CFM56-7B - Southwest - ESN874265 - AGB input gearshaft roller bearing failure

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CFM56-7B - Southwest - ESN874265 - AGB input gearshaft roller bearing failure

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Portion of inner ring surface free from significant wear

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Page 1 CFM Proprietary Data Unauthorized Disclosure Prohibited
CFM56-7B - Southwest - ESN874265 - AGB input gearshaft roller bearing failure
1- Background
 On June, 21, 2002, SWA CFM56-7B ESN 874265 experienced a commanded IFSD after the oil filter
bypass light illuminated in flight.
 Ground investigation revealed metal debris in the AGB/TGB MCD.
 During further removal of the AGB, it was found :
 liberation of key locks coming from the 3 studs that secure the roller bearing outer race to AGB
housing,
 wear-ovalization of the AGB housing at the 3 threaded holes receiving the 3 studs,
 good condition of the 3 studs remained attached with the roller bearing outer race,
 excessive radial play on all five AGB mounts links,
 residual AGB alignment condition (dim. « A » - dim. « B ») checked at 0.051’ (1,29mm) vs. .002’
(0,05mm) required,
 good condition of horizontal drive shaft splines (no visual wear).
2- Engine and AGB history
 CFM56-7B22 ESN 874265 delivered in July 1998 installed on #2 on Boeing 737-700 N7183W.
 One maintenance action reported on AGB since EIS related to HMU replacement (line 6) made in july
1999 without any connection with failed line 3 roller bearing.
 Engine & AGB TSN/CSN = 14804/9478 and 14268/9112 since HMU replacement.
 AGB quality inquiry revealed one minor deviation : 6 tooth dim. of line 3 gearshaft check -4μm under mini.
limit (42,765 vs. 42,769 to 42,823 required) ; accepted thru departure record DN 15H06030A.
Page 2 CFM Proprietary Data Unauthorized Disclosure Prohibited
CFM56-7B - Southwest - ESN874265 - AGB input gearshaft roller bearing failure
3- Part identification (see charts 9 & 20)
 AGB P/N 340-046-503-0 S/N WQ 1193
 Damaged control alternator made of :
 Stator P/N 9387M17P09 S/N HTL 10296
 Rotor P/N 9387M16P02 S/N HTLR 4329
 Gearshaft line 3 P/N 340-051-801-0 S/N UN 00225 equipped with :
 Failed roller bearing P/N 301-480-926-0 S/N UR 29717
 Ball bearing P/N 305-115-306-0 S/N UR 29633
 Ball bearing housing P/N 335-301-000-0
 Starter pad assy P/N 340-047-802-0 equipped with :
 gearshaft line 4 P/N 340-051-901-0 S/N UN 07643
 Fuel pump – HMU pad assy equipped with :
 Gearshaft line 5 P/N 340-055-202-0 S/N UR 00454
 Gearshaft line 6 P/N 335-302-902-0 S/N UN 21379
 Gearshaft line 7 P/N 335-303-002-0 S/N U 28596
 AGB links returned for wear on spherical bearings :
 Adjustable turnbuckle link P/N 340-029-501-0 equipped with 2 links P/N 340-103-701 / 801
 Rear links (x2) P/N 340-029-401-0
 Upper link P/N 340-032-801-0
Page 3 CFM Proprietary Data Unauthorized Disclosure Prohibited
CFM56-7B - Southwest - ESN874265 - AGB input gearshaft roller bearing failure
4- Findings
4-1 Parts as received (see chart 9)
 All the 5 gearshafts from lines 3 to 7 and associated pads were reinstalled on AGB housing.
 Control alternator stator & rotor were received removed and badly worn by rotor sectorial interference (90°).
 On the alternator rotor the wear is limited to one sector compare to the stator that is affected on 360°.
4-2 After AGB disassy (see charts 10 & 11)
 Line 3 (control alternator) roller bearing outer race found totally loose due to hole elongation of the 3 securing
studs that machined the AGB housing over 10mm long in gearshaft rotation opposite direction.
