CFM56 Engine Details and MEL Starting Tips

CFM56-5A/B Powers the Airbus A318, A319, A320 & A321

Introduction:

CFM International is a 50/50 joint share between French Snecma Motors and American General Electric.

The CFM56 engines, are all of turbo fan type, has been designed to power  Short, Medium and Long range commercial and military aircraft since 1974. There  are currently ranging from 18,500 to 34,000 pounds of thrust.

It incorporates a second generation Full Authority Digital Electronic Control (FADEC), noise reduction improvements, and increased climb thrust.

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CFM56-5A/B 

Powers the Airbus A318, A319, A320 and A321

Dimensions:

Fan Diameter: 1,730 millimeter(68 inch);
Length: 2.60 meter (102 inch;
Dry Weight: 2,381 kilogram (5,249 pound);
Thrust: 33,000 pound

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Engine Summary:

The CFM56-5B engine is a dual-rotor, variable stator, high bypass ratio, axial flow turbo fan power plant.

• N1 Rated

• 80 % of the thrust is produced by the fan.

• 20 % of the thrust is produced by the engine core. 

• It has 4 major modules:

1. Fan & LP Compressor Module
2. Core Engine Module
3. Low Pressure Turbine & Turbine Frame Module
4. Trancfer & Accessory Drive Module

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1. Fan & LP Compressor Module

Includes The fan and Booster module which accelerate air overboard to generate thrust, and increase the pressure of the air directed to the HPC, and consists of:

• 1 Fan consisting of 36 titanium alloy,mid-span shrouded fan Blades,(Clockwise rotation/numbering)
• Spinner front and rear cones
• 4 Stages Low Pressure Compressor, which is driven by the LP Turbine (N1 Shaft)

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2. Core Engine Module

Core Engine  is a high pressure, high speed, gas generator that produces the power to drive the engine, and consists of:

• 9 Stages High Pressure Compressor (HPC), which is driven by HP Turbine (N2 Shaft)
• Combustion Section, (Annular combustion chamber)
• 1 Stage High Pressure Turbine

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3. Low Pressure Turbine & Turbine Frame Module

The Turbine frame module is one of the engine major structural assemblies, and is located at the rear of the engine, its made of a hub and an outer casing, it supports the:

• 4 Stages Low Pressure Turbine, which drives the forward Fan and LP Compressor

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4. Trancfer & Accessory Drive Module

The Accessory drive system is located at the 6 o'clock position.
It drives the engine and aircraft accessories through the:

• Inlet Gear Box (IGB)
• Radial Drive Shaft (RDS)
• Transfer Gearbox (TGB)
• Horizontal Drive Shaft (HDS)
• Accessory Gearbox (AGB)

Which in terms drives the:

• IDG (electrical power generation)
• FADEC Control Alternator
• Hydraulic pump (hydraulic power generation).
• The fuel pump and HMU .
• lubrication unit ( lube pump) . 

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• Main station numbers and usage:

SATION#	Location	Usage
0	Ambient	P0 Ambient Static Pressure used for FADEC
12	Fan Inlet	T12 = Fan ( Booster Inlet Temp.) used for FADEC. P12 = Fan ( Booster) Inlet Press. (PT2) used for FADEC.
13	Fam Exit	PS13 = Static Pressure of Fan Bypass Air Flow used for Monitoring.
25	LP Compressor, Booster Exit	T25 = High Pressure Compressor Inlet Temp. used for FADEC. P25 = High Pressure Compressor Inlet Press. used for FADEC
30	H.P. Compressor	T3 = High Pressure Compressor Discharge Temp. (CDT) PS3 = Compressor Discharge Pressure ( CDP ) used for FADEC
42	H.P. Turbine exit	T case = HPT Shroud Support Temperature used for HPT Active Clearance Control
49	L.P. Stage 2 Turbine inlet	T49.5 = Exhaust Gas Temp. (EGT) used for Cockpit Indication.
50	Exhaust	T5 = Total Temp. Turbine Rear Frame Plane used for Monitoring.

