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Boeing 737-800 NG · Interactive FCOM

Full manual

Organised like the official Flight Crew Operating Manual with maintenance by ATA chapter. Search across every section.

Unverified — check your manualText on this page is written from general knowledge. Figures marked ✓ are checked against official FAA/EASA data.See verified data

General

Engines	CFM56-7B (NG) / LEAP-1B (MAX)
MTOW	79,016 kg (-800)
Typical seats	162–189
Range	~2,935 nm
MMO	M 0.82
Ceiling	41,000 ft

Model applicability

737-800 NG — 1998 – 2020 · S/N By line number / tab — see FCOM preface
737 MAX 8 — 2017 – present · S/N By line number

Limitations

Speeds

VMO / MMO✓ FAA	340 kt / M 0.82
Gear extended / extension	320 kt / M 0.82 · 270 kt / M 0.82
Gear retraction	235 kt
Max demonstrated crosswind (guidance)	33 kt

Flight envelope

Max operating altitude✓ FAA	41,000 ft
Load factor flaps up	+2.5 / −1 g
Load factor flaps down	+2 / 0 g

Engine (CFM56-7B)

EGT takeoff limit	950 °C
EGT start limit	725 °C
Starter cutout	56% N2

Abnormal & Emergency Procedures

Engine Fire / Severe Damage / Separation

Autothrottle (if engaged)	DISENGAGE
Thrust lever (affected)	CLOSE
Engine start lever (affected)	CUTOFF
Engine fire switch (affected)	PULL
Engine fire switch	ROTATE to stop & hold 1 s
If after 30 s still illuminated	ROTATE to other stop & hold 1 s

QRH memory items. Source: 737 QRH Section 8.

Rejected Takeoff

Thrust levers	CLOSE
Autothrottle	DISENGAGE
Brakes	MAXIMUM MANUAL (or verify RTO autobrake)
Speed brakes	UP
Reverse thrust	MAX consistent with conditions
ATC	NOTIFY

Runaway Stabilizer

Control column	HOLD FIRMLY
Autopilot (if engaged)	DISENGAGE
Autothrottle (if engaged)	DISENGAGE
If runaway continues: STAB TRIM CUTOUT switches	CUTOUT (both)
If runaway continues: Stabilizer trim wheel	GRASP & HOLD

Cabin Altitude Warning / Rapid Depressurization

Oxygen masks & regulators	ON, 100%
Crew communications	ESTABLISH
Pressurization mode selector	MAN
Outflow valve switch	CLOSE
If cabin alt uncontrollable: Pax oxygen switch	ON
Emergency descent	INITIATE

Normal Procedures

Expanded, step-by-step versions with explanations: open the interactive procedures →

APU Start (amplified)

1. Battery switch — ON (guard closed)
Powers APU start circuitry.
2. Left aft fuel pump (if AC available) — ON
Provides positive fuel pressure to the APU, reducing wear on its fuel control.
3. APU switch — START (hold, release to ON)
Spring-loaded START position initiates the sequence.
4. APU GEN OFF BUS light — ILLUMINATED (blue)
APU is running and ready to power the busses.
5. APU GEN switches — ON BUS
Transfers both busses to APU power.
6. APU BLEED — ON
Supplies air for packs and engine start.

Engine Start (amplified)

1. ANTI-COLLISION light — ON
Mandatory before start.
2. PACK switches — OFF
Maximises duct pressure available for the starter.
3. Duct pressure — CHECK (~30 psi min, adjusted for altitude)
Insufficient pressure → slow/hung start.
4. ENGINE START switch 2 — GRD
Opens start valve; air turbine starter spins N2.
5. N2 rotation & oil pressure — VERIFY
Oil pressure must rise; N1 rotation by 40% N2.
6. Engine start lever 2 — IDLE at 25% N2 (or max motoring, min 20%)
Introduces fuel and ignition at the right rotor speed.
7. Fuel flow, EGT — MONITOR
EGT rises as light-off occurs; watch for hot start.
8. ENGINE START switch — Moves to OFF at 56% N2
Starter cutout — if it doesn't, move it OFF manually.
9. Engine stabilised at idle — CHECK
Then repeat for engine 1.

Shutdown (amplified)

1. Parking brake — SET
Before cutting the engines.
2. Electrical power — APU / EXT PWR ON BUS
Ensures uninterrupted power.
3. Engine start levers — CUTOFF
Shuts off fuel and ignition.
4. ANTI-COLLISION light — OFF
Engines spooled down.
5. FUEL PUMPS — OFF
No longer needed.
6. HYD pumps — OFF / as required
Electric pumps off unless ground crew need pressure.

Takeoff (amplified)

1. Thrust levers — ADVANCE to approx. 40% N1, stabilise
Symmetrical spool-up.
2. TO/GA switch — PRESS
Autothrottle sets takeoff N1.
3. FMA — N1 / TO/GA — VERIFY
Correct modes.
4. Engine instruments — MONITOR
Callouts if exceedance.
5. Callouts — 80 kt (THR HLD), V1, ROTATE
Crew cross-check.
6. Rotate — Approx. 2–3°/s to 15°
Avoid tail strike.
7. Positive rate — GEAR UP
Drag.
8. Autopilot — ENGAGE above 400 ft
Workload.
9. Flaps — RETRACT on schedule
Speed bugs.

