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Captain’s EHSI. On the simulated return sweep, the radar looks at the
First Officer’s tilt control and sends the appropriate return data to the
First Officer’s EHSI.
737
Flight Manual Continental
Sec. 3 Page 301
Rev. 11/15/02 #41
Resolution
There are several factors which affect the resolution of the radar system.
Range
Increasing range will decrease the radar return. The system compensates for
this by automatically varying the system gain with range, thereby giving as
accurate a return as possible at varying ranges.
Attenuation
Intervening precipitation and increasing range tend to attenuate the beam. The
radar compensates for precipitation or range attenuation, so that the correct
color is displayed on the indicator. This feature, called penetration
compensation, allows more accurate presentation of storm cells even when
viewed through intervening rainfall.
Caution: Although this special circuitry compensates for areas of
precipitation, weather radar should not be used for penetration of
thunderstorm areas where the precipitation between aircraft and
target is moderate to heavy.
The storm behind the storm may not be displayed under extreme attenuation
conditions. Do not penetrate strong targets assuming there is nothing behind it.
If the ground cannot be painted behind the storm, then the attenuation
compensation is not effective due to extremely high attenuation.
Sec. 3 Page 302
Rev. 11/15/02 #41 Continental
737
Flight Manual
Nature Of Target
Storm targets differ in their ability to return a signal. Precipitation tends to
absorb part of the transmitted signal and “masks” targets behind heavy
precipitation areas.
Rain
Wet Hail
Dry Hail
Snow/Ice Crystals
H143
THROUGH
(TRANSMITTED)
(RETURNED)
As the tilt control is used to sweep a storm target, the return may change color,
not due to a change in precipitation rate, but to the type of precipitation target
encountered.
Gain Control And Turbulence
Normally the radar may be opposite to that previously encountered on other
aircraft. AUTO is the normal position, however manual gain control is available
in all modes.
Turning the gain knob clockwise increases the gain until, fully clockwise, the
gain is at the maximum (MAX) setting. The variable gain control may be used to
reduce the receiver’s sensitivity to aid in determining the relative intensity of
multiple thunderstorms and embedded cells.
Caution: Manual gain settings of maximum, 9 and 8 will somewhat
enhance radar receiver sensitivity, but as the gain is reduced there
is a chance that all radar displays will be eliminated.
737
Flight Manual Continental
Sec. 3 Page 303
Rev. 11/15/02 #41
Selecting the TURB position causes all weather targets (precipitation and
turbulence) to be displayed. Turbulence detection is limited to the first 50 NM
regardless of the range selected. It will be displayed in magenta on the indicator
superimposed over the weather information. This feature allows the detection
of storm related turbulence by measuring the doppler shift of detected particles.
Precipitation must be present for this mode to operate. Clear air turbulence
(CAT) will not be detected. Manual gain is available in TURB mode, but should
have no effect on turbulence targets.
Selecting the WX position will cause all precipitation targets to be displayed.
Detectable weather will be displayed in three colors: red, yellow, and green.
Inflight Operations
Antenna Tilt Operations
Takeoff And Landings:
Operations below 10,000 feet usually require a tilt setting of 2 - 3 degrees
upward tilt. This will provide target detection up to 40 NM without excessive
ground returns and eliminate frequent tilt adjustment. The tilt setting should be
adjusted as necessary to optimize target display. A solid ground return between
35 to 40 NM ensures targets within 35 NM will be detected. If tilt settings
below 4 degrees are used for takeoff, some ground return will be detected until
passing 5,000 feet AGL. This is due to minor sidelobes. Set of 7 degrees up
initially for takeoff.
Middle Altitudes (Near 20,000 Feet):
Antenna tilt settings should be roughly 0 degrees or slightly down. For over
land operation, adjust tilt control until a small arc of ground return appears at
the outer edge of the display. Storm cells displayed between half scale and the
outer edge of the display should be monitored; tilting the antenna down and
alternate range setting as necessary to avoid overscanning as you approach these
cells.
Higher Altitude (Around 35,000 Feet):
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737 FLIGHT MANUAL 737飞行手册2(70)
