Inertial Reference System

Question 1

ADIRS (Air Data Internal Reference System)

Answer 1

• Supplies flight data:
• Speed
• altitude and attitude

Question 2

ADIRS (Air Data Internal Reference System)

Answer 2

• Supplies flight data:
• Speed
• altitude and attitude

Question 3

ADIRU (Air Data Internal Reference Unit)

Answer 3

• There are 2x ADIRU

- Each ADIRU contains Internal reference and Air Data parts

Question 4

IRS supplement

Answer 4

• L/R IRS supply altitude, heading, vertical speed, and other data for the flight instruments
• L/R IRS supply pos, wind and other data to the FMC
• L/R IRS also supply data for the A/T, flight control computers and other systems

Question 5

IRS Pre-flight alignment

Answer 5

• IRSs sense altitude, true north and position
• They use gravity to calculate initial attitude
• The earth’s rotation to calculate true north and position
• Make sure there earth’s rotation is the only movement sensed by the IRS the airplane must not be moving
• 5-10 minutes alignment. 5 minutes at the Equator and 10 minutes at 70 degrees latitude. High latitudes (70 degrees to 78) 17 minutes

Question 6

ADIRU (Air Data Internal Reference Unit)

Answer 6

• There are 2x ADIRU

- Each ADIRU contains Internal reference and Air Data parts

Question 7

IRS (Internal Reference System)

Answer 7

-IRS contains:
-Electronic sensors
-non-mechanical laser gyroscopes
(which measure the airplanes movement on all 3 axis)

Signals form sensors calculate:

• True and magnetic heading
• Acceleration
• Vertical speed
• Ground speed
• Track
• Wind
• Latitude/Longitude
• The 737’s IRSs replace:
• Mechanical gyros
• Internal navigation

Question 8

IRS supplement

Answer 8

• L/R IRS supply altitude, heading, vertical speed, and other data for the flight instruments
• L/R IRS supply pos, wind and other data to the FMC
• L/R IRS also supp

Question 9

IRS Mode Selector Unit (MSU)

Answer 9

• DC lights indicate IRSs are doing DC power test
• Must put airplane’s position during alignment
• The IRS compare sensed position with one put in the FMC and last position IRSs were shut down
• If flash it on align occurs if the IRS sensed position is too far away from CDU pos or from last pos

Question 10

IRSs during flight

Answer 10

• Each IRS calculates its pos
• There are no updates form other sensors
• Although IRSs are very accurate, errors accumulate
• The FMC also uses navigation radio data to calculate and show its pos

Question 11

High altitude IRS ops

Answer 11

-Near magnetic poles, IRSs cannot provide magnetic heading in some areas. The IRSs continue to supply true heading

Question 12

IRS recommendations

Answer 12

-During a turn-around, IRS shutdown and realignment recommended (waits 30 seconds after shutdown)

Question 13

IRS fast realignment

Answer 13

• Not sufficient time for a fill realignment
• No movement
  1. Turn mode selectors to align
  2. Turn mode selectors to nav
  3. Alignment completes in 30 seconds or less

Question 14

ISD/ISDU (Inertial System Display )

Answer 14

• ISDU shows IRS data
• Display selector shows IRS data
• ISDU to PPOS to enter Latitude and Longitude in case needed to enter