Controlled Unclassified Information
Air Force Life Cycle Management Center
Innovate, Accelerate, Thrive – The Air Force at 75
54H60 Propeller
Barrel Cracking
Peter Christiansen, NH-04
C-130 Chief Engineer
Controlled Unclassified Information
1
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UNCLASSIFIED
Background
• Three 54H60 barrels found with cracking
• Cracking not previously identified at this location
• Barrels removed from service due to persistent leaks
• Barrel histories show that each removed several times for reseal due to leakage
• Barrel 2017080043 crack identified 15 March 22 at 296.7 flight hours
• Prop routed to prop shop from PDM aircraft due to leakage
• Barrel 2013020019 crack identified 9 May 22 at 844.8 flight hours
• Prop inducted into overhaul due to leakage
• Barrel 2020120063 crack identified 5 July at 332.5 flight hours
• Youngstown ARB identified crack based on maintenance advisory due to leakage
• Cracking on barrels initiated from the “2” in the serial number
• Serial number etched during initial propeller build-up at WR-ALC
• Technical Order requires the use of “electrolytic etching” or an “acid pen”
• Serial numbers were etched using electric arc pen – not authorized
• Unknown when electric arc pen was introduced
• Likely used on all barrels since and some barrels prior to prop overhaul restart in 2018
As of:
Innovate, Accelerate, Thrive – The Air Force at 75
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2
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Barrel 2017080043
As of:
Innovate, Accelerate, Thrive – The Air Force at 75
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3
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Barrel 2013020019
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Innovate, Accelerate, Thrive – The Air Force at 75
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4
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Barrel 2013020019
As of:
Innovate, Accelerate, Thrive – The Air Force at 75
UNCLASSIFIED
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5
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Barrel 2020120063
As of:
Innovate, Accelerate, Thrive – The Air Force at 75
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6
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Discussion
• Use of electric arc pen to mark the barrel induced multiple issues
• Localized areas at marking locations heated to >1400oF
• Heating introduced 3 negative effects, any of which can cause cracking to initiate
• Heating altered the microstructure causing untempered martensite to form
• Untempered martensite is extremely hard but brittle (low fracture toughness)
• Untempered martensite zone extended up to 0.012” below the surface
• Likely present everywhere the pen was used
• Heating in etched areas also eliminates the fatigue resistance provided by shot peening
• May have also introduced liquid metal embrittlement from cadmium coating
• Crack propagation
• Microcracking may be present anywhere arcing pen was used
• Front and rear halves all along the serial number
• Large cracks have only formed in highly stressed fillet radius at #1 blade boss
• Assessment
• All cracked barrels have exhibited persistent hydraulic fluid leakage
• Cracking could lead to catastrophic loss of blade/propeller/aircraft if left undetected/in-service
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Innovate, Accelerate, Thrive – The Air Force at 75
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7
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Untempered Martensite
As of:
Innovate, Accelerate, Thrive – The Air Force at 75
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8
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Areas of High Stress Concentrations
Takeoff Condition
As of:
Innovate, Accelerate, Thrive – The Air Force at 75
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Analysis
• Cracked barrels removed from service due to Hydraulic fluid leaks
• Aircraft with cracked barrels performed 7 flights (22 Takeoff/landings) after leaks first detected
• Without detection of hydraulic fluid leaks a catastrophic failure would have occurred
• Analysis indicates that crack propagates to critical length quickly once leak detectable
• Estimate 1-4 flights from leak to potential failure
• Crack on 2017080043 was at or near critical length and could have failed during the next flight
• Barrel 2020120063 visually examined by engineering
• Known crack could not be identified visually
• Indicates the visual inspection directed by TCTO 3H1-18-517 not likely to identify cracking
• TCTO does provide detailed pictures of the barrel etching for assessment
• Additional undetected cracks are likely present on barrels in USAF fleet
• Collins conducted quantitative risk assessment
• Risk assessment projects up to 3 failures if left unmitigated
• Failures correlate
a HIGH
CannottoEnsure
Allrisk
Cracks will be Detected Before Catestrophic Failure
As of:
Innovate, Accelerate, Thrive – The Air Force at 75
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10
54H60 HUB FRACTURE MECHANICS MODEL 4.1
ASSUMPTIONS
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“Typical” Flight
NASGRO Model SC31
Start Crack
a=0.012, a/c = 0.15
Matl = 4340, UTS = 180
K1c = 80
1P load TO/CL = 1min
GW = 130 K lbs
Max / Min Stress = 2D
Cruise for 120 min
125 K lbs
Reverse every flight
Max / Min 2 D Stress
GAG every flight
0 to Max TO/CL
Limit Load 2.5g bank, 155 GW
none
Crit Crack Size (c+c1) = 3.73
Dist from org, c = 1.96
Flights = 177
Last Chance Leak at 176
Critical Crack size –
TOTAL LENGTH,
“c+c1” (in.)
