737 MAX Flight Crew Operations Manual
Air Systems -
Bleed Air System Description
2.20.2
MN-FLT-OH-201
Bleed Sensors
Bleed sensors illuminate the respective BLEED light when engine bleed air
temperature or pressure exceeds a predetermined limit. The respective engine
bleed air valve closes automatically. The BLEED light also illuminates with a
failure within the bleed air system, and both BLEED lights illuminate if an
incorrect bleed configuration is present after takeoff or go-around. In case of a
bleed system failure, the light might not be resettable. In the case of a
configuration discrepancy, the lights illuminate 45 seconds after the flaps are up,
and extinguish when either bleed switch is placed ON. Ten minutes after the flaps
are up, the airplane can be configured for landing with both engine bleeds OFF
and the BLEED lights will not illuminate. The timer resets when the flaps are
extended.
Duct Pressure Transmitters
Duct pressure transmitters provide bleed air pressure indications to the respective
(L and R) pointers on the bleed air duct pressure indicator. The indicator is AC
operated. Differences between L and R duct pressure on the bleed air duct pressure
indicator are considered normal as long as there is sufficient air for cabin
pressurization.
Isolation Valve
The isolation valve isolates the left and right sides of the bleed air duct during
normal operations. The isolation valve is AC operated.
With the isolation valve switch in AUTO, both engine bleed air switches ON, and
both air conditioning pack switches AUTO or HIGH, the isolation valve is closed.
The isolation valve opens if either engine bleed air switch or air conditioning pack
switch is positioned OFF. Isolation valve position is not affected by the APU bleed
air switch.
Fan Air Modulating Valve
The Fan Air Modulating Valve (FAMV) is electrically controlled and
pneumatically activated. It is spring loaded to the open position.
Precooler
The precooler is used to cool the hot bleed air from the engine. Cooling airflow
is extracted from the engine fan-air duct and controlled by the FAMV.
External Air Connection
An external air cart/source provides an alternate air source for engine start or air
conditioning.
March 1, 2021
