34-41-00
 E. The INS is characterized by the following features:

 (1)  
Automatic self-alignment and calibration are accomplished each time the INS is turned on.

 (2)  
Provides continuous cyclic ground alignment.

 (3)  
Uses (but does not require) inputs from external navigation aids.

 (4)  
Monitors its own performance and furnishes warning indications when output signals and displayed data are unreliable.

 (5)  
Insertion of present position, waypoint, and destination data is easily accomplished by using a keyboard.

 (6)  
Operates accurately within any latitude and longitude encountered in flight, including polar flights.

 (7)  
Indicating lights and displays can be replaced while INS is operating without hazard to equipment or personnel.

 (8)  
Can be used to produce only attitude (roll, pitch, and yaw) stabilization signals if navigation and/or steering signals become unreliable.

 (9)  
Although true airspeed from the central air data computer is an input to the INS, loss of this input will not affect INS operation; there will be a loss of wind display only.

 (10)
 INS performance can be improved during flight by making a position fix when an accurate present position reference is available.

 (11)
 On airplanes with PMS, INS receives updated present position from the PMS.

 (12)
 The INS can be used to simulate airplane attitude movements as an aid in avionic system interface testing. This is accomplished with an attitude slew test feature that provides the capability to tilt the INS platform about both its pitch and roll axes.

 F.  Principal airplane systems and indicators that are connected to the INS (Fig. 2) are listed below.
 (1)  
AC Power System (24-22-00)

 (2)  
Central Air Data Computer (CADC) (34-12-00)

 (3)  
Autoflight Systems (Chapter 22)

 (4)  
Weather Radar (34-43-00)

 (5)  
Magnetic Heading Reference System (MHRS) (34-21-00)

 (6)  
Attitude Director Indicator (ADI)

 (7)  
Horizontal Situation Indicator (HSI)

 (8)  
Performance Management System, PMS (when installed).

 (9)  
Optional navigation data displays capable of using synchro, analog, or digital input signals.

 G.  Power and true airspeed signals are the only electrical inputs required by the INS. A barometric altitude signal is supplied to the system but is not used.
 (1)  Three types of 400-Hz ac power are required from the airplane electrical system. These are 115 volts, 26 volts, and variable 0 to 5 volts. The 0 to 5 volts is used for panel lighting in the mode selector unit and for panel and keyboard lighting in the control/display unit. The 26 volts is used in the navigation unit for excitation of synchro signal outputs. The 115 volts supplies all other power requirements during normal operation.
 EFFECTIVITY AIRPLANES WITH LTN-72 INS  
  CONFIG  01 A Page 5  Apr 25/86

34-41-00
 (2)  The true airspeed input signals to the INS from the central air data computer are used for determination of wind speed and wind direction.
 H.  The navigation information relationships determined by the inertial navigation system are best described by referring to Fig. 3. These relationships are displayed in digital form on the control/display units and in analog form on the pilots' flight instruments.
 (1)  
True heading (TH) is the angle between the airplane centerline and true north.

 (2)  
True airspeed (TAS) is the airspeed of the airplane with respect to the surrounding air.

 (3)  
Wind speed (WS) is the magnitude of the wind velocity vector in knots.

 (4)  
Wind direction angle (WD) is the angle between true north and the wind velocity vector.

 (5)  
Ground track angle (TK) is the angle between true north and an imaginary line on the earth's surface connecting successive position points over which the airplane has flown (ground track).

 (6)  
Ground speed (GS) is the velocity with which the airplane is moving over the earth's surface.

 (7)  
Drift angle (DA) is the angle between the airplane's true heading and ground track.

 (8)  
Desired track angle (DTK) is the angle between true north and an imaginary line on the ground connecting successive position points desired to overfly; this line being the great circle segment that lies between two successive way points.
　
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