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E. On airplanes with PMS, when the INS is in the PMS waypoint control mode, the INS responds to all data received from the PMS and rejects all data inserted at the INS CDU. (INS CDU operates only as a display unit). However, present position coordinates are inserted only at the INS CDU. These coordinates may be loaded into the INS, when the INS is in either the PMS waypoint control mode or the INS waypoint control mode. To operate the INS totally independent of the PMS, open the PMS circuit breakers.
NOTE: A blank FROM/TO display on the INS CDU indicates PMS waypoint
____
control.
An illuminated FROM/TO display on the INS CDU indicates INS waypoint control.
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2. Trouble Shooting Tips_____________________
A. Trouble shooting of the INS is facilitated by the inherent self-testing features of the system which provide one or more warning indications when a failure occurs. The WARN lamp on the control/display unit (CDU) provides a master warning for most malfunctions occurring in the navigation unit (NU). Malfunctions occurring in the mode selector unit (MSU) or CDU are not accompanied by malfunction codes but will normally be obvious because of abnormal indications on displays and lamps. In general, an abnormal display accompanied by a WARN light indicates a NU malfunction; an abnormal display not accompanied by a WARN light indicates a CDU malfunction. A battery unit malfunction will cause the INS to automatically shut down if the system is operating on battery power. When this happens, the WARN light on the CDU and the BAT light on the MSU will illuminate. In addition to visual indications on the CDU and MSU, the INS produces separate output voltages to other airplane systems to indicate that true heading, navigation, primary pitch and roll attitude, auxiliary pitch and roll attitude, and platform heading output signals from each INS are valid.
NOTE: If WARN light on CDU and BAT light on MSU illuminate during a
____ predeparture check, delay may be averted or minimized by switching system OFF and then to NAV. Battery may then be replaced while system is aligning. Check replacement battery by momentarily opening INS PWR circuit breakers and observing that BAT light illuminates.
B. The INS cannot be turned on unless appropriate battery unit is in place, battery unit circuit breaker is closed and STANDBY IGNITION switch on overhead panel P5 is in the NORM position.
C. An overtemperature in the NU will cause an INS to automatically shut down when the mode selector is at STBY or ALIGN during ground operation. The WARN lamp on the CDU will illuminate and will not extinguish until the mode selector is rotated to OFF. The operation of the equipment cooling and INS fans should be checked as well as the integrity of the gaskets (air flow seals) on the NU mounting trays. The NU should be replaced if this overtemperature failure persists.
D. Ground Crew Call Horn Sounding
(1) The INS will automatically transfer to battery power if the INS is not turned off before ground power is removed from the airplane. In order to protect the INS batteries from inadvertent discharge, a ground crew call horn, located in the nose wheel well, activates 30 (| 10) seconds after the INS transfers to battery power with the airplane sitting on the ground. The horn will also sound if the equipment cooling system detects no airflow. If either of these conditions occurs, the INS should be shut off immediately.
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(2) The ground crew call horn sounds when one or more INS systems operate on battery power for a cumulative time of more than 30 (| 10) seconds. If the time delay module in any one airplane has a shorter than average time delay (20 to 30 seconds), it is possible that the ground crew call horn might sound briefly during INS alignment. Battery power is used for a 10-second battery test period during the alignment phase of each of the INS systems. When the three INS systems are successively switched from STANDBY to ALIGN at 8- to 10-second intervals, an uninterrupted accumulation of battery "on" time of 20 to 30 seconds can cause the ground crew call horn to sound. The horn will continue to sound for a maximum of 10 seconds, i.e., until the last INS system has cycled off the battery and returned to airplane power.
E. Remote Data Loading Problems
(1)
The trouble shooting tree is based on the operation of one INS and, therefore, does not include a check of the remote data loading and displaying functions. Each INS system is completely separate except for remote loading and display of data, and trouble analysis of one system prevents interference with an operating INS. If a problem concerns remote data loading, first determine that all three INS are operating by loading and displaying data on each INS separately. With all three INS in the REMOTE mode, enter data through one CDU into the other INS. If the data does not load (or loads incorrectly) repeat loading process two or three times and/or use a different INS to do the loading. Also recycle system through OFF to restart computer timing which may have been out of synchronism with other systems. If each INS will accept the data at least once, no component change is necessary.
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