Report 1102-13

Airmotive Engineering Corp.

2100 Mannix

San Antonio, TX 78217-5994

Tel (210) 820-2450

Fax (210) 820-2451

REPORT 1102-13

Prepared By: D. Kenton, Donald J. Kenton, Sc. D., LLC

4/30/2011 Analysis of AEC631397 Cylinder Assembly 

Head - Barrel Separations

Technical Report
Report 1102-13

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CONTENTS

ABSTRACT.................................................................................................................. 2

BACKGROUND ........................................................................................................... 3

TECHNICAL APPROACH............................................................................................... 3

Design and Service Bulletin Data...................................................................................... 3

Production and Warranty Data ........................................................................................ 4

Visual Examination ........................................................................................................... 4

Summary Listing of Separated Cylinders.......................................................................... 4

Statistical Assessment ...................................................................................................... 4

Analysis of Head-Barrel Interface..................................................................................... 6

RESULTS AND DISCUSSION......................................................................................... 7

Design and Service Bulletin Data...................................................................................... 7

Production and Warranty Data ...................................................................................... 11

Visual Examination ......................................................................................................... 13

Summary Listing of Separated Cylinders........................................................................ 15

Statistical Assessment .................................................................................................... 22

Cylinder Population Group MSB4-1............................................................................. 22

Population Group SB6-2............................................................................................... 28

Population Group Post SB6-2....................................................................................... 34

Repaired Cylinder Assemblies...................................................................................... 38

Analysis of Head-Barrel Interface................................................................................... 39

Population Group Identification and Material Properties........................................... 39

Coefficient of Sliding Friction....................................................................................... 41

Interference Fit Estimates at Operating Temperature ................................................ 42

Removal Force Estimates............................................................................................. 48

FINDINGS AND RECOMMENDATIONS ........................................................................62

Findings........................................................................................................................... 62

Recommendations.......................................................................................................... 64

ATTACHMENT 1. FAA MDR AS OF 1/13/04, AEC631397 SEPARATIONS ......................66

ATTACHMENT 2. TENSILE STRENGTH - TEMPERATURE GRAPH FOR A242.0................67

ATTACHMENT 3. THERMAL EXPANSION COEFFICIENT FOR SAE4140 STEEL ................68

ATTACHMENT 4. COMPUTATION OF THE EFFECTIVE FRICTION COEFFICIENT .............69

Push-Off Test Data Provided by Airmotive Engineering .............................................. 69

Calculations for Friction Coefficient............................................................................. 69
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ATTACHMENT 5. THERMAL EXPANSION COMPUTATIONS .........................................72

ATTACHMENT 6. REMOVAL FORCE GRAPHICAL SUMMARY NOMINAL, MAXIMUM, AND MINIMUM 

FIT CONDITONS.........................................................................................................76

REFERENCES..............................................................................................................88

ABSTRACT

Airmotive Engineering produced 43,767 replacement cylinder assemblies for TCM 520/550 

series engines from 8/29/02 through 12/31/10. This analysis identified four separate 

populations, SB4-1, SB6-2, Post SB6-2, Post SB6-2-INT-A, defined by mandatory service bulletins 

and design adjustments. Visual inspection and analysis confirmed three failure modes:

1. Fatigue in the head shrink band to dome fillet radius

2. Fatigue in the first loaded head thread

3. Stripped threads in repaired cylinders

Weibull statistical analysis for population group MSB4-1 projected risk of failures driven by 

thread fatigue. Head fillet radius fatigue failure dominated risk projections of group MSB6-2. 

Weibull statistical analysis for group Post SB6-2 revealed a cumulative distribution function for 

thread fatigues failures with a shape characteristic similar to that of distributions observed for

populations prone to fatigue failures in the head fillet radius. Risk projections for group Post 

SB6-2 suggested 5% of the in service population had a significant risk for thread fatigue failure.

Diametrical interference and press fit removal force computations showed groups SB4-1, SB6-2, 

and Post SB6-2 will transfer most, or all, of the combustion load into the thread below the 

maximum design interface temperature, if assembled at nominal or minimum interference fit. 

Current production cylinders, Post 6-2-INT-A, assembled at nominal or greater interference fit 

will support more than 50% of combustion load to the threads at maximum interface design 

temperature of 375F. At minimum interference fit, Post 6-2-INT-A cylinders will transfer about 

85% of the combustion load to the threads at 375F interface temperature. Increasing the 

interference fit of current production cylinders by 0.007-inch should avert all transfer of load to 

the threads at minimum interference up to 425F interface temperature.

For improved tracking and management of continued operational safety, we recommend 

installation of a sequential serial number assignment system for cylinder assemblies.

We recommend continuing repetitive inspections described in service bulletin MSB6-2 for groups 

SB4-1 and SB6-2, and adding an examination for cracks at fins 5 - 7 and 9 - 10 counting from 

the bottom of the head. 

We recommend creating a service bulletin for group Post MSB6-2 calling for repetitive

inspections beginning at 250-hours culminating in permanent removal of these service at the next 

scheduled overhaul. 

We recommend testing to measure actual cylinder interface temperatures, and consideration of a 

service bulletin calling for removal and rework of cylinders consuming oil from improper break-in.
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Report 1102-13

A N A L Y S I S O F A E C 6 3 1 3 9 7 C Y L I N D E R A S S E M B L Y H E A D -

B A R R E L S E P A R A T I O N S

BACKGROUND

Airmotive Engineering (AE) AEC631397 cylinder assemblies, produced under parts manufacturing 

approval, intended for use in Teledyne Continental (TCM) 520/550 series engines have experienced a 

number of head - barrel separation events attributable to manufacturing induced deficiencies, 

inherent design deficiencies, and in-service operation beyond the design operating parameters. AE has 

issued mandatory service bulletins to address field service issues, and has incorporated a number of 

design adjustments to mitigate inherent and induced deficiencies in the assembly. This report 

investigates head barrel separation events related to cylinders produced beginning in September 2002

through December 2010. 

Our investigation will include review of relevant design drawings to identify cylinder assembly 

configurations, direct examination of available separated cylinder assemblies, assessment of failure 

frequency and projected risk through statistical methods, and use of material characteristics combined 

with mechanics to provide guidelines for continued operational safety as well as further design 

optimization.

TECHNICAL APPROACH

Broadly speaking our technical approach will comprise a number of elements:

1. Use available data to determine cylinder assembly configuration.

2. Review production and warranty service data to determine the relevant cylinder assembly 

populations.

3. Conduct visual inspections of separated cylinder assemblies on site at AE facilities.

4. Compile a summary listing of separated cylinder assemblies.

5. Statistically assess the cylinder populations to project failure frequency and risk factors for the 

relevant populations.

6. Use design information, projected operating conditions, known material properties, and 

mechanics to determine guidelines for assessing robustness of the head - barrel interface 

cylinders and offer guidelines for potential interface design improvements.

Design and Service Bulletin Data

This study focuses on those AEC631397 cylinders intended for use in TCM 520/550 series, identified as 

classes 71.2, 71.4, 76.0, and 76.3, and excludes the GTSIO520 series. With emphasis on the head 

configuration and head - barrel interface, this study examined the following drawings:

1. AEC631397, Cylinder Assembly for Classes 71.2, 71.4, 76.0, and 76.3

2. AEC65385, Cylinder Head
Report 1102-13

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3. AEC631399, Thread and Pilot diameters

4. AEC65415, Machining, Cylinder Head

5. AEC634501, Barrel, Cylinder 5.25-inch Bore 

6. AE65041, Choke Configurations - Opposed Engines

Along with the design data, two service bulletins apply to the subject cylinder assemblies: 

1. Mandatory Service Bulletin (MSB) 4-1 originally issued 3/4/04.

2. MSB 6-2 originally issued 8/25/06.

From this data, we identified the relevant cylinder assembly populations based that would correlate 

with the applicable MSB and relevant design configuration.

Production and Warranty Data

AE queried its production database to provide tabular data of all cylinders shipped from 8/29/02 

through 12/31/10. Based on the identified cylinder assembly populations, we created individual 

databases for each population.

Visual Examination

The AE quality assurance department retrieved from storage several TCM 520 cylinders that 

experienced a head - barrel separation. A visual examination of these units identified the failure 

location and confirmed the cyclic propagation of the failure. 

Summary Listing of Separated Cylinders

Using FAA Maintenance Difficulty Reports (MDR) and AE data, we compiled a consolidated list of 

traceable cylinders experiencing a head - barrel separation. For completeness, we compiled a second 

listing of those cylinders identified in the MDR's as separated, but not relevant to this study or not 

traceable. This group includes several repaired cylinders experiencing a head - barrel separation. 

Separately, the FAA provided a listing of cylinders belonging to the population addressed by MSB4-1 

that had failed. Subsequently, we utilized the FAA provided data and data from repaired cylinders to 

assist in estimation of failure rates associated with different failure modes.

Statistical Assessment

Life limited populations generally conform to a cumulative distribution curve first proposed by Waloddi 

Weibull1. These distributions are of the form

EQUATION 1 

 / 

( ) 1 tF t e



 

 

Where:

F(t) = Fraction failing up to time t (Cumulative Distribution Frequency)
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t = Failure time

β = Shape parameter (slope of a straight line on a log-log plot)

η = Characteristic life (63.2% of population will fail by characteristic life)

e = base for natural logarithms (2.718281828)

Best practice fitting data to these curves uses median ranked regression analysis rather than mean 

based rank because of the skew in the data to toward longer lives. Our analysis will rely on the same 

procedure and use software developed by Abernethy's group (Ref. 1) for this purpose.

Risk projection involves computation of the "Now Risk", which uses the cumulative distribution curve 

to confirm the actual numbers of failed articles. Assuming actual reported failures generally agrees 

with the computed Now Risk, we can use the cumulative failure distribution function to project the risk 

of failure for units in the field. 

Now Risk is given by:

EQUATION 2

   

1 1

2

r s

i i

i i

NowRiskRBA F t F t

 

   

Where:

NowRiskRBA = Now Risk with reduced bias adjustment

F(ti) = Cumulative Failure Distribution curve for the population

r = number of failures

s = number of units still operating (suspensions)

Equation 3 mathematically describes the Failure Forecast:

EQUATION 3

   

1  

i i

i

F t u F t

FailureForecast

F t

 







Where:

F(ti) = probability of failure of unit i in first ti hours

F(ti+u) = probability of failure of unit I in the usage period, u

Using best practices, we fit a Weibull type cumulative damage function to each population. When the 

plots and engineering knowledge suggest multiple failure modes are in play, we will use best practices 

methodology to identify and group cylinders associated with each failure mode, which permits creation

of separate cumulative damage functions for each failure mode.

Our statistical analysis will apply the Weibull distribution to the identified failures without field 

suspensions to assess the curve characteristics. We then assessed the identified populations 
Report 1102-13

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incorporating the in service suspensions. This will allow reasonable estimates of failure rate projection 

and failure forecasting.

Field failures use time in service (TIS), typically hours since installation. However, we do not know TIS 

for the population in the field. For in service suspensions the general aviation industry commonly 

accepts an aircraft use rate of 100 hours per year. Therefore, based on the shipping date for each 

cylinder identified in the population still in service, we used a service accumulation rate of 100 hours 

per year to estimate TIS.

When warranty data indicates a cylinder returned to AE for consideration, we considered that cylinder 

as permanently removed from service. Thus, our standard practice assumed all cylinders on the 

production list, less failures and warranty returns, remain in service.

