737 MAX Flight Crew Operations Manual
Fuel
Chapter 12
System Description
Section 20
MN-FLT-OH-201
12.20.1
20 System Description
System Description
File Highlight
Introduction
The fuel system supplies fuel to the engines and the APU. Fuel is contained in
three tanks located within the wings and wing center section.
Refer to Chapter 7, Engines, APU, for a description of the engine and APU fuel
systems.
Fuel Feed
Both engines are normally pressure fed from the center tank until the center tank
quantity decreases to near zero. The engines are normally then pressure fed from
their respective main tanks. Check valves are located throughout the fuel system
to ensure the proper direction of fuel flow and to prevent transfer of fuel between
tanks.
Nitrogen Generation System (NGS)
The NGS converts bleed air to nitrogen-enriched air (NEA) during all phases of
flight. The NEA is delivered to the center fuel tank to reduce flammability of the
tank. The operation of the NGS is transparent to the flight crew; it does not require
any flight crew action to operate the system, nor are there any flight deck
indications. The NGS automatically starts operating after take-off and runs
continuously through climb, cruise, descent, landing and during taxi for a short
period of time. The NGS shuts down after a specified period of time or when bleed
pressure is no longer available. The NGS also automatically shuts down during the
following non-normal flight conditions:
• Aircraft on the ground and not in test mode
• Either engine is not running in flight
• Fire or smoke detection in the cargo or main deck areas
• Left air conditioning pack overheat
• Center tank refueling valve is open
The fuel tanks are primarily protected by precluding ignition sources; hence
dispatch with the NGS inoperative is acceptable under MEL procedures.
The NGS has an operability indicator located in the main wheel well adjacent to
the APU fire control panel.
March 1, 2021