ILS Approach & Landing (amplified)

1. APP mode — ARM — VOR/LOC and G/S
Captures the ILS.
2. Flaps — 1 → 5 → 15 → GEAR DOWN → 30
Configure at manoeuvre speeds.
3. Speed brake — ARMED
Automatic ground spoilers.
4. Autobrake — SET (1/2/3/MAX)
Deceleration rate.
5. Stabilised — BY 1,000 ft
Go-around otherwise.
6. Autopilot — DISENGAGE by minimums (manual landing)
Hand fly the flare.
7. Flare and idle — THRUST LEVERS CLOSE
Touchdown.
8. Reverse thrust — AS REQUIRED, idle by 60 kt
Avoid FOD ingestion and compressor stalls.

Rejected Takeoff (amplified)

1. Thrust levers — CLOSE
Disconnects autothrottle.
2. Autothrottle — DISENGAGE
Prevents re-advance.
3. Braking — VERIFY RTO autobrake / MAX manual
Max deceleration.
4. Speed brakes — VERIFY UP
Weight onto wheels.
5. Reverse thrust — MAX as needed
Additional stopping force.
6. Notify — ATC and cabin
Fire services.
7. Parking brake / evacuation — AS REQUIRED
Hot brakes — consider evacuation checklist.

Engine Failure after V1 (amplified)

1. Rotate — VR, approx. 12–13°
V2 to V2+20.
2. Rudder — STEP ON THE GOOD ENGINE
Control yaw; centre control wheel.
3. Positive rate — GEAR UP
Drag.
4. Engine-out altitude — LEVEL / accelerate
Clean up.
5. Thrust — MCT
Single-engine climb.
6. Non-normal checklist — COMPLETE
Identify and secure engine.

Preliminary Cockpit Preparation (amplified)

1. Battery — ON, guard closed
Powers the hot battery bus.
2. Standby power — AUTO
Automatic transfer to battery.
3. APU — START
Electrical and bleed power.
4. IRS mode selectors — NAV
Alignment approx. 10 min.
5. FMC — POS INIT, ROUTE, PERF INIT
Flight plan entry.
6. MCP — SET course, speed, heading, altitude
Clearance.
7. Hydraulic pumps — ELEC ON (check ground crew clear)
Pressurise for control checks.

FMC Preflight & Route Entry (amplified)

1. IDENT page — CHECK model, engine & nav data
Current database.
2. POS INIT — ENTER gate / GPS position into SET IRS POS
Aligns IRS.
3. RTE page 1 — ORIGIN, DEST, RUNWAY, FLT NO
Route basics.
4. RTE page 2 — VIA (airway) / TO (fix) entries
Builds the route.
5. DEP/ARR — SELECT SID and runway; STAR later
Departure procedure.
6. ACTIVATE → EXEC — PRESS
The route becomes active only after EXEC.
7. LEGS page — CHECK vs flight plan; clear discontinuities
Both pilots cross-check.
8. PERF INIT — ZFW, fuel, reserves, CI, CRZ ALT
Weight and performance.
9. TAKEOFF REF — Flaps, V1/VR/V2, derate / assumed temp
Takeoff speeds set on the speed tape.

Autopilot & Autothrottle (MCP) (amplified)

1. Flight directors — ON (PF side first)
Guidance for takeoff.
2. A/T ARM — ARM
Autothrottle ready for N1 on takeoff.
3. LNAV / VNAV — ARM / SELECT after takeoff (LNAV above 50 ft, VNAV above 400 ft typical)
Follow FMC route and profile.
4. CMD A — PUSH (above 400 ft)
Engages autopilot A; check CMD on FMA.
5. ALTITUDE window — SET cleared level
Autopilot won't climb or descend through it.
6. LVL CHG / V/S — Use for tactical changes
LVL CHG: speed on elevator, thrust fixed; V/S: set rate.
7. HDG SEL — For ATC vectors
Leaves LNAV.
8. VOR LOC / APP — ARM for ILS; CMD B for dual autoland
Captures localiser and glideslope.
9. AP disconnect — Switch on control wheel
Press twice to silence the warning.

Go-Around & Missed Approach (amplified)

1. TO/GA switch — PUSH
A/T advances to GA thrust, FD commands go-around pitch.
2. Rotate — Approx. 15° nose up
Follow the flight director.
3. Flaps — 15
Go-around flap setting.
4. Positive rate — Gear UP
Reduces drag.
5. Above 400 ft — Select roll mode (LNAV/HDG)
Follow the missed approach.
6. At acceleration height — Select LVL CHG / retract flaps on schedule
Clean up while climbing.

Engine Fire / Severe Damage (amplified)

1. Autothrottle — DISENGAGE
Memory item.
2. Thrust lever (affected) — CLOSE — confirm
Both pilots confirm the engine.
3. Start lever (affected) — CUTOFF — confirm
Shuts fuel at the engine.
4. Engine fire switch — PULL — confirm
Closes fuel, hydraulics, bleed, generator trips.
5. Engine fire switch — ROTATE to stop, hold 1 s
Discharges a bottle.
6. If after 30 s still on — ROTATE to other stop
Second bottle.

Cruise Monitoring (amplified)

1. PROGRESS page — CHECK fuel at destination
Compare with plan each waypoint.
2. Fuel quantity — CHECK balance
Imbalance > 1,000 lb (typical) needs crossfeed.
3. Center tank pumps — OFF when center tank empty
Prevents pumps running dry.
4. Step climb — Evaluate on VNAV CRZ page
Saves fuel as weight drops.
5. Weather radar — SET tilt / range
Avoid thunderstorms.