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• FADEC : Full Authority Digital Engine Control.

The FADEC system provides full range control of the engine to achieve steady state and transient performance when operated in combination with aircraft subsystems.
The engine control is built around a FADEC system, which serves as an interface between the aircraft and the engine control and monitoring components.
The FADEC consists of the Engine Control Unit ( ECU ), Hydromachanical Unit ( HMU ) and its peripheral components and sensors used for control and monitoring.

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  Compressor Control:

To limit compressor surge and to provide good acceleration, the engine equipped with:

•  Variable Bleed Valve (VBV) system
• Variable Stator Vane (VSV) system.

Both systems are fuel operated by the Hydro-mechanical Unit (HMU) and controlled by the Electronic Control Unit (ECU).

VBV system controls airflow from the LP compressor to the HP compressor by using 12 valves.
Which discharges the LP compressor air to the fan air stream to match LP/HP compressor at low speed.

VSV system controls airflow through the HP compressor by controlling the angle of the first four rows of pivoting vanes.
The VSV’s provide aerodynamic matching of the HP compressor stages to prevent engine surge. 

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Compressor & Turbine clearance control & Cooling:

In order to Optimize engine performance, the gap between the blade and tips and the casing is actively controlled.
This is done by:

• Directing cool air to shrink the LP and HP turbine casings.
• Directing hot air into the HP compressor cavity in order to expand it.

 These systems controlled by the Electronic Control Unit (ECU) and actuated from the Hydro-Mechanical Unit (HMU).

Engine clearance adjustment are provided by:
    -Low Pressure Active Clearance Control (LPTACC)
    -High Pressure Active Clearance Control (HPTACC)
    -Rotor Active Clearance Control and Start Bleed (RASCB)

The RASCB system uses stage 5 HP compressor air to heat the rotor cavity during cruise.
During starts and transients, it unloads the HP compressor by discharging stage 9 air.

The HPTACC system uses stage 4 HP and stage 9 HP air to heat or cool the High Pressure Turbine shroud support structure, it is monitored by the ECU.

The LPTACC system uses Fan air for external case cooling of the LP turbine.

ECU and Nacelle Cooling :

The Electronic Control Unit (ECU) is aerodynamically cooled to maintain its internal temperature below maximum limits.
A flush air scoop, located on the inlet cowl outer barrel, supplies ram air through a duct to the ECU.
This air is then discharged into the fan compartment ventilation zone.

The fan and core compartments which form the nacelle, are air cooled to provide airflow around the engine during its operation. 

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• Thrust Reverser:

• reduce the speed of the aircraft after landing and is achieved by reversing the direction of the fan airflow using four pivoting blocker doors.
• The four pivoting blocker doors is operated by a hydraulic actuator, which receives fluid from a Hydraulic Control Unit that is controlled by the Electronic Control Unit.
• Blocker doors are maintained in the stowed position by A latch mechanism.
• The latches are hydraulically released at the beginning of the deploy sequence.
• Door positions are monitored by stow and deploy switches.
• Hydraulic Control Unit(HCU)lever top right hand side

       

​KEEP IN MIND:

• There are 9 borescope inspection ports located at 5 o'clock position, Which are used to inspect the compressor and turbine blades,
This requires rotation of the core engine, and is accomplished by using a 3/4 inch square drive tool into the drive pad on the forward face of the accessory gearbox above the drive pad and rotating the engine.

• The CFM56-5B consists of 2 independent rotating systems: N1 & N2 supported by 5 Bearings:

 - 3 LP Bearings(1 Ball, 2 Roller)
 - 3 HP Bearings (1 Ball, 2 Roller)

            - (Ball (B) bearings absorb axial loads) 
           - (Roller (R) bearings absorb radial loads)  

• There are 20 Fuel Nozzles and 2 igniter plugs located at 4 and 8 o'clock positions 

•  Three adjustable tension latches are provided on the fan cowl door.

