TM 55-1510-221-10resynchronize to the vertical mode. Example: withIAS mode selected, the pilot may depress the CWSpushbutton and manually change airspeed. Oncetrimmed at the new airspeed the CWS pushbutton isreleased, and the autopilot will hold this airspeed. Ifa large pitch attitude change is made, the pilotshould trim the aircraft normally before releasingthe CWS button.and by the 20-ampere circuit breaker on the front ofthe INS battery unit.6. Controls/Indicators and Functions (INSMode Selector Unit, fig. 3-24).N O T EEither pilot’s CWS button will permitchanging of the autopilot regardless ofwhich pilot has control of the autopilot.However, use of the CWS will cancel theother pilot’s flight director GA mode.(1.) READY NAV lamp. Illuminates toindicate INS high accuracy alignment has beenattained. If attained during ALIGN mode, lightremains illuminated until NAV mode is selected.Light illuminates momentarily during alignment, ifalignment is accomplished while in NAV mode.(2.) BAT lamp. Illuminates to indicateINS shutdown due to low battery unit voltage.(3.) Mode select knob. Controls INS acti-vation and selects operating modes.3-30. INERTIAL NAVIGATION SYSTEM.(a.) OFF. Deactivates INS.a.Description. The Inertial Navigation Sys-tem (INS) is a self-contained navigation and attitudereference system. It is aided by (but not dependentupon) data obtained from its own TACAN system,the GPS, the aircraft encoding altimeter and thegyromagnetic compass system. The position andattitude information computed by the INS is sup-plied to the automatic flight control system, weatherradar system, horizontal situation indicator, andradio magnetic indicators. In conjunction with otheraircraft equipment, the INS permits operation underInstrument meteorological Conditions (IMC). TheINS provides a visual display of present positiondata in Universal Transverse Mercator (UTM) coor-dinates or conventional geographic (latitude-longitude) coordinates during all phases of flight.When approaching the point selected for a legswitch, an ALERT light will illuminate informingthe pilot of an imminent automatic leg switch or theneed to manually insert course change data. TheINS may be manually updated for precise aircraftpresent position accuracy by flying over a referencepoint of known coordinates. The INS may beupdated automatically by the TACAN system or theGPS. Altitude information is automatically insertedinto the INS computer by an encoding altimeterwhenever the INS is operational.(b.) STBY. Moving to STBY fromOFF mode: Starts fast warmup of system to operat-ing conditions; activates computer so informationmay be inserted; all INS controlled warning flagswill indicate warning. Moving to STBY from anyother mode: INS operates as if in attitude referencemode.(c.) ALIGN (ground use only,parked). Moving to ALIGN from OFF mode: Level-ing starts after fast warmup heaters are off. Movingto ALIGN from STBY: Alignment starts if fast war-mup heaters are off. Moving to ALIGN from NAVmode: INS is not downmoded, but will allow auto-matic shutdown if overtemperature is detected.(d.) NAV. Activates normal naviga-tion mode after automatic alignment is completed;must be selected before moving aircraft. Moving toNAV from STBY mode causes INS to automaticallysequence through STBY and ALIGN to NAV mode,if present position is inserted and aircraft is parked.NAV mode is used to shorten time in STBY and tobypass battery test, if stored heading is valid.The Mode Selector Unit (MSU) (fig. 3-24) con-trols system activation and selects operating modes.The Control Display Unit (CDU) (fig. 3-25) pro-vides controls and indicators for entering data intothe INS and displaying navigation and system statusinformation.(e.) ATT. Activates attitude refer-ence mode. Used to provide only INS attitude sig-nals. Shuts down computer and CDU leaving onlyBAT and WARN lights operative. Once selected,INS alignment is lost.c. Controls/Indicators and Functions, (INSControl Display Unit, fig. 3-25).The INS system is protected by the 10-ampereINS AC POWER and the 5-ampere INS HTR ACPOWER circuit breakers on the mission AC/DCpower cabinet, by the 5-ampere INS CONTROL cir-cuit breaker on the overhead circuit breaker panel(1.) HOLD key. Used with other CDUcontrols to stop present position display from chang-ing, in order to update position and to displayrecorded malfunction codes. Lights when pressedfirst time; goes out when pressed second time orwhen inserted data is accepted by computer. When3-46
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