After Landing & Parking (amplified)

1. Speedbrake — DOWN
Clear of the runway.
2. Flaps — UP
Prevent damage from debris.
3. APU — START (as required)
Power before engine shutdown.
4. Parking brake — SET
Hold at the gate.
5. Start levers — CUTOFF
Engines shut down.
6. Anti-collision light — OFF
Ground crew may approach.
7. Fuel pumps — OFF
Not needed.

Exterior Inspection — Nose Area

Probes, sensors, ports	CLEAR, NO DAMAGE
Nose gear steering lockout pin	INSTALL / AS REQUIRED
Nose tires, strut, doors	CHECK
Radome & windows	CONDITION

Wings & Engines

Engine inlet, fan, cowl	CONDITION
Exhaust & reverser	STOWED
Leading edges / Kruegers / slats	CONDITION
Wingtip, winglet, lights	CONDITION
Trailing edge flaps & spoilers	CONDITION
Main gear, brakes, wheel wells	CHECK
Fuel measuring sticks	FLUSH & SECURE

Tail Area

Stabilizer, elevator, rudder	CONDITION
APU inlet / exhaust	CLEAR
Tail skid	CONDITION
Outflow valve	CHECK

Flight Deck Preflight

Battery switch	ON, guard closed
IRS mode selectors	NAV
Fuel & hydraulic panels	CHECK
Oxygen	TEST
FMC (POS, ROUTE, PERF)	COMPLETE
MCP	SET

Before Start

Flight deck door	CLOSED & LOCKED
Fuel	___ KGS, PUMPS ON
Passenger signs	SET
Windows	LOCKED
MCP	V2 ___, HDG ___, ALT ___
Takeoff speeds	V1, VR, V2
CDU preflight	COMPLETED
Rudder & aileron trim	FREE & 0
Taxi & takeoff briefing	COMPLETED
Anti-collision light	ON

Takeoff

Thrust levers	ADVANCE to ~40% N1, stabilize
TO/GA	PUSH
80 kt	CHECK
V1	CALL
VR	ROTATE
Positive rate	GEAR UP
Flaps	RETRACT on schedule

Landing

Engine start switches	CONT
Speed brake	ARMED
Landing gear	DOWN
Flaps	___, GREEN LIGHT

Performance

Airline performance is computed with the operator's approved performance software (e.g. Airbus FlySmart / Boeing OPT) — not tabulated here.

Airplane & Systems Description

Flight Deck ATA 22, 23, 31, 34, 35

Six-screen Common Display System with conventional control columns and the dual-FMC flight management system.

Control columns and wheels move cables to hydraulic power control units (PCUs) — no fly-by-wire on the NG; manual reversion if hydraulics are lost.
Autopilot Flight Director System (AFDS) with two FCCs; Mode Control Panel (MCP) on the glareshield.
Two Air Data Inertial Reference Units (ADIRUs) provide attitude and air data.
Master Caution with system annunciator 'six-pack' panels; failures are handled with the paper/electronic QRH.

CFM56-7B Turbofans ATA 26, 36, 71, 72, 73, 74, 78, 79

CFM56-7 with fan cowl open — note the flattened lower nacelle · *illustrative image*

Two high-bypass turbofans with EEC (Electronic Engine Control) and the distinctive flat-bottomed nacelles.

The EEC sets N1 based on thrust lever position; normal and alternate modes.
Engine-driven hydraulic pumps: ENG 1 → System A, ENG 2 → System B (plus electric pumps on the opposite system).
Integrated Drive Generators provide 90 kVA AC per engine.
Flattened 'hamster pouch' nacelle bottom gives ground clearance for the large fan on the low-slung 737.
Fire detection by dual loops; two shared extinguisher bottles can discharge to either engine.

Wings & Flight Controls ATA 27, 28, 30, 57

Wing with winglet, spoilers, flaps and leading-edge devices · *illustrative image*

Swept wing with leading edge slats and Krueger flaps, triple-slotted trailing edge flaps, spoilers, and winglets.

Ailerons are powered by Systems A and B; aileron movement is assisted by flight spoilers.
Flap lever settings: 1, 2, 5, 10, 15, 25, 30, 40. Trailing edge flaps driven hydraulically by System B (electric alternate).
Leading edge devices: Krueger flaps inboard, slats outboard; Autoslat function extends slats near stall.
Fuel in two main wing tanks and a center tank.

Landing Gear ATA 29, 32

Main gear and open wheel well (no main gear doors on the 737) · *illustrative image*

Retractable tricycle gear powered by System A hydraulics; main gear retracts into wheel wells without doors.

Gear lever UP/OFF/DN; manual extension via three handles that release uplocks so gear free-falls.
Main gear wheels are exposed in flight — fairings seal around the tires instead of doors.
Brakes: normal System B, alternate System A, with accumulator for parking brake.
Autobrake RTO, 1, 2, 3, MAX; anti-skid on each wheel.

Fuselage, Air & Electrical ATA 21, 24, 25, 52, 53

Narrow fuselage (same cross-section as the 707/727) with two packs and a digital pressurization controller.

Bleed air drives two air conditioning packs; recirculation fans mix cabin air.
Pressurization: AUTO, ALTN and MAN modes controlling one outflow valve; max differential 9.1 psi.
Electrical: two IDGs and APU generator; transfer buses with bus tie; 28 V DC from TRUs; standby power from main battery.
Forward and aft cargo holds with smoke detection and fire suppression.

