The pilot should:
• Make all turns away from the ridge. [ Figure 10-20A] A turn toward the ridge creates unnecessary risk, even if
positioned well away from the ridge. The groundspeed on the downwind portion of the turn may increase dramatically
and lead to a collision with the ridge. Even if above the ridge, a downwind turn may take the glider over the ridge
crest and into heavy sink.
• Not fly directly above or below another glider. [ Figure 10-20B] Pilots in gliders in close vertical proximity might
not see the other glider. A slight change in climb rate between the gliders can lead to a collision.
• Pass another glider on the ridge side, anticipating that the other pilot might turn away from the ridge. [Figure 10- 20C]
If the space available to pass appears inadequate or if the overtaking glider encounters sink, turbulence, etc., it may
maneuver away from the ridge. The passing glider should either turn back in the other direction (away from the
ridge if spacing permits) or fly upwind away from the ridge and rejoin the slope lift as traffic allows. If using a radio,
the pilot passing can try to contact the pilot of the other glider and coordinate. Procedures may differ outside of the
United States.
• Understand that Title 14 of the Code of Federal Regulations (14 CFR) requires both aircraft approaching head-on to
give way to the right. If a glider with the ridge to the right does not have room to move in that direction, the glider
with its left side to the ridge should give way as needed. [ Figure 10-20D] In general, gliders approaching head-on
are difficult to see; therefore, when piloting the glider with its right side to the ridge, the pilot should ensure the
approaching glider yields early on. While ridge soaring, pilots should enhance their vigilance. The use of a radio
may provide additional safety. Pilots should look at 14 CFR part 91, section 91.111, Operating near other aircraft,
and section 91.113, Right-of-way rules: Except water operations.
Bowls & Spurs
With wind blowing at an angle to the ridge, bowls or spurs, formations with recessed or protruding rock formations
extending from the main ridge, can create better lift on the upwind side and sink on the downwind side. If at or near the
height of the ridge, the pilot can detour around the spur to avoid the sink, then drift back into the bowl to take advantage
of the better lift. [Figure 10-21] After passing such a spur, the pilot should consider any other traffic and not make abrupt
turns toward the ridge. If soaring hundreds of feet above a spur, the pilot may consider flying over it and increase speed in
any sink. This requires caution since a thermal in the upwind bowl, or even an imperceptible increase in the wind, can cause
greater than anticipated sink on the downwind side. The pilot should always have an escape route available.
Sink
Lift
Wind
Figure 10-21. Avoid sink on the downwind side of spurs by detouring around them.
Slope Lift & Thermalling
Combinations of thermals with slope lift can occur, and slope soaring can provide lift when thermals temporarily shut
down. A pilot encountering a thermal along the ridge can make a series of S-turns with each turn into the wind. The glider
can drift back to the thermal after each turn if needed. The glider pilot should never continue the turn toward the ridge.
Speed helps to control any encounter with strong sink that can occur on the sides of the thermal. The maneuver takes
practice, but when done properly, the pilot can make a rapid climb in the thermal to a point well above the ridge crest,
where thermalling 360° turns can begin. Even when well above the ridge, the pilot should use caution and ensure the
glider does not drift into the lee-side sink during a slow climb. Before trying an S-turn, the pilot should ensure it would not
interfere with other traffic along the ridge. [Figure 10-22]
Wind
Figure 10-22. One technique for catching a thermal from ridge lift.
A pilot can use a second technique for catching thermals when slope soaring by heading upwind away from the ridge. This
works best when Cu mark potential thermals, and aids timing. If not finding a thermal, the pilot should cut the search short
while still high enough to dash back downwind to the safety of the upwind slope lift. [Figure 10-23]
Wind
Figure 10-23. Catching a thermal by flying upwind away from the slope lift.
Obstructions
A risk of collision exists when flying at extremely low altitudes along a ridge (tree top level). Obstructions include
wires, cables, and power lines, all of which the pilot might not see. The pilot should ensure completion of an adequate
reconnaissance when flying at these altitudes. Aeronautical charts show high-tension towers that have many wires between
them, and soaring pilots familiar with the area can also provide useful information regarding local ridge obstructions.
