(e)
For detected faults, the altitude processor will output failure warning codes on the ARINC 429 data buses. When computed data is not available for reasons other than equipment failure, a no computed data (NCD) code is output. The type of fault will be indicated at the control display units (CDUs), in LRU fail terms at the R/T front panel LCD display when manual self-test is initiated at the R/T front panel TEST switch, and in R/T submodule fail terms by the alphanumeric fault annunciator in the R/T unit (if provided). LRU and subassembly failure data may also be called up and identified at the L, C, and R CDUs.
Self-Test at the Radio Altimeter R/T
(a)
The self-test is initiated by pushing the TEST switch on the R/T front panel. When this happens, a test command is sent to the switching circuit as in the automatic self-test during normal operation. The incoming signal is blocked and the 300-foot delay signal is coupled to the signal mixer. The 300-foot delay signal is processed and checked in the same manner as for normal operation. The LCD screen provides status of the R/T self-Test.
(b)
When the front panel TEST switch is pushed and released, the TEST IN PROGRESS display is shown on the LCD screen and the transceiver goes through a self-test. The test continues for approximately 5 seconds. The TEST COMPLETE NO FAILURES display is shown for a test pass condition. The TEST COMPLETE FAILURES display is shown for a test fail condition. Pushing and releasing the RETURN switch shows the P/N and S/W display. Pushing and releasing the WHY switch shows the failures if a test fail condtion has occurred.
(c)
Pushing and releasing the TEST switch will also cause an altitude of 40 +/- 2 feet to be indicated on the EADI. This altitude will remain for 30 seconds after the TEST switch is pushed and released.
(d)
The self-test function is inhibited below 1500 feet by a test inhibit discrete recieved from the flight control computer during a normal automatic landing.
When the radio altitude ground test is initiated at a CDU, or the test button at the R/T is pressed, a test altitude of 40 feet is displayed on the PFD. This altitude remains displayed until the test button is released at the R/T. When the test is initiated at a CDU, the 40-foot test altitude is displayed for a short time.
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747-400
MAINTENANCE MANUAL
B. Control
(1)
Provide electrical power (Ref 24-22-00/201, Electrical Power MP (Manual Control))
(2)
Close the following radio altimeter system circuit breakers on panel P7 in pilots' control cabin.
(a)
7B3 RADIO ALTM L (B73)
(b)
7B4 RADIO ALTM C (B74)
(c)
7C21 RADIO ALTM R (B507)
(3)
Energize the integrated display system (IDS) (31-61-00/201).
(4)
Make sure that the radio altitude display reads -6 |2 feet at Capt and F/O PFDs.
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747-400 FAULT ISOLATION/MAINT MANUAL
RADIO ALTIMETER SYSTEM
COMPONENT 102 SHT FIG. QTY ACCESS/AREA REFERENCE AMM
ANTENNA - RADIO ALTIMETER RECEIVE, B76, B78, B546 1 3 BOTTOM FWD FUSELAGE UNDER WING 34-33-03
ANTENNA - RADIO ALTIMETER TRANSMIT, B75, B77, B545CIRCUIT BREAKER - 1 3 BOTTOM FWD FUSELAGE UNDER WING FLT COMPT, P7 34-33-03
RAD ALTM CENTER, C1349 1 1 7B4 *
RAD ALTM LEFT, C755 1 1 7B3 *
COMPUTER - (FIM 45-10-00/101) RAD ALTM RIGHT, C754 L CENTRAL MAINT, M7373 R CENTRAL MAINT, M7374 1 1 7C21 *
CONTROL KNOB - RST (RESET) -- 2 CONTROL PANELS, M7354, M7364 FLT COMPT, P10 CAPT, F/O EFIS
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