Air Data Inertial Reference System

Question 1

ADIRS

Answer 1

Air Data Inertial Reference System

Question 2

ADIRS provide

Answer 2

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

Question 3

ADIRS components

Answer 3

ADM (Air Data Module)
ADIRU (Air Data Internal Reference Unit)
SAARU (Secondary Attitude Air data Reference Unit)

Question 4

ADIRU and SAARU

Answer 4

The AIDRU is the primary flight data source, while the SAARU acts as an automatic backup to the ADIRU

Question 5

SAARU capabilities

Answer 5

-SAARU is the dedicated data source for the standby attitude indicator

Question 6

ADM (Air Data Modules)

Answer 6

• 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

Question 7

ADM + standby indicators

Answer 7

-Two standby modules provide dedicated inputs to the standby airspeed indicator and altimeter

Question 8

ADIRU (Air Data Internal Reference Unit) + SAARU (Secondary Attitude Air Data Reference Unit) calculations

Answer 8

• 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

Question 9

ADIRU (Air Data Internal Reference Unit) + SAARU (Secondary Attitude Air Reference Unit) with AOA

Answer 9

• The ADIRU and SAARU receive data from 2 AOA sensors

- 1 Total Air Temperature probe (TAT) displayed on the eicas display

Question 10

ADIRU composition

Answer 10

• The ADIRU:
• contains electronic sensors
• non-mechanical laser gyroscopes (measures the airplane movement in all 3 axes)

Replaces old tech:

• IRUs
• Mechanical gyros
• INSs

Question 11

ADIRU Sensors and Gyros

Answer 11

Calculate:

• Heading
• Ground track
• Ground Speed
• Airplane’s latitude
• Airplane’s longitude

Question 12

ADIRU calculating alignment

Answer 12

• 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

Question 13

ADIRU errors

Answer 13

• 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

Question 14

ADIRU variation data

Answer 14

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)

Question 15

SAARU backup

Answer 15

-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