Analysis of Head-Barrel Interface

Fatigue failure of the first loaded head thread is a known failure mode for these cylinders. Work 

performed on AEL65102 cylinder assemblies2has shown that insufficient interference will result in 

cyclic load transferred to the threads. Our assessment of the AEC631397 cylinder configuration will 

begin with estimation of interference fits at head-barrel interface temperatures between 350F and 

425F, based on known cylinder configurations and thermal expansion coefficients of the head and 

barrel material for the following conditions:

1. Nominal

2. Condition 1 - Maximum interference at the shrink band and the threads

3. Condition 2 - Minimum interference at the shrink band and the threads

4. Condition 3 - Maximum interference in the threads, minimum interference in the shrink band

5. Condition 4 - Minimum interference in the threads, maximum interference in the shrink band

These curves will provide diametrical data necessary to compute removal force from press fit 

assemblies.

Next, we estimated removal force on press fit cylinder heads and barrels for the following conditions

1. Nominal

2. Condition 1 - Maximum interference at the shrink band and the threads

3. Condition 2 - Minimum interference at the shrink band and the threads

An Excelcals.com program based on press fit formulas found in standard texts on machine design3

offered a convenient means to estimate press fit removal force. Assuming the threaded area acts as a 

smooth wall cylinder at the thread pitch diameter we calculated separate removal forces for the shrink 

band and threaded areas, then added the separate forces to determine the total resistance to removal. 

These calculations require knowledge of a number of mechanical and physical properties of the 

materials of construction including material tensile properties, Young's modulus, Poison's ratio, and 

friction coefficient between head and barrel. Besides shrink band and thread-pitch diameters, the
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calculations require estimation of the following cylinder characteristics at the required operating 

temperature including:

1. Respective contact lengths of the shrink band and threaded sections

2. Outer radius of the cylinder head

3. Inner radius of the cylinder barrel

4. Diameter of the piston at the interface temperature and knowledge of measured peak cylinder

pressures

The removal force calculations result in Force - Temperature curves for each relevant cylinder interface 

geometry, assembly interference fit, and interface operating temperature with reference to the 

estimated maximum combustion pulse force experienced by the cylinder. A total removal force less 

than the computed combustion pulse force will indicate cyclic load transfer to the threads. 

RESULTS AND DISCUSSION

Design and Service Bulletin Data

As noted in the Technical Approach, a number of subordinate drawings provide technical data input 

necessary to manufacture AEC631397 cylinder assemblies:

1. AEC65385, Cylinder Head

2. AEC65415, Machining, Cylinder Head

3. AEC631399, Thread and Pilot diameters

4. AEC634501, Barrel, Cylinder 5.25-inch Bore 

5. AE65041, Choke Configurations - Opposed Engines

Table 1 provides a summary listing for relevant drawings and dimensional features supporting 

AEC631397 cylinder assemblies applicable to output classes 71.2, 71.4, 73.0, and 73.6, intended as 

replacement cylinder assemblies for TCM 520/550 series engines.

TABLE 1. SUMMARY OF SUBORDINATE DRAWING DATA

Table 1A. AEC65385 Head Casting

Dwg No. Rev Date Changes/Adjustments Comments

AEC65385 C Bench mark 1. Effective drawing on 8/29/02

2. Combined casting and machining drawing

Effective at start of SB4-1 

Oberdorfer casting

D 3/7/03 Redrawn to separate head machining from 

casting

Effective through end of SB4-1 and 

through SB6-2

E 5/11/05 Added material to exterior wall contour on 

exhaust side to minimize cracking

Implemented 11/12/05 and covers 

post SB6-2 period through 2/06.

F 2/2/06 1. Minor changes to improve 

manufacturability and tracking

2. No changes to wall thickness

Effective for SB6-2 through 11/09. No 

change in exhaust side exterior wall 

contour
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Dwg No. Rev Date Changes/Adjustments Comments

J 12/03/09 Added material to fuel injector boss to 

minimize cracking in this area 

1. Rev. G, H not produced

2. No change in exhaust side exterior 

wall contour

3. Introduced 1/10

Table 1B. AEC65415 Head Machining

Dwg No. Rev Date Changes/Adjustments Comments

AEC65415 IR 3/7/03 Redrawn from AEC65385 Rev. C No effect on cylinder interface or head 

cracks

A 5/3/05 Minor adjustments No effect on cylinder interface or head 

cracks

B 3/3/06 Minor adjustments No effect on cylinder interface or head 

cracks

C 3/19/07 Minor adjustments No effect on cylinder interface or head 

cracks

D 7/11/08 Reinstated Allison style back intake valve seat 

configuration

1. Increase wall thickness on intake 

valve side of cylinder head.

2. Implemented in 10/08

E 9/23/09 Minor change to notes No effect on cylinder interface or head 

cracks

Table 1C. AE65041 Choke Configuration

Dwg No. Rev Date Characteristic 

Cylinder ID

(Dia F) (in)

Changes/Adjustments Comments

AE65041 F Bench mark 5.2530

5.2510

1. Effective drawing on 8/29/02

2. Use for establishing nominal ID of barrel

No effect on cylinder interface

G 9/27/02 5.2530

5.2510

Minor changes No effect on cylinder interface

H 8/1/05 5.2530

5.2510

Minor changes No effect on cylinder interface

J 11/30/06 5.2530

5.2510

Minor changes No effect on cylinder interface

K 2/28/07 5.2530

5.2510

Minor changes No effect on cylinder interface

Table 1D. AEC631399 Cylinder Head Thread and Pilot Diameters

Dwg No. Rev Date Interference 

(in)

Dome Fillet 

Rad. (in)

J - Head Pitch 

Max. Dia. (in)

J - Head Pitch 

Min. Dia. (in)

H - Head 

Band Max. 

Dia. (in)

H - Head 

Band Min. 

Dia. (in)

AEC63199 G 2/1/2001 >= 0.007 .025-.035 5.554 5.552 5.459 5.457

H 12/2/2003 >= 0.007 .025-.035 5.554 5.552 5.459 5.457

J 3/17/2004 .009-.014 .040-.050 5.554 5.552 5.459 5.457
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Dwg No. Rev Date Interference 

(in)

Dome Fillet 

Rad. (in)

J - Head Pitch 

Max. Dia. (in)

J - Head Pitch 

Min. Dia. (in)

H - Head 

Band Max. 

Dia. (in)

H - Head 

Band Min. 

Dia. (in)

K 3/25/2005 .009-.014 .040-.050 5.554 5.552 5.459 5.457

L 1/23/2007 .009-.014 .040-.050 5.554 5.552 5.459 5.457

M 3/11/2009 Up to 0.020 .045-.055 5.552 5.550 5.455 5.453

N 8/18/2009 Up to 0.020 .045-.055 5.552 5.550 5.453 5.451

Notes to Table 1D:

1. Dome fillet radius in the clearance area was set at 0.03-inch nominal through 11/05.

2. Revision K implemented in 11/05 introduced a larger fillet radius.

3. Revision H through L retained same shrink band and thread diameters establishing the 

interference levels shown.

4. Revision N implemented 10/13/09 adjusted the shrink band and thread diameters to increase 

interference fit.

Table 1E. AEC634501 Barrel, Cylinder 5.25-inch Bore

Dwg No. Rev Date Interference (in) X - Barrel Pitch 

Max. Dia. (in)

X - Barrel Pitch 

Min. Dia (in)

Y - Barrel Band 

Max. Dia. (in)

Y - Barrel Band 

Min. Dia. (in)

AEC634501 N 2/28/2002 .009-.014 5.566 5.563 5.471 5.468

P 1/22/2004 .009-.014 5.566 5.563 5.471 5.468

R 4/28/2004 .009-.014 5.566 5.563 5.471 5.468

T 6/27/2005 .009-.014 5.566 5.563 5.471 5.468

U 11/10/2005 .009-.014 5.566 5.563 5.471 5.468

V 3/23/2006 .009-.014 5.566 5.563 5.471 5.468

Notes to Table 1E:

1. Barrel thread pitch diameter and shrink band diameter have not changed throughout the 

production run from 8/29/2002 through 12/31/2010.

Examination of Table 1 shows AE addressed three significant issues affecting cylinder cracking. First,

AE introduced AEC65385 Revision E with increased wall thickness on the exhaust port side to prevent 

thermal fatigue cracks associated with these areas identified by MSB6-2. Later AE introduced 

AEC65385 Revision J to address observations of cracks in the fuel injector boss found during overhaul 

of cylinders4.

Second AE adjusted AEC631399 thread and pilot dimensions to increase the shrink band to dome fillet 

radius in the clearance area between the barrel shrink band and cylinder head, implemented in 

November 2005. 

Third, AE adjusted AEC631399 to increase the interference fit, implemented in October 2009. As our 

analysis will demonstrate, the latter changes had significant effect on the integrity of the head-barrel 

interface area.
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Table 2 summarizes applicable mandatory service bulletins that resulted in service removals or 

warranty rework.

TABLE 2. SUMMARY OF SERVICE BULLETINS

Group From To SN Start SN End Description Issue

MSB4-1 9/1/2002 5/12/2003 1 7708 1. Sporadic deviation occurred from approved 

heat treatment 

2. Cracks could occur at fin 9 or 10 counting 

from shrink band. Remove from service for 

inspection

3/1/2004

MSB6-2 5/13/2003 11/29/2005 7709 33696 1. Inspect cylinders for cracks that may lead to 

loss of compression 

2. Recurring inspections each 50 hours starting 

at 500 hours 

3. Cracks associated with 7th fin from bottom 

of head on exhaust side

8/25/2006

Notes to Table 2:

1. The FAA issued AD2004-08-10 to insure compliance with MSB4-1. 

These drawings and service bulletins form the basis for segregating the cylinder assembly population 

into sub-groups aligned with service bulletins and drawing configurations. Thus, we have:

1. Group SB4-1 (4-1), cylinders produced affected by the mandatory service bulletin to inspect or 

replace cylinders that did not receive proper heat treatment.

2. Group SB6-2 (6-2), cylinders produced affected by the mandatory service bulletin of repetitive 

inspections for wall cracks.

3. Group Post SB6-2 (P6-2), cylinders produced from a head casting with greater wall thickness, 

including assemblies incorporating the Allison style back on the intake valve seat

4. Group Post SB6-2-INT-A (P6-2INT-A), cylinders produced with thicker walled head castings and 

incorporating improved interference fit with Allison style backed intake valve seats

Table 3 summarizes pertinent identification and configuration information for each identified 

population group.

TABLE 3. IDENTIFIED AEC631397 CYLINDER POPULATION GROUPS

Group From To SN Start SN End AEC65385

Head

AEC631399

Head 

Threads

AEC634501

Barrel

AEC65414

Head 

Machining

MSB4-1 9/1/2002 5/12/2003 1 7708 C G N IR, A

MSB6-2 5/13/2003 11/29/2005 7709 33696 D H N, P, R, T, A
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Post 6-2 10/26/2005 10/12/2009 33745-01 64016-22 E, F K, L U, V C, D

P6-2INT-A 10/13/2009 Current 64016-23 Current F, J N V E

Notes to Table 3:

1. The shrink band diameter, shrink band length, thread pitch diameter, and thread pitch length 

shown in AEC634501 remain constant over the production run. 

2. AEC65385 Rev. E introduced increased wall thickness on the exhaust side.

3. AEC631399 Rev. K introduced an increased head shrink band to dome transition radius.

4. AEC631399 Rev. N introduced an increased interference fit.

5. Allison backed intake valve seats to increase wall thickness were introduced with AEC65414 

Rev. D.

6. Characteristic cylinder barrel inside diameter defined by AE65041 did not change over the 

production run.