Empennage & APU ATA 49, 55

Tail with APU exhaust, rudder and stabilizer · *illustrative image*

Stabilizer trim with electric and manual (trim wheels) operation, elevators, rudder, and APU in the tail.

Stabilizer trim: main electric (yoke switches), autopilot trim, and manual trim wheels; STAB TRIM CUTOUT switches disconnect electric trim.
Elevators powered by Systems A & B with manual reversion through tabs.
Rudder powered by A & B plus a standby rudder PCU.
APU (Honeywell 131-9B) provides bleed and electrical power.

Annunciators & Fault Messages

Open the interactive fault finder →

LOW OIL PRESSURE	Oil pressure at or below the red line.
HYD PUMP LOW PRESSURE (A)	Output pressure of a system A pump low.
BLEED TRIP OFF	Engine bleed overheat or overpressure — bleed valve closed automatically.
AUTO FAIL (pressurization)	Automatic pressurization controller failure.
TRANSFER BUS OFF	A transfer bus has lost power.
STAB OUT OF TRIM	Autopilot is not trimming the stabilizer properly.
ENGINE FIRE / SEVERE DAMAGE / SEPARATION	Fire bell, master FIRE WARN lights, engine fire handle illuminated.
RUNAWAY STABILIZER	Uncommanded continuous stabiliser trim movement.
CABIN ALTITUDE WARNING / RAPID DEPRESSURIZATION	Intermittent horn and CABIN ALTITUDE light — cabin altitude above about 10,000 ft.
LOSS OF THRUST ON BOTH ENGINES	Both engines flamed out or failed.
AIRSPEED UNRELIABLE	IAS DISAGREE / ALT DISAGREE or incorrect indications.
ENG OVERHEAT	Overheat detected in the engine nacelle — lower temperature than fire.
FUEL LOW / IMBAL	Main tank fuel below about 453 kg, or imbalance more than about 453 kg between mains.
GEAR DISAGREE	Gear position disagrees with lever position.
Tail strike on takeoff / landing	Aft fuselage contacted the runway. The -800 and -900 have a tail skid; possible pressure-hull damage.
Dual BLEED TRIP OFF	Both engine bleeds tripped: no supply to the packs, cabin will depressurise.
PACK (L/R) trip off	Pack overheat — the pack valve closes.
Trailing edge flap asymmetry / disagree	Flap position needles split, or flaps stop. Hydraulic drive shuts off to protect the aircraft.
STANDBY PWR OFF	One or more standby buses unpowered. Standby instruments and essential radios at risk.
GPWS 'TERRAIN — PULL UP'	Enhanced GPWS predicts terrain conflict. Escape manoeuvre immediately.

Systems In Depth (engine, gear, controls…)

Deep dive · ATA 21

Air Conditioning & Pressurisation — in depth

Packs & zones

Two packs (air cycle machines) in the wheel well area. Each pack takes bleed air via the pack valve; outlet air goes to the mix manifold, with recirculation fans. NG has three temperature zones (flight deck, forward and aft cabin) with trim air.

PACK switch AUTO/HIGH: in AUTO, high flow only when one pack operates in flight with flaps up.

Pressurisation

Two automatic controllers (AUTO and ALTN) and a MAN mode drive the outflow valve (aft fuselage, lower right) plus an overboard exhaust valve. The pilot sets FLT ALT and LAND ALT on the pressurisation panel before takeoff.

Safety relief valves limit differential to about 8.65 psi; negative relief prevents inward pressure.

Max differential	8.35 psi normal, 8.65 relief
Cabin altitude at FL410	approx. 8 000 ft
CABIN ALTITUDE warning	10 000 ft (intermittent horn)
Masks deploy automatically	approx. 14 000 ft cabin

Lessons — Helios 522

The pressurisation mode selector was left in MAN after maintenance; the outflow valve stayed open. The cabin altitude warning horn was misidentified as a takeoff configuration warning. Lesson: always check the pressurisation panel on the before-start checklist and react to the cabin altitude warning with oxygen masks first.

Warning · Intermittent warning horn in climb = cabin altitude. Masks on, establish communication, descend.

Deep dive · ATA 22

Auto Flight — AFDS, A/T and FMC in depth

Components

Two flight control computers (FCC A, B) driving the autopilot servos (CMD A / CMD B), the Mode Control Panel (MCP), the autothrottle computer, and two FMCs with CDUs. On the MAX the FCC also hosts MCAS logic.

Roll modes	LNAV, HDG SEL, VOR/LOC, APP
Pitch modes	VNAV, LVL CHG, V/S, ALT HOLD, G/S, TO/GA
A/T modes	N1, MCP SPD, FMC SPD, RETARD, ARM, THR HLD
Autoland	Dual channel (CMD A + B) — FLARE, ROLLOUT

Disconnect logic

Autopilot disconnects with the yoke button, MCP disengage bar, or forcing the controls (CWS override on some). Autothrottle disconnects with buttons on the thrust levers. Disconnect warnings: flashing red A/P light and wailer; flashing red A/T light.

Deep dive · ATA 24

Electrical Power — in depth

Generation

Two IDGs (90 kVA, 115 V 400 Hz), one APU generator (90 kVA, usable on ground and in flight), external power. DC via three TRs (TR1, TR2, TR3) and a main battery (plus an auxiliary battery on NG). A static inverter supplies the AC standby bus from the battery.

