737 MAX Flight Crew Operations Manual
Flight Management, Navigation -
Flight Management Computer
MN-FLT-OH-201
11.32.5
To indicate the source of fuel being used for FMC calculations the PERF INIT
page includes the following suffix labels:
• CALC (Calculated): The FMC will generate a CALCULATED fuel
value using input data from the FQIS, engine Fuel Flow data from the
EECs, and fuel flow data from the APU. The 2L data field will display
CALC if the fuel weight is sourced from the FMC Calculated value.
• MAN (Manual): Manual entry of fuel is allowed when the FMC CALC
fuel is the source and engines are running (or when dashes or box
prompts are displayed in 2L). Prior to engine start, the calculated value
is set to agree with and track the FQIS value if it is valid or to prompt
for a manual fuel entry if it is not (box prompts will be displayed in 2L).
• SENS (Sensed): If TOTALIZER is the selected system fuel value then
SENS is displayed in the PERF INIT 2L data field.
• PLAN: Fuel entries are also permitted before engine start if the PLAN
fuel FMC option is activated. PLAN fuel entries facilitate pre-flight
calculations of takeoff speeds and trip fuel predictions based on
anticipated takeoff fuel load and GW. PLAN fuel entries are deleted at
engine start and are replaced by totalizer fuel quantity if valid or else by
a manual fuel entry.
When the FMC receives a positive fuel flow signal at engine start, the calculated
value is disconnected from the FQIS and decreases at the fuel flow rate as received
from the Electronic Engine Controllers. This fuel quantity value is displayed on
the PROGRESS 5/5 page as CALCULATED (6R).
Following engine shutdown, FUEL QTY values remain displayed, but are reset to
ZERO when the FMC receives a positive fuel flow at the next engine start.
Pilot entry of a fuel quantity value is permitted on the PERF INIT 2L data field
after engine start when CALCULATED fuel is selected as the active system fuel
and results in the entered value being displayed with MAN to show the source.
The manual value is then updated by the FMC using fuel flow.
If fuel flow data becomes invalid after engine start, the calculated value will be
considered invalid and the FQIS quantity will be used by the FMC for
performance computations. In this case, fuel quantity will be displayed as SENS
on the PERF INIT page and the TOTALIZER value on PROGRESS 5/5 page will
be <ACT>.
After engine start, the FMC snap shots the total fuel load on board as provided by
the FQIS and calculates a fuel value using fuel flow inputs from the EECs.
The Engine Display advisory message FUEL DISAGREE is displayed if the FMC
determines a difference (exceeds the MEDB specified value for more than 5
continuous minutes) between the total sensed fuel quantity and calculated fuel
quantity values.
March 1, 2021