737 Flight Crew Operations Manual
Flight Management, Navigation -
Navigation Systems Description
Boeing Proprietary. Copyright © Boeing. May be subject to export restrictions under EAR. See title page for details.
11.20.12 D6-27370-866-EGP
OverFlight protection is designed to prevent thunderstorms that are in the aircraft
flight path from falling below the radar beam and off the radar display during high
altitude cruise. At extended ranges the upper MultiScan radar beam scans the wet,
reflective portion of a thunderstorm in the same manner that conventional radar
scans weather. As the aircraft approaches the storm and the cell begins to fall
below the upper radar beam, MultiScan utilizes 6000 ft of bottom beam
information to keep the reflective part of the storm in view. Within approximately
15 NM of the aircraft, MultiScan compares the stored digital image of the
thunderstorm with the latest sweep information and shows whichever return is
greater. If a cell that is a threat to the aircraft begins to fall below the radar beam,
MultiScan shows the stored digital image of the storm to make sure that any threat
thunderstorm remains on the display until it moves behind the aircraft. OverFlight
protection is operational above 22000 ft MSL
Windshear
On takeoff Warnings and Cautions are enabled from the beginning of the takeoff
roll (0 knots) until the aircraft reaches 80 knots. From 80 knots until the aircraft
passes 400 ft, only Warnings are enabled. From 400 ft through 1200 ft, Warnings
and Cautions are enabled. All new alerts are disabled from the time the aircraft
passes 100 knots until it reaches 50 ft.
On descent, below 2300 ft the weather scan switches from a 180 degree scan to a
120 degree scan, which indicates the windshear detection system is activated. The
smaller scan sector allows faster updates and also allows weather and windshear
events to be shown simultaneously during the entire windshear event. Windshear
detection is always activated when the aircraft is below 2300 ft in the takeoff and
landing environment even when the radar is turned off. Warnings and Cautions are
enabled from the time the aircraft passes 1200 ft until 400 ft. From 400 ft until 50
ft, only Warnings are enabled. From 50 ft until touchdown (0 ft), all new alerts are
disabled.
Windshear detection is activated during both manual and automatic radar
operation.
If the radar is on in the MAP or TEST mode and the system detects a windshear
event, the system display automatically changes to the WX+T mode to show the
weather and windshear icons. The selected range does not change automatically.
A windshear WARNING is generated whenever a detected windshear event
occurs within ± 0.25 NM of the longitudinal axis of the aircraft and within ± 30
degrees of the aircraft heading. When the aircraft is on the ground (takeoff roll),
the windshear WARNING occurs for windshear events within 3 NM.
A windshear CAUTION is generated whenever a detected windshear event occurs
outside the windshear warning region and within ± 30 degrees of the aircraft
heading and less than 3 NM from the aircraft.
March 27, 2014
To Next Page
Loading...