IDG	90 kVA each
APU GEN	90 kVA
TRs	3
Battery standby time	approx. 30–60 min (aux battery fitted)

Bus logic (NG)

The NG uses a 'split system' with automatic Bus Transfer: each generator normally powers its own transfer bus; if one source fails, the BUS TRANSFER switch in AUTO lets the opposite generator pick up the transfer bus. The pilot connects generators by momentary GEN 1/2 switches on the overhead — the new source disconnects the old one ('break before make').

Standby power: with all AC lost, the battery powers the hot battery bus, battery bus, DC standby bus and, through the static inverter, AC standby bus — flight instruments, one radio, standby compass lighting.

Indications

TRANSFER BUS OFF	Transfer bus unpowered
SOURCE OFF	No source selected for the transfer bus
GEN OFF BUS	IDG not supplying the bus
DRIVE	IDG low oil pressure (disconnect per checklist)
STANDBY PWR OFF	AC/DC standby bus unpowered

Warning · IDG disconnect is irreversible in flight. Hold the switch only as long as the checklist states.

Deep dive · ATA 26

Fire Protection — in depth

Detection

Engines: two overheat/fire detector loops (A and B) per engine; the OVHT DET switch selects NORMAL (both loops, AND logic), A or B. APU: single loop. Main wheel well: fire detector loop. Cargo compartments: dual smoke detectors. Lavatories: smoke detector and waste bin extinguisher.

Extinguishing

Two engine fire bottles shared between both engines — each bottle can discharge into either engine (left or right rotation of the fire handle). One APU bottle. Cargo fire bottle with a high-rate and a metered (low-rate) discharge for extended diversion.

Pulling the engine fire handle closes the engine fuel valve, bleed valve, hydraulic shutoff and disconnects the generator, and arms the bottle squibs; rotating it discharges.

Engine bottles	2 (shared)
APU bottle	1
Cargo	1 bottle (dual discharge)
Test	FAULT/INOP and OVHT/FIRE test switch on the fire panel

Engine fire (outline)

1.Autothrottle disengage.
2.Thrust lever (affected) close.
3.Start lever (affected) CUTOFF.
4.Engine fire handle pull.
5.Rotate to the stop and hold 1 s.
6.If after 30 s the fire light is still on: rotate to the other stop.

Warning · Teaching outline only — use the approved QRH.

Deep dive · ATA 27

Flight Controls — in depth

Primary controls

Conventional cable-driven controls powered by hydraulic power control units (PCUs). Roll is by ailerons assisted by flight spoilers; pitch by elevators with a moving horizontal stabilizer for trim; yaw by a single rudder.

The stabilizer is moved by a jackscrew driven by an electric trim motor (main electric trim / autopilot) or by the cockpit trim wheels through cables.

Speed trim & MCAS

Speed Trim System (STS) automatically trims the stabilizer at low speed/high thrust to improve speed stability. On the 737 MAX, MCAS adds nose-down stabilizer at high angle of attack with flaps up. Since 2020 MCAS compares both AoA sensors, activates only once per event and is limited in authority.

Warning · Runaway stabilizer: hold the control column firmly, autopilot and autothrottle disengage, STAB TRIM CUTOUT switches to CUTOUT, then trim manually with the wheel.

Deep dive · ATA 28

Fuel System — in depth

Tanks & pumps

Main tank 1 (left wing), main tank 2 (right wing), centre tank in the wing-box and fuselage. Each main tank has two AC boost pumps (FWD and AFT); the centre tank has two override/jettison-style pumps with higher output pressure so centre fuel is used first.

A cross-feed valve connects the left and right manifolds. If all pumps fail, suction feed from the main tanks is possible at lower altitudes.

Total usable (NG)	approx. 26 000 L / approx. 20 800 kg
Main tanks (each)	approx. 3 900 kg
Centre tank	approx. 13 000 kg
Fuel temp minimum	3 °C above freezing point / −43 °C

Operating rules

Centre tank pumps ON when centre tank contains more than about 453 kg; OFF when LOW PRESSURE lights illuminate. Main tanks must be full if centre tank contains fuel (structural rule).

Imbalance: the FUEL IMBALANCE alert shows on EICAS/upper display when the main tanks differ by more than about 453 kg.

Warning · Never run centre tank pumps dry with low pressure lights on — risk of pump overheating and fuel-vapour ignition (see TWA 800 / SFAR 88).

Maintenance

Sump draining	Daily per MPD
Measuring sticks	Drip sticks under the wing for manual quantity
Pump replacement	Canister type — can be changed without draining the tank

Deep dive · ATA 29

Hydraulics — in depth

Systems

System A	Engine 1 EDP + electric motor-driven pump (EMDP). Ailerons, rudder, elevators, spoilers, gear, NWS, alternate brakes, reverser 1
System B	Engine 2 EDP + EMDP. Flight controls, flaps/slats, normal brakes, autobrake, yaw damper, reverser 2
Standby	Electric pump. Backup rudder, LE devices (full extend), reversers
Pressure	3000 psi
Reservoirs	Pressurised by bleed air

Manual reversion

If both A and B fail, ailerons and elevators are flown mechanically through cables and servo tabs ('manual reversion') — heavy but controllable. Rudder is powered by the standby system. Flaps can be extended electrically (alternate flaps).

Deep dive · ATA 30

Ice & Rain Protection — in depth

Systems

Wing anti-ice: bleed air to the three inboard leading-edge slats (NG) per wing; on the ground the valves close automatically at takeoff thrust (thrust lever/air-ground logic). Engine anti-ice: cowl valves per engine. Window heat for the flight-deck windows, probe heat for pitot, AOA vanes, TAT. Wipers per side.

