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course, altitude needed to glide to each turnpoint
should be determined using a manual or electronic
glide calculator with corrections for wind on each leg.
If other airports are nearby, practice finding and
switching to their communication frequency and listening
to local traffic. As progress is made along each
leg of the triangle, frequently cross check the altitude
needed to return to the home airport and abandon the
course if needed. Setting a minimum altitude of 1,500
feet or 2,000 feet AGL to arrive back at the home site
adds a margin of safety. Every landing after a soaring
flight should be an accuracy landing.
11-9
Determining winds aloft while en route can be difficult.
Often an estimate is the best that can be achieved.
A first estimate is obtained from winds aloft forecasts
provided by the AFSS. Once aloft, estimate wind speed
and direction from the track of cumulus shadows over
the ground, keeping in mind that the winds at cloud
level are often different than those at lower levels. On
cloudless days, obtain an estimate of wind by noting
drift while thermalling. If the estimate was for headwind
of 10 knots but you seem to lose more height on
glides than the glide calculator indicates, the headwind
estimate may be too low and needs to be adjusted.
When flying with GPS, determine wind speed from
TAS by simple subtraction. Some flight computers
automatically calculate the winds aloft while other GPS
systems estimate winds by calculating the drift after
several thermal turns.
It is important to develop skill in quickly determining
altitude needed for a measured distance using one of
the glide calculator tools. For instance, while on a
cross-country flight you are over a good landing spot
and the next good landing site is a distance of 12 miles
into a 10-knot headwind. [Figure 11-9] The glide calculator
shows that 3,200 feet is needed to accomplish
the glide. Add 1,500 feet above ground to allow time
to set up for an off-field landing if necessary, to make
the total needed 4,700 feet. The present height is
only 3,800 feet, not high enough to accomplish the
12-mile glide, but still high enough to start along
course. Head out adjusting the speed based on the
MacCready ring or other speed director. After two
miles with no lift, altitude is almost 3,300 feet, still
not high enough to glide the remaining 10 miles, but
high enough to turn back to the last landing site. After
Figure 11-9. Example of a flight profile during a cross-country flight.
Figure 11-8. Examples of practice cross country courses
11-10
almost 4 miles, a 4-knot thermal is encountered at about
2,700 feet and you are able to climb to 4,300 feet.
During the climb, the downwind drift of the thermal
moves the glider back on course approximately a halfmile.
Now there is almost 9 miles to glide to the next
landing spot, and a check of the glide calculator indicates
2,400 feet needed for the glide into the 10 knot
headwind, plus 1,500 feet at the destination, for a total
of 3,900 feet. Now there is 400 feet above the minimum
glide with a margin to plan the landing.
In the previous example, had the thermal topped at
3,600 feet (instead of 4,300 feet) there would not be
enough altitude to glide the 9 miles into the 10-knot
headwind. However, there would be enough height to
continue further on course in hopes of finding more lift
before needing to turn downwind back to the previous
landing spot. Any cross-country soaring flight involves
dozens of decisions and calculations such as this. In
addition, safety margins may need to be more conservative
if there is reason to believe the glide may not
work as planned, for example, other pilots reporting
heavy sink along the intended course.
On any soaring flight there is an altitude when a decision
must be made to cease attempts to work thermals
and commit to a landing. This is especially true of
cross-country flights in which landings are often in
unfamiliar places and feature additional pressures like
those discussed in Chapter 8—Abnormal and
Emergency Procedures. It is even more difficult on
cross-country flights to switch the mental process from
soaring to committing to a landing. For beginners, an
altitude of 1,000 feet AGL is a recommended minimum
to commit to landing. A better choice is to pick a landing
site by 1,500 feet AGL, which still allows time to
be ready for a thermal while further inspecting the
intended landing area. The exact altitude where the
thought processes should shift from soaring to landing
preparation depends on the terrain. In areas of the
　
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