Production and Warranty Data

AE provided production run data that included ship date, class, and serial number. Separately, AE 

provided a listing of warranty returns. We cross referenced the warranty returns against the 

production run, and relocated warranty matched units to a separate listing for each for each identified 

cylinder population. Subsequent statistical analysis included failed cylinders and all cylinders not 

reported as failed or removed from service by warranty action.

Based on shipping date and a simple conversion from the recognized standard annual aircraft use rate 

of 100 hours/per year to hours per day, we computed days in service and accumulated hours for each 

cylinder in service. For known failures, we used the reported time in service.

The size of the lists for each population necessitated placing this data into four supplements, 1 through 

4, corresponding to each of the identified population groups:

1. Group SB4-1 (4-1)

2. Group SB6-2 (6-2)

3. Group Post SB6-2 (P6-2)

4. Group Post SB6-2-INT-A (P6-2INT-A)

Certain policies and procedures in use by AE to manage production and traditional warranty claims 

have introduced a degree of uncertainty into product tracking. AE and its Precision Machined Airparts

affiliate assign serial numbers to each cylinder head as well as the cylinder barrel. Field tracking uses 

the cylinder head number. However, Airparts controls plant workflow by work order, with component 

inventory withdrawals for assembly on a first in - first out basis by lot and not by serial number. This 

introduces an out of sequence serial number progression at assembly resulting in shipping dates not 

fully synchronized with serial numbers. This mismatch adds a degree of complexity in determining 

date ranges for design changes or service bulletins. Field technicians or quality personnel require both 

dates and serial numbers to determine the status of a particular unit.
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Another issue stems from traditional tracking of repair station services, which affects utility of 

warranty data. Engine Components assigns a new serial number to all units returned for warranty 

work or repair station work. While this allows the repair station to track its work, identifying the 

underlying originally manufactured unit is impractical unless the customer service staff specifically 

records incoming the serial number as part of a mandatory service bulletin or AD action. In this study 

warranty data clearly identified cylinders affected by MSB6-2 and a smaller number of cylinders 

assigned to the Post MSB6-2 population. We found no alignment in the warranty data to the other 

groups. However, the warranty data did identify some cylinders included as failed units in the FAA's 

MDR database.

With the exception of group SB6-2, we must recognize some degree of uncertainty on the remaining 

numbers of units in the field. This uncertainty causes a small overstatement of field suspensions (inservice units) for groups Post SB6-2 and Post SB6-2-INT-A, but it creates a major uncertainty for those 

units identified as belonging to group SB4-1. MSB4-1 addressed a heat treatment condition. All 

reported head - barrel separations occurred in 2003. The production records show over 2,500 units 

still in service, which suggests a batch problem. However, the inherent design of cylinders in this 

population matches that of group MSB6-2 suggesting that head barrel separations should have 

occurred after year 2003. In this case, we confront two possibilities:

1. MSB4-1 removed the cylinders prone to failure from the population.

2. MSB4-1 removed all cylinders from this population.

The author believes most, but not all of the cylinders associated with MSB4-1 have been withdrawn 

from service because one cylinder associated with the MSB4-1 population appeared in AE files with a 

reported separation date of 12/2/2008. Based on design configuration, any remaining cylinders in this 

population will have characteristics similar to the SB6-2 population group. In fact, MSB6-2 includes 

those units covered by MSB4-1. However, the degree of uncertainty associated with the SB4-1 

population suspensions argue against adding these suspensions to the SB6-2 population suspensions.

With respect to group Post MSB6-2 and group Post MSB6-2-INT-A, we must assume all units not failed,

or identified specifically in warranty reports, remain in the field. Given these issues, the author 

strongly recommends assigning a sequential serial number to each cylinder assembly, and other 

products that directly affect operational safety, at the point of shipping. Each tracking serial number 

would link to a product management database with complete information for each serialized unit on 

the sub-components used in manufacture, process records, and service information. This system 

would lead to prompt identification and resolution of continued operation safety issues as they may 

arise. 

Traceability issues notwithstanding, Table 4 summarizes pertinent information relating to the 

population of each identified cylinder group.
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TABLE 4. CYLINDER GROUP POPULATIONS - SUMMARY OF DATA

Group Qty 

Produced

Basic 

Configuration

Base + 

Allison Style 

Intake Valve 

Seat Back

Improved 

Interference + 

Allison Style 

Intake Valve 

Seat Back

Failures Warranty 

Removals

Net in 

Service

4-1 2,572 2,572 0 0 4 0 2,568

6-2 13,615 13,615 0 0 21 756 12,838

P6-2 20,937 16,436 4,501 0 8 40 20,889

P6-2-INT-A 6,643 0 0 6,643 0 0 6,643

Totals 43,767 32,623 4,501 6,643 33 796 42,938

Visual Examination

We conducted a visual assessment of cylinders in storage at AE that experienced head-barrel 

separation in parallel with the statistical evaluation. Visually, we observed three failure modes:

1. Fatigue failure of the first loaded head thread

2. Fatigue failure in the head clearance area for the barrel at fillet transition between the shrink 

band and the dome

3. Stripped threads associated with some repaired cylinders

Knowing the existence of multiple failure modes, we would expect generally poor fits of consolidated 

separation data associated with each population. Indeed, the statistical assessment of consolidated 

separation data presented later shows a classical pattern of multiple failure modes.

Figure 1 illustrates the thread fatigue failure. Externally, the position of the first loaded thread falls 

between fins 5 through 7 counting from the bottom of the cylinder head. Cylinder SN33947-29 

illustrated in Figure 1 shows the classic striation pattern for fatigue over about 40% of the cross section 

area before final failure occurred from overload. Notice the transition fillet radius is separated from 

the thread by the shrink band.
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FIGURE 1. CYLINDER ASSEMBLY SN33947-29, THREAD FAILURE

Figure 2 illustrates the radius fatigue failure. Externally, the position of the fillet radius between fins 9 

and 10 counting from the bottom of the cylinder head. MSB4-1 specifically instructs the aviation 

maintenance technician to examine this region of the head for cracks. Referring to Table 1D we find 

drawing AE631399 Rev. H calls out a 0.025 - 0.035-inch radius. Based on production data, AE used this 

version of the cylinder thread and pilot diameter drawing for cylinders shipped from 8/29/02 through 

11/29/05. Beginning with cylinder serial number 33745-01 shipped on 10/26/05, AE incorporated at 

least a 0.040-inch radius in the fillet. Supported by visual observation, statistical review confirms that 

increasing the fillet radius eliminated this failure. Therefore, we conclude that population groups SB4-

1 and SB6-2 would have exposure to thread fatigue and radius fatigue modes. The head - barrel 

interface in population group Post SB6-2 has exposure only to the head thread fatigue failure mode.

Qualitatively, failures in the head transition fillet show a smaller fatigue striation area with a much 

coarser striation pattern than the thread fatigue failure illustrated in Figure 1. This justifies statistically

attempting to create separate cumulative failure distributions for each failure mode.

FATIGUE ORIGIN

SHRINK BAND

FILLET RADIUS
Report 1102-13

Page 15

FIGURE 2. CYLINDER ASSEMBLY SN23217-13, RADIUS FAILURE

In stripped thread failures, the threads incurred severe mechanical damage from the extensive relative 

motion between the head and barrel. Other than gross thread damage, the head and barrel remain 

intact. More subtlety, this failure mode suggests the threads will not withstand the operational loads 

in the absence of interference between the head and barrel. 

Summary Listing of Separated Cylinders

Table 4 lists all traceable cylinder failures. When known, we listed the location of the failure and 

identified the applicable population group. 

FATIGUE AREA

FILLET RADIUS
Report 1102-13

Page 16

TABLE 5. CONSOLIDATED LISTING OF AEC631397 HEAD BARREL SEPARATIONS

S/N Type Class Engine Shipped Reported/ 

Removed

TIS 

(hrs)

Failure 

Location

AEC631399 

Rev. Level

FAA MDR ID MSB

4464-24 TIST 71.2A IO-520F 1/20/2003 3/31/2003 87 dome 

radius

G-H CY42003F00000 4-1

4360-32 TIST 71.2B TSIO-520 1/15/2003 12/2/2008 218.1 dome 

radius

G-H 4-1

5482-19 TIST 71.2A 2/14/2003 9/3/2003 283 G-H 4-1

7141-16 TIST 71.2A 4/14/2003 11/15/2003 269 G-H 4-1

7819-23 TISN 71.2B TSIO-520NB 5/23/2003 4/23/2004 204 H BHA05RS 6-2

8013-28 TISN 71.2B 5/19/2003 8/12/2009 960 dome 

radius

H MT2 6-2

12612-5 TISN 71.2B TSIO-520NB 10/10/2003 4/28/2004 200 H BIER200401060 6-2

13515-11 TISN 71.2B TSIO520-NB 1/5/2004 6/15/2010 360 thread H 6-2

13515-26 TISN 76.0 IO-550D 2/5/2004 8/12/2008 338 thread H 6-2

13670-3 TISN 71.2C 1/22/2004 4/18/2006 1301 H 2006FA0000455 6-2

16757-6 TISN 71.2B TSIO-520NB 4/1/2004 3/18/2005 475 H 2005FA0000427 6-2

18700-1 TISN 71.2A IO-55F 6/17/2004 5/1/2009 663 thread H MTPH-1 6-2

19441-28 TISN 71.2A IO-520D 7/23/2004 6/5/2007 290 H MTPH-10 6-2

20940-22 TISN 76.0 IO-550F 8/19/2004 12/12/2005 89 H AU510001488 6-2

21327-19 TISN 71.2B TSIO-520 9/10/2004 2/7/2005 721 H MTPH-7 6-2

21432-10 TISN 71.2C IO-550C 8/31/2004 10/14/2008 355 dome 

radius

H 2008FA0000681 6-2

21994-21 TISN 71.2B TSIO-520NB 9/16/2004 5/11/2006 330 H 2006FA0000498 6-2

21590-14 TISN 71.2C IO-550B 9/10/2004 4/27/2009 150 dome 

radius

H MTPH-2 6-2

22241-24 TISN 71.2B TSIO-520NB 10/11/2004 7/14/2010 264 H MTPH-11 6-2

22389-9 TISN 71.2B IO-550B 10/5/2004 5/3/2006 170.2 H MT1-

2006FA0000489

6-2

22537-24 TISN 71.2B IO-550B 10/5/2004 5/3/2006 171.7 H 2006FA0000489 6-2

22838-19 TISN 71.2B TSIO-520WB 10/20/2004 3/11/2009 390 dome 

radius

H MTPH-5 6-2

23217-13 TISN 71.2B TSIO-520NB 10/19/2004 12/30/2008 257 dome 

radius

H 6-2

23343-15 TISN 71.2B 10/26/2004 8/1/2005 505 H MTPH-8 6-2

23258-14 TISN 71.2B TSIO-520 11/1/2004 5/18/2008 423.9 dome 

radius

H 6-2

33947-29 TISN 71.2C IO-550B 11/22/2005 11/20/2008 210 thread J-K-L p6-2
Report 1102-13

Page 17

S/N Type Class Engine Shipped Reported/ 

Removed

TIS 

(hrs)

Failure 

Location

AEC631399 

Rev. Level

FAA MDR ID MSB

34684-13 TISN 71.2C IO-550A 11/6/2005 10/1/2010 1061 J-K-L MT5 p6-2

35955-22 TISN 71.2B TSIO-520NB 1/6/2006 5/20/2009 1163 thread J-K-L J7B2009F00000 p6-2

45312-15 TISN 71. 2 TSIO-520WB 3/2/2007 9/12/2009 1095 thread J-K-L p6-2

50785-26 TISN 71.3B TSIO-520WB 11/20/2007 4/3/2009 196 thread J-K-L p6-2

51847-12 TISN 71.2B TSIO-520 1/23/2008 7/30/2010 71.2 thread J-K-L p6-2

51973-08 TISN 71.2B TSIO-520 1/28/2008 8/4/2009 835 J-K-L MT4 P6-2

52884-22 TISN 76.0 IO-550F 6/4/2008 11/13/2008 415.8 thread J-K-L p6-2

Total 33

MSB4-1 4

MSB6-2 21

Post MSB6-2 8

Examination of Table 5 leads to several observations relevant to head-barrel separations:

1. No particular engine model has a pronounced tendency for incurring head-barrel separations.

2. Direct visual observation confirmed two failure modes associated with the head-barrel 

interface, fatigue failure in the first loaded thread and fatigue failure in the shrink band to 

dome transition radius.

