A320 Engines Explained | CFM56 & IAE V2500 FADEC Systems

Q: How do you start an A320 engine?

A320 engine start sequence: Move ENG MASTER switch to ON, FADEC initiates automatic start sequence including valve opening, ignition, fuel introduction, N2 spool-up. Start is automatic and monitored by FADEC. Typical start time is 60-90 seconds from ENG MASTER ON to stable idle.

The Airbus A320 family is powered by either CFM International CFM56-5B or IAE (International Aero Engines) V2500 turbofan engines. Both are high-bypass turbofans controlled by Full Authority Digital Engine Control (FADEC) systems. Understanding engine operation, start sequence, thrust modes, and FADEC logic is essential for A320 type rating exams.

Engine Options

A320 operators choose between two engine manufacturers at aircraft purchase. The engines are not interchangeable - an aircraft has either CFM or IAE engines for its entire service life.

CFM56-5B

CFM International (GE/Safran joint venture). Most common on A320 family. Thrust range: 22,000-27,000 lbf depending on variant.

IAE V2500

International Aero Engines consortium. Alternative engine option. Similar thrust ratings: 22,000-25,000 lbf depending on variant.

FADEC

Full Authority Digital Engine Control manages all engine functions automatically. Two independent channels per engine for redundancy.

Accessories

Each engine drives: hydraulic pump, integrated drive generator (IDG), fuel pump, pneumatic system (bleed air).

FADEC (Full Authority Digital Engine Control)

FADEC is a computerized engine management system providing full authority digital control of all engine functions. Pilots set thrust via thrust levers; FADEC does everything else automatically.

FADEC Authority and Power

Full Authority: FADEC has complete control over engine operation - fuel flow, ignition, start sequence, thrust management, protection limits
Dedicated Alternators: Each engine FADEC powered by dedicated alternators that are independent of aircraft electrical system (ensures FADEC remains operational even with total aircraft electrical failure)
Fuel Metering During Start: FADEC meters fuel based on N2 speed and EGT to ensure safe light-up and acceleration
Automatic Relight: FADEC automatically attempts engine relight if flameout detected in flight

FADEC Functions

Engine Start: Completely automatic sequence from ENG MASTER ON
Thrust Control: Manages fuel flow to achieve commanded thrust
Engine Protection: Prevents over-temp, over-speed, stall, surge via automatic fuel flow modulation
VBV Control: Adjusts Variable Bleed Valves (VBV) to optimize compressor stability and prevent surge/stall
Optimization: Adjusts for altitude, temperature, aircraft configuration
Reversers: Controls thrust reverser deployment and operation

🖥️ FADEC Redundancy

Each engine has TWO independent FADEC channels (A and B). Normally channel A is active, channel B is standby. If channel A fails, automatic seamless switchover to channel B occurs. The pilot never knows which channel is active - the system is completely transparent. Loss of both channels on one engine requires engine shutdown.

VBV (Variable Bleed Valves)

Variable Bleed Valves are controlled by FADEC to bleed air from compressor stages during low-speed operation (start, idle, deceleration). This prevents compressor stall/surge by managing airflow through the compressor. VBVs close at higher power settings when airflow is sufficient.

Engine Start Sequence

A320 engine start is fully automated by FADEC. The pilot simply moves ENG MASTER switch to ON position.

Automatic Start Sequence

ENG MASTER ON: Pilot action initiates start
Engine Valve Opens: Pneumatic start valve opens automatically
N2 Spool-Up: Starter motor (pneumatic) spins N2 (high-pressure compressor and turbine)
Ignition ON: FADEC activates igniters (typically around 16% N2)
Fuel Introduction: FADEC opens fuel valve and meters fuel based on N2 and EGT (typically around 20% N2)
Light-Up: Fuel ignites, EGT rises, N1 and N2 accelerate
Self-Sustaining: Around 50% N2, engine becomes self-sustaining
Starter Cutout: Starter automatically cuts out around 55% N2
Idle: Engine stabilizes at idle N1 (approximately 20%)

⚠️ Monitoring Engine Start

Pilots must monitor:
• N2 rotation (confirms starter working)
• EGT rise after ignition (confirms light-up)
• EGT limits (FADEC modulates fuel flow to prevent exceedance, but monitor manually)
• N1/N2 stabilizing at idle

Hung Start: N2 stagnates below expected value and does not accelerate to idle. FADEC detects and aborts automatically, or pilot can abort manually.
Hot Start: EGT exceeds limits during start - abort immediately by ENG MASTER OFF.
No Light-Up: No EGT rise after fuel introduction - dry motor, abort start.

