18.11. Radio Altimeter (ra) в737.
Подробно рассматривается в [4] рекомендуемой литературы.
General
The radio altimeter (RA) system measures the vertical distance from the airplane to the ground. The radio altitude shows in the flight compartment on the display units (DU). The radio altitude is computed with the receiver transmitter unit by comparing the transmitted signal to the received signal. The R/T unit transmits a radio signal then receives the reflected RF signal back from the ground to determine the altitude of the aircraft. The R/T sends computed altitude data out on two ARINC 429 data buses to user systems on the aircraft.
The flight crew and other airplane systems use the altitude data during low altitude flight, approach, and landing.
The system has a range of -12 to 2500 feet.
An adjustable radio minimums alert operates with the radio altitude system and is independently selectable from 0 to 999 feet on the captains and first officers EFIS control panels. The radio minimums altitude selection is compared and processed in the display electronics units (DEUs) with the existing radio altitude value output from the radio altitude R/T. When the airplane descends to the selected radio minimums altitude a flashing radio minimums alert is displayed on the applicable DU.
Abbreviations and Acronyms
ADI - attitude direction indication
AID - aircraft installed delay
altm - altimeter
ant - antenna
approx - approximately
ARINC - Aeronautical Radio, Inc.
BITE - built-in test equipment
CAPT - captain
CDS - common display system
conn - connector
CP - control panel
CW - continuous wave
DEU - display electronics unit
DH - decision height
DME - distance measuring equipment
DU - display unit
EFIS - electronic flight instrument system
F - frequency
FCC - flight control computer
FDAU - flight data acquisition unit
FM - frequency modulation
F/O - first officer
freq - frequency
fwd - forward
gnd - ground
GPWC - ground proximity warning computer
ILS - instrument landing system
LCD - liquid crystal display
LED - light emitting diode
LRU - line replaceable unit
maint - maintenance
MDA - minimum descent altitude
mins - minimums
PFD - primary flight display
P/N - part number
RA - radio altimeter
RA - radio altitude
rec - receiver
RF - radio frequency
rst - reset
R/T - receiver transmitter
S/W - software
sys - system
T - time
TCAS - traffic alert and collision avoidance system
VCO - voltage controlled oscillator
WXR - weather radar
xmit - transmit
Ra system - general description General
The radio altimeter system has two receiver/transmitters (R/ Ts). Each R/T has a transmit and a receive antenna. The radio altimeter R/T makes a frequency modulated continuous wave RF signal that is sent to the ground and reflected back to the airplane. The time that it takes for the signal to travel from the transmit circuit of the R/T to the receive circuit of the R/T is changed into absolute altitude. The number one system altitude shows on the captain display and the number two system shows on the first officer display.
The altitude data and signal validity is sent on two ARINC 429 data buses.
ARINC 429 data bus 1 sends data to these components:
Flight control computers (FCC)
Autothrottle computer.
ARINC 429 data bus 2 sends data to these components:
Ground proximity warning computer (GPWC)
Traffic alert and collision avoidance system (TCAS) computer
Flight data acquisition unit (FDAU)
Weather Radar (WXR)
Common display system (CDS) display electronic units (DEU).
The receiver/transmitters get discrete inputs from the proximity switch electronics unit (PSEU) used to count flight legs for fault recording.
RA SYSTEM - COMPONENT LOCATION – 1
General
The RA receiver/transmitters are on the E3 rack in the electronic equipment (EE) compartment.
The RA antennas are on the bottom of the fuselage.
RA SYSTEM - COMPONENT LOCATION - 2
General
These are the components in the flight compartment that interface with the RA system:
Left and right EFIS control panels
Common display system (CDS) display units (DU).
RA SYSTEM - POWER, ANTENNA, AND DISCRETE INPUTS
Power
Power for the RA receiver/transmitter 1 is 115v ac from xfer bus 1.
RA receiver/transmitter 2 receives 115v ac from xfer bus 2.
Antenna Interfaces
The transmit antenna sends radio frequency (RF) signals to the ground. The receive antenna sends reflected RF signals to the receiver circuits of the RA receiver/transmitter.
Flight Control Computer Discrete
The flight control computers (FCC) supply a test inhibit signal to the RA receiver/transmitter. This signal prevents an RA test when ILS mode is selected.
