737 MAX Flight Crew Operations Manual
Flight Management, Navigation -
Navigation Systems Description
MN-FLT-OH-201
11.20.11
IRS initialization on the ground requires AC or DC input power and the IRS mode
selector to move from OFF to ALIGN, or NAV. To avoid loss of IRS alignment
during engine start or electrical power bus transfers, AC and DC input power
circuit breakers should all be closed. If the IRS losses input power, or if the mode
selector is turned to OFF, a full 5-17 minute alignment must be completed again.
If the IRS mode select is turned OFF in flight, full NAV mode cannot be restored
again until the airplane is on the ground.
When the IRS mode selector is turned OFF, the IRS remains operational for
approximately 30 seconds to perform a power down sequence and store position
data. The ALIGN light illuminates until the system is completely shut down
indicating it is acceptable to remove ADIRU AC and DC input power.
Inertial System Display Unit (ISDU)
The ISDU is located on the aft overhead panel and displays data according to the
position of the display selector and system selector. The ISDU also contains a
keyboard for entry of present position and magnetic heading (ATT mode).
Note:
The ISDU displays true heading (not magnetic).
Mode Select Unit (MSU)
The MSU is located on the aft overhead panel and is used to select the operating
mode for each IRS. Indicator lights on the MSU show status of each IRS.
IRS Transfer Switch
Should either IRS fail, the IRS transfer switch is used to switch the connected
systems (Flight Control [autopilot and Autothrottle], Displays, Weather Radar,
and Digital Flight Data Acquisition Unit) to the functioning IRS.
All other airplane systems, not mentioned above, cannot be switched and are not
affected by the IRS transfer switch.
March 1, 2021