With derated takeoff selected, the thrust setting parameter is considered a
limitation for takeoff; therefore, thrust levers should not be advanced further
except in an emergency. A further thrust increase following an engine failure
could result in a loss of directional control while on the ground. Use the takeoff
speeds supplied by the FMC or specified in Chapter PI, Performance-Inflight, for
the selected derate condition.

Derated takeoff rating can be further reduced by assumed temperature.

YA613, YA626, YA801 - YA809, YC411 - YD655
Use the takeoff speeds provided by the FMC or specified in Chapter PI,
Performance–Inflight, for the selected derate or variable takeoff rating condition.

YA686 - YA722, YC153, YC154, YK101 - YK104
Use the takeoff speeds specified in Chapter PI, Performance–Inflight, for the
selected derate or variable takeoff rating condition.

Assumed Temperature Thrust Reduction Takeoff
A takeoff thrust less than the full rated thrust may be achieved by using an assumed temperature that is higher than the actual temperature. The desired thrust level is obtained through entry of a SEL TEMP value on the N1 LIMIT page or TAKEOFF REF page 2. Use approved sources for selecting the assumed temperature.
The maximum thrust reduction authorized is 25 percent below any certified rating. Do not use assumed temperature reduced thrust if conditions exist that affect braking, such as slush, snow, or ice on the runway, or if potential windshear conditions exist.
If the assumed temperature method is applied to a fixed derate, application of additional power should not exceed the fixed derate N1 limit as loss of directional control could occur while on the ground.
When the assumed temperature method is used with full rate, the reduced thrust setting is not considered a limitation. If conditions are encountered where additional thrust is desired, the crew can manually apply full thrust.
Copyright . The Boeing Company. See title page for details.
Flight Management, Navigation -Flight Management Computer 737 Flight Crew Operations Manual

Derated Thrust Climb
Two fixed climb thrust derates can be selected on the N1 LIMIT page. CLB–1 provides a climb limit reduced by 3% N1 (approximately 10% thrust). CLB–2 provides a climb limit reduced by 6% N1 (approximately 20% thrust). The reduced climb setting gradually increases to full rated climb thrust by 15,000 feet. In cruise, the thrust reference automatically changes to CRZ. The reference can be manually selected on the N1 LIMIT page.
Use of an assumed temperature reduced thrust takeoff or takeoff derate affects the FMCs climb derate computation. If a reduced thrust takeoff has been specified on the TAKEOFF REF page, the FMC will re-compute CLB-1 and CLB-2 values as required to avoid a climb N1 value greater than the reduced thrust takeoff N1 value.
Use of derated climb thrust reduces engine maintenance costs, but increases total trip fuel.
Fuel Monitoring
The FMC receives fuel data from the fuel quantity indicating system. Fuel
quantity values show on the PERF INIT page and on PROGRESS page 1/3. The scratchpad message VERIFY GW AND FUEL shows if total fuel quantity data is invalid. The PERF INIT page FUEL line changes to dashes. The FMC uses the last valid fuel quantity for performance predictions and VNAV operation. The flight crew should manually enter estimated fuel weight. Periodic fuel weight update is required for the remainder of the flight to keep gross weight current. The FMC does not update the manual fuel weight entry. The scratchpad message VERIFY GW AND FUEL shows again each 30 minutes if subsequent entries are not performed. The scratchpad message does not show during descent with Vref selected.
The scratchpad message CHECK FMC FUEL QUANTITY shows if the FMC has detected an unexpected drop in fuel quantity.
The FMC continually estimates the amount of fuel that will remain when the destination airport is reached if the active route is flown. The CDU message USING RSV FUEL is displayed if the estimate is less than the fuel reserve value entered on the PERF INIT page. The CDU message INSUFFICIENT FUEL is displayed if predicted fuel at destination will be 2000 lb. (900 kg) or less.
Copyright . The Boeing Company. See title page for details.
11.32.4  June 1, 2003

Flight Management, Navigation -Flight Management Computer 737 Flight Crew Operations Manual
Loss of FMC Electrical Power
The FMC requires continuous electrical power to operate. When the electrical power is interrupted for less than ten seconds:
.  
LNAV and VNAV disengage

.  
all entered data is retained by the FMC

.  
the FMC resumes normal operation when power is restored.

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.
　
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