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747-400
MAINTENANCE MANUAL
3) The PSEU non-volatile memory will be erased when you do the PSEU system test from the CMC.
(h) BITE has four modes as follows:
-BIT
-Power-Up Test
-Ground Functional Test
-In-Flight BITE.
1) BIT mode continuously makes sure the internal components and operations in the PSEU work correctly. Signals of all input buses, sensor and switch positions are continuously monitored.
2) The power-up test mode supplies a test which automatically starts after 250 milliseconds or more without power. This test occurs in ground mode . BITE ground mode is (PRI NG COMPRESSED and ALL PRI LG TRUCKS NOT TILTED) or (ALT NG COMPRESSED and ALL ALT LG TRUCKS NOT TILTED).
3) The ground functional test mode operates in the BITE ground mode. This mode only operates when it receives a signal from the CMC and the Test Enable Switch is in the Test position. It does as follows:
a) It makes sure all sensors have the correct inductance and makes sure sensor wiring is not open or shorted.
b) It makes sure all sensor circuits are in the correct target near and target far position.
c) It makes sure all logic and output driver circuits work correctly.
d) It makes sure inputs which do not agree are found. Input groups are compared to the input that does not agree.
4) In-flight BITE mode starts a test in the flight mode when a failure is found. PSEU flight mode is (PRI NG NOT COMPRESSED and ALL PRI LG TRUCKS TILTED) or (ALT NG NOT COMPRESSED and ALL ALT LG TRUCKS TILTED). This test does as follows:
a) It makes sure only the components related to the output signal which caused the failure are tested.
b) It makes sure sensors have correct inductance and makes sure the sensor wires are not open or shorted.
c) It makes sure target signals that do not agree are found. A group of target signals are compared to the signal that does not agree.
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747-400 MAINTENANCE MANUAL
d) It identifies the Line Replaceable Unit (LRU) that caused the failure by LRU number and identifies shop repairable faults by card and signal.
(4) There are several EICAS messages that indicate a fault condition. These messages show in the upper right corner of the main EICAS display: (Fig 4)
-
GEAR DISAGREE
-
GEAR TILT
-
GEAR DOOR
-BODY GEAR STRG
-A/G DISAGREE
-NOSE A/G DISAGREE
-GEAR MONITOR
(a) The GEAR DISAGREE message tells that:
-The primary and alternate systems both show that any gear does not agree with landing gear position lever
-
All gears are not up
-
All gears are not down.
(b) The GEAR TILT message tells that:
-The primary and alternate systems both show that any gear is not tilted when in the air.
(c) The GEAR DOOR message tells that:
-The primary and alternate systems both show any landing gear door is not closed. This message shows when the gear is not in transit. The message is stopped when the alternate gear extend is selected.
(d) The BODY GEAR STRG message tells that:
-
The primary and alternate systems both show the body gear steering actuator is not locked when the wheel speed is greater than 20 knots.
-
The primary and alternate systems both show the body gear steering actuator is locked when the wheel speed is less than 20 knots.
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