Fast enough for a refresh. Clear enough to be useful.
Quick Notes are intentionally short. For deep understanding, open the linked technical resource or learning path.
ATA 21 in one line
Pneumatic air is conditioned by packs, distributed and recirculated through the cabin, adjusted for temperature demand, while a separate pressure-control loop regulates outflow.
2 min · Open note →Memory refresher · 737 MAX · ATA 21Pack on is not proof of cooling
Separate command, airflow, heat rejection and delivered-air temperature. A normal switch state proves very little by itself.
2 min · Open note →Quick fact · 737 MAX · ATA 22FCC channel mapping
DFCS BITE Channel A corresponds to FCC-A; Channel B corresponds to FCC-B.
2 min · Open note →Difference note · 737 MAX · ATA 22MCP versus FCC
The MCP selects modes/targets; the FCC computes guidance/control using those selections plus valid sensor/interface data.
2 min · Open note →System snapshot · 737 MAX · ATA 24Electrical evidence chain
Source generation → control/protection acceptance → contact path → bus → local load. A switch position is only one part of that chain.
2 min · Open note →Component note · 737 MAX · ATA 24IDG mental model
Engine mechanical energy drives an integrated generator; control/protection determines whether its electrical output can feed the aircraft network.
2 min · Open note →System snapshot · 737 MAX · ATA 28Fuel feed in one line
Tank fuel + boost pressure + an open manifold/valve path = usable feed. Keep source pressure and routing logic separate.
2 min · Open note →Component note · 737 MAX · ATA 28Crossfeed reminder
Crossfeed connects feed manifolds; it does not generate pressure.
2 min · Open note →Memory refresher · 737 MAX · ATA 29A/B pump pairing
System A is paired with ENG 1 EDP and ELEC 2 EMDP; System B with ENG 2 EDP and ELEC 1 EMDP.
2 min · Open note →Memory refresher · 737 MAX · ATA 29Five questions before chasing a hydraulic component
A short reasoning checklist for separating source, hydraulic, indication and consumer evidence.
2 min · Open note →Safety boundary · 737 MAX · ATA 29Hydraulic power means movement hazard
Supplying hydraulic pressure can move major aircraft surfaces and mechanisms quickly.
2 min · Open note →Safety boundary · 737 MAX · ATA 29Power removed ≠ zero hydraulic energy
Stopping the hydraulic pressure source is not automatically the same as depressurizing every part of the system.
2 min · Open note →Quick fact · 737 MAX · ATA 29Pressure is not flow
A system can establish pressure yet still lack useful flow under demand if leakage or another abnormal demand consumes capacity.
2 min · Open note →System snapshot · 737 MAX · ATA 29PTU — system snapshot
The PTU transfers hydraulic energy through a motor-pump mechanical coupling rather than mixing the two hydraulic fluids.
2 min · Open note →System snapshot · 737 MAX · ATA 29Standby hydraulics — system snapshot
The standby circuit has its own electric pressure source and pressure-module hardware for selected backup-function context.
2 min · Open note →System snapshot · 737 MAX · ATA 31MDS core chain
Aircraft data/interfaces → DPC processing/software → display buses → four display units → selected presentation.
2 min · Open note →Difference note · 737 MAX · ATA 31REAL vs snapshot
REAL shows current system data; MANUAL/AUTO can preserve captured events for later analysis.
2 min · Open note →System snapshot · 737 MAX · ATA 34ADIRS mental model
Air-data sensors/modules + inertial sensors/processing → ADIRUs → shared navigation/air-data outputs for many consumers.
2 min · Open note →Memory refresher · 737 MAX · ATA 34Alignment purpose
Alignment establishes a valid inertial reference. Position quality, aircraft movement and geographic latitude affect the setup environment.
2 min · Open note →System snapshot · 737 MAX · ATA 36Pneumatic source choices
Engine bleed, APU bleed or external ground air can supply the pneumatic distribution system under appropriate conditions.
2 min · Open note →Memory refresher · 737 MAX · ATA 36Pneumatic users
Think packs, engine/wing anti-ice, engine start, hydraulic-reservoir pressurization and water-tank pressurization.
