737 MAX Flight Crew Operations Manual
Flight Management, Navigation -
Navigation Systems Description
MN-FLT-OH-201
11.20.5
Normal alignment between 78 degrees 15 minutes North or South is initiated by
rotating the MSU switch from OFF to NAV. The IRS performs a short power-up
test, during which the ON DC light illuminates. When the ON DC light
extinguishes and the ALIGN light illuminates, the alignment process begins. With
hybrid GPS-inertial reference, present position is entered automatically using
GPS position. Alignment time varies from five minutes to seventeen minutes
depending on airplane latitude.
The automatically entered present position can be seen auto-populated on the
ISDU PPOS display screen and at the 1R position of the CDU POS INIT page.
The POS INIT page displays prompt boxes in the SET IRS POS line to allow the
option of manually entering present position if needed. When the IRS completes
its alignment and enters NAV mode, the prompt boxes will clear from the CDU
POS INIT page.
When a GPS present position is available, but the flight crew chooses to manually
enter a present position or the flight crew mistakenly starts entering a present
position through the CDU or ISDU before alignment is complete, the
automatically entered present position will be overridden by the manually entered
position from the flight crew. The flight crew then has the option to complete the
IRS alignment using the manually entered present position IRS alignment
procedure or re-initiating the automatically entered present position alignment.
Re-initiating the automatically entered present position alignment is
accomplished by rotating the MSU switch from NAV to OFF, wait 30 seconds, and
rotating the MSU switch from OFF to NAV to re-initiate the full alignment. No
additional flight crew's inputs are required.
During transit or through-flight stops with brief ground times, a thirty second fast
realignment and zeroing of ground speed error may be performed by selecting
ALIGN while the airplane is parked. To exit fast alignment and return to Nav
mode, present position input is required. In an ADIRU with hybrid GPS-inertial
enabled, GPS position can be used as an automatic source of position entry but
pilot position entries are optional and have priority over the GPS position source.
March 1, 2021
