SWA B737 - Navigation

Question 1

(Navigation) What does the Inertial Reference System (IRS) compute?

Answer 1

• Airplane Position
• Ground Speed
• Attitude Data

Question 2

(Navigation) How many Inertial Reference Units comprise of the Inertial Reference System (IRS)?

Answer 2

Two - and one Mode Select Unit.

Question 3

(Navigation) What Reference Data do the Inertial Reference Units (IRU’s) provide for the aircraft avionics?

Answer 3

• Pitch and Roll
• Heading
• Acceleration
• Wind Data
• Calculated Data (Flight Path Angle, Roll and Pitch rates, Vertical Speed, and Yaw Data).

Question 4

(Navigation) What is the difference between “NORMAL” and “BOTH ON L” or “BOTH ON R” on the IRS Transfer Switch on the Overhead Panel?

Answer 4

• NORMAL - All the data comes to the Pilot’s displays from the default (same side) IRU.
• “BOTH ON L” or “ BOTH ON R” - All the data comes to the Pilot’s displays from the Left IRU or the Right IRU respectively.

Question 5

(Navigation) What powers the Inertial Reference Units (IRU’s)?

Answer 5

Each IRU has two power sources (one 115 V AC and the other 28 V DC - either is sufficient, but in most cases 28 V DC is a back-up source).

Question 6

Navigation) What normally powers the L IRU?

Answer 6

AC Standby Bus

Question 7

(Navigation) What normally powers the R IRU?

Answer 7

AC Transfer Bus 2

Question 8

(Navigation) If AC power is lost or not normal, what power source will automatically take over for the IRU’s?

Answer 8

Switched Hot Battery Bus

Question 9

(Navigation) What does the ON DC light on the IRS MODE SELECTOR UNIT on the Overhead Panel indicate when illuminated?

Answer 9

The IRS is on Battery Power.

Question 10

(Navigation) What does an illuminated DC FAIL light on the IRS MODE SELECTOR UNIT on the Overhead Panel indicate?

Answer 10

The respective DC Power is not normal.

Question 11

(Navigation) You just turned each IRU to OFF using the switch on the IRS MODE SELECTOR UNIT on the Overhead Panel - the IRU stays powered for approximately 30 seconds, how do you know the system is shutdown?

Answer 11

The ALIGN light will remain illuminated until the system completely shuts down.

Question 12

(Navigation) How is a normal alignment of the IRU’s accomplished?

Answer 12

By rotating the IRS Mode Selector switch from OFF to NAV on the IRS MODE SELECTOR UNIT panel on the Overhead Panel.

Question 13

(Navigation) What indicates that the IRU’s have begun the alignment process?

Answer 13

ON DC light will illuminate for approximately 2 seconds then extinguish and the ALIGN light illuminates.

Question 14

(Navigation) What does a flashing ALIGN light on the IRS MODE SELECTOR UNIT on the Overhead Panel indicate?

Answer 14

• No present position has been entered

* The entered position is unreasonable and does not pass the internal position comparison test.

Question 15

Navigation) How is a fast alignment (on a through flight) of the IRU’s accomplished?

Answer 15

Move the switches on the IRS MODE SELECTOR UNIT on the Overhead Panel to ALIGN, within 30 seconds enter the ICAO Code and Gate Number - when the coordinates are input in the MCDU move the switches back to NAV.

Question 16

(Navigation) What would an illuminated FAULT light and a Flashing ALIGN light on the IRS on the IRS MODE SELECTOR UNIT on the Overhead Panel indicate?

Answer 16

that the aircraft moved during the alignment

Question 17

(Navigation) What is the purpose of the ATT switch position on the IRS MODE SELECTOR UNIT panel on the Overhead Panel?

Answer 17

if IRS alignment is lost when airborne, both present position and ground speed outputs are unreliable. The ATT can re-level the system and provide an attitude reference

Question 18

(Navigation) What would an illuminated FAULT light on the IRS on the IRS MODE SELECTOR UNIT on the Overhead Panel indicate?

Answer 18

that the IRS has detected a system fault