ADIRS
Air Data Inertial Reference System
ADIRS provide
Speed, Position, Altitude and Attitude (pitch) for the:
- Flight Displays
- Flight Management Computers
- Flight Controls
- Engine Controls
- Other systems that require inertial or air data
ADIRS components
ADM (Air Data Module)
ADIRU (Air Data Internal Reference Unit)
SAARU (Secondary Attitude Air data Reference Unit)
ADIRU and SAARU
The AIDRU is the primary flight data source, while the SAARU acts as an automatic backup to the ADIRU
SAARU capabilities
-SAARU is the dedicated data source for the standby attitude indicator
ADM (Air Data Modules)
- ADM are remote sensors which electronically supply pitot static pressure information to the flight controls data bus:
- Pitot pressure
- Static pressure
-The ADM modules receive and process data from 3 pitot probes, 6 static ports, 2 per module
ADM + standby indicators
-Two standby modules provide dedicated inputs to the standby airspeed indicator and altimeter
ADIRU (Air Data Internal Reference Unit) + SAARU (Secondary Attitude Air Data Reference Unit) calculations
- ADIRU+SAARU receive 3 independent bus inputs to calculate: airspeed, Mach, attitude and other air data parameters
- Both independently compare the inputs and validate which signals should be used in their calculations
ADIRU (Air Data Internal Reference Unit) + SAARU (Secondary Attitude Air Reference Unit) with AOA
- The ADIRU and SAARU receive data from 2 AOA sensors
- 1 Total Air Temperature probe (TAT) displayed on the eicas display
ADIRU composition
- The ADIRU:
- contains electronic sensors
- non-mechanical laser gyroscopes (measures the airplane movement in all 3 axes)
Replaces old tech:
- IRUs
- Mechanical gyros
- INSs
ADIRU Sensors and Gyros
Calculate:
- Heading
- Ground track
- Ground Speed
- Airplane’s latitude
- Airplane’s longitude
ADIRU calculating alignment
- Must do a pre-flight alignment
- Pre-flight alignment is to calculate the airplane’s relationship to the north (done independently from any nav aids
- To sense attitude the sensed gravity forced is used to calculate the airplane’s attitude
- Earth’s rotation is used to to determine true north
- Airplane must remain stationary (to properly sense earth and gravity rotation) and wait for 6-15 minutes to align
- Global Positioning System coordinates are the most accurate (ADIRU compares GPS pos compared to last ADIRU pos and geog latitude)
- when process complete the ADIRU enters the navigate mode
ADIRU errors
- After entering navigation mode errors start to accumulate
- To compensate, the FMC calculates its own pos using the AIDRU and other data
- If dual FMC failure, to provide nav backup, ADIRU contains an identical magnetic variation table
ADIRU variation data
Variation data is for all locations between North and South 82 degrees latitude
-(except for some areas near the magnetic poles, is stored in both systems)
SAARU backup
-If data from the data becomes invalid, the SAARU automatically provides flight critical data to the systems and provides:
- Speed
- Altitude
- Attitude
- The SAARU can’t provide internal navigation functions. The FMC route map will be lost if GOS data is not available
- The SAARU can only provide a temp heading reference