Critical Crack Length
USAF cracks
506
1st Leak Chance at 172
6 flights to
fracture after
break through
of the wall
(177-171)
NDI detectable limit
11
© 2022 Collins Aerospace. | Collins Aerospace proprietary per title slide. | U.S. Export Classification: EAR 9E991, CLS20331006, 20 Jul to 26 Sep 2022
Note: Gold items added by USAF
54H60 HUB FRACTURE MECHANICS MODEL 4.1
ASSUMPTIONS
•
•
•
•
•
•
•
•
•
•
•
•
•
NASGRO Model SC31
Start Crack
a=0.012, a/c = 0.15
Matl = 4340, UTS = 180
K1c = 80
1P load TO/CL = 10 min
GW = 130 K lbs
Accounts for TAGs
Max / Min Stress = 2D
Cruise for 120 min
125 K lbs
Reverse every flight
Max / Min 2 D Stress
GAG every flight
0 to Max TO/CL
Limit Load 2.5g bank, 155 GW
none
Crit Crack Size (c+c1) = 3.2
Dist from org, c = 1.63
Flights = 43
Training Flight
Last Chance Leak at 42
1st Leak Chance at 40
Critical Crack size –
TOTAL LENGTH,
“c+c1” (in.)
4 flights to
fracture after
break through
of the wall (4339)
12
© 2022 Collins Aerospace. | Collins Aerospace proprietary per title slide. | U.S. Export Classification: EAR 9E991, CLS20331006, 20 Jul to 26 Sep 2022
Note: Gold items added by USAF
54H60 HUB FRACTURE MECHANICS MODEL 4.1
ASSUMPTIONS
•
•
•
•
•
•
•
•
•
•
•
•
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Long Flight
NASGRO Model SC31
Start Crack
a=0.012, a/c = 0.15
Matl = 4340, UTS = 180
K1c = 80
1P load TO/CL = 1min
GW = 130 K lbs
Max / Min Stress = 2D
Cruise for 540 min
125 K lbs
Reverse every flight
Max / Min 2 D Stress
GAG every flight
0 to Max TO/CL
Limit Load 2.5g bank, 155 GW
none
Crit Crack Size (c+c1) = 4.0
Dist from org, c = 2.95
Flights = 151
1 Leak Chance at 150
Critical Crack size –
TOTAL LENGTH,
“c+c1” (in.)
2 flights to
fracture after
break through
of the wall
(151-149)
13
© 2022 Collins Aerospace. | Collins Aerospace proprietary per title slide. | U.S. Export Classification: EAR 9E991, CLS20331006, 20 Jul to 26 Sep 2022
Note: Gold items added by USAF
CUI
UNCLASSIFIED
Way Forward and Current Status
Aircraft with 54H60 Propellers
• Categorize propellers as follows:
• High risk (Red) – Barrel etched with electric arc pen in the fillet radius
• Serious risk (Yellow) – Barrel etched with electric arc pen, not in radius
• Nominal risk (Green) – Barrel etched with approved methods
• 116 active aircraft with 54H60 propellers (100 C-130H, 7 EC, 1 TC, 8 MC)
• 464 propellers needed
• 417 propellers installed IAW CEMS – 26 Sep 2022
• 408 reported in AIRCAT IAW TCTO 3H1-18-517, 9 have not been reported
• 384 High risk (Red), Note: 62 of 384 could be yellow or green - pictures insufficient
• 23 Serious Risk (Yellow)
• 1 Marked appropriately (Green)
• 186 spare/uninstalled props reported in AIRCAT IAW TCTO 3H1-18-517
• 174 High risk (Red), Note: 19 of 174 could be yellow or green - pictures insufficient
• 9 Serious Risk (Yellow)
• 3 Marked appropriately (Green)
Currently No Aircraft with 4 Yellow/Green Propellers Installed
As of:
Innovate, Accelerate, Thrive – The Air Force at 75
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Recommendations
• Do not accept High risk and discontinue operations for all aircraft
with at 1 or more Red propellers
• Accept Serious risk and allow operations for aircraft with all
Yellow/Green propellers only
• Issue Immediate action TCTO to force all Red propellers to be
removed from aircraft before flight
• Requires concurrence from CAE
• Issue 2 safety supplements to the job guides
• Installation of Red props not allowed during propeller or prop/engine install
• Develop recovery plan
• Long term: Develop burn-down plan to force attrite Yellow
propellers
• Notify US Navy and FMS operators
• Do not transfer EDA aircraft with Red propellers
As of:
Innovate, Accelerate, Thrive – The Air Force at 75
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Backup
As of:
Innovate, Accelerate, Thrive – The Air Force at 75
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16
54H60 HUB FRACTURE MECHANICS MODEL 4.1
ASSUMPTIONS
•
•
•
•
•
•
•
•
•
•
•
•
•
NASGRO Model SC31
Start Crack
a=0.012, a/c = 0.15
Matl = 4340, UTS = 180
K1c = 80
1P load TO/CL = 1min
GW = 130 K lbs
Max / Min Stress = 2D
Cruise for 120 min
125 K lbs
Reverse every flight
Max / Min 2 D Stress
GAG every flight
0 to Max Limit Load
Limit Load 2.5g bank, 155 GW
30 seconds per flight
Crit Crack Size (c+c1) = 3.14
Dist from org, c = 1.64
Flights = 52
Last Chance Leak at 51
1st Leak Chance at 48
Critical Crack size –
TOTAL LENGTH,
“c+c1” (in.)
5 flights to
fracture after
break through
of the wall,
(52-47)
17
© 2022 Collins Aerospace. | Collins Aerospace proprietary per title slide. | U.S. Export Classification: EAR 9E991, CLS20331006, 20 Jul to 26 Sep 2022