Tips & Techniques
Observe the ridges slope for collectors or dividers of the wind flow and determine which of the slopes could gather wind
flow. [Figure 10-24] Due to the changes in wind direction and or sun angle, wind flow can change in a few minutes.
Figure 10-24. Analyze sloping ground for collectors and dividers of wind.
• Collectors include mountain/ridge bowls and ends of canyons that can offer extreme areas of lift when the wind
blows into them. Remember to have a way out.
• Dividers are ridges parallel with the wind and separate airflow. A collector downwind from a divider may receive
more airflow, making better lift possible.
The downwind side of any ridge or hill produces turbulence and sink. Larger or higher ridges and greater wind velocities
create wider areas of turbulence. During these conditions, the pilot should remember to keep the seat and shoulder harness
tight. Sink calls for speed, and turbulence and speed stress the glider airframe and reduce pilot comfort. Pilots should
not exceed glider limitations set forth in the GFM/POH including the design speed for maximum gust intensity (Vb).
[Figure 10-25]
Figure 10-25. Expect turbulence and sink on the downwind side of any hill.
Pilots should assume airflow starts down at the ridge crest. While steep ridges with narrow ridge tops can collect thermal
action from both sides of the crest and the best lift may exist directly above the crest, the pilot should not plan to use that
lift and always remain upwind of the crest. [Figure 10-26]
Figure 10-26. The crest is where rising air starts back down.
Deeply shaded areas along the ridge often enhance sinking air. If strong lift exists on the sunny side of the ridge, then strong
sink usually exists on the shady or dark side of the ridge. This often happens with low sun angles in the late afternoon.
[Figure 10-27]
Figure 10-27. Deep shade can enhance sink.
A thermal source occurs where drainage areas along the ridge meet. For example, an area with numerous ridges or peaks
that slope down into a valley. Canyons or large bowls hold areas of warm air.
Cloud streets may form above the ridge. A glider pilot can try to climb in a thermal to reach these streets. Pilots can use fast
cruising speeds under these streets but should stay upwind of the ridge when using the air circulation marked by the streets.
Since glider pilots tend to seek the same known good conditions for lift, thermals and areas of ridge lift can attract
significant traffic. Pilots should remain alert for conflict with other aircraft including low flying airplanes and helicopters
that use the same area. Sharing a common radio frequency for traffic calls may enhance safety, but nothing replaces a good
visual scan for other aircraft.
Density altitude and true airspeed increase as the glider climbs. At 10,000 feet mean sea level (MSL), a pilot needs
approximately 40 to 45 percent more room to maneuver. The air is less dense by 2 percent per one thousand feet of altitude
gained. [Figure 10-28]
Figure 10-28. At 10,000' MSL, 44 percent more room is needed to complete a turn due to density altitude.
Wave Soaring
Almost all high-altitude glider flights use mountain lee waves as the primary source of lift. As covered in Chapter 9, Glider
Flight and Weather, lee wave systems can contain separate rotor turbulence and smooth wave flow. The use of lee waves
for cross-country soaring has enabled flights exceeding 1,500 miles, with average speeds of over 100 mph. [Figure 10-29]
Cap Cloud
Lenticular
Clouds
Rotor cloud
Figure 10-29. Rotor and cap clouds with lenticulars above.
Preflight Preparation
Special areas within the continental United States allow glider operations in Class A airspace above 18,000 feet MSL under
visual flight rules (VFR). Air Traffic Control (ATC) may open a “wave window” to a specific altitude at specified times.
Each wave window has its own set of procedures agreed to by ATC through a Letter of Agreement. Glider pilots should
understand the special provisions in the letter of agreement before flying within a wave window.
A flight above 18,000 feet MSL requires extensive preflight preparation. Pilots planning wave flights to lower altitudes can
reduce the list of preparation items accordingly.
