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737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
34-33-00-009
RA Data NCD
RA data NCD causes the RA display and rising runway symbol
to be removed. The NCD occurs when the return RA signals are
too weak or the radio altitude is more than 2500 feet. Also, the
rising runway will not show when the ILS is not captured.
RA Data Invalid
Invalid RA data causes a amber RA flag to show in the radio
altitude position. Invalid RA also causes the rising runway
symbol to be removed. The invalid data occurs when the RA
receiver/transmitter finds a failure in the RA system.
Radio Minimums Data Invalid
Invalid EFIS control panel data on the ground or above 1000 feet
causes the amber displays control panel flag to show and the
letters RADIO and the radio minimums value to go out of view.
Between 0 and 1000 feet, the amber controls display panel flag
shows and the radio minimums bug is removed.
Also, the vertical speed indication (VSI)is grey. There is no VSI
fail flag for this condition.
RA SYSTEM - OPERATION - 2
EFFECTIVITY
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737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
34-33-00-010
RA SYSTEM - OPERATION - 2
RA SYSTEM - OPERATION - 2
EFFECTIVITY
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BOEING PROPRIETARY - Copyright#- Unpublished Work - See title page for details.
737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
34-33-00-010
General
The radio altimeter transmits a frequency modulated/
continuous wave (FM/CW) signal through the transmit
antenna. This signal is a CW carrier that scans linearly from
4,235 to 4,365 MHz 145 times a second.
Transmit and Receive
The ground causes a reflection of the transmit signal. The
receive antenna receives the signal. The RF processor mixes
the transmit and receive signals to make a difference
frequency. The difference frequency is in proportion to the
time it takes the signal to go to the ground and come back. The
main processor changes the difference frequency to radio
altitude. The radio altitude goes out on two ARINC 429 data
buses. The two buses supply radio altitude and status
information to these components:
* FCC A or FCC B
* Autothrottle computer
* DEU 1 and DEU 2
* GPWC
* TCAS computer
* FDAU.
Input Program Pins
The system select program pin input sets the system
modulation rate and system identification. The modulation
rate for the RA 1 system is 145Hz, the RA 2 system is 155Hz.
The aircraft installation delay (AID) program pin is grounded to
the 57 feet selection. This calibrates the system so that the radio
altitude is 0 feet at touchdown. It makes an allowance for these
conditions:
* Length of the antenna cables
* Fuselage to ground distance
* Flare angle.
When grounded, the continuous data program pin selects noninterrupted
RA data output at all times.
RA SYSTEM - RF PROCESSING
EFFECTIVITY
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BOEING PROPRIETARY - Copyright#- Unpublished Work - See title page for details.
737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
34-33-00-011
RA SYSTEM - RF PROCESSING
RA SYSTEM - RF PROCESSING
EFFECTIVITY
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737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
34-33-00-011
BITE Module
The built-in test equipment (BITE) module monitors the circuits
in the RA receiver/transmitter for faults. The flight fault memory
stores the number of faults for each flight leg. Shop personnel
use the automatic test equipment (ATE) connector to read the
fault memory contents.
Test
A test switch on the front of the RA receiver/transmitter starts an
RA self-test. LEDs show the results of the self-test.
The self-tests do a check of these:
* Receiver/transmitter internal status
* ARINC 429 output transmitters status
* Antennas and coaxial cables.
The flight control computers (FCCs) supply a test inhibit signal
to the receiver/transmitters. This prevents an RA test when the
FCC is in the approach mode.
RA SYSTEM - FAULT DETECTION
EFFECTIVITY
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BOEING PROPRIETARY - Copyright#- Unpublished Work - See title page for details.
737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
34-33-00-012
RA SYSTEM - FAULT DETECTION
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