• Four adjustable tension latches are provided on the thrust reverser cowling.

KEEP IN MIND:

- Engine Starting:

•Starter Engagement N2 > 20%

•EGT limits:
     - Engine start: 725c
     - MCT: 915°c
     - Take off: 950c

•Start Oil Temperature limit:
     - Starting: -40°.
     - Take off: -10°.

•Oil Temp Limit: 140° (continuous), 155° (15 minutes).

•Oil Quantity: 9,5qts + 0,5/hr.

•Oil Press (N” 80%): min 24 psi, max 60 psi.

•RPM limits:
    - N1: 104%
    - N2: 105%

•Starter duty cycle:
   - 2 Min ON > 20 Sec OFF ✖️ (4)
   - 15 Min OFF

Or

    - 5 Min ON > 2 Min OFF
   - 15 Min ON > 15 Min OFF

During Engine Start, Keep Your Eyes On Below Sequence:
-Start Valve Opens, 
- N2 rise
-IGN A (B), 
- Fuel Flow,
- EGT increase,
- Oil Press Rise
- at N2 > 50% Start Valve Closes
- Note Peak EGT & Engine vibrations

Average IDLE Parameters(Engine stabilized):
    N1 ~ 20%,
    N2 ~ 60%,
    EGT 400
    FF ~ 300Kg/h

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🔴CFM 56, HOT START:

>• Inspection/check after the Engine has exceeded the operational limits(AMM 72-00-00-200-008):

1• EGT 725-750 for less than 30 sec:
  -Use TSM 77-00-00-810-849  to identify the cause.
  (Read DMU exceedance and specific data report for operational limits AMM 73-21-60-740-060/027, if none available get the data from AIDS or DFDR)
  If EGT due to TAT inversion, no maintenance is required,
  If not do the related trouble shooting as per TSM.
  A maximum service extension of 5 flight cycle is allowed before you correct the problem

2• EGT 750-800 for less than 10 sec:
   Borescope inspection is required For HPT & 1 LPT
  Use TSM 77-00-00-810-849  to identify the cause
  A maximum service extension of 1 start is permitted, and if the start is satisfactory, 1 cycle is permitted before you correct the problem.

3. EGT is greater than above:
  Use TSM 77-00-00-810-849  to correct the fault before any subsequent flight.

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- IDG Servicing: Fan Cowl right hand side to be opened
 AMM 12-13-24-612-041-B

- IDG Level Check: Fan Cowl right hand side to be opened
AMM 24-21-00-210-046-A

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🔹PRV BLEED valve = Left hand Side(Thrust reverser cowl has to be opened)
AMM 36-11-00-040-001-A (Located Above of HP valve)

🔸HP BLEED Valve  = Left hand Side(Thrust reverser cowl has to be opened)
AMM 36-11-00-040-003-A (Located Below of PRV)

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🔷 Operational Test of the FADEC on the Ground (with Engine non Motoring)AMM  73-29-00-710-040.

🔶 Operational Test of the FADEC on the ground (with engine motoring) AMM  73-29-00-710-040A.

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MEL/DEACTIVATION

🔒🔩 Thrust Reverser De-Activation for Flight

-, Hydraulic Control Unit(HCU)lever top right hand side ➡️  OFF position
-, Disconnect the connectors for Pressurizing & directional valve
-, Remove lock-out faring & it's screw from each pivoting door.
-, Remove lock-out plates & bolts from lower forward right side.
-, Install lock out  bolt in each pivoting door to attach the door to frame structure.

🔓Manual Opening of Pivoting Doors:

-, Hydraulic Control Unit(HCU)lever top right hand side ➡️  OFF position.
-, On the corresponding hydraulic latch
-, Turn Manual unlocking knob to unlock position ➡️ make sure door does not open, otherwise replace actuator.
-, Turn the Manual unlocking square on the actuator to unlock position
-, Pull the pivoting door, install safety sleeve.

Credit :    Rabindar Singh

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