Abs val(sin (lat est) - sin (lat ent)) less than or equal to
0.01234.
The alignment is completed after 10 minutes if a valid position
data has been received and verified by the IR.
If not, the automatic sequencing to the NAV mode will be delayed
(up to 1 minute) after position data is received.
R 1EFF : 051-099, 106-149, 204-299, 301-399, 1 34-14-00Page 14 1401-499, 1Config-3 Aug 01/05 1 1 1CES 1 The operations to enter position and the warnings associated to the tests performed in alignment mode are described in para. 3 (operation/control and indicating). The IR also offers the possibility to enter into a variant of the alignment mode called "rapid realign" or "30-second realign". This mode is selected by moving the CDU selector switch from NAV to OFF, then to NAV within five seconds, when the aircraft is on ground (ground speed less than 20 knots). Valid position data must be received. During the "rapid realign" mode, all computed velocities are set to zero and a fine tuning of the alignment is performed using the attitude reference vertical and the heading data available from the last NAV phase as initial conditions. During the alignment mode, the IR outputs on the ARINC 429 bus may not be available. The chronology of the validation of the outputs during the alignment is given in para. 2-D (IR output data).
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(2) Navigation (NAV) mode (Ref. Fig. 003) The NAV mode is the primary operating mode for the IR and is implemented in software as unaided strapdown inertial navigation computation. The basic operating elements consist of three integration functions (attitude, velocity and position) driven by input gyro and accelerometer strapdown sensor data. The equations used to compute the main parameters are the following:
-
body pitch, roll, yaw rates (labels 326, 327, 330): they are representative of the aircraft body rotations relative to the aircraft body axes and are directly measured by the laser gyros.
-
body longitudinal, lateral, normal accelerations (labels 331, 332, 333): they are directly measured by the accelerometers but with the gravity effect substracted to have 0g on the normal acceleration when in level.
-pitch and roll attitude rate (labels 336, 337)
Pitch Att rate = Q. cos (Ra) - R. sin (Ra)
Q. sin (Ra) + R. cos (Ra) Roll Att rate = P + -------------------------cos (Pa)/sin (Pa) where : Ra = Roll angle
Pa = Pitch angle P = Body roll rate Q = Body pitch rate R = Body yaw rate
-flight path angle (label 322) = angle between the aircraft velocity vector and the horizontal plane (VZ) FPA = Arc tan (--) (VG)
where : VZ = inertial vertical speed (label 365) VG = ground speed (label 312)
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ADIRU - Navigation Mode Functions
Figure 003
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-flight path acceleration (label 323) = aircraft acceleration along the total velocity vector Vx.Ax + Vy.Ay + Vz.Az Flt Path Accel = ---------------------______________ / 2 2 2
V Vx + Vy + Vz where : Ax, Ay, Az, Vx, Vy, Vz: accelerations and velocities in the earth frame.
-wind speed and direction computation (labels 315 and 316) ___________________ / 2 2 Wind speed = V Vwind N + Vwind E (Vwind E) Wind direction = Arc tan (-------) + 180 deg.
(Vwind N) Vwind E = Veast - cos (Pa). sin (Hdg). TAS
Vwind N = Vnorth - cos (Pa). cos (Hdg). TAS
where : Veast = east velocity = label 367 Vnorth = north velocity = label 366 Pa = pitch angle = label 324 Hdg = heading = label 314 TAS = true airspeed.
The TAS is received from the ADR. The ADR source to be used is selected according to the configuration of the discretes described in para. 2.B.(3)(d). The IR does not compute the wind if the TAS is less than 100 knots or if the air data sources are no more available. In this case, the wind labels are sent with their status matrix coded NCD (No Computed Data).
-inertial vertical speed and inertial altitude computation (labels 365 and 361) The IR software contains a baro-inertial loop to compute the Inertial Vertical Speed and Inertial Altitude. This loop permits to take advantage of the different qualities of the inertial and air data systems. The IR brings its better behaviour in dynamic maneuvers while the ADR brings its stability in time (no drift of the outputs like in IR). The principle of the baro-inertial loop is given in: the figure (Ref. Fig. 004)
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