 As a consequence of the roller bearing outer race looseness, respective centering diameters of both outer race
and AGB housing hole were affected by superficial fretting – wear.
 Examination of all other studs installed in the AGB housing did not reveal any unusual shaking or unlocked
condition especially related to the similar studs.
4-3 Gearshaft line 3 (control alternator)
 Inspection of gearshaft input splines, matching with horizontal drive shaft, as well as gear teeth showed good
condition.
 Bearing journals : good condition (no wear readable).
4-3-1 Line 3 ball bearing
 Good condition (no spalling, no corrosion, no shaking evidence except local fretting marks on 1 out of the 3
outer race securing lugs.
Page 4 CFM Proprietary Data Unauthorized Disclosure Prohibited
CFM56-7B - Southwest - ESN874265 - AGB input gearshaft roller bearing failure
4-3-2 Line 3 roller bearing
 Outer race : general quite good condition except : (see chart 12)
 dents caused by particles related to roller and inner raceway spalling.
 presence on outer raceway of double superficial wear lines (shiny appearance) formed
by the roller ends passing through the inner raceway sectorial spalling demonstrates
that the outer race stud breakaway and subsequent axial displacement of the outer race
(~1,5mm) likely occurred as a consequence of vibrations induced by inner ring spalling.
 fretting wear on outer diameter (already mentioned),
 good condition of shoulders with no roller contact indication .
 Rollers : all of the 14 rollers are affected by dents and spalling craters only distributed on track fwd edge and
consistent with dents observed on fwd edge of outer raceway (see chart 13).
 Cage : good condition. Note the unusual roller contact mark characterized by a conical shape with larger
contact area on fwd side of cage separator.
 Inner race : (see charts 14 & 15)
 sectorial spalling (~90°) initiated from the forward edge of the track and more developed on the fwd
edge,
 maximum spalling depth measured about 0,1mm,
 after reinstallation of the alternator rotor as it was initially, the inner raceway sectorial spalling
appears to be located in the quite same angular position as the alternator rotor sectorial wear.
 good condition of the remaining portion only affected by dents and a blue discoloration of the track on fwd
edge.
Control alternator damage is the result of rotor interfering with stator , due to rotor offset motion
consecutive to sectorial spalling of the roller bearing inner race and subsequent outer race looseness.
Page 5 CFM Proprietary Data Unauthorized Disclosure Prohibited
CFM56-7B - Southwest - ESN874265 - AGB input gearshaft roller bearing failure
4-4 Other gearshafts & associated bearings
 Inspection of all other received gearshafts and associated bearings did not revealed significant findings especially
regarding :
 tooth pattern : no significant wear,
 exposed roller bearings : good condition of rollers and outer raceway,
 ball bearings : no hard point or defect detectable by hand rotation.
4-5 Additional exam
4-5-1 Dimensional (see chart 16)
 Except the dimension related to alternator rotor for which we don’t have the B/P limits, all the other checked
dimensions meet specifications.
4-5-2 Metallurgical examination of Line 3 roller bearing inner race and rollers (see charts 17 to 19)
 Inner race : examination of the 2 cross sections made through the spalling sector revealed : (see charts 17 & 18)
 some white spots characterized by butterfly appearance corresponding to material ferrite transformation
indicative of material fatigue damaging.
 general correct M50 microstructure : normal carbide distribution, fine martensitic needles, correct hardness (63
HRC vs 61 to 64),
 microstructure hammered condition as secondary damage.
 Rollers : correct hardness (63,5 HRC) and M50 microstructure except usual hammering condition of spalling cracks
(chart 19).
Metallurgical exam of inner raceway showed presence of butterflies facing sectorial spalling typical of fatigue
material damaging
Page 6 CFM Proprietary Data Unauthorized Disclosure Prohibited
CFM56-7B - Southwest - ESN874265 - AGB input gearshaft roller bearing failure
5- AGB links examination (see chart 20 to 23)
 Quite good condition of upper link exhibiting only few axial and radial gap (0,15mm & 0,05mm respectively) at
spherical bearing matching with AGB upper mount.