Warning · Engine anti-ice must be ON in icing conditions on the ground and in flight, including descent, before entering icing, not after ice accretes.

Deep dive · ATA 32

Landing Gear — in depth

Configuration

Tricycle with twin wheels. Main gear retracts inboard into wheel wells with no doors — the outer side of the tyre stays exposed in flight and forms part of the fuselage contour, sealed by brush seals. The nose gear retracts forward into a doored well.

Normal operation from hydraulic system A. If A fails, gear retraction can come from system B through the landing gear transfer unit (when engine 1 N2 drops below a threshold).

Main tyres	H44.5 × 16.5-21, approx. 205 psi
Nose tyres	27 × 7.75-15, approx. 190 psi
VLO extension	270 kt / M 0.82
VLO retraction	235 kt
VLE	320 kt / M 0.82

Manual extension

Three T-handles in a floor hatch behind the first officer's seat release the uplocks for right main, nose and left main. Each gear free-falls and locks with gravity and air load. Pull each handle up to about 24 in.

Brakes & autobrake

Normal brakes	Hydraulic system B with anti-skid
Alternate brakes	System A with anti-skid
Accumulator	Several applications if both lost; parking brake source
Autobrake	RTO, 1, 2, 3, MAX — deceleration from approx. 4 ft/s² to 14 ft/s²
Carbon or steel brakes	Carbon on most NG; brake temperature monitoring shows 0–9 scale

Nose wheel steering

Tiller ±78°, rudder pedals ±7°. Hydraulic system A normally; system B as alternate when the NOSE WHEEL STEERING switch is set to ALT. A towing lever on the nose gear depressurises steering for pushback.

Deep dive · ATA 34

Navigation & Avionics — in depth

ADIRS

Two ADIRUs (left and right), each combining air data (from the pitot-static probes through ADMs) and an inertial reference system with ring-laser gyros. Mode selector OFF/ALIGN/NAV/ATT; alignment about 10 minutes. An IRS can be used in ATT mode in flight (attitude only) after a nav failure.

Common Display System

Six identical displays: outboard (PFD), inboard (ND), upper centre (engine primary / EICAS-like) and lower centre (secondary engine / systems). Two Display Electronics Units (DEU). Source selectors on the forward panel switch display sources if a unit fails.

Radio navigation & surveillance

VHF NAV	2 multi-mode receivers (VOR/ILS/GLS)
DME	2
ADF	1–2
Radio altimeters	2
GPS	2 (integrated in MMR)
Surveillance	TCAS II, Mode S transponders, EGPWS, predictive windshear radar

Deep dive · ATA 36

Pneumatic — in depth

Sources & ducting

Bleed air comes from the 5th stage (normal) and 9th stage (low power) of the CFM56-7B HP compressor, through the PRSOV and precooler. The APU and ground air connectors also feed the manifold. An isolation valve separates left and right ducts (AUTO opens it if one bleed or pack is off).

Duct pressure normal	approx. 30–45 psi
BLEED TRIP OFF	Over-temperature/over-pressure — reset after cooling
WING-BODY OVERHEAT	Duct leak detected — isolate
DUAL BLEED	APU and engine bleed both open — thrust limit

Deep dive · ATA 49

APU — in depth

Construction

Honeywell 131-9B (NG) gas turbine in the tail cone. Electronic Control Unit (ECU) controls start, governing and protective shutdowns. Fuel from the left main fuel manifold (no separate APU tank). Air inlet door on the right side of the tail.

Generator	90 kVA (ground and flight)
Bleed use	Up to approx. 17 000 ft
Electrical use	Up to 41 000 ft
Start: 3-position switch	OFF / ON / START (spring to ON)

Indications

MAINT	Maintenance problem — APU usable
LOW OIL PRESSURE	Auto shutdown (except during start)
FAULT	Auto shutdown — cause recorded in the ECU
OVERSPEED	Auto shutdown

Deep dive · ATA 72

Engines — CFM56-7B (and LEAP-1B on MAX)

Engine architecture

Two-spool high-bypass turbofan: fan + 3-stage booster on N1 driven by 4-stage LPT; 9-stage HPC on N2 driven by a single-stage HPT. Bypass ratio about 5.1–5.5 : 1.

The engine is mounted forward and high on the wing. Because the 737 sits low to the ground, the nacelle has a flattened lower lip (the 'hamster pouch') to fit the larger fan; accessories are moved to the sides of the fan case.

Thrust	19,500–27,300 lbf
Fan diameter	61 in
N1 redline	104 %
N2 redline	105 %
EGT redline takeoff	950 °C
EGT start limit	725 °C
Oil capacity (tank)	approx. 20 qt usable

EEC (FADEC)

Dual-channel Electronic Engine Control in NORMAL mode schedules N1 from the thrust lever angle corrected for altitude, temperature and bleed. If required inputs are lost it reverts to ALTERNATE mode (soft or hard), where N1 is less precise and protection is reduced — thrust levers should be retarded before selecting ALTN.

Ground start sequence

1.Bleed air available (APU bleed ON, isolation valve AUTO/OPEN), packs OFF for maximum duct pressure (approx. 30 psi minimum at sea level).
2.ENGINE START switch to GRD: start valve opens, starter drives N2. Oil pressure rises.
3.At 25% N2 (or max motoring) — start lever to IDLE: igniters fire, fuel flows.
4.Watch EGT rise (light-off within 10 s) and stay within limits.
5.At 56% N2: start switch releases to OFF automatically, the start valve closes. Stabilised idle about 60% N2.