PSEU
The RA receiver/transmitter keeps internal and external faults in a nonvolatile fault memory. The RA receiver/transmitter keeps these faults by flight segments. The RA identifies the faults as airborne faults or ground faults. The proximity switch electronics unit (PSEU) gives the air/ground condition.
Input Program Pins
These are the radio altimeter program pins:
Continuous data. When grounded, lets continuous altitude data be transmitted to user systems
Aircraft installed delay (AID) of 57 feet. This lets the RA system compensate the altitude calculation for antenna cable length and distance of the RA system antennas from the ground at touchdown
System select. Used to identify which system.
Indicator Discrete
The indicator discrete supplies the status of flight compartment radio altitude indicators. This system does not use radio altitude indicators.
RA SYSTEM - DATA BUS OUTPUTS, DECISION HEIGHT INTERFACE
General
The RA system supplies radio altitude (RA) data to these components:
FCC A and the FCC B
Autothrottle computer
Display electronics unit (DEU) 1 and the DEU 2
Weather radar R/T
GPWC
FDAU
TCAS computer.
RA Receiver/Transmitter Outputs
Each FCC uses radio altitude from its on-side RA receiver/ transmitter. The FCCs use radio altitude in the approach control and low altitude flight calculations.
The autothrottle uses radio altitude in the TO/GA calculations and autothrottle flare calculations.
The DEUs use radio altitude data to calculate the type of radio altitude display and the radio altitude value to show on the display units.
The weather radar R/T uses radio altitude to turn on or off the predictive windshear function and to enable/disable display and alert functions.
The GPWC uses radio altitude in its ground proximity alert and warning logic calculations.
The FDAU records radio altitude values.
The TCAS computer uses radio altitude to set the sensitivity levels for intruder advisory calculations and to find if an intruder aircraft is on the ground.
EFIS Control Panel Interface
The EFIS control panels supply radio minimums values to the DEUs. The DEUs use radio minimums and radio altitude to calculate radio minimums alerts that show on the display units.
RA SYSTEM - RA RECEIVER/TRANSMITTER
Purpose
The RA receiver/transmitter calculates radio altitude.
The RA receiver/transmitter has a non-volatile memory which stores fault information from the last 63 flights. It can store up to 13 faults per flight. Only shop personnel read the non-volatile memory information.
Description
These are the operation limits of the receiver/transmitter:
Frequency = 4235 Mhz to 4365 Mhz
Transmit power = 500 mw nominal
Operating range = -12 to 2500 feet.
A test connector on the front panel connects test equipment for shop tests.
Operation
These are the three LED status indicators on the front panel:
Red or green LRU STATUS LED shows the receiver/
transmitter operational status. It comes on green when the
receiver/transmitter is OK. It comes on red when the
receiver/transmitter has a fault
Red XMIT ANT FAIL LED shows a transmission antenna or coax cable fault
Red REC ANT FAIL LED shows a receive antenna or coax cable fault. You push the test switch to start a self-test.
RA SYSTEM - RA ANTENNA
Purpose
The RA system uses four antennas that transmit and receive RF signals. Each RA receiver/transmitter has a transmit and receive antenna. The transmit and receive antennas are the same and interchangeable.
Physical Description
Four screws attach each antenna to the bottom of the fuselage.
There is an O-ring seal in a groove around the coax connector. The O-ring seal gives moisture protection. The radiation side of the antenna has red markings “FWD” and “DO NOT PAINT”.
Training Information Point
Do not paint the radiation surface or the back plate of the antenna. Paint does not permit the antenna to send or receive RF signals.
RA SYSTEM - OPERATION - 1
EFIS Control Panel
The EFIS control panel controls the radio minimums value and resets the radio minimums alert display to a normal display. The radio minimums shows on the captain and first officer display units. The left EFIS control panel controls the captain display units. The right EFIS control panel controls the first officer display units.
The minimums controls have these three controls:
A two-position rotary switch (minimums reference selector)
A spring loaded rotary switch (minimums altitude selector)
A radio minimums reset (RST) switch.
You use the radio position on the minimums reference selector to set the radio minimums.
To set a radio minimums value, use the rotary switch to adjust the value between -1 feet and +999 feet.
Push the radio minimums reset (RST) switch to set the radio minimums alert display back to normal.