 Bad condition of all 3 other received links affected by heavy wear (1,7mm axial max, 0,55 radial max) at each
spherical bearing consistent with wrong AGB adjustment measured by customer prior AGB removal (see table
of chart 20).
 On condition : (see charts 21 & 22)
 spherical bearings mainly worn on one side locally dug on 1 sector by interference with one of the 2
shoulders designed to keep in place the anti friction liner bonded to the outer ring,
 mount to interference marks.
 Good condition of ball bearing bores receiving the pins (no wear noticable).
 After cutting of the bearing exhibiting the maximum play : (see chart 23)
 anti-friction liner partially missing on one side,
 heavy wear of bearing outer journal at anti-friction missing location and adjacent shoulder that totally
disappeared by rubbing with spherical inner journal,
 hammered condition of spherical journal only noticeable at remaining–missing transition of anti-friction liner.
 The above findings, similar to those already done on Southwest –7B ESN 875402, confirm the spherical
bearing wear mechanism induced by relative movement of the bearing elements under vibrations.
Except upper link found in quite good condition, spherical bearing of all other 3 links exhibited heavy wear
as a consequence of vibrations as already identified on Southwest –7B ESN 875402 engine.
Page 7 CFM Proprietary Data Unauthorized Disclosure Prohibited
CFM56-7B - Southwest - ESN874265 - AGB input gearshaft roller bearing failure
6- AGB spherical bearing wear
 During removal of this AGB for the above bearing failure, spherical bearing of AGB links were found
worn.
 4 out of the 5 links were returned for investigation.
 Except quite good condition of upper link, all spherical bearings of the 3 rear links exhibited heavy wear
(until 1,7mm in axial direction and 0,55mm in radial) caused by relative movement of bearing elements
under dynamic loads.
 These findings are consistent with the wear mechanism already identified on Southwest –7B ESN
875402 after TSN/CSN = 10857/6864.
Note ; change in design study in progress to introduce new spherical plain bearing.
Page 8 CFM Proprietary Data Unauthorized Disclosure Prohibited
CFM56-7B - Southwest - ESN874265 - AGB input gearshaft roller bearing failure
7 – Conclusion : AGB input gearshaft “line 3” roller bearing failure
 Bearing failure cause : inner raceway spalling
 Consequences
 spalling of all the 14 balls
 looseness of both cage rails
 shaking - break away of outer race securing 3 studs,
 machining of AGB housing by rotation of the outer race and associated 3 studs over 10mm long,
 alternator rotor offset and contamination until interference with alternator stator…
 Dimensional part inspection did not show any nonconformity.
 Metallurgical examination of the inner race did not reveal any material anomaly other than material fatigue
evidenced by the presence of subsurface fatigue butterflies in raceway .
 Operating time accumulated by this bearing (14804h/9478cy) and spalling mechanism (initiation at inner
raceway fwd edge and subsequent roller spalling on fwd ends) leads to make an hypothesis that bearing
failure is consecutive to a constant inner race radial load potentially induced by an alternator rotor
unbalance ; however, no analysis on alternator parts to verify this hypothesis could be done, due to their
high damage condition
 Note : ESN874265’s is 1st reported case of failed AGB input gearshaft bearing SEIS in the CFM56-7B
20thSept.02, Southwest ESN 874171, TSN 16160 / CSN 10408 suffered a similar event; CFM has
requested hardware of this 2nd event back for investigation .
 No relation ship between roller bearing failure and AGB link wear has been evidenced ; CFMI experience on
CFM56-3 & -7B shows AGB misalignment consequences to be either ball bearing damage or horizontal drive
shaft crack-separation without any noticed consequence on roller bearing condition.