Continuous Ignition

FADEC automatically activates continuous ignition (igniters remain on) to provide flameout protection during:

Heavy precipitation or icing conditions
Engine surge/stall conditions
Severe turbulence
Single-engine operation

Automatic Shutdown on Ground

FADEC automatically shuts down the engine (ENG MASTER to OFF) on the ground if severe exceedances occur (e.g., extreme over-temp, over-speed) to prevent catastrophic engine damage.

Start Sources

Start Source	When Used	Notes
APU Bleed	Normal on ground	Most common, APU provides pneumatic power
External Pneumatic	Ground when available	Ground cart provides air pressure
Cross-Bleed Start	Second engine start	First engine provides bleed for second engine
In-Flight Start	After engine failure	Windmilling provides airflow, APU bleed assists

Thrust Modes and Ratings

A320 thrust is managed via detents on the thrust levers. FADEC automatically provides the appropriate thrust based on lever position and flight phase.

Thrust Lever Detents

MAX REV: Maximum reverse thrust (ground only)
IDLE (on ground): Ground idle, minimum thrust for taxi
IDLE (in flight): Flight idle, provides some thrust in descent
CL (Climb): Maximum continuous climb thrust
FLX/MCT: Flexible takeoff or Maximum Continuous Thrust
TOGA: Takeoff/Go-Around, maximum rated thrust

TOGA vs Approach Idle

TOGA (Takeoff/Go-Around): Maximum rated thrust - highest thrust setting for takeoff and go-around maneuvers
Approach Idle: Higher idle setting during approach phase to maintain bleed air supply and ensure faster thrust response if go-around required

🎯 Autothrust & Thrust Modes

When autothrust active, thrust levers remain in CL detent during cruise. FADEC and autothrust system automatically adjust thrust to maintain speed or climb/descent profile. Pilot can always override by manually moving thrust levers.

Takeoff Thrust Ratings

A320 uses reduced thrust takeoff (flex temp) to extend engine life:

TOGA: Maximum takeoff thrust, used when required (short runway, contaminated, engine out)
FLX XX: Reduced thrust based on assumed temperature (flex temp), typical for normal ops

Engine Parameters

Pilots monitor several key engine parameters on ECAM:

N1 - Low Pressure Spool Speed

N1 is the LP (low-pressure) spool consisting of the fan and LP turbine. Speed displayed as percentage. N1 directly relates to thrust produced. Typical values:

Idle: ~20%
Climb: 85-95%
Takeoff (TOGA): ~97-100%

N2 - High Pressure Spool Speed

N2 is the HP (high-pressure) spool consisting of the high-pressure compressor (HPC) and HP turbine. Used primarily during start monitoring. Typical values:

Idle: ~60%
Climb/Cruise: 90-98%
Max: ~100%

EGT - Exhaust Gas Temperature

Temperature of exhaust gases leaving the engine. Critical parameter for engine health. FADEC modulates fuel flow to prevent EGT exceedances automatically.

Normal Operations: Typically 400-650°C depending on thrust setting
Start Monitoring: Pilot monitors EGT during start to detect hot start condition
EGT Protection: FADEC automatically modulates fuel flow to prevent over-temp in all phases of flight
Takeoff Limit: FADEC manages automatically, typically 5 minutes
Continuous Limit: Lower than takeoff, for sustained operations

🚨 EGT Limits and Protection

Exceeding EGT limits damages engine turbine blades and reduces engine life significantly. FADEC automatically prevents EGT exceedance under normal conditions by modulating fuel flow. If EGT exceeds limits during start (hot start), abort the start immediately by moving ENG MASTER to OFF.

Fuel Flow (FF)

Fuel consumption rate in kg/h or lb/h. Monitored for fuel planning and engine performance.

Oil Quantity, Pressure, Temperature

Engine oil system parameters monitored for engine health. Low oil pressure or high oil temperature indicates engine problems requiring immediate attention.

Thrust Reversers

A320 uses thrust reversers to decelerate after landing. Reversers redirect engine thrust forward, creating braking force.