3. Increasing the head shrink band to dome transition radius beginning with AEC631399 Rev. J 

eliminated fatigue failures in the head shrink band to dome transition radius.

4. Of the four head-barrel separations associated with the serial number range covered by MSB4-

1, one failure occurred in December 2008, and confirmed as a dome radius failure.

With reference to separations associated with MSB4-1, we recall that some portion of this population 

did not receive the correct heat treatment after the casting process. The bulletin requires inspectors 

to pay particular attention to cracks located at fin 9 or 10 counting from the bottom of the head, which 

corresponds to cracks at the head shrink band to dome transition fillet. However, this instruction does 

not preclude the possibility that other failure modes may be in operation. If so, improper heat 

treatment would exacerbate these tendencies and foreshorten the fatigue life of cylinder assemblies 

prone to any particular failure mode. 

In an effort to provide a better basis for analysis, Mr. Pete Hakala, Propulsion Engineer, FAA ASW-190, 

forwarded failure information on cylinders associated with MSB4-1

5

. Table 6 extracts data from the 

information provided. Attachment 1 contains to complete content of the information provided.
Report 1102-13

Page 18

TABLE 6. FAA MDR LISTING AEC631397 SEPARATIONS AS OF 1/13/04

Date A/C Model Engine Horsepower Cyl No. TIS (hrs)

2/21/2003 C414A TSIO-520NB 335 6 45

4/3/2003 C340A TSIO-520NB 335 6 100

4/9/2003 C414 TSIO-520NB 335 2 100

4/14/2003 C310R TSIO-520EB 300 6 100

4/14/2003 C414 TSIO-520NB 335 6 80

4/15/2003 C340A TSIO-520NB 335 6 70

4/24/2003 C402C TSIO-520VB 325 6 193

5/2/2003 C414A TSIO-520NB 335 6 70

5/28/2003 C414A TSIO-520NB 335 6 100

6/10/2003 C340A TSIO-520NB 335 6 64.9

6/13/2003 C414A TSIO-520NB 335 6 177

6/20/2003 C414A TSIO-520NB 335 6 177

6/24/2003 C340A TSIO-520NB 335 6 113.7

6/29/2003 C340A TSIO-520NB 335 6 78

7/2/2003 C402C TSIO-520VB 325 6 348.7

7/5/2003 C414A TSIO-520NB 335 2 100

7/7/2003 C414 TSIO-520NB 335 6 107

7/14/2003 C340A TSIO-520NB 335 4 64.9

7/16/2003 C310R TSIO-520EB 300 6 200

7/17/2003 C414A TSIO-520NB 335 6 102

7/23/2003 C340A TSIO-520NB 335 2 116

7/25/2003 C414 TSIO-520NB 335 6 150

7/29/2003 C340A TSIO-520NB 335 6 125

8/20/2003 C402C TSIO-520VB 325 3 373

10/1/2003 C402C TSIO-520VB 325 1 580

10/30/2003 C340A TSIO-520NB 335 4 208.6

11/4/2003 C414A TSIO-520NB 325 2 120

11/7/2003 C340A TSIO-520NB 335 1 191.2

11/12/2003 A36 IO-550B 300 6 150.3

11/20/2003 C414 TSIO-520NB 335 2 100

11/24/2003 C340A TSIO-520NB 335 2 122

Total 31

Count Cyl. 6 20
Report 1102-13

Page 19

Table 6 lists 31 additional failures, all with time in service less than 600 hours, which is consistent with 

the four additional units listed in Table 5. This report suggests cylinder 6 as the most troublesome, 

which strongly indicates installation configuration, cooling baffles, and operational patterns will affect 

statistical results. The data infer that cylinders experiencing head-barrel separations after 12/31/03 

had the correct heat treatment, or were not removed as part of the MSB4-1 program. The information 

available does not permit us to distinguish which condition holds. Therefore, our treatment will 

assume MSB4-1 suspensions remain in the field and that 35 failures have occurred in this group, with 

one reported in late 2008. Unfortunately, this may distort the actual distribution because the late 

2008 failure implies many late suspensions.

Population group SB6-2 will require consideration for multiple failure modes. However, the correct 

heat treatment increased the fatigue resistance of the machined head, which reduced the frequency of 

premature failures. For population group Post SB6-2, we need only consider one failure mode, fatigue 

of the first loaded thread.

Table 7 summarizes reported cylinder separations not traceable to the production listings. Of the five 

reported with unknown serial numbers, one is associated with a TCM 470 series engine, which this 

study does not address. Four cylinders were confirmed or probable repaired units. Three experienced 

stripped threads. As with new production cylinders, we recommend establishing a post repair tracking 

system that retains reference to the original manufacturer's serial number. Statistically, we will create 

a cumulative failure distribution for the stripped thread failure mode to establish a baseline 

characterization. However, without information regarding the number of units serviced or the 

numbers still in service after the last depot visit, we cannot adjust the base curve to reflect the active 

suspensions.

TABLE 7. AEC631397 HEAD-BARREL SEPARATIONS NOT TRACEABLE TO THE PRODUCTION LISTS

S/N Type Class Engine Shipped Reported/ 

Removed

TIS Failure 

Location

AEC631399 

Rev. Level

FAA MDR ID/Notes MSB

8009-00 FRST 71.2C IO-550B 12/2/2003 1/11/2005 409 stripped 

threads

H 2005FA0000117/ 

Freedom cylinder

NA

17029-28 CCCN71.2B TSIO-520-NB 4/19/2004 10/28/2009 267 stripped 

threads

H MTPH-4/Freedom NA

31265-20 TISN 71.2B IO-520C 7/27/2005 6/15/2009 417 stripped 

threads

H MTPH-3/Freedom NA

32803-1 TISN 71.2B TSIO-520M 9/12/2009 1095 H OW62009F00000/ 

Probable Freedom

NA

47932-06 TISN 71.2B TSIO-520VB 7/27/2007 10/15/2010 1254 NA K MT-6/ Repaired NA

9138-00 TISN 71.2AIO-520 4/6/2005 1787 H MTPH-9 NA

UNK-1 TISN 71.2B TSIO-520NB 2/23/2010 421 ? 2010FA0000179 NA
Report 1102-13

Page 20

S/N Type Class Engine Shipped Reported/ 

Removed

TIS Failure 

Location

AEC631399 

Rev. Level

FAA MDR ID/Notes MSB

UNK-2 TISN 71.2B TSIO-520N 3/12/2008 105 ? CA080410009 NA

UNK-3 O-470R 2/18/2010 151 ? CA100218008 NA

UNK--5 TISN 71.2AIO-520F 6/21/2005 489 H FXT2005F00000 NA

Total 10

The TCM 520/550 engines power aircraft used in charter, cargo, and contracted utility work. For these 

aircraft, the generally accepted use rate of 100 flight hours per year for general aviation aircraft may 

not be valid. Table 5 provides a sample basis to test this assumption. Table 8 takes data from Table 5 

and computes the standard use hours (STD Hrs) based on shipping and removal dates for each 

traceable cylinder with a confirmed head - barrel separation. For the individual distributions of 

reported time in service hours and standard hours, the coefficient of variation (standard 

deviation/mean) suggests significant scatter in each. The relationship of time in service (TIS) to STD Hrs

suggest a ratio of about 3/1, but the coefficient of variation exceeds 1, indicating an invalid correlation 

caused by widely scattered data as shown in Figure 3. The graph shows a weak positive relationship 

with extensive scatter, negating any value in using a modifier to adjust in service suspension times for 

each population.

TABLE 8. SAMPLE POPULATION USED FOR EVALUATING A POTENTIAL TIS/STD HRS RELATIONSHIP

S/N Group Shipped Removed TIS (Hrs) STD ()Hrs TIS/STD 

4464-24 4-1 1/20/2003 3/31/2003 87 19.2 4.54

4360-32 4-1 1/15/2003 12/2/2008 218.1 588.5 0.37

5482-19 4-1 2/14/2003 9/3/2003 283 55.1 5.14

7141-16 4-1 4/14/2003 11/15/2003 269 58.9 4.57

7819-23 6-2 5/23/2003 4/23/2004 204 92.1 2.22

8013-28 6-2 5/19/2003 8/12/2009 960 623.8 1.54

12612-5 6-2 10/10/2003 4/28/2004 200 55.1 3.63

13515-11 6-2 1/5/2004 6/15/2010 360 644.7 0.56

13515-26 6-2 2/5/2004 8/12/2008 338 452.1 0.75

13670-3 6-2 1/22/2004 4/18/2006 1301 223.8 5.81

16757-6 6-2 4/1/2004 3/18/2005 475 96.2 4.94

18700-1 6-2 6/17/2004 5/1/2009 663 487.4 1.36

19441-28 6-2 7/23/2004 6/5/2007 290 286.8 1.01

20940-22 6-2 8/19/2004 12/12/2005 89 131.5 0.68
Report 1102-13

Page 21

S/N Group Shipped Removed TIS (Hrs) STD ()Hrs TIS/STD 

21327-19 6-2 9/10/2004 2/7/2005 721 41.1 17.54

21994-21 6-2 9/16/2004 5/11/2006 330 164.9 2.00

21432-10 6-2 8/31/2004 10/14/2008 355 412.3 0.86

21590-14 6-2 9/10/2004 4/27/2009 150 463.0 0.32

22241-24 6-2 10/11/2004 7/14/2010 264 575.9 0.46

22389-9 6-2 10/5/2004 5/3/2006 171.7 157.5 1.09

22537-24 6-2 10/5/2004 5/3/2006 170.2 157.5 1.08

22838-19 6-2 10/20/2004 3/11/2009 390 439.2 0.89

23217-13 6-2 10/19/2004 12/30/2008 257 420.0 0.61

23343-15 6-2 10/26/2004 8/1/2005 505 76.4 6.61

23258-14 6-2 11/1/2004 5/18/2008 423.9 354.5 1.20

33947-29 p6-2 11/22/2005 11/20/2008 210 299.7 0.70

34684-13 p6-2 11/6/2005 10/1/2010 1061 490.4 2.16

35955-22 p6-2 1/6/2006 5/20/2009 1163 337.0 3.45

50785-26 p6-2 11/20/2007 4/3/2009 196 137.0 1.43

51847-12 p6-2 1/23/2008 7/30/2010 71.2 251.8 0.28

51973-08 P6-2 1/28/2008 8/4/2009 835 151.8 5.50

52884-22 p6-2 6/4/2008 11/13/2008 415.8 44.4 9.37

Mean 274.7 2.90

Standard Deviation 196.9 3.51

Coefficient of Variation 0.72 1.21
Report 1102-13

Page 22

FIGURE 3. PLOTTED TIS/STD HRS DATA

Statistical Assessment

Cylinder Population Group MSB4-1

We begin our statistical analysis with the combined population group 4-1 separation data from Tables 