Warning · Abort the start for no EGT rise within 10 s, EGT rapidly approaching 725 °C, no N1 rotation by 40% N2, or no oil pressure.

Thrust reversers

Cascade type, translating sleeves. Engine 1 reverser from hydraulic system A, engine 2 from system B, with standby system backup. Reverse can only be selected with thrust levers at idle and the aircraft on the ground (radio altimeter < 10 ft or air/ground sensing).

Maintenance Task Cards

Recirculation filter replacement

ATA 21 · Per MPD (approx. 4 000–6 000 FH)

Access · Forward cargo / mix bay

Tools & materials · Gloves · Mask · Bags for disposal

Warning · Wear protective mask and gloves when handling used filters.

1.Electrical power off for recirculation fans (open breakers, tag).
2.Remove the filter housing cover and old HEPA filter.
3.Bag the old filter (may contain biological contamination).
4.Install the new filter with arrow in flow direction; close cover; close breakers; run fans.

Filter type

HEPA, part number per IPC

Ref: B737 AMM 21-25-00

IDG oil level check & servicing

ATA 24 · Per MPD

Access · Left fan cowl

Tools & materials · IDG servicing cart · Approved oil

1.Engine shut down 5 min minimum.
2.Open fan cowl; read the IDG sight gauge.
3.Service with pressure fill until oil flows from the overflow.
4.Check filter delta-P indicator; close cowls.

Oil	MIL-PRF-23699

Ref: B737 AMM 24-11-00

Engine fire detection & extinguishing test

ATA 26 · Preflight (crew) / per MPD (maint.)

Access · Flight deck fire panel

Tools & materials · None

1.Hold FAULT/INOP test switch: check FAULT, APU DET INOP, MASTER CAUTION and OVHT/DET annunciators.
2.Hold OVHT/FIRE test: fire bell, fire handles, wheel well light, MASTER FIRE WARN, ENG OVERHEAT lights.
3.Press EXTINGUISHER TEST 1 and 2: three green squib lights per test.
4.Check bottle pressures (maintenance) against chart.

All test lights

Must illuminate

Ref: B737 AMM 26-11-00 / FCOM SP

Stabilizer trim jackscrew lubrication

ATA 27 · Per MPD (approx. C-check / 1800–3600 FH)

Access · Aft equipment area, stabilizer compartment

Tools & materials · Approved grease (e.g. Aeroshell 33) · Grease gun · Torque check tooling

Warning · Lack of lubrication on a stab trim screw has caused fatal accidents (e.g. Alaska 261 on an MD-83).

1.Remove access panels to the jackscrew.
2.Clean old grease from the screw threads.
3.Apply new grease and run the stabilizer full travel to distribute.
4.Check the end play of the ballnut against the limit.
5.Reinstall panels; operational test of main electric and manual trim.

Ballnut end play

AMM limit (wear indicator)

Ref: AMM 12-21-27 / MPD

Fuel tank sump drain

ATA 28 · Daily / per MPD

Access · Under each wing and centre tank

Tools & materials · Drain tool · Sample jar

1.Allow fuel to settle.
2.Drain each main and centre tank sump until clear.
3.Check for water and microbial contamination (dark slime).
4.Close and check for leaks; record.

Free water

None after draining

Ref: B737 AMM 12-11-28

Tyre pressure & wheel inspection

ATA 32 · Daily

Access · Gear on ground

Tools & materials · Calibrated gauge · Nitrogen

Warning · Never stand in line with the wheel axle.

1.Check cold tyres; correct to placard.
2.Look for cuts, bulges, worn tread to the bottom of a groove.
3.Check thermal fuse plugs and wheel tie bolts.
4.Record and remove per loss limits (same as 5 % / 10 % rule).

Max daily loss

5 %

Ref: AMM 12-15-31

APU oil level check

ATA 49 · Daily / per MPD

Access · APU access door (left side tail cone)

Tools & materials · Approved oil

1.APU off (wait as specified).
2.Read the oil sight gauge; LOW OIL QUANTITY indication on the upper display.
3.Service to FULL via gravity fill.
4.Close door; record quantity added (trend monitoring).

Oil	MIL-PRF-23699

Ref: B737 AMM 12-13-49

HPT borescope inspection

ATA 72 · Per EGT margin / bird strike / every A-check per program

Access · Borescope ports on core case

Tools & materials · Video borescope · Core rotation tool (N2 drive pad)

1.Engine cooled; install the manual turning tool on the AGB.
2.Insert borescope through the HPT port.
3.Rotate N2 and inspect each blade for burns, cracks, coating loss, tip curl.
4.Measure damage against AMM limits; record images.
5.Remove tools, install port plugs with torque and safety.

Tip erosion / burn

within AMM-defined zones

Ref: AMM 72-00-00 Inspection/Check

Engine oil servicing (CFM56-7B)

ATA 79 · Daily / as required

Access · Right side fan cowl oil fill door

Tools & materials · Approved oil · Lint-free cloth

Warning · A cap not locked can cause total oil loss in flight.

1.Service within 30 min of shutdown for an accurate reading (or after motoring the engine).
2.Open the oil filler access; read sight gauge.
3.Remove the cap slowly, fill to FULL.
4.Install cap — check the locking handle is fully down and flush.
5.Record quantity for consumption trend.