2 min · Open note →System snapshot · 737 MAX · ATA 47NGS purpose
The NGS reduces center-tank flammability by producing nitrogen-enriched air onboard and routing it to the tank environment.
2 min · Open note →Component note · 737 MAX · ATA 47ASM reminder
The air separation module needs controlled, clean inlet air. Contamination can damage its fibers and shorten life.
2 min · Open note →Sequence note · 737 MAX · ATA 21Temperature complaint: first split
Classify the complaint as source airflow, pack cooling, distribution/recirculation, local trim control or sensing before chasing a component.
2 min · Open note →System snapshot · 737 MAX · ATA 21Pressurization mental model
Air enters the pressure vessel; controlled outflow regulates cabin pressure. Think sensing → controller → outflow valve → pressure response.
2 min · Open note →Component note · 737 MAX · ATA 21Equipment cooling evidence
A running fan is not the same as proven cooling airflow. Add flow sensing, restrictions and temperature response to the evidence.
2 min · Open note →Difference note · 737 MAX · ATA 21ATA 21 ↔ ATA 36
ATA 36 supplies pneumatic energy; ATA 21 conditions and manages environmental air. Weak upstream supply can mimic an ATA 21 problem.
2 min · Open note →Difference note · 737 MAX · ATA 22Flight director versus autopilot
Flight director provides guidance cues; autopilot adds automatic control authority when engaged and permitted.
2 min · Open note →Memory refresher · 737 MAX · ATA 22Autothrottle BITE
Autothrottle maintenance BITE is accessed through the FMC CDU in the source set; BITE results still lead to approved fault isolation.
2 min · Open note →Sequence note · 737 MAX · ATA 22Mode complaint checklist
Selection accepted? mode armed/active? FCC channel healthy? inputs valid? control authority available? indication consistent?
2 min · Open note →Safety boundary · 737 MAX · ATA 22BITE suspect LRU
A BITE suspect LRU is evidence, not permission to replace hardware. Use the corresponding approved IFIM/FIM procedure.
2 min · Open note →Acronym · 737 MAX · ATA 24TRU reminder
TRU = transformer rectifier unit. Think AC in → DC out → DC bus, so some DC problems can begin upstream on the AC side.
2 min · Open note →Difference note · 737 MAX · ATA 24Battery versus generator
A generator continuously converts mechanical input to electrical power; a battery stores energy and can support selected loads when commanded/connected.
2 min · Open note →Memory refresher · 737 MAX · ATA 24External power clue
External power physically connected does not prove the aircraft buses accepted it. Separate source presence from source acceptance and bus connection.
2 min · Open note →Memory refresher · 737 MAX · ATA 24Standby-power question
Ask which selected loads should retain power, what source feeds them, and whether conversion is required. Do not assume “standby” means the whole aircraft stays powered.
2 min · Open note →Memory refresher · 737 MAX · ATA 28Center tank clue
Center-tank operation includes dedicated boost pumps, supervision/auto-shutoff logic and a scavenge relationship for residual fuel.
2 min · Open note →Difference note · 737 MAX · ATA 28Quantity is evidence, not fuel flow
A fuel-quantity indication reports sensed/processed tank quantity. It does not by itself prove a pump is delivering fuel to a consumer.
2 min · Open note →Safety boundary · 737 MAX · ATA 28Fuel safety boundary
Bonding, ignition prevention, tank entry and CDCCL/ALI-related work are controlled maintenance topics. Use current approved data exactly.
2 min · Open note →System snapshot · 737 MAX · ATA 28ATA 28 ↔ ATA 47
ATA 28 handles fuel storage/feed/servicing; ATA 47 supplies nitrogen-enriched air to reduce center-tank flammability.
2 min · Open note →Difference note · 737 MAX · ATA 29EDP vs EMDP in one minute
Separate the hydraulic source by its energy origin: engine mechanical drive versus electric motor drive.