5 and 6. The consolidated data illustrated in Figure 4 indicates multiple modes. Abernethy's software 

program (Ref. 1) suggested insufficient data to split the data into two curves. Subsequently, we 

manually split the data into three separate curves, and obtained good data fits as illustrated in Figure 

5. This suggests the reported failures include some or all of the previously identified failure modes:

1. Fatigue failure of the first loaded head thread

2. Fatigue failure in the fillet radius at the head shrink band to dome clearance transition

3. Stripped head threads of repaired cylinders.

0

200

400

600

800

1,000

1,200

1,400

0 200 400 600 800 1,000 1,200 1,400

Time in Service Hours

Standard Hours

Time in Service - Standard Hour Relationship
Report 1102-13

Page 23

FIGURE 4. GROUP SB4-1 CONSOLIDATED DISTRIBUTION OF REPORTED SEPARATIONS 

Segregating the reported separations into three distributions resulted in excellent data fits. If we 

assume the listing of separated cylinders do not include repaired cylinders with stripped threads, we 

can explain the three cumulative distributions in terms of the incorrect heat treatment identified in 

MSB4-1. At the time of MSB4-1 publication, customers would have returned very few cylinder 

assemblies attributed to AE manufacture to the EC Services repair station. This would make it highly 

unlikely that Mode 1 failure identified in Figure 5 would represent a cumulative failure distribution for 

stripped threads. Thus, we can deduce the Mode 1 failure mode most likely represents fatigue cracks 

in the dome transition radius of those cylinders identified in MSB4-1 that did not receive the correct 

heat treatment. 

The Mode 2 failure distribution identified in Figure 5 would represent a cumulative failure distribution 

for those cylinders correctly heat treated that manifest a fatigue crack in the dome fillet radius. The 

Mode 3 distribution would represent correctly heat treated cylinders experiencing fatigue cracks in the 

first loaded thread. The slope of this distribution is consistent with that identified in Ref. 2 for 

AEL65102 cylinders separating by propagation of a fatigue crack in the first loaded thread.

Table 9 provides the summary of data points used for each distribution. The small number of data 

points permitted manual estimation of the groupings. Any effort to improve the fit of Mode 1 by 

distributing data points to the other modes resulted in severely degraded curve fit quality indicated by 

a pve well below 10%. As defined by Abernethy (Ref. 1), pve is the percentile rank of the correlation 
Report 1102-13

Page 24

coefficient against all possible correlation coefficients. By experience and demonstration, pve ranks of 

at least 10% indicate acceptable data fit.

FIGURE 5. GROUP SB4-1 SEGREGATED DISTRIBUTIONS FOR THE REPORTED SEPARATIONS

TABLE 9. DATA POINTS FROM FIGURE 4 ASSIGNED TO IDENTIFIED FAILURE MODES

Time in Service (hours)

Mode 1 Mode 2 Mode 3

45 100 150 150.3

70 100 177 269

70 102 177 283

78 107 191.2 348.7

80 113.7 193 373

87 116 200 580

100 120 208.6

100 122 218.1

100 125

100
Report 1102-13

Page 25

Building upon the analysis of the separation data of group 4-1 without the suspension, we examine the 

effect of suspensions on the cumulative failure distribution. For this analysis, we will present 

consolidated data including the FAA supplied information less the separations presumed associated 

with head fillet failures attributable to incorrect heat treatment as noted in MSB4-1. Next, we will 

segregate the separation presumed associated with thread failures and failures in the head transition 

radius. 

Figure 6 presents the adjusted consolidated data for population group 4-1 using the suspension data 

given in Report 1102-13 Supplement 1 without any adjustment to the computed standard hours in 

service. Notice the curve clearly shows a multiple failure mode pattern. Figure 7 presents group SB4-1 

cumulative distribution frequency curves for Mode 2 and Mode 3 failures by separately combining the 

presumed in-service suspensions with Mode 2 and Mode 3 data points. 

Table 10 offers a statistical summary of the data presented in Figure 7. Statistically, as indicated by pve 

and the correlation coefficients, the data has a good fit to the presented cumulative distribution 

functions. Fatigue fractures in the dome fillet radius shown by the Mode 2 curve would normally 

represent a serious concern. However, nearly all reported failures for this population occurred in 

2003. Figure 6 indicates a batch problem and an underlying failure mode. In this case, the batch 

problem would represent the fatigue fracture of the dome fillet radius. Further, we can infer that 

cylinders produced at the low end of the established fillet radius tolerance of 0.035/0.025-inch would 

have a greater propensity for initiation of a fatigue crack than those produced at the upper end of the 

tolerance band. By 12/31/2010, service bulletin action and field experience should have removed the 

cylinders in this population most likely to experience fatigue cracking in the dome fillet radius. MSB4-1 

required removal of cylinders most likely to experience this failure mode, and given that the standard 

fleet hours accumulated by this population now exceed the characteristic life of about 485 hours for 

correctly heat treated cylinders exhibiting this failure mode, we can reasonably conclude nearly all of 

the cylinders that would have a tendency for fillet radius fatigue have been removed from the 

population. The 2003 dates for the vast majority of the reported dates of head-barrel separations for 

this population supports this conclusion. No further action for this failure mode in population group 4-

1 is necessary.

The underlying failure mode distributed in the population would be the fatigue fracture of the first 

loaded thread. This makes sense from an engineering standpoint because the separation data shows 

that increasing the fillet radius greatly reduces any propensity for fatigue fracture in the dome fillet 

radius. Cylinders in the group SB4-1 population produced with an interference fit set near the design 

minimum would have an increased risk of thread failure in service depending on actual interference 

and engine operating conditions. The population of group SB4-1, not affected by MSB4-1, falls under 

the requirements of MSB6-2. This bulletin requires continuing inspections for head cracks. These 

inspections should provide some early warning detection of thread cracks in the remaining population.
Report 1102-13

Page 26

FIGURE 6. GROUP SB4-1 WITH SUSPENSIONS ADJSUTED TO REMOVE MODE 1 SEPARATIONS

FIGURE 7. GROUPSB 4-1 WITH SUSPENSIONS, SEGREGATED MODES
Report 1102-13

Page 27

TABLE 10. STATISITCAL SUMAMRY OF WEIBULL DATA FOR CYLIDNER GROUP SB4-1

Mode Points Susp. r r

2

ccc2pve % η

(hrs)

β B times (hrs)

1% 2% 5%

2 2576 2568 0.9798 0.960 0.8425 77.44 484.6 7.023 251.7 278 317.5

3 2574 2568 0.9656 0.915 0.8203 44.23 13,724 1.816 1,090 1,601 2,674

Table 11 and Figure 8 presents results of the risk projection for thread fatigue separation (Mode 3) 

using software from Reference 1, assuming only half the suspensions remain in the field and a use rate 

of 8.333 hours per month. The analysis projects ten additional failures over the next sixty months. We 

suggest reducing risk by removing these cylinders from service at the next engine tear down or 

scheduled overhaul interval, whichever comes first.

TABLE 11. RISK PROJECTION THREAD FATIGUE FAILURES FOR CYLINDER GROUP SB4-1
Report 1102-13

Page 28

FIGURE 8. GRPAHICAL PROJECTION OF PROJECTED SEPARATIONS FOR GROUP SB4-1

Population Group SB6-2

Figure 9 shows the consolidated Weibull plot derived from Table 5 for reported head - barrel 

separations on cylinders with serial numbers associated with group SB6-2. Although the curve fit pve 

of about 24% suggests an adequate fit, we know from direct observation that two separation modes 

are active within this population, fatigue cracking at cylinder head shrink band to dome fillet radius and 

fatigue cracking in the first loaded thread.

Figure 10 displays the consolidated Weibull cumulative distribution function (CDF) for the entire 

population based on the production data contained in Report 1102-13 Supplement 2. Adding the 

suspensions degrades the curve fit as shown by a pve below 1% and exacerbates the effect of the 

multiple failure modes in play. As expected the consolidated CDF for group SB6-2 with suspensions 

closely resembles the consolidated CDF for group SB4-1 with suspensions shown in Figure 6.
Report 1102-13

Page 29

FIGURE 9. GROUP SB6-2 CONSOLIDATED DISTRIBUTION OF REPORTED SEPARATIONS

FIGURE 10. GROUP SB6-2 WITH SUSPENSIONS 
Report 1102-13

Page 30

Figure 11 and Table 12 shows the results of splitting data points into two CDFs. These curves were 

created by manual iteration starting from Table 5 and assigning known dome radius separations into a 

separate distribution from those separations as identified or presumed thread fatigue failures. We 

next added suspension data from Report 1102-13 Supplement 2 to each CDF obtaining preliminary 

curves. Based on examination of the curves, we shifted cylinder serial number 13670-3 from the 

thread failure group to the radius failure group, obtaining the CDF's displayed. Mode 1 represents the 

CDF for the dome radius, fatigue crack separation mode, and Mode 2 represents the CDF for the 

thread fatigue separation mode. As shown in Table 13, the slopes of both curves are very consistent 

with the CDF's generated for group SB4-1, affirming the validity of the analysis. 

FIGURE 11. GROUP SB6-2 WITH SUSPENSIONS, SEGREGATED MODES

TABLE 12. STATISITCAL SUMAMRY OF WEIBULL DATA FOR CYLIDNER GROUP SB6-2

Mode Points Susp. r r

2

ccc2pve % η

(hrs)

β B times (hrs)

1% 2% 5%

1 12834 12827 0.9418 0.887 0.8325 26.15 1,268 5.853 578 651 763

2 12851 12837 0.9664 0.934 0.8829 35.31 35,947 1.604 2,041 3,155 5,640
Report 1102-13

Page 31

TABLE 13. CHARACTERISTIC VALUE COMPARISON OF CDF PLOTS FOR GROUPS SB4-1 AND SB6-2

Group Dome Radius Failure Head Thread Failure

Beta Eta (hours) Beta Eta (hours)

4-1 7.023 484.6 1.816 13,724

6-2 5.853 1,268 1.604 35,947

The potential for dome radius cracks complicates the assessment of risk. We must determine whether 

the potential for dome radius cracking represents a significant risk. Examining the data from Report 

1102-3 Supplement 2 we find the for cylinders in this group manufactured in November 2005, the 

standard time in service projection of about 509 hours correspond to a cumulative failure of 0.48%. A 

B time of 2% corresponds to about 650 hours in service. However, using the Abernethy Risk 

Assessment (Ref. 1) we find that forcing the Now Risk agreement with the number of failures assigned 

to this mode required removing 98% of the suspensions. This implies only about 2% of the remaining 

population, a batch, would have a propensity for service conditions to cause a fatigue crack in the 

transition fillet radius. On a numerical basis, approximately 250 to 260 units of the in service 

population may have exposure to fatigue crack formation in this transition radius. As the calculations 

and cumulative graphical plots indicate, the small numbers of units in the SB6-2 population with 

exposure to cracking in this transition radius dominate the overall projected risk. The projection 

indicates about 7 separations due to transition radius cracks will occur in the next year, and nearly half 

this small population of about 256 units will fail over the next five years. The 0.035/0.0025 transition 

radius is an inherent design defect present in OEM cylinders of the same generation. Population group 

Post SB6-2 eliminated this deficiency. Most likely, the projections overstate the risk based on the 

numbers of OEM cylinders operating, but we do not have a sound method to establish a risk reduction 

factor. Table 14 presents the results of the risk projection calculations. Figure 12 presents the results 

graphically. 

