(1) Alignment mode The alignment is the initialization mode for the IR. Its primary function is to initialize the attitude, velocity and position integration functions implemented in the navigation mode. This mode operates on the ground only. The IR alignment mode is divided into three parts:
 -coarse level processing The coarse level processing is engaged during the first 30 seconds of the IR alignment mode. This processing estimates the local vertical using the three accelerometers and the measured gravity. During coarse level processing of the alignment mode, the software computes the level coordinate frame, pitch and roll, and associated rates and accelerations.
 -gyro-compass (or azimuth) processing and level processing Gyro-compass processing is engaged after the 30 seconds of the IR alignment mode (coarse level complete) and runs for a minimum of
 9.5 minutes.
 Gyro-compass processing is used to orient body frame to North
 (using earth rotation detection by gyros).
 During this alignment submode, an estimated latitude is computed
 using local vertical component of the earth rotation.
 During this submode, the results of the coarse level processing are
 sharpened to have a better knowledge of the coordinate frame.

 -position entry data processing This position initialization can take place in coarse level processing or gyro-compass processing. The latitude and longitude pair processed for position initialization is received from the same source (FMGC 1, FMGC 2 or CDU). As soon as a valid position initialization pair is received, the software performs three BITE tests to check if the entered latitude and longitude are within the following limits versus the position recorded at the end of the last power-up cycle:
 3+3T test: the entered position and the position from the previous navigation mode must not differ by more than 3NM+(3NM/HR)*T, where T is the duration in hours of the previous navigation mode.
 Abs val( lat entered - lat recorded ) less than or equal to 1 deg.
R 1EFF : 001-004, 1 34-14-00Page 10 1 1 Config-1 May 01/03 1 1 1CES 1 Abs val( long entered - long recorded ) less than or equal to 1 deg/cos(latitude) (Ref. 34-18-00).

 A third BITE test is performed on the entered latitude when an estimated latitude is available during the gyro-compass processing:
 Abs val(lat est) - (lat ent) less than or equal to 0.5..
 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 after position data is received. 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 the 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. Position initialization of the ADIRU is transmitted to the GPSSU for its own initialization . In addition to position, the GPSSU requires initialization data of date and UTC. The IR portion receives date and UTC from the FMGC and transmits the data to the GPSSUs. The GPIR NAV mode alignment performs coarse level and ground align processing. All the system state transitions are slaved to the IR functions. The coarse level processing of the GPIR NAV mode initializes a parallel virtual platform to provide hybrid navigation data. The GPIR NAV mode ground align processing duplicates to the IR gyro-compass processing. The chronology of the validation of the outputs during the alignment is given in para. 2-D (IR output data).
 (2) Attitude mode The attitude mode is a reversionary mode which can be activated only by manual selection of the ATT mode on the CDU. The mode can be activated on the ground or in flight and is intended to provide a rapid attitude/heading restart capability if the IR has experienced total power shutdown or failures which do not disable the mechanization of the attitude computation. The necessity of selecting
R 1EFF : 001-004, 1 34-14-00Page 11 1 1 Config-1 May 01/03 1 1 1CES 1 1EFF : 001-004, 1 34-14-00Page 12 1 1 Config-1 Aug 01/03 1 1 1CES 1R D. IR, GPS and GPIRS Output Data

 ATT is indicated by the IR on its action code (label 350 - code 04 =
 select ATT) and this data is used by the FWC to display a message on
　
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