Page 9 CFM Proprietary Data Unauthorized Disclosure Prohibited
CFM56-7B - Southwest - ESN874265 - AGB input gearshaft roller bearing failure
Starter pad assy Line 3 gearshaft
MFP-HMU pad assy
Control
alternator
1 & 2- AGB as received
3 & 4- Control alternator stator - rotor wear condition resultant from rotor offset
3-
4-
5- Line 3 ball bearing view : no
evidence of damage
AGB
Wear
on 360°
Sectorial
wear (90°)
Page 10 CFM Proprietary Data Unauthorized Disclosure Prohibited
CFM56-7B - Southwest - ESN874265 - AGB input gearshaft roller bearing failure
Cross section showing line 3 configuration
1- General view of line 3 gearshaft after removal 2- Wear of outer race OD & condition of
the 3 studs remained attached with the outer race
3 & 4- Housing wear condition : elongation of the 3 stud holes and bore matching with outer race
Roller bearing outer race found
break away from AGB housing
3- 4-
Failed
bearing
Page 11 CFM Proprietary Data Unauthorized Disclosure Prohibited
CFM56-7B - Southwest - ESN874265 - AGB input gearshaft roller bearing failure
Detail views showing AGB housing hole elongation
10mm = stud
displacement
Thread marks
Gearshaft
rotation
direction
Page 12 CFM Proprietary Data Unauthorized Disclosure Prohibited
CFM56-7B - Southwest - ESN874265 - AGB input gearshaft roller bearing failure
1- Roller bearing outer raceway : general
quite good condition
First superficial
wear lines
formed
before studs
breakaway
2- Picture 1 detail showing the quite good condition of the roller
track except double wear lines caused by roller ends.
Second superficial
wear lines
formed
after studs
breakaway
& 1,5mm outer race
axial displacement
1,5mm (outer race rearward displacement)
Page 13 CFM Proprietary Data Unauthorized Disclosure Prohibited
CFM56-7B - Southwest - ESN874265 - AGB input gearshaft roller bearing failure
1- Roller & cage view : good condition
of the cage but all 14 rollers exhibit
spalling evidence at fwd edge side 2- Detail of spalling condition at fwd edge side
representative of all 14 rollers
3- Complementary views showing roller
condition representative of the 14.
Spalling Sliding
marks
Fwd face
Page 14 CFM Proprietary Data Unauthorized Disclosure Prohibited
CFM56-7B - Southwest - ESN874265 - AGB input gearshaft roller bearing failure
1- 3- 2-
1 to 3- Rotor/gearshaft relative angular positions - matching marks
Control alternator rotor Line 3 gearshaft
4- Same angular position of bearing inner
raceway spalled sector and alternator rotor wear sector
5- (opposite to 4-) quite good condition of both
alternator rotor & roller bearing inner raceway
Sectorial
spalling
(115°)
Wear
sector
(90°)
Page 15 CFM Proprietary Data Unauthorized Disclosure Prohibited
CFM56-7B - Southwest - ESN874265 - AGB input gearshaft roller bearing failure
1 & 2- Roller bearing inner race sector spalling
originating from fwd edge of the raceway
3 & 4- Good condition of race - out of spalled sector - .
Note : blue discoloration of fwd edge of roller raceway
Initiation
area
Blue
discoloration
Roller
passing
direction
Page 16 CFM Proprietary Data Unauthorized Disclosure Prohibited
CFM56-7B - Southwest - ESN874265 - AGB input gearshaft roller bearing failure
Dia. Dia.OR
A
Dia.
Dia.B IR
Dim. checked B/P
Values
Measured values
Prior removal After removal Comments
Dia. A 34,992 to 35 --- 34,999 to 35,000 Conform (interference fit = 28μm)
Dia. B / outer race 61,991 to 62,000 --- 62,00 Conform
Dia. B / AGB housing 61,80 to 62,20 --- 61,98 Conform
Dia. IR 40,35 (at spalling location)
to 40,475 (90° apart) 40,450
Dia. OR
Defined through
radial clearance
--- 56,475
Roller dia. 8 --- 7,996 to 7,997
Correct values and radial gap
32μm vs. 31 to 50 required
IR shoulder width Defined through axial
gap --- 8,03
Roller length 8 --- 7,997 to 7,999
Correct axial gap
31 to 33μm vs. 20 to 50 required
Dia. C / gearshaft 12,976 to 12,994 --- 12,975
Dia. C / rotor 13,000 to 13.010 --- 12,990
Correct
Dia. D / gearshaft 22,199 to 22,221 --- 22,20
Dia. D / rotor 22.238 to 22.250 --- 22,24
Correct
Dia. E 35,026 to 35,038 --- 35,028 Conform
Dia. F 45,026 to 45,038 --- 45,030 Conform
Page 17 CFM Proprietary Data Unauthorized Disclosure Prohibited
CFM56-7B - Southwest - ESN874265 - AGB input gearshaft roller bearing failure
A
B
1- Location of
cross sections
made through inner race
2- Labeled “A” micrographic view showing axial grain flow.