As with the dome transition radius, we forced the Now Risk computation to have reasonable 

agreement with the fourteen units assigned to the thread crack CDF. In this case, using 75% of the 

suspensions forced the Now Risk to agree with the actual recorded separations. The projection 

indicates seven thread failures in the year and twenty-tow over the sixty month forecast period. Table 

15 presents the risk assessment. Figure 12 presents the results graphically. 
Report 1102-13

Page 32

TABLE 14. RISK PROJECTION DOME FILLET RADIUS FAILURES FOR CYLINDER GROUP 6-2

TABLE 15. RISK PROJECTION HEAD THREAD FAILURES FOR CYLINDER GROUP 6-2
Report 1102-13

Page 33

As demonstrated in Figure 12, the projection for failure occurrence in the dome transition radius 

dominates the cumulative projected total numbers of failures. Based on the adjusted number of 

suspension to force Now Risk agreement in group SB6-2 we find:

1. A small number of cylinders, about 2% (256 units) that have insufficient margin in the dome 

transition radius dominate the cumulative failure projections.

2. Seventy-five percent of the population has measurable risk for thread failure.

3. Approximately twenty-three per cent of the population has minimal risk for either failure mode.

Taking all of this into consideration, we recommend the following continued operational safety actions:

1. Continue the MSB6-2 repetitive inspection program.

2. Amend MSB6-2 to include visual inspections at fins 9 - 10 and 5 - 7 in addition to fin 17.

3. Amend MSB6-2 to require removal of these cylinders at the next engine tear-down or published 

limits for time between overhauls, whichever is first.

4. Ensure MSB6-2 includes a clear statement that precludes repair and return of these cylinders to 

service.

FIGURE 12. PROJECTED SEPARATIONS FOR GROUP SB6-2
Report 1102-13

Page 34

Population Group Post SB6-2

With group Post SB6-2, AE introduced a new head casting, AEC65385 Rev. D, providing increased wall 

thickness on the exhaust port side to reduce thermal fatigue cracking in the exhaust port area as 

identified in MSB6-2. In addition, AE increased the transition fillet radius effectively eliminating the 

risk of a transition radius failure. Thus, in this population the first loaded thread cracking is the 

dominant failure mode as influenced by operational factors.

Figure 13 shows the Weibull plot derived from Table 5 for reported head - barrel separations on 

cylinders with serial numbers associated with Post MSB6-2. A Beta close to 1 indicates extensive 

randomization, which suggests mixed failure modes are in operation, or that operational factors 

strongly influence the observed performance. In this case, we have identified only one head-barrel 

interface separation mode. Therefore, operational factors must have a strong influence on the Weibull 

distribution.

FIGURE 13. GROUP POST MSB6-2 DISTRIBUTION OF REPORTED SEPARATIONS

Figure 14 presents the cumulative distribution function combining suspensions from Report 1102-13 

Supplement 3 with the separations listed in Table 5. Suspensions degraded the curve fit as measured 

by pve, but they tightened the distribution characterized by a Beta of 4.838. A large number of low

suspensions relative to some of the failures caused this phenomenon. Based on the accepted standard 

of 100 hour/year in service, the longest in-service unit has accumulated 518 hours in service as of 

12/31/2010. Four reported separations had time in service of 835, 1061, 1085, and 1163 hours, 

exceeding the standard by at least 60% to as much as 220%. As the fleet ages, the beta value of the 
Report 1102-13

Page 35

distribution will drop and more closely resemble the thread separation distributions exhibited by the 

other population groups. 

Without having direct observation identifying one active failure mode, the point scatter shown in 

Figure 14 could justify employing a multiple mode data fitting procedure. In this case, we have 

identified thread failure modes of the outlier points in Figure 14, negating any justification for splitting 

the data into two separate cumulative distribution functions. Possible causes of data scatter include:

1. Incorrect reporting of the time in service for separated cylinders

2. Revised cylinder head casting with altered wall configuration

3. Variable and unknown field operating conditions resulting in the head barrel interface 

temperature exceeding the maximum design temperature limit of 375F

While not likely, the improved cylinder head casting with increased exhaust side wall thickness 

introduced by AE may have influenced the rate of fatigue crack propagation, thereby altering the 

distribution shape factor.

The large number of short suspensions, based on an unreliable estimate of time in service, associated 

with the eight recorded separations will result in a degraded fit quality found by regression analysis.

The short suspensions allow the higher time failures to bias the distribution as exhibited by the 

increase in Beta.

Incorrect time in service reporting would account for some of the data scatter from the best fit curve. 

Undoubtedly, off-specification and variable operating conditions, combined with inaccurate cylinder 

head temperature measurements and improper break,-in may result in some cylinders operating at

head-barrel interface temperatures exceeding the maximum temperature design limit resulting in loss 

of interference fit. 

Upon examination of Figure 14, we find four relatively short time failures and four relatively long-time 

failures with no points between the extremes. From additional examination of separated cylinders at 

AE, we observed evidence of improper break-in. This condition would allow hot gas to flow by the 

piston rings and raise the interface temperature. Considering the indentified factors, we can explain 

the observed distribution of the separated cylinder data points as follows:

1. The Post MSB6-2 cylinder population as designed has insufficient interference fit margin to 

compensate effectively for non-optimum field operating conditions.

2. The high time separation points probably represent cylinders operating with excessive cylinder 

head temperature.

3. The low time separation points probably represent cylinders not receiving a proper break-in.

In the next section, we will estimate the resistance force to remove press fit units at temperature, 

allowing an assessment of the capability of the cylinder to withstand abnormal operation.
Report 1102-13

Page 36

FIGURE 14. GROUP POST SB6-2 WITH SUSPENSIONS

TABLE 16. STATISITCAL SUMMARY OF WEIBULL DATA FOR CYLIDNER GROUP POST MSB6-2

Mode Points Susp. r r

2

ccc2pve % η

(hrs)

β B times (hrs)

1% 2% 5%

1 20897 20889 0.9386 0.881 0.8425 20.17 1,157 4.873 450 519 629

Not surprisingly, the abnormal distribution for cylinder head thread failures leads to issues with risk 

projection. Using all the suspensions produced a Now Risk of 93 units failed against 8 reported. This is 

indicative of a batch problem, attributable to variations in the head - barrel interference fit. Assuming 

only 5% of the suspensions have a propensity for thread failure forced the Now risk to agree with the 8

recorded separations. This result suggests that 95% of the suspended cylinders have sufficient 

interference fit to remove at least some load from the threads, which will significantly improve thread 

fatigue life allowing these cylinders to reach the published overhaul time limit for the engine. Table 17 

and Figure 15 present the results of the risk assessment calculation. The risk assessment for group 

Post SB6-2 projects 8 failures during the next twelve months and 26 failures over the next two years.
Report 1102-13

Page 37

TABLE 17. RISK PROJECTION HEAD THREAD FAILURES FOR CYLINDER GROUP POST SB6-2

FIGURE 15. PROJECTED SEPARATIONS FOR GROUP POST SB6-2
Report 1102-13

Page 38

Since this group has the same interface design as group SB6-2, we would expect thread failures to 

occur. The tighter clustering of the Weibull distribution curve with a characteristic life of 1,157 hours 

prompts a very conservative approach on how to treat this population group. The best approach 

would be to find and remove cylinders that may have less than sufficient interference fit, but complete 

production records are not available for these units. We base the following recommendations on 

MSB6-2 and the foregoing statistical analysis:

1. Issue a mandatory service bulletin calling for repetitive inspections of cylinders beginning at 250 

hours.

2. Focus the inspection for cracks at fin 5 - 7 as well as fin 17.

3. Require retirement all cylinders in this population group at the engine mandatory overhaul 

limit.

4. Require mandatory checks for oil consumption and examination of cylinders if oil consumption 

exceeds a predetermined limit. 

5. Require removal of cylinders consuming excessive oil for rehoning, reinstallation, and break-in 

to prevent excessive cylinder interface temperature.

Repaired Cylinder Assemblies

Cylinders identified as repaired units in Table 7 that experienced a stripped thread separation. Figure 

16 provides a preliminary Weibull curve for this failure mode in the interest of establishing a baseline 

for further investigation. The distribution presented in Figure 16 is characteristic of a typical fatigue 

wear out failure. Lack of available data precludes any further analysis at this time.

AE issued repair station instructions in 2009 requiring repaired and reassembled cylinders to have 

head- - barrel interference fits set at current standards. As part of an overall COS program, we 

recommend establishing a serial number tracking system for repaired units. This would allow better 

assessment of in-service performance and identify necessary improve activities as needed for the 

repaired products.
Report 1102-13

Page 39

FIGURE 16. PRELIMINARY DSITRUTION FOR REPAIRED CYLINDERS WITH STRIPPED THREADS

Analysis of Head-Barrel Interface

Population Group Identification and Material Properties

For the purposes of assessing the effectiveness of the head - barrel interference fit, two groups 

governed by the revision level of AEC631399 represent the entire cylinder population:

1. Group H-J-K-L including Groups 4-1, 6-2, and Post 6-2

2. Group N representing Group Post 6-2-INT-A

Table 18 recasts Table 1D for base line fit dimensions at the interface.

TABLE 18. BASELINE HEAD-BARREL INTERFACE DIAMETERS FROM AEC631399

Group Date

Start

Date End J - Head Pitch 

Max. Dia. (in)

J - Head Pitch 

Min. Dia. (in)

H - Head 

Band Max. 

Dia. (in)

H - Head 

Band Min. 

Dia. (in)

H-J-K-L 8/29/02 10/12/09 5.554 5.552 5.459 5.457

N 10/13/09 Current 5.552 5.550 5.453 5.451

Calculation of interference fit and removal force require additional data. Table 19 lists dimensional 

data taken from published drawings or the type certificate6and Table 20 lists physical and mechanical 
Report 1102-13

Page 40

property data for the materials of construction taken from published literature for Aluminum 242.07, 

for Piston Aluminum Alloy A40328and for SAE4140 steel9. The characteristics listed in Table 19 are 

common to all drawing revisions covering the production run. For convenience, we referred to the 

latest revision level. 