14 CFR part 91, section 91.211 requires that crewmembers use supplemental oxygen for flight of more than 30 minutes
above cabin pressure altitudes of 12,500 feet MSL up to and including 14,000 feet MSL. While above cabin pressure
altitudes of 14,000 feet MSL, required crewmembers must use supplemental oxygen. Pilots should preflight the oxygen
system, understand signs of hypoxia, know their reactions to high altitude, and consider using oxygen at altitudes well
below 12,500 feet MSL.
When flying at high altitudes, the outside air chills the glider interior. Sunlight can help warm portions of the pilot’s upper
body, but the pilot’s lower extremities and feet normally get cold. Pilots planning for a long flight in cold air should wear
thermal underwear, warm socks, and shoes and have gloves easily accessible during the flight. Clothing with rechargeable
electric heating components can provide hours of warmth.
True airspeed (TAS) becomes a consideration at higher altitudes. To avoid flutter, some glider manuals reduce never-exceed
speed (VNE) as a function of altitude. For instance, the Pilot’s Operating Handbook (POH) for one common two-seat glider,
lists a VNE at sea level of 135 knots. However, at 19,000 feet MSL, it lowers to only 109 knots. Pilots should study the
glider’s POH carefully for any indicated airspeed limitations.
Some flights might not contact the wave. Sink on the downside of a lee wave can reach 2,000 fpm or more. In addition,
missing the wave often means a trip back through the turbulent rotor. To reduce the workload and stress, pilots should
calculate minimum return altitudes from several locations before flight. In addition, pilots should plan for worst-case
scenarios and consider available off-field landing options if the planned minimum return altitude proves inadequate.
The pilot should begin with a normal preflight of the glider. In addition, the pilot should check the lubricant used on control
fittings. Some lubricants get stiff when cold. The pilot should ensure the glider is totally devoid of excess water before
flying into freezing temperatures. This includes checking the bottom of the fuselage where water can freeze around rudder
and elevator cables and checking spoilers or dive brakes for water from rain or from melting snow cleared from the wing.
Water in the spoilers or drive brakes at altitude can freeze and make them difficult or impossible to open. Checking the
spoilers or dive brakes occasionally during a high climb helps avoid this problem.
The pilot should check for a freshly charged battery since cold temperatures can reduce battery effectiveness and affect the
avionics. The preflight should include checking the radio and accessory equipment, such as the microphone in the oxygen
mask. Other specific items to check depend on the systems in the glider.
A briefing with the tow pilot should occur before a wave tow. Prior to flight, the pilots should discuss routes, minimum
altitudes, rotor avoidance (if possible), anticipated tow altitude, and other potential situations.
A pilot wearing a bail-out parachute on wave flights should check its proper fitting and use. When wearing a parachute,
the seat can suddenly seem cramped. Once seated in the glider, the pilot should check for full, free rudder movement
since larger than normal footwear can affect rudder control. In addition, given the bulky cold-weather clothing, the pilot
should check canopy clearance. The pilot’s head can break a canopy in rotor turbulence, so seat and shoulder belts should
be tightly secured even if difficult to achieve with the extra clothing. Proper placement of the oxygen mask should make
it easily accessible within a few seconds since the climb in the wave can be very rapid. Securing everything else before
takeoff prevents disorder while encountering the rotor.
Getting into the Wave
Access into the wave occurs in two ways: soaring into it or being towed directly into it. Three main wave entries while
soaring include thermalling into the wave, climbing the rotor, and transitioning into the wave from slope soaring.
At times, an unstable layer lower than the mountaintop has a strong, stable layer cap, which may support lee waves. A
line of cumulus clouds downwind of and aligned parallel to the ridge or mountain range suggests the presence of these
waves. With these conditions present, the pilot can avoid the rotor area and thermal into the wave. Whether lee waves are
suspected or not, the air near the thermal top may become turbulent. At this point, the pilot should attempt a penetration
upwind into the smooth wave. [Figure 10-30]
Figure 10-30. Thermalling into wave.
Depending on the topography near the soaring site, it may be possible to transition from slope lift into a lee wave created
by upwind topography where multiple ridges exist. In this case, the pilot climbs as high as possible in slope lift, then
penetrates upwind into the lee wave. With the lee waves in phase with the topography, the pilot can often climb from slope