Usable tank

approx. 20 qt

Ref: AMM 12-13-11

Maintenance Overview (by ATA)

ATA 21 — Air Conditioning & Pressurization

Door seal, escape slide and emergency equipment checks.
Lap joint and skin corrosion inspections per ALS / SSID.
Pack and heat exchanger maintenance per MPD.

ATA 22 — Auto Flight

ADIRU and FCC BITE tests per AMM Chapter 22/34.
Pitot-static leak checks and probe heat tests.
CDS software part numbers verified against configuration.

ATA 23 — Communications

ADIRU and FCC BITE tests per AMM Chapter 22/34.
Pitot-static leak checks and probe heat tests.
CDS software part numbers verified against configuration.

ATA 24 — Electrical Power

Door seal, escape slide and emergency equipment checks.
Lap joint and skin corrosion inspections per ALS / SSID.
Pack and heat exchanger maintenance per MPD.

ATA 25 — Equipment / Furnishings

Door seal, escape slide and emergency equipment checks.
Lap joint and skin corrosion inspections per ALS / SSID.
Pack and heat exchanger maintenance per MPD.

ATA 26 — Fire Protection

Engine oil quantity check at each daily/transit; consumption trending.
Borescope inspections per CFM ESM / MPD; fan blade lubrication.
Thrust reverser functional and lockout checks per AMM 78.

ATA 27 — Flight Controls

Flap track and carriage lubrication and wear checks per MPD.
Inspect winglets and leading edges for damage.
Fuel sump drains and water checks per operator schedule.

ATA 28 — Fuel

Flap track and carriage lubrication and wear checks per MPD.
Inspect winglets and leading edges for damage.
Fuel sump drains and water checks per operator schedule.

ATA 29 — Hydraulic Power

Tire pressure and brake wear pin checks daily.
Strut servicing (nitrogen/fluid) per AMM 12/32.
Gear swing / retraction tests per MPD.

ATA 30 — Ice & Rain Protection

Flap track and carriage lubrication and wear checks per MPD.
Inspect winglets and leading edges for damage.
Fuel sump drains and water checks per operator schedule.

ATA 31 — Indicating / Recording

ADIRU and FCC BITE tests per AMM Chapter 22/34.
Pitot-static leak checks and probe heat tests.
CDS software part numbers verified against configuration.

ATA 32 — Landing Gear

Tire pressure and brake wear pin checks daily.
Strut servicing (nitrogen/fluid) per AMM 12/32.
Gear swing / retraction tests per MPD.

ATA 34 — Navigation

ADIRU and FCC BITE tests per AMM Chapter 22/34.
Pitot-static leak checks and probe heat tests.
CDS software part numbers verified against configuration.

ATA 35 — Oxygen

ADIRU and FCC BITE tests per AMM Chapter 22/34.
Pitot-static leak checks and probe heat tests.
CDS software part numbers verified against configuration.

ATA 36 — Pneumatic

Engine oil quantity check at each daily/transit; consumption trending.
Borescope inspections per CFM ESM / MPD; fan blade lubrication.
Thrust reverser functional and lockout checks per AMM 78.

ATA 49 — Airborne Auxiliary Power (APU)

Stabilizer jackscrew lubrication and end-play checks — critical item per MPD.
APU oil and fire detection tests.
Elevator tab free-play checks.

ATA 52 — Doors

Door seal, escape slide and emergency equipment checks.
Lap joint and skin corrosion inspections per ALS / SSID.
Pack and heat exchanger maintenance per MPD.

ATA 53 — Fuselage

Door seal, escape slide and emergency equipment checks.
Lap joint and skin corrosion inspections per ALS / SSID.
Pack and heat exchanger maintenance per MPD.

ATA 55 — Stabilizers

Stabilizer jackscrew lubrication and end-play checks — critical item per MPD.
APU oil and fire detection tests.
Elevator tab free-play checks.

ATA 57 — Wings

Flap track and carriage lubrication and wear checks per MPD.
Inspect winglets and leading edges for damage.
Fuel sump drains and water checks per operator schedule.

ATA 71 — Power Plant

Engine oil quantity check at each daily/transit; consumption trending.
Borescope inspections per CFM ESM / MPD; fan blade lubrication.
Thrust reverser functional and lockout checks per AMM 78.

ATA 72 — Engine

Engine oil quantity check at each daily/transit; consumption trending.
Borescope inspections per CFM ESM / MPD; fan blade lubrication.
Thrust reverser functional and lockout checks per AMM 78.

ATA 73 — Engine Fuel & Control

Engine oil quantity check at each daily/transit; consumption trending.
Borescope inspections per CFM ESM / MPD; fan blade lubrication.
Thrust reverser functional and lockout checks per AMM 78.

ATA 74 — Ignition

Engine oil quantity check at each daily/transit; consumption trending.
Borescope inspections per CFM ESM / MPD; fan blade lubrication.
Thrust reverser functional and lockout checks per AMM 78.

ATA 78 — Exhaust / Thrust Reverser

Engine oil quantity check at each daily/transit; consumption trending.
Borescope inspections per CFM ESM / MPD; fan blade lubrication.
Thrust reverser functional and lockout checks per AMM 78.

ATA 79 — Oil

Engine oil quantity check at each daily/transit; consumption trending.
Borescope inspections per CFM ESM / MPD; fan blade lubrication.
Thrust reverser functional and lockout checks per AMM 78.

EDUCATIONAL USE ONLY. Content is summarised from manufacturer documentation for learning. It is not approved flight or maintenance data. Always use the current, aircraft-specific POH/AFM, FCOM, QRH, AMM and operator procedures.