TABLE 19. SUPPLEMENTAL DIMENSION DATA REQUIRED FOR FORCE CALCULATIONS

Location Characteristic Drawing Rev. Nominal (in)

Head Outside Diameter AEC65385 J 6.750

Head Thread Length AEC631399 N 0.6875

Head Estimated Shrink Band Engaged Length AEC631399 N 0.336

Barrel Inside Diameter AE65041 K 5.252

Barrel Thread Length AEC634501 V 0.6875

Barrel Estimated Shrink Band Engaged Length AEC634501 V 0.3360

Piston Diameter (From type certificate data) FAA E8CE 21 5.250

TABLE 20. PHYSICAL AND MECAHNICAL PROPERTIES OF CYLINDER HEAD AND BARREL MATERIALS

A242 Material Properties T77 Temperature (F)

68 212 375 400 425 600

Ultimate Strength (psi) 30,000 30,000 21,500 20,000 18,700 8,000

Yield Strength (psi) 23,000 23,000 16,000 15,000 13,800 4,000

%El 2 2 3 20

Modulus (psi) 1.03E+07 1.03E+07 1.03E+07 1.03E+07 1.03E+07

Poison Ratio 0.33 0.33 0.33 0.33 0.33

Expansion Coefficient 1.360E-05 1.360E-05 1.360E-05 1.360E-05

A242 Head Geometry Temperature (F)

68 300 375 400 425

Head Outside Diameter (inch) 6.7500 6.7713 6.7782 6.7805 6.7828

Nominal Thread Length (inch) 0.7500 0.7531 0.7534 0.7536

Temperature (F)

AISI 4140 Material Properties -

Austenize + Oil Quench + Temper

68 212 375 400 425

Ultimate Strength (psi) 158700 158700 158700 158700 158700

Yield Strength (psi) 142300 142300 142300 142300 142300

%El 14.8 14.8 14.8 14.8 14.8

%RA 48.9 48.9 48.9 48.9 48.9

Modulus (psi) 2.90E+07 2.90E+07 2.90E+07 2.90E+07 2.90E+07

Poison Ratio 0.3 0.3 0.3 0.3 0.3

Expansion Coefficient 7.120E-06 7.120E-06 7.170E-06 7.170E-06
Report 1102-13

Page 41

AISI 4140 Barrel Geometry Temperature (F)

68 300 375 400 425

Barrel Inside Diameter (inch) 5.2520 5.2574 5.2635 5.2645 5.2654

Nominal Thread Length (inch) 0.7500 0.7508 0.7516 0.7518 0.7519

Est. Shrink Band Length (inch) 0.34800 0.34836 0.34876 0.34883 0.34889

Data to Calculate Combustion Force

Alloy 4032 Temperature (F)

68 300 375 400 425

Piston Diameter 5.2500 5.2643 5.2689 5.2704 5.2719

Piston Alloy 4032 Exp. Coeff. 1.17E-05 1.17E-05 1.17E-05 1.17E-05

Peak Pressure (AEC data) psi 900 900 900 900 900

Force on Piston (lb) 19,483 19,589 19,623 19,634 19,646

Notes to Table 19:

1. T77 Heat treatment: Solutionize at 960F - 4Hr - Still Air Quench, age at 650F - 2Hr

2. Aluminum ultimate and yield strength at 375F was extrapolated from a graph constructed from 

the published data 212F, 400, and 600. See Attachment 2.

3. A242 coefficient of thermal expansion is valid to 512F

4. SAE 4140 Steel Heat Treatment: Normalize at 1625F - 3Hr air cool, austenize at 1600F - 1/2Hr 

oil quench, temper at 1100F - 2Hr air cool

5. Thermal expansion coefficients for steel from 68F to 400F and 425F were extrapolated from a 

plot of maximum temperature vs. expansion coefficient. See Attachment 3.

Coefficient of Sliding Friction

For cylinders, Equation 4 shows press fit removal force directly related to coefficient of friction, contact 

pressure, and the contact area:

EQUATION 4. F rL   2

Where:

F = Removal force

μ = coefficient of sliding friction

σ = Radial contact pressure

r = Common radius between inner and outer sleeves

L = Length of contact area

Knowing the geometry, measured removal force, and contact pressure allows for direct computation 

of the coefficient of friction. AE conducted push-off tests and reported the results in terms of 

measured pressure and diametrical interference fit on AEC631397 cylinder geometry set at nominal 

and maximum interference10. Using Equation 4 and the supplied data, the author computed the 

friction coefficient. 
Report 1102-13

Page 42

Attachment 4 presents the raw data and details of the calculations giving an effective coefficient of 

friction at two interference fit levels. Figure 17 presents the computations from Attachment 4 as a plot 

of the coefficient of friction as a function of radial interference. Removal force calculations discussed 

later would incorporate the empirical relationship of coefficient of friction with radial interference 

shown on the plot.

FIGURE 17. RELATIONSHIP OF COEFFICIENT OF FRICTION TO RADIAL INTERFERENCE

Interference Fit Estimates at Operating Temperature

Using data from Tables 18, 19 and 20, we calculated expanded thread pitch and shrink band diameters

and the related interference fits from 350F through 425F at 25F intervals using Equation 4 for the 

following assembly interference fit conditions:

1. Nominal

2. Condition 1 - Maximum interference at the shrink band and the threads

3. Condition 2 - Minimum interference at the shrink band and the threads

4. Condition 3 - Maximum interference in the threads, minimum interference in the shrink band

5. Condition 4 - Minimum interference in the threads, maximum interference in the shrink band

y = 224.68x + 0.2311

0

1

2

3

4

0.0000 0.0020 0.0040 0.0060 0.0080 0.0100 0.0120

Coefficient of Friction

Radial Interference (in)

Estimated Friction Coefficient
Report 1102-13

Page 43

EQUATION 5. D D T f i f    1 68   

Where:

Df = Diameter at temperature

Di = Diameter at 68F

α = Mean coefficient of thermal expansion between 68F and the operating temperature

Tf = Operating temperature (F)

Attachment 5 presents the tabulated results of these computations for each indentified cylinder

interface configuration. Figures 18 through 22 show the graphical relationship of diametrical 

interference for each condition at each selected cylinder thread operating temperature including:

1. 350F, an operating condition 25F below design maximum thread temperature

2. 375F, design maximum thread temperature

3. 400F, an operating condition 25F above design maximum thread temperature

4. 425F, an operating condition 50F above design maximum thread temperature

Study of Figures 18 through 22 leads to a number of observations for the various assembled 

interference fit conditions:

1. At nominal interference fit group H-J-K-L, which includes all cylinder assemblies with reported 

head barrel separations, loses positive head - barrel interference fit at about 385F or just above 

design point maximum operating temperature of the interface.

2. At nominal interference fit, group N retains positive interference fit through 425F.

3. At Condition 1 interference fit, group H-J-K-L retains positive interference fit to 425F.

4. At Condition 1 interference fit, group N retains positive interference fit through 425F.

5. At Condition 2, minimum interference fit, group H-J-K-L loses positive interference fit at 325F.

6. At Condition 2, group N thread pitch diameter loses positive interference fit at 375F while the 

shrink band retains positive interference fit through 425F.

7. At Condition 3, maximum thread interference with minimum band interference, group H-J-K-L 

retains positive interference fit of the thread pitch diameter to 425F, but the shrink band loses 

positive interference fit at 325F.

8. At Condition 3, group N retains positive interference fit through 425F.

9. At condition 4, minimum thread interference with maximum band interference, group H-J-K-L

retains a positive shrink band interference fit through 425F, but the thread pitch diameter loses 

positive interference fit at 325F.

10. At Condition 4, group N retains a positive shrink band interference fit through 425F, but the 

thread pitch diameter loses positive interference fit at 375F.

For group H-J-K-L, cylinders with Nominal or Condition 1 interference fits will withstand engine 

operating conditions better than cylinders assembled to the Condition 2, minimum, interference fit. At 

fit Condition 2, the threads will carry the combustion pulse load at head - barrel interface
Report 1102-13

Page 44

temperatures above 325F. In fit Conditions 3 and 4 the thread pitch diameter or shrink band diameter 

retain a positive interference fit to about 425F. Interference fit removal force estimates will shed more 

light on the relative contributions of the shrink band and thread length to the overall load carry 

capacity of the assembly, as well as providing more quantitative guidelines for targeting cylinders at 

greater risk of experiencing a head - barrel separation.

Similarly, we find group N retains positive interference fit through 425F at both the thread pitch 

diameter and the shrink band diameter for Nominal, Condition 1, or Condition 3 interference fit. The 

thread pitch diameter loses positive interference fit at 375F for Condition 2 and Condition 4. This 

suggests the thread pitch diameter requires increase interference at assembly. Interference fit 

removal force calculations will provide quantitative guidelines for optimizing the interference fit 

settings of group N, current production cylinders. 

FIGURE 18. NOMINAL - DIA. INTERFERENCE FIT AT INTEFACE OPERATING TEMPERATURES

-0.0040

-0.0020

0.0000

0.0020

0.0040

0.0060

0.0080

0.0100

0.0120

0.0140

0.0160

0.0180

0.0200

0 50 100 150 200 250 300 350 400 450

Interference (in.)

Interface Temperature (F)

Condition - Nominal Interference Fit

HKL Shrink Band HKL Threads N Shrink Band N Threads
Report 1102-13

Page 45

FIGURE 19. CONDITION 1 - DIA. INTERFERENCE FIT AT INTEFACE OPERATING TEMPERATURES

0.0000

0.0020

0.0040

0.0060

0.0080

0.0100

0.0120

0.0140

0.0160

0.0180

0.0200

0.0220

0 50 100 150 200 250 300 350 400 450

Interference (in.)

Interface Temperature (F)

Condition 1 - Maximum Interference Fit

HKL Shrink Band HKL Threads N Shrink Band N Threads
Report 1102-13

Page 46

FIGURE 20. CONDITION 2 - DIA. INTERFERENCE FIT AT INTEFACE OPERATING TEMPERATURES

-0.0060

-0.0040

-0.0020

0.0000

0.0020

0.0040

0.0060

0.0080

0.0100

0.0120

0.0140

0.0160

0 50 100 150 200 250 300 350 400 450

Interference (in.)

Interface Temperature (F)

Condition 2 -Minimum Interference Fit

HKL Shrink Band HKL Threads N Shrink Band N Threads
Report 1102-13

Page 47

FIGURE 21. CONDITION 3 - DIA. INTERFERENCE FIT AT INTEFACE OPERATING TEMPERATURES

-0.0060

-0.0040

-0.0020

0.0000

0.0020

0.0040

0.0060

0.0080

0.0100

0.0120

0.0140

0.0160

0.0180

0 50 100 150 200 250 300 350 400 450

Interference (in.)

Interface Temperature (F)

Condition 3 - Max. Thread, Min. Band 

Interference

HKL Shrink Band HKL Threads N Shrink Band N Threads
Report 1102-13

Page 48

FIGURE 22. CONDITION 4 - DIA. INTERFERENCE FIT AT INTEFACE OPERATING TEMPERATURES

Removal Force Estimates

Using the at-temperature computed diameters and parameters listed in Tables 18 through 20 and the 

empirical formula for friction coefficient shown in Figure 17, we applied standard formulations 

provided by Excelcalcs.com (ref. 3) to compute estimated press fit removal force contributions from 

the shrink band and thread pitch line for each nominal, maximum (C1), and minimum (C2) interface fit 

conditions. Additionally, we computed wall contact stress at the interface for each condition. The 

preceding review of the current production cylinder population, identified for this analysis as group N,

suggested that current interference fit parameters would result in the thread pitch line losing positive 

interference at the maximum design operating temperature. This prompted an evaluation of a 

potential modification of group N by increasing interference fit by 0.004-inch and by 0.009-inch from 

the current settings. We begin by considering the interface condition identified by HKL, which 

represents cylinders produced through 10/12/2009 and includes identified populations SB4-1, SB6-2 

and Post SB6-2.

-0.0060

-0.0040

-0.0020

0.0000

0.0020

0.0040

0.0060

0.0080

0.0100

0.0120

0.0140

0.0160

0.0180

0.0200

0.0220

0 50 100 150 200 250 300 350 400 450

Interference (in.)

Interface Temperature (F)

Condition 4 - Min. Thread, Max. Band 

Interference

HKL Shrink Band HKL Threads N Shrink Band N Threads
Report 1102-13

Page 49

GROUP HKL

Table 21 relates the computed room temperature diametrical interference of the thread pitch and 

shrink band diameter to each fit condition. Tables 22 and 23 summarize results of removal force 

computations for the thread and shrink band sections of the interface, computed at 68F, 300F, 375F 

and 400F (Attachment 5). Refer to Report 1102-13 Supplement 5 for details of these computations.

TABLE 21. SUMMARY OF INTEFERENCE SETTINGS FOR GROUP HKL

Fit Condition Description Shrink Band 

Interference (in.)

