Advanced Trim Balance [CFML]

TASK 71-00-00-750-805-A
Advanced Trim Balance

WARNING: BE CAREFUL WHEN YOU DO WORK ON THE ENGINE PARTS AFTER THE ENGINE SHUTDOWN. USE APPLICABLE THERMAL GLOVES. THE ENGINE PARTS CAN STAY HOT FOR ONE HOUR AFTER SHUTDOWN AND CAN BURN YOU.

ZONE: 400

1. Reason for the Job
The trim balance procedure is used to reduce unbalance in the N1 rotor. It must not be used to correct unbalance caused by mechanical problems.
Examples of mechanical problems are:

N1 rotor blades with broken airfoils, missing airfoils or airfoils with bad deformation.

An other option is available for engine trim balancing:

One Shot Trim Balance (recommended).

2. Job Set-up Information
A. Fixtures, Tools, Test and Support Equipment

REFERENCE	QTY	DESIGNATION
No specific	1	ACCESS PLATFORM 1M(3 FT)
No specific	1	FLASHLIGHT
No specific	1	MAT - PROTECTIVE
No specific	AR	WARNING NOTICE(S)

B. Work Zones and Access Panels

ZONE/ACCESS	ZONE DESCRIPTION
400	POWER PLANT, NACELLES AND PYLONS

C. Referenced Information

REFERENCE	DESIGNATION
TASK 71-00-00-710-813-A	Vibration Check
TASK 72-21-40-000-801-A	Removal of the Front Spinner
TASK 72-21-40-400-801-A	Installation of the Front Spinner
TASK 72-21-43-000-801-A	Removal of the Platform Front Shroud Balance Weight
TASK 72-21-43-400-801-A	Installation of the Platform Front Shroud Balance Weight
TASK 73-29-00-710-804-A	Weight Configuration (Menu Mode)
TASK 73-29-00-710-805-A	Conduct a Ground Run (Menu Mode)
TASK 73-29-00-740-808-A	Engine Trim Balancing via Menu Mode
TSM 77-11-00-810-824	N1 Vibration Exceedance
Vibration Fan Conversion MILS.DA/CU
Weight Reference
Position of the Balancing Weight

3. Job Set-up
Subtask 71-00-00-941-164-A

A. Safety Precautions
(1) On the center pedestal, on ENG panel 115VU:
(a) Make sure that the ENG/MODE selector switch is in the NORM position.
(b) Make sure that the ENG/MASTER 1(2) control switch was in the OFF position not less than five minutes before you do this procedure.
(c) Put a WARNING NOTICE(S) in position to tell persons not to operate:

The ENG/MODE selector switch
The ENG/MASTER 1(2) control switch.

(2) On the ENG section of maintenance panel 50VU:
(a) Make sure that the ON legend of the FADEC GND PWR/1(2) pushbutton switch is off.
(b) Put a WARNING NOTICE(S) in position to tell persons not to energize FADEC 1(2).
(3) Put an ACCESS PLATFORM 1M(3 FT) in position.
(4) Install a MAT - PROTECTIVE in the lower half of the inlet cowl.

Subtask 71-00-00-860-256-A

B. Names and definitions
(1) Vibration amplitude:
(a) The vibration level caused by either the low or high pressure rotor unbalance.
(2) Low pressure rotor related vibration:
(a) This is caused by unbalance of the low pressure rotor. Low pressure rotor related vibration levels are displayed in cockpit units (0-10). The EEC flight history data is displayed in mils double amplitude (peak to peak).

Vibration Fan Conversion MILS.DA/CU

(3) The cockpit displays two values for N1 and N2 related vibration:
Each value is the higher value between the two accelerometers No. 1 bearing accelerometer and the Turbine Center Frame (TCF) accelerometer.
(4) Phase angle:
The angle between the signal from the vibration transducer and the signal from the once per revolution N1 speed reference.
(a) Positive angles are measured counterclockwise (forward looking aft).
(b) Zero degree corresponds to the top of the platform front shroud.

