(2)
The position of the range switch will determine the range of the data displayed on the EHSI. The map mode display switches will have no affect on the operation of the system.
(3)
The following additional data are also displayed in the expanded NAV mode:
(a)
Airplane heading from the IRS
(b)
Track, drift angle, desired track, cross track deviation, Distance to go and ETA to the next waypoint, vertical deviation, FMC/IRU position difference, wind direction and speed from the FMC
(c)
Selected heading from the DFCS MCP
(d)
Weather radar mode, gain, and antenna tilt from the weather radar system
J. EHSI Fault Displays (Fig. 4A)
(1)
When a specific input to the symbol generator becomes invalid, the symbol or data value associated with it on the EHSI is blanked. In most cases, a yellow fault flag is also displayed, in place of the invalid symbol or data.
(2)
When the status of a data source, for any given symbol or data value, changes from valid to NCD (no-computed-data), the symbol or data value normally blanks, or is replaced by a series of dashes.
9. EFI Transfer Switch___________________
A. The EFI transfer switch is a three position switch. The switch function is to select a symbol generator as the source of display data on EADIs and EHSIs. This is to provide a backup source in the event of a symbol generator failure. The positions of the EFI transfer switch are: NORMAL, BOTH ON 1, and BOTH ON 2.
(1)
When the EFI transfer switch is in NORMAL position, the left EFIS symbol generator provides display data to the left EADI and EHSI. Similarly, the right EFIS symbol generator provides display data to the right EADI and EHSI.
(2)
When the EFI transfer switch is in BOTH ON 1 position, the left EFIS symbol generator provides display data to the left and right EADIs and EHSIs.
(3)
When the EFI transfer switch is in BOTH ON 2 position, the right EFIS symbol generator provides display data to the left and right EADIs and EHSIs.
10. EFIS Symbol Generator (Fig. 1)_____________________
A. General Description
(1)
The EFIS symbol generator receives data from the EFIS control panel and the airplane's navigation and guidance systems. The symbol generator then processes the data and provides video signals for display on the EADI and EHSI.
(2)
The input data is received on ARINC 429 low speed and high speed data buses, as well as ARINC 453 weather radar high speed buses, and discrete inputs.
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737-300/400/500MAINTENANCE MANUAL
(3)
There are two connectors at the rear of the unit. Program pins permit selection of various displays on the EADIs and EHSIs.
(4)
Two symbol generators are located on the E2-1 rack. Each symbol generator weighs 21 pounds (9.5 kg) and is packaged in a size 6 MCU case.
(5)
The TEST switch on the front of the symbol generator initiates a self-test of the EFIS. The BITE (Built-in Test Equipment) circuitry within the symbol generator detects existing faults and identifies the faulty line replaceable unit. A record of the failures detected by BITE is stored in nonvolatile memory of the symbol generator.
B. Symbol Generator Computed Displays
(1) Most of the parameters displayed on the EADI and EHSI utilize signals that originate from various systems on the airplane. However, the display of a number of parameters requires computations based on inputs from several systems. The computations for these parameters are performed by the symbol generator. The symbol generator computed displays are as follows (Fig. 5):
(a)
DH Alert
1) The decision height (DH) value selected on the EFIS control panel and the actual radio altitude, are compared when the radio altitude is below 2500 feet. When the actual radio altitude decreases to the DH value, the symbol generator provides alert signals, which cause the DH and radio altitude display to change, on the EADI. The DH circuit is reset when the RESET button is pressed on the EFIS control panel; or the radio altitude increases to 75 feet above selected DH (during go-around); or when the actual radio altitude equals zero. 中国航空网 www.aero.cn 航空翻译 www.aviation.cn 本文链接地址：737-300 400 500 AMM 飞机维护手册 导航 NAVIGATION 1(111)