Reverser Types

CFM56: Uses cascade-type thrust reversers on fan duct
V2500: Uses blocker door-type reversers

Reverser Operation

Landing: After touchdown, thrust levers to IDLE
Deployment: Pilot pulls REV levers, reversers deploy (takes ~1-2 seconds)
Reverse Thrust: Advance REV levers to MAX REV detent for maximum braking
Stowage: Below 70 kt, reduce to IDLE reverse, reversers automatically stow

⚠️ Reverser Limitations

• Ground use only (thrust reversers locked out in flight)
• Do not use reverse thrust below 70 kt (FOD risk from debris)
• Immediate reverse stowage if unlocked lights appear (asymmetric reverse dangerous)
• Crosswind limitations may apply for reverse thrust usage

Engine Failures and Abnormals

Engine Failure After Takeoff

A320 can safely fly and land with one engine inoperative. FADEC on operating engine automatically provides maximum available thrust.

Engine Fire

Engine fire requires immediate action per ECAM:

Thrust lever IDLE
ENG MASTER switch OFF
Fire pushbutton PUSH (fuel shutoff)
Agent 1 discharge if fire persists
Agent 2 available if needed

Engine Stall/Surge

Indicated by loud bang, fluctuating N1/N2, high EGT. FADEC normally prevents stalls, but can occur in severe conditions (volcanic ash, severe icing, rapid thrust changes at high altitude).

Frequently Asked Questions

What engines are on the A320?

The A320 family uses either CFM International CFM56-5B turbofan engines or IAE (International Aero Engines) V2500 turbofans. Both are high-bypass turbofans producing approximately 22,000-27,000 lbf thrust depending on specific variant and rating. The engine choice is made at aircraft purchase and cannot be changed. Operationally, both engine types perform similarly and are controlled identically via FADEC.

What is FADEC on A320 engines?

FADEC (Full Authority Digital Engine Control) is a computerized engine control system that manages all aspects of engine operation automatically. It controls fuel flow, ignition timing, start sequence, thrust management, engine protection limits, and thrust reverser operation. Pilots command thrust via thrust levers, FADEC translates that into precise fuel flow and engine parameters while preventing over-temp, over-speed, stall, and surge. Each engine has two independent FADEC channels for redundancy.

How do you start an A320 engine?

A320 engine start is fully automated. The pilot simply moves the ENG MASTER switch to ON position. FADEC then executes the entire start sequence automatically: opening pneumatic start valve, spinning N2 via starter motor, activating ignition around 16% N2, introducing fuel around 20% N2, managing light-up and acceleration to idle. The pilot monitors N2 rotation, EGT rise and limits, and idle stabilization. Typical start time is 60-90 seconds from ENG MASTER ON to stable idle.

What is a hot start on A320?

A hot start occurs when EGT exceeds limits during engine start sequence (typically 750°C depending on engine type). This indicates too much fuel relative to airflow, often caused by insufficient starter air pressure, tailwind, or FADEC malfunction. Hot starts can severely damage turbine blades. If EGT approaches or exceeds the start limit, abort the start immediately by moving ENG MASTER to OFF. Wait for cooldown before attempting another start, and investigate the cause.

What is flex temp takeoff on A320?

Flex temp (flexible temperature) takeoff uses reduced thrust to extend engine life. Instead of using maximum TOGA thrust, the crew enters an assumed higher temperature into the FMGS. FADEC calculates the reduced thrust as if operating on a hotter day (when engines produce less thrust). This reduces engine wear significantly. Flex temp can only be used when runway, obstacle clearance, and weather allow. If conditions require maximum performance (short runway, contaminated surface, engine failure), TOGA thrust must be used.

Can you fly an A320 with one engine?

Yes, the A320 can safely fly and land with one engine inoperative (OEI - One Engine Inoperative). The remaining engine provides sufficient thrust for continued flight, climb (reduced performance), and normal landing. ETOPS (Extended Operations) certified A320s can fly up to 180 minutes from nearest suitable airport on one engine. However, single-engine performance is degraded - lower climb rate, lower maximum altitude, reduced speed. Pilots must follow specific OEI procedures including blue hydraulic system management (if yellow engine failed) and drift-down procedures if above single-engine ceiling.

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