If power is lost for ten seconds or more on the ground, all preflight procedures and entries must be done again when power is restored.
If power is lost for more than ten seconds in flight:
.  
LNAV and VNAV disengage

.  
all entered data is retained by the FMC, and when power is restored the
MOD RTE LEGS page is displayed with the advisory message SELECT
ACTIVE WPT/LEG.

Before LNAV can engage, the FMC must be instructed how to return to the route. Select the desired active waypoint and proceed direct or intercept a course to the waypoint.
Copyright . The Boeing Company. See title page for details.
11.32.4   December 6, 2002

Flight Management, Navigation -Flight Management Computer 737 Operations Manual
FMC Failure Single FMC Installation
If the FMC fails, the FMC alert light will illuminate. On CDUs with a MENU page, the MENU page will appear for selection of other available subsystems. On CDUs without a MENU page, the FMC/CDU FAIL light will appear, and both CDUs will display failure modes. “VTK” will appear on both EHSIs. LNAV and VNAV will disengage. After 25 to 30 seconds, both EHSI maps will display failure information.
Dual FMC Installation Failure of Right FMC with FMC Source Select Switch in NORMAL
If the right FMC fails, the FMC ALERT light and the FMC message light will illuminate. The message SINGLE FMC OPERATION will appear in both scratch pads. “VTK” will appear on the right EHSI (in MAP or NAV mode). LNAV and VNAV will disengage if autopilot B is in use (can be reengaged if autopilot A is selected). After 25–30 seconds, the right EHSI map will display failure information. The right EHSI may be restored by placing the FMC source select switch to BOTH ON L.
Note:  If the above indications are observed with no “VTK” on the right EHSI,
there is a disagreement between left and right FMC data. Moving the FMC
source select switch to BOTH ON L should allow the two FMCs to
resynchronize. The switch may then be returned to NORMAL when the
message DUAL FMC OP RESTORED is displayed on both scratch pads.
Failure of Left FMC with FMC Source Select Switch in NORMAL
If the left FMC fails, the FMC ALERT light will illuminate. The FMC/CDU FAIL light will appear on both CDUs, and both CDUs will display failure modes. “VTK” will appear on the left EHSI (in MAP or NAV mode). LNAV and VNAV will disengage but can be reengaged if autopilot B is in use or selected. After 25–30 seconds, the left EHSI map will display failure information. Limited FMC operation may be continued using the right FMC (no changes may be made on the CDU). To restore full operation, the FMC source select switch must be moved to BOTH ON R.
Note:  On airplanes with U10, during an FMC software restart, the navigation display map track may rapidly slew to 0 degrees then to the correct value.
Flight Management, Navigation -Flight Management Computer 737 Operations Manual

Dual FMC Failure
If both FMCs fail, the FMC Alert light will illuminate. On CDUs with a MENU page, the MENU page will appear for selection of other available subsystems. On CDUs without a MENU page, the FMC/CDU FAIL light will appear and both CDUs will display failure modes. “VTK” will appear on both EHSIs. LNAV and VNAV will disengage. After 25–30 seconds, both EHSI maps will display failure information.
Copyright . The Boeing Company. See title page for details.
11.32.6  December 1, 2000

Introduction
Completion of the preflight requires data entry in all minimum required data locations. Completing all required and optional preflight data entries ensures the most accurate performance possible.
Preflight Page Sequence

IDENT
POS INIT
RTE
POS INIT>

ROUTE>

ACTIVATE>

EXEC lIGHT ILLUMINATES
ACT RTE
PERF INIT
PERF/INIT>

TAKEOFF>

TAKEOFF REF

Prior to U10
Flight Management, Navigation -FMC Preflight 737 Operations Manual

U10
The normal preflight sequence follows paging prompts on each CDU page.
The normal FMC power–up page is the IDENT page. Preflight flow continues in
this sequence:

.
Identification (IDENT) page

.
Position Initialization (POS INIT) page

.
Route (RTE) page

.
Departures (DEP/ARR) page (no automatic prompt)

.
Performance Initialization (PERF INIT) page

.
(U10) N1 LIMIT page

.
Takeoff Reference (TAKEOFF REF) page. Some of these pages are also used in flight. The airplane inertial position is required for FMC preflight and flight instrument

operation.
A route must be entered and activated. The minimum route information is origin
　
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