(b)
If an error is noticed after the INSERT pushbutton was depressed, simply reload the data and press the INSERT pushbutton as before.
(7)
System Alignment
(a)
When the INS is turned on, and automatic self-alignment sequence starts. The sequence contains eight subsequences, during each of which specific alignment functions are accomplished.
(b)
During the first sequence, status 90, the platform is caged to the INU's axes, and consequently to the airplanes axes. Also, electric heaters in the analog section bring it up to operating temperature. Toward the end of status 90 (approximately the last 40 seconds, after the gyroscopes in the platform are up to operating temperature), the gyroscopes are run up to operating speed. Status 90 lasts as long as it takes to bring the analog section up to operating temperature. The minimum time is approximately 1 minute; the nominal time, based on an ambient temperature of 21.C (70.F), is 3 minutes; the maximum time that the INS will remain in status 90 without a malfunction code being generated (usually indicating an analog heating problem) is 6 minutes.
EFFECTIVITY AIRPLANES WITH LTN-72 INS
CONFIG 01 A Page 44 Aug 25/87
34-41-00
(c)
The second sequence, status 80, lasts for 2 minutes except that it will last indefinitely if the present position coordinates are not inserted and the mode selector switch is set to ALIGN or NAV. When the coordinates insertion and switch setting are done before the INS is ready to go from status 80 to 70, the status will remain in 80 for the scheduled 2 minutes and then become 70 when the 2 minutes is over. When the 2 minutes are over before the switch is set, the status will remain 80 until the switch is set, at which time it will become 70. A fast gyro leveling of the stable element occurs during this status.
(d)
The computer enters into the digital alignment sequence during status 70, and levels the stable element for 100 seconds.
(e)
The 25 seconds of status 60 includes a computer check of the correctness of the present position latitude that was inserted into the system. When the latitude is incorrect, the system will remain in status 60 and the computer will cause the WARN annunciator to flash on and off. This condition will continue until the latitude is corrected or the system is turned off.
(f)
After status 60, the system progresses through status 50, 40, and 10. During this time, which lasts 10 minutes, the computer continues to fine-level the stable element and to perform other functions necessary for the successful completion of the alignment sequence. The computer times the duration of status 40 and 10 and, if it exceeds 10 minutes and the status has not become 02, causes the WARN annunciator to flash on and off.
(g)
When status 10 is complete, the status becomes 02 and either of two things will occur; if the mode selector switch is set to NAV after the present position coordinates were inserted, the status will immediately become 01 to indicate that the system has automatically gone into the navigate mode; if the switch was set to ALIGN, the READY NAV annunciator will come on and the status will remain in 02 until the switch is set to NAV, when the annunciator will go out and the status will become 01. The computer continues to perform the alignment sequence during status 02 so that, if it determines that the stable element has gone out of status 02 alignment limits (for whatever reason), it will return the status to 10 and cause the READY NAV annunciator to go out until the stable element again is leveled to within limits.
(8) Automatic Operation
EFFECTIVITY AIRPLANES WITH LTN-72 INS
CONFIG 01 A Page 45 Aug 25/87
34-41-00
(a)
Automatic track selection is accomplished with the AUTO/MAN/RMT switch in the AUTO position. The FROM-TO waypoint display will initially show 0-0, and the pilot must manually select the first track leg, which normally would be the departure point and the first checkpoint. This is accomplished by pushing the TK CHG pushbutton causing the FROM-TO display to extinguish and the TK CHG and INSERT pushbuttons to illuminate. The initial track leg, which would be 0 (departure point) to 1 (first waypoint), is selected from the data entry keyboard and entered into the computer by pushing INSERT. The TK CHG and INSERT pushbuttons will extinguish, and steering data will be with respect to the 0-1 track leg. The 0 position will be the present position of the aircraft at the time the INSERT is pushed. This position could be the ramp, runway or any position after takeoff.
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本文链接地址：747飞机维护手册AMM CHAPTER 34 - NAVIGATION 第34章导航2(121)