2- Typical M50 microstructure except hammering
condition underneath spalling damage
3- Detail showing correct martensitc microstructure
with small carbide networks
Good condition of the shoulders free from wear and or overheat
Inner race track
Roller passing
direction
Page 18 CFM Proprietary Data Unauthorized Disclosure Prohibited
CFM56-7B - Southwest - ESN874265 - AGB input gearshaft roller bearing failure
1 to 3- Cross section labeled “B” on previous chart
6- Hammered condition of the microstructure as
a consequence of repetitive roller impact when
passing spalling step
4- Spalling cracks and correct
microstructure
5- Fatigue butterfly detail
1- End of spalling at roller entry side 2- Spalling sector close to initiation site 3- End of spalling at roller exit side
Page 19 CFM Proprietary Data Unauthorized Disclosure Prohibited
CFM56-7B - Southwest - ESN874265 - AGB input gearshaft roller bearing failure
1- Illustration showing location
of cross section
2- Micrographic view of spalling cracks
3- Spalling cracks detail 4- Typical correct M50 microstructure 5- Spalling crack with flaking partially liberated
Roller rotation direction
Page 20 CFM Proprietary Data Unauthorized Disclosure Prohibited
CFM56-7B - Southwest - ESN874265 - AGB input gearshaft roller bearing failure
Upper link
Rear link “1”
Rear link “2”
Adjustable turnbuckle link
Upper link Rear link “Characterization 1” Adjustable link Rear link “2”
of axial and
radial gap Axial Radial Axial Radial Axial Radial Axial Radial
Spherical bearing
“A”
0,15
mm
0,05
mm
1.20
mm
0,25
mm
0,90
mm
0,25
mm
1,30
mm
0,55
mm
Spherical bearing
“B” 0 0 0,35
mm
0,13
mm
1,70
mm
0,50
mm
0,95
mm
0,40
mm
Spherical bearing
“C” 0 0 --- --- --- --- --- ---
A
C B
A B
A B
A B
View of received AGB links randomly repositioned due to the none marking of the parts prior disassembly
Axial
Radial
Page 21 CFM Proprietary Data Unauthorized Disclosure Prohibited
CFM56-7B - Southwest - ESN874265 - AGB input gearshaft roller bearing failure
Adjustable turnbuckle link
2 & 3- Detail showing wear condition of each ball bearings
Wear
groove
Wear
groove
Wear
Page 22 CFM Proprietary Data Unauthorized Disclosure Prohibited
CFM56-7B - Southwest - ESN874265 - AGB input gearshaft roller bearing failure
1 to 3- Supposed rear upper link views showing
wear condition of ball bearings
4 to 6- Same as above for supposed rear lower link
Interference wear marks
Page 23 CFM Proprietary Data Unauthorized Disclosure Prohibited
CFM56-7B - Southwest - ESN874265 - AGB input gearshaft roller bearing failure
1 & 2- Complementary views showing the wear condition of both outer journal
and anti-friction liner partially missing
3- Wear condition of the ball bearing
4- Detail of fretting wear condition
associated with missing anti-friction liner
5- Preferential contact area on 6- Illustration showing missing
shoulder at 1 outer ring side
Shoulder
still present
Shoulder
totally
worn out
Anti-friction
liner
Portion of inner ring surface
free from significant wear