737 MAX Flight Crew Operations Manual
Flight Management, Navigation -
Navigation Systems Description
11.20.18
MN-FLT-OH-201
Windshear
The Predictive Windshear (PWS) feature detects the presence of windshear ahead
of the aircraft, giving 10 to 60 seconds of warning before the encounter.
Windshear detection mode operates automatically below 1800 ft. Above Ground
Level (AGL), with alerts available at 1200 ft. AGL and below. If a Windshear
event is detected, the system automatically provides the crew with Caution and/or
Warning annunciations, and a Windshear icon appears on the weather display.
This system is meant to supplement other means of detecting and avoiding
hazardous Windshear conditions. It will not detect all possible hazardous
Windshear conditions such as extremely dry events or events masked by unusual
radar clutter. The PWS mode can generate three types of alerts; Advisory, Caution,
and Warning. These depend on the location of the Windshear event, not the
strength. When a Windshear event is encountered below 1200 ft. AGL, the
appropriate alert is issued and the icon automatically appears on the display.
If the display is showing data other than weather (such as ground proximity terrain
data) when a Windshear event takes place, the display automatically switches into
weather mode for presentation of the Windshear icon. The Windshear Icon will be
overlaid on the radar display indicated by the mode selection knob on the control
panel.
If a Windshear event is encountered while the system is in TEST, the test pattern
will be replaced, and the Windshear icon will be overlaid on an AUTO weather
display.
WXR-2100 Multiscan Radar
1B785, 1B786, 1J585 - 1J594
A MultiScan weather radar emulates an ideal radar beam by taking information
from different radar scans and merging the information into a total weather
picture. Ground clutter suppression algorithms are then used to eliminate ground
clutter. The result is the ability for flight crews to view all significant weather from
0 to 320 NM on a single display that is essentially clutter free. With the multiscan
process two scans are taken, each optimized for a particular region in front of the
aircraft. In general, the upper beam detects intermediate range weather while the
lower beam detects short and long range weather by automatically adjusting the
beams tilt and gain settings. The information is then stored in a temporary
database. When the captain or first officer selects a range, the computer extracts
the appropriate portions of the desired information, merges the data, then
eliminates the ground clutter. The result is an optimized weather display for
whichever range scale the flight crew selects. During automatic operation,
multiscan uses variable gain that is based on atmospheric temperature profiles to
compensate for variations in geographic location, time of day, and altitude in order
to optimize weather returns in all phases of flight. Gain is thus adjusted to suit the
environment in which the aircraft is flying and provide the optimum weather
picture in the prevailing conditions.
March 1, 2021
