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ADIRS -SAARU AIR DATA FUNCTION -2

Total Air Temperature (TAT)
The TAT signal is corrected for the small temperature rise that occurs when the air flow through the probe slows down.
Static Air Temperature (SAT)
The calculate static air temperature function receives TAT, mach and CAS inputs. The SAT signal goes to the output memory buffer.
True Air Speed (TAS)
The calculate TAS function uses static temperature CAS to calculate TAS. The corrected TAS goes invalid when the CAS is less than 50 knots.
Corrected Angle Of Attack (AOA)
The corrected AOA, from the AOA redundancy management, goes invalid when the CAS is less than 50 knots.
Mach and Computed Air Speed (CAS)
The calculate mach and CAS function uses impact pressure to calculate mach and CAS. The corrected mach goes invalid when the CAS is less than 50 knots.
Impact Pressure
The calculate impact pressure function receives static pressure inputs from the static ADM redundancy management logic. The calculate impact pressure function also receives pitot pressure from the pitot ADM redundancy management. The impact pressure signal goes to the output memory buffer.
Altitude and Altitude Rate.
The calculate altitude and altitude rate function gets signals from the static and pitot ADM redundancy management logic. Altitude and altitude rate signals go to the output memory buffer.
Pitot Pressure and Static Pressure
Pitot and static pressure come directly from the pitot and static ADM redundancy management logic. These pressures go to the output memory buffer.
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ADIRS -SAARU AIR DATA FUNCTION -2

Single Channel Operation
If the ADIRU and SAARU air data parameters from the redundancy management logic are invalid, the flight deck displays show single channel air data from the ADIRU and SAARU. Single channel air data parameters bypass the redundancy management logic that the flight displays show during normal operation. Air data from the right pitot ADM and right static ADM goes to the SAARU single channel operation function. This function calculates these single channel quantities:
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Mach

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Airspeed

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Static pressure

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Barometric altitude

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Total pressure.

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777 AIRCRAFT MAINTENANCE MANUAL

ADIRS -SAARU AIR DATA FUNCTION -2

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ADIRS -SAARU AIR DATA FUNCTION -3

Air Data Outputs
The secondary attitude air data reference unit (SAARU) sends data on the center flight control ARINC 629 bus. The data goes to the:
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Primary flight computers (PFCs)

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AIMS cabinets

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Autopilot flight director computers (AFDCs).

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ADIRS -SAARU AIR DATA FUNCTION -3

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ADIRS -SAARU BACKUP NAVIGATION

General
The ADIRU supplies navigation data to the autopilot flight director system (AFDS) and the primary flight control system (PFCS). The AFDS uses the SAARU backup navigation data if the ADIRU fails.
ADIRU Tracking
When the ADIRU data from the SAARU input memory buffer is valid, the SAARU tracks the ADIRU navigation outputs. This makes the SAARU backup navigation data the same as the ADIRU.
If the ADIRU data goes invalid, the SAARU does not follow the ADIRU outputs. The SAARU continues to calculate backup navigation data independent of the ADIRU. The fiber optic gyros do not supply sufficiently accurate data for autopilot operation for extended periods of time, therefore, the backup navigation function goes invalid after 3 minutes.
ADIRU Inputs
The ADIRU supplies these inputs to the SAARU:
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Roll angle

*
Pitch angle

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Magnetic heading

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True heading

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Along-track horizontal acceleration

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Cross-track horizontal acceleration

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North velocity

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East velocity.

The SAARU monitors the ADIRU inputs. If one or more inputs are invalid and the true airspeed (TAS) from the SAARU is more than 80 knots, the SAARU starts to calculate backup navigation data independent of the ADIRU.
Tracking Loops
The tracking loops make the SAARU follow the ADIRU data. If the ADIRU is valid, the SAARU backup navigation data out of the tracking loops and into the output buffer follows the ADIRU data. If the ADIRU fails, the tracking loops let the SAARU data go to the output memory buffer.
　
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