2 min · Open note →Acronym · 737 MAX · ATA 29EMDP / ACMP terminology
ATA 29 uses EMDP; some Boeing documents may call the electric hydraulic pump an ACMP.
2 min · Open note →Sequence note · 737 MAX · ATA 29Hydraulic indication chain
A displayed hydraulic condition sits downstream of both the physical hydraulic state and the sensing/electrical path.
2 min · Open note →Memory refresher · 737 MAX · ATA 29Internal leakage — quick refresher
Internal leakage can consume hydraulic flow without creating an obvious external fluid leak.
2 min · Open note →Quick fact · 737 MAX · ATA 29Main-system pressure — orientation only
ATA 29 maintenance checks commonly operate with main-system pressure in the high-2000 to low-3000 psi region; exact task limits remain approved-data items.
2 min · Open note →Memory refresher · 737 MAX · ATA 31MAINT light mindset
A MAINT light can represent one or more unconfirmed status messages. Identify the underlying messages before reasoning about cause.
2 min · Open note →Difference note · 737 MAX · ATA 31NORMAL/FAULT/CONFIG
NORMAL = no fault in that tested area now; FAULT = detected functional issue; CONFIG can indicate a software/configuration mismatch.
2 min · Open note →Sequence note · 737 MAX · ATA 31Display problem split
Is the source data wrong everywhere, or only one display/presentation? That split helps separate source-system faults from display/selection faults.
2 min · Open note →Quick fact · 737 MAX · ATA 31MDS cross-ATA role
MAX maintenance data pages can expose data from several ATA systems, making ATA 31 a useful evidence interface rather than the source of every fault shown.
2 min · Open note →Quick fact · 737 MAX · ATA 34GPS hybrid role
The supplied MAX source supports GPS-assisted automatic ADIRS alignment using GPS position from the multi-mode receiver.
2 min · Open note →Component note · 737 MAX · ATA 34Radio-altitude clue
Radio altitude is an ATA 34 source used by several downstream functions; one sensor problem can create messages in other systems.
2 min · Open note →Memory refresher · 737 MAX · ATA 34TCAS dependencies
TCAS operation/testing depends on air-data, ATC, display and radio-altimeter functions—good evidence that avionics faults cross ATA boundaries.
2 min · Open note →Sequence note · 737 MAX · ATA 34Navigation troubleshooting split
Identify the bad data item → producer/source → processing path → consumers → compare independent sources → use approved fault isolation.
2 min · Open note →Component note · 737 MAX · ATA 36PRSOV mental model
Pressure regulating and shutoff valve: one component can participate in normal regulation and in isolation/protection.
2 min · Open note →Component note · 737 MAX · ATA 36Isolation valve clue
Isolation-valve state changes left/right manifold connectivity. Never interpret source pressure without considering the manifold configuration.
2 min · Open note →Difference note · 737 MAX · ATA 36Duct pressure is not a diagnosis
A duct-pressure indication describes manifold condition; it does not by itself identify which upstream source/valve/sense path is at fault.
2 min · Open note →Safety boundary · 737 MAX · ATA 36Hot-air safety boundary
Pneumatic ducts can retain hot, high-pressure air. Switches OFF are not proof of a zero-energy state; approved depressurization/isolation data controls maintenance.
2 min · Open note →Difference note · 737 MAX · ATA 47NEA versus OEA
The separation process produces nitrogen-enriched air and oxygen-enriched air. The NEA stream supports the tank-inerting function.
2 min · Open note →Component note · 737 MAX · ATA 47NEADS integrity
NEADS includes protected distribution features such as check valves and flame arresting. Leaks or backflow are system/safety concerns.
2 min · Open note →Safety boundary · 737 MAX · ATA 47Low-oxygen hazard
Nitrogen-enriched air can create an oxygen-deficient atmosphere. Treat personnel exposure as a real hazard, not just a performance issue.
2 min · Open note →Memory refresher · 737 MAX · ATA 47BITE is evidence
Existing faults, fault history and ground tests help organize evidence; approved fault isolation still controls the actual maintenance path.
2 min · Open note →