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

the area of greatest turbulence, and, in case of emergency, provides
insufficient turning space.
D. Do not rely solely on terrain elevations or contour lines
printed on aeronautical charts. Errors in position, altimeter setting,
or chart information may result in less terrain clearance than
anticipated.
E. For safety, mountainous search areas should be assigned to
multi-engine aircraft when possible.
F. ELT signals can "bounce" and be blocked in mountainous areas.
Homing may be difficult. Occasionally, location of an ELT will require
coordination of SARSAT alert data with both high- and low-flying
aircraft.
821 Mountain Helicopter Considerations
A. High altitude causes several undesirable effects on
helicopters. Available power and hovering ability is reduced.
Helicopters are also susceptible to blade stall, aggravated by high
forward speed, high gross weight, high altitude, low r.p.m., induced "G"
loading, and turbulence. Since power-to-weight ratio may be critical,
shallow turns and slow air speeds will be required. Thermal heating in
mountainous terrain may cause "heat bubbles" localized higher
temperatures. Higher than expected temperatures should be anticipated,
and power or SRU selection made for that air density.
B. Extreme caution should be used when operating or hovering near
objects or foliage. Turbulence may reduce clearances suddenly and the
rotor tips may be below the landing gear or skids at angles of bank over
45 degrees.
822 Contour Search Patterns
Contour search patterns are often used in mountainous and hilly
areas.
A. Contour Single-Unit (OS). For safety, only one SRU is assigned
in any one area for contour searches. As shown in Figure 8-3, the SRU
searches from top to bottom, starting above the highest peak and flies
around the mountain "tucked in" closely to the mountain side. As one
contour circuit is completed, the altitude is normally decreased 500
feet (descending 360 degree turn opposite to direction of search
pattern) and a new contour circuit begun. Contour searches can be
extremely dangerous and ineffective, unless:
1. The crew is experienced, well briefed, and possesses accurate
large-scale contour maps.
2. Weather conditions are good, with both good visibility and
lack of turbulence. Flight should be avoided in mountainous
areas when winds exceed 30 knots, because downdrafts can
exceed 2000 ft/min.