S 744-050
(22) Do the Antenna BITE Test
(a)
Push and hold the TEST switch on the radio altimeter R/T that is connected to the antenna.
(b)
After approximately 6 to 9 seconds, make sure the red ANT failure light at the R/T is not on.
NOTE: If the red ANT light remains on, the receive or transmit
____ antenna or the coaxial cable to the antenna has a bad connection or defects.
S 714-039
(23) Do the ground test for the radio altimeter system connected to the removed and installed antenna (AMM 34-33-00/501).
G. Put the Airplane Back to Its Usual Condition
S 864-056
(1) If electrical power is not necessary, do this procedure to remove electrical power: Manual Control (AMM 24-22-00/201).
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400 MAINTENANCE MANUAL
WEATHER RADAR SYSTEM - DESCRIPTION AND OPERATION
________________________________________________
1. General_______
A. The weather radar system presents the pilots with a topographic map type display of moisture laden weather formations or major terrain features such as rivers, coastlines, major mountain peaks, and cities for position fixing (MAP). The weather displays permit the pilot to avoid storm penetration and the associated turbulence. During landing and takeoff on airplanes with predictive windshear (PWS) equipment the pilot is advised of any windshear events in front of the airplane.
B. Predictive Windshear General Description
(1)
The weather radar system operates at a nominal frequency of 9345 MHz X-band and has a penetration range through relatively light intervening rainfall to detect distant rainfall storm areas at ranges of up to 320 miles. A frequency agility feature shifts the frequency up and down from 9360 to 9330 MHz to reduce mutual interference with nearby transmitters. For the ranges of 0 to 40 miles the weather data is processed to determines the velocity distribution of precipitation returns to verify there is turbulence. The weather displays permits the pilots to avoid storm penetration and the associated turbulence.
(2)
These airplanes have a weather radar system with operational predictive windshear capabilities. Weather radar systems with predictive windshear systems detect the most dangerous form of windshear microbursts and provide alerts to the flight crew up to 60 seconds prior to entry.
(3)
Windshear is an unstable, rapidly changing wind condition. It may be caused by low-level temperatures inversions, microbursts in the frontal zone or thunderstorm. It may occur at any level in the atmosphere, but the unexpected changes in wind speed and direction can be especially hazardous to airplanes at low altitudes on approach to and departing from the airport.
(4)
The weather radar detects windshear by using doppler shifts to measure horizontal movements of reflective matter in the air mass. Radar energy is emitted through the radome in order to gather atmospheric information such as wind and direction. The weather radar receiver/transmitter then processes this information, in conjunction with air data and inertial data, to determine the presence of a windshear event. The R/T identifies wind velocilty characteristics, such as outflows,that are unique to microbursts and alerts the flight crew if a microburst is of sufficient intensity. The predictive windshear warnings and cautions are issued based on the location of the threat with respect to the airplane, when preset threat levels are exceeded.
C. The weather radar system consists of two receiver/transmitter units, a control panel, waveguide, a waveguide switch, and an antenna assembly. Equipment location is shown in Fig. 1.
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