advent of GPS.  Since GPS systems are not 100 percent free from failure,  pilots must still be able use the sectional chart and compass  for navigation. It is important to have an alternate plan in  the event of becoming lost. As discussed earlier, preflight  Special Situations Course Deviations Lost Procedures 1 2 3 4 A A A A B B B B C C C D or extra distance 1. Visualization of increase in  distance 2. Comparison: increase  caused by same-size  detour closer to goal 3. Unnecessarily large  increase by returning to  original course too soon 4. Unnecessarily large  increase by recognizing  need for detour too late Distance increase caused by  detours (A straight line from A to B equals the direct course. = increase) - Course distance - Total flight distance - Extra distance flown (A 2  + B 2  = C 2  to calculate  distance as the navigation  triangle develops with the  deviation distance) Figure 11-16.  Effects of starting course deviations at different times. Red arrows show extra course distance and indicate the benefit of  early course deviations. 11-14