Subtask 71-00-00-860-257-A

C. Preparation for Trim Balance Procedure
(1) The fan engine trim balance procedure corrects unbalance by adding balancing weights. There are three configurations of balancing weights.

Weight Reference

(a) Hole free
(b) Hole with bolt (screw and nut)
(c) Hole with bolt and weight.
(2) The platform front shroud features 72 positions for the installation of the balancing weights. However, for each trim balance of the engine, a maximum of 36 only can be used, and in addition limited to one half of the platform front shroud circumference.

Position of the Balancing Weight

(3) Check the location of existing bolts and weights before the engine trim balance as follows:

NOTE: This check is used to make sure the installed bolt and weight agree with the EEC data.

(a) Get access to the platform front shroud (Ref. AMM TASK 72-21-40-000-801).
(b) On the platform front shroud, record for each 36 positions the presence of bolt with or without balance weights.

NOTE: A spherical mark is machined on the platform front shroud to show the fan blade No.1 location. The fan blade No.1 is located in front of the mark, forward looking aft (the blades are counted counterclockwise).

NOTE: Use a FLASHLIGHT or other light source to examine the platform front shroud for existing bolts or weights.

(4) Compare the physical weight configuration with the weight configuration recorded into the EEC and update the ECC if necessary (Ref. AMM TASK 73-29-00-710-804).

4. Procedure
Subtask 71-00-00-750-121-A

A. Advanced Engine Trim Balance
(1) Do the advanced engine trim balance via menu mode function (Ref. AMM TASK 73-29-00-740-808).

NOTE: This method computes the engines trim balancing solution using selectable flight leg and/or ground run vibration data with either generic or specific trim coefficients. The preferred record selection shall be the record with the higher number of bins.

The operator can use the following options:
(a) Advanced balance - generic coefficients:
1 This option shall be selected if the ONE SHOT trim balance cannot be used (alternative method available) and the operator wants to avoid a specific engine run to record data using the ground run acquisition.
2 The operator can use either one of the ten previous flight leg (LEG X) or use the average of the last ten flight legs (AVG).
(b) Advanced balance - specific coefficients (alternative method):
1 This procedure shall only be used if the one shot trim balance and advanced trim balance with generic coefficient were not successful to obtain an acceptable engine N1 rotor balance.
2 This procedure also allows the operator to calculate new trim coefficients if enough valid data is present. This option corresponds to a "Vectorial Balance" means and it requires N1 vibration data recorded with two different balance weights solutions.
(2) Installation or removal of balance weights according to test results.

CAUTION: MAKE SURE THAT THE FINAL WEIGHT CONFIGURATION AGREES WITH THE NEW BALANCE WEIGHT CONFIGURATION. IF NOT, THE TRIM BALANCE SOLUTION WILL NOT BE SATISFACTORY.

(a) Install or remove balance weights as necessary to match fan balance weights per the recommended solution (Ref. AMM TASK 72-21-43-000-801) and (Ref. AMM TASK 72-21-43-400-801).
(3) Install the front spinner (Ref. AMM TASK 72-21-40-400-801).
(4) Do the engine vibration check (Ref. AMM TASK 71-00-00-710-813).

NOTE: The ground run acquisition (GND) (Ref. AMM TASK 73-29-00-710-805) can be performed instead of vibration check in case of engine trim balance performed after fan blade change.

(a) If the engine vibration values are still not satisfactory according to conditions specified by troubleshooting per TSM 77-11-00-810-824, contact your CFM representative.

5. Close-up
Subtask 71-00-00-942-083-A

A. Put the aircraft back to its initial configuration.
(1) Make sure that the work area is clean and clear of tools and other items.
(2) Remove the MAT - PROTECTIVE.
(3) Remove the access platform(s).
(4) Remove the WARNING NOTICE(S).

[Rev.10 from 2021] 2026.04.02 06:33:16 UTC