JP 3-50 National Search and Rescue Manual Vol I - US Navy

Figure 8-1. Wind Flow Over Gorge or Canyon
Figure 8-2. Wind Flow in Valley or Canyon
4. When wind blows parallel to the valley or canyon axis, typical
turbulence patterns are as shown in Figure 8-2.
C. When an aircraft is operated at or near its "service ceiling"
and encounters a downdraft, the aircraft may be forced to descend.
Although the downdraft may not continue to the ground, the rate of
descent may be such that the aircraft will continue descending and crash
even though it is no longer affected by the downdraft. Therefore, the
procedure to transit a mountain pass is to fly close to that side of the
pass or canyon which affords an upslope wind. This provides additional
lift for an exit in case of emergency. Maximum turning space is
available, and a turn into the wind will be a turn to lower terrain.
Flying through the middle of a pass to avoid mountains is dangerous, as
this is frequently
8-4