737 MAX Flight Crew Operations Manual
Supplementary Procedures -
Adverse Weather
SP.16.18
MN-FLT-OH-201
# Maximum Cooling on the Ground - APU Bleed
During ground operation the following considerations will help keep the
airplane as cool as possible:
• While the airplane is electrically powered, packs should be run or
cooling air supplied to the airplane when the OAT exceeds 40° C
(103° F) to protect the reliability of electrical and electronic
equipment in the airplane.
• If cooling air is available from an outside source, the supply should
be plugged in immediately after engine shutdown and should not be
removed until just prior to engine start.
• Keep all doors and windows, including cargo doors, closed as much
as possible.
• Electronic components which contribute to a high temperature level
in the flight deck should be turned off while not needed.
• Open all passenger cabin gasper outlets and close all window shades
on the sun–exposed side of the passenger cabin.
Note:
If only cooling air from a ground air conditioning cart is supplied
(no pressurized air from the APU or ground external air), then the
TAT probes may not be aspirated. Because of high TAT probe
temperatures, the FMC’s may not accept an assumed temperature
derate. Delay selecting an assumed temperature derate until after
bleed air is available.
If these actions do not reduce cabin temperatures sufficiently:
PASSENGER CABIN temperature
selector ......................................................................... AUTO COOL
PACK switches ......................................................................... HIGH
After engine start with the engines at ground idle, the pneumatic pressure
available to the bleed air system may not be sufficient to provide
adequate cooling during extended ground operations. Use of APU bleed
air instead of engine bleed air to supply the packs while on the ground
can significantly increase cabin cooling. If additional cooling is needed
during extended ground operations:
Engine BLEED 1 air switch ..............................................................OFF
Engine BLEED 2 air switch ..............................................................OFF
ISOLATION VALVE switch ..........................................................OPEN
APU BLEED air switch ..................................................................... ON
March 1, 2021