Thread Pitch Diameter 

Interference (in.)

Nominal Nominal interference settings 0.0115 0.0115

1 Maximum interference 0.014 0.014

2 Minimum Interference 0.009 0.009

3 Minimum band, maximum thread 

interference

0.009 0.014

4 Maximum band, minimum thread 

interference

0.014 0.009

TABLE 22. GROUP HKL REMOVAL FORCE ESTIMATES FOR PRESS FIT CONDITIONS

Interface Temperature (F) Force Shrink Band (lb) Force Threads (lb) Total Force (lb)

Nominal

68 14,287 34,881 49,168

300 1,649 3,920 5,569

375 177 299 476

400

Condition 1 (maximum)

68 20,679 50,387 71,066

300 4,251 10,362 14,613

375 1,394 3,556 4,950

400 751 1,921 2,672

Condition 2 (minimum)

68 9,084 22,223 31,307

300 217 421 638

375 0 0

400 0 0

Condition 3

68 9,084 50,387 59,471

300 217 10,579
Report 1102-13

Page 50

Interface Temperature (F) Force Shrink Band (lb) Force Threads (lb) Total Force (lb)

375 0 3,556 3,556

400 0 1,921 1,921

Condition 4

68 20,679 22,223 42,902

300 4,251 421 4,672

375 1,394 0 1,394

400 751 0 751

Table 23 presents a consolidated summary of total removal force for press fit cylinder head - barrel 

assemblies at various temperatures. 

TABLE 23. SUMMARY OF TOTAL PRESS FIT REMOVAL FORCES FOR CYLINDER GROUP HKL

Interface 

Temperature (F)

Total Estimated Removal Force (lb)

Nominal Condition 1 

(maximum)

Condition 2 

(minimum)

Condition 3 Condition 4

68 49,168 71,066 31,307 59,471 42,902

300 5,569 14,613 638 10,579 4,672

375 476 4,950 0 3,556 1,394

400 0 2,672 0 1,921 751

Using the 900 psi maximum peak pressure measured by AE11 for the TCM 520/550 series engines and 

allowing for piston expansion, we computed estimated peak pressure load pulses for these cylinder

assemblies in Table 20. The head - barrel assembly must resist this computed peak load. If the total 

estimated press fit removal force does not match or exceed the peak cyclic force, then the threads will 

have to absorb the portion of the load not withstood by the interference fit. As more load transfers 

into the threads, the fatigue characteristics of aluminum 242 alloy at the interface temperature

determines the operational life of the cylinder assembly. Experience has shown that cyclic loads in the 

threads cause failure in between 500 and 1,000 hours in service or approximately 8 x 106to 3.2 x 107

fatigue cycles based on an engine operating at 2700 rpm and producing peak power for 10% of the 

total operating time. The cyclic stress - cycles to failure relationship is quite flat in this region of the 

fatigue curve, implying that small changes in cyclic load will have a significant impact on extending the 

longevity of cylinders12. Figure 23 graphically presents the results of these calculations. The shaded 

area in the figure represents the region in which threads to begin absorbing cyclic loads. Attachment 6

contains graphical presentations of the individual components for the nominal, maximum, and 

minimum interference fit conditions.
Report 1102-13

Page 51

FIGURE 23. TOTAL REMOVAL FORCE FOR GROUP HKL

At 900 psi peak combustion pressure, our removal force estimates suggest that cylinders assembled at 

the minimum interference limit will begin transferring load to the threads at about 250F with the 

threads absorbing all the combustion force at 325F. Cylinders produced with the nominal interference 

fit will carry about 28% of the combustion force load at 300F and 10% of the combustion force load at 

350F. Similarly, cylinders produced with maximum interference fit will carry about 75% of the 

combustion force load at 300F and 25% of the combustion force load at 375F. These interference fit 

load bearing estimates suggest actual operating interface temperatures and/or peak combustion 

pressure for the majority of the cylinders must be below 375F because of the relatively few reported 

separations. 

Based on the Weibull plots with the implication of lower than estimated maximum interface 

temperature and peak combustion pressure, cylinders assembled with nominal or greater interference 

will perform in the field to the scheduled overhaul limit. For group SB6-2, we have shown the major 

risk appears due to cylinders machined at the minimum limit of the shrink band to dome transition 

radius, which is not related to the thread fatigue failure. Meanwhile, the removal force estimates 

0

10,000

20,000

30,000

40,000

50,000

60,000

70,000

50 100 150 200 250 300 350 400 450

Total Removal Force (lb)

Interface Temperature (F)

HJKL Temperature - Force Relationship

Nom. Total C1 Total C2 Total C3 Total C4 Total
Report 1102-13

Page 52

suggest that any cylinder assembled with near minimum interference fit will carry a higher risk of 

thread fatigue failure, yet the Weibull risk assessment suggests only a small fraction of this population 

is prone to the thread fatigue failure. Therefore, we believe our previously stated recommendations to 

remove these cylinders from service at the next engine teardown require no modifications.

As with the MSB6-2 population, the Post SB6-2 population has risk of thread fatigue failure, which is 

entirely understandable based on removal force calculations. As previously stated, we recommend 

issuing a mandatory service bulletin requiring a number of actions:

1. Require repetitive inspections each 50-hours for Post MSB6-2 cylinders beginning at 250 hours.

2. Focus the inspection for cracks at fin 5 - 7 as well as fin 17.

3. Require retirement all cylinders in this population group at the engine mandatory overhaul 

limit.

4. Require mandatory checks for oil consumption and examination of cylinders if oil consumption 

exceeds a predetermined limit. 

5. Require removal of cylinders consuming excessive oil for rehoning, reinstallation, and break-in 

to prevent excessive cylinder interface temperature.

6. If records are available, we recommend identifying cylinders produced at the minimum 

interference fit and require their removal within the next 200-hours. 

GROUP N

Report 11-02-13 Supplement 5 contains the detailed estimates of removal force for the nominal, 

maximum, and minimum interference fit conditions incorporating expanded thread pitch and shrink 

band diameters previously calculated as well as information presented in Tables 19 and 20. Tables 24, 

25, and 26 present the removal force estimate and summary for group N, which represents the current 

production group identified as Post SB6-2-INT-A. Attachment 6 presents a graphical summary of the 

thread and shrink band contribution to removal force for the nominal, maximum, and minimum press 

fit conditions.

The interface load carrying capacity of the current production units represent a significant 

improvement over the cylinder assemblies produced through October 2009. As illustrated in Figure 24, 

press fit conditions nominal, maximum, C3, and C4 will carry at least 50% of the combustion load 

through 375F. The minimum fit condition will carry 20% of the combustion force load at 350F and 10% 

of the load at 375F. Based on the statistical behavior shown in the HKL population group as well as 

inference of lower than anticipated head-barrel interface temperature and peak combustion pressure, 

we believe there is no immediate cause for concern. 

Clearly, operating conditions, break-in procedures, and cooling baffle configuration have a direct 

bearing on the service life of any cylinder because they influence the actual cylinder head - barrel 

interface temperature. Lower interface temperatures will result in greater cylinder longevity with 

reduced risk of thread fatigue. Taken together, the statistical data, uncertainty of actual operating 

conditions at the head - barrel interface, the ambiguity of peak combustion pressure, and the push-off 

resistance force calculations showing load transfer to the threads at interface temperatures well below 
Report 1102-13

Page 53

design maximum strongly suggest AE should conduct tests to directly measure the head - barrel 

interface temperature and peak combustion pressure.

The press fit removal force estimates for current production cylinders produced at or above nominal 

interference indicate these units will perform up to the maximum design temperature of 375F. With 

respect to current production cylinders produced at minimum interference and considering the 

influence of operating conditions we recommend the following actions:

1. Review production records and identify any current production cylinders produced with 

minimum interference.

2. Conduct tests to directly measure head - barrel interface temperature and peak combustion

pressure of an operating TSIO-520NB at these suggested conditions:

a. Maximum manifold pressure, rated maximum cylinder head temperature

b. Maximum manifold pressure, rated maximum cylinder head temperature plus 25F

c. Maximum manifold pressure, rated maximum cylinder head temperature plus 50F

3. If head - barrel interface temperature exceeds 300F at maximum head temperature, consider 

issuing a service bulletin call for removal of cylinders produced at minimum interference after 

84 months or 700-hours in service, replacing them with cylinders having greater assembly 

interference.

4. Consider issuing a service guideline bulletin to all ECi customers explaining the necessity for: 

a. proper break-in of cylinders 

b. inspection for and removal of cylinders incorrectly broken in

c. Inspection and restoration of all cooling baffles and devices to their properly certified 

configuration to minimize heat stress on the cylinder joints 

5. Adjust assembly interference fit requirements to avoid thread load transfer up at head - barrel 

interface temperature corresponding to rated maximum head temperature plus 50F

6. As a precaution, AE should produce current production cylinders with interference fit levels set 

at nominal or above.

7. Pending definitive determination of the head - barrel interface temperature corresponding to 

head temperatures 50F above maximum limit, AE should consider adjusting assembly 

interference fit to avoid load transfer to the threads up to 425F head - barrel interface 

temperature.

TABLE 24. SUMMARY OF INTEFERENCE SETTINGS FOR GROUP N

Fit Condition Description Shrink Band 

Interference (in.)

Thread Pitch Diameter 

Interference (in.)

Nominal Nominal interference settings 0.0175 0.0135

1 Maximum interference 0.020 0.016

2 Minimum Interference 0.015 0.011

3 Minimum band, maximum thread 

interference

0.015 0.016

4 Maximum band, minimum thread 0.02 0.011
Report 1102-13

Page 54

interference

TABLE 25. GROUP N REMOVAL FORCE ESTIMATES FOR PRESS FIT CONDITIONS

Interface Temperature (F) Force

Shrink Band (lb)

Force 

Threads (lb)

Total Force (lb)

Nominal

68 8,407 15,804 24,211

375 3,208 2,913 6,121

400 2,802 1,882 4,684

Condition 1 (maximum)

68 9,645 18,765 28,410

375 4,842 5,835 10,677

400 4,025 4,832 8,857

Condition 2 (minimum)

68 7,179 12,853 20,032

375 2,003 0 2,003

400 1,588 0 1,588

Condition 3

68 7,179 18,765 25,944

375 2,003 5,835 7,838

400 1,588 4,832 6,420

Condition 4

68 9,645 12,853 22,498

375 4,421 0 4,421

400 4,025 0 4,025

TABLE 26. SUMMARY OF TOTAL REMOVAL FORCES OF CYLINDER GROUP N

Interface 

Temperature 

(F)

Total Estimated Removal Force (lb)

Nominal Condition 1 

(maximum)

Condition 2 

(minimum)

Condition 3 Condition 4

68 24,211 28,411 20,032 25,944 22,498

375 6,121 10,256 2,003 7,838 4,421

400 4,684 8,857 1,588 6,420 4,025
Report 1102-13

Page 55

FIGURE 24. TOTAL REMOVAL FORCE FOR GROUP N

GROUP N MODIFICATIONS

As a means of improving robustness of the cylinder interface, we next examine cylinders modified to 

increase interference by 0.004-inch, identified as N+004, and by 0.009-inch, identified as N+009. From 

the resistance force estimates on these cylinders, we can construct an engineering curve to better 

estimate the minimum increase in interference fit that will result in no load transfer to the threads at 

interface temperatures between 375F and 425F.

Table 27 provides the interference settings for both configurations. Report 11-02-13 Supplement 5

contains the detailed estimates of removal force for the nominal, maximum, and minimum 

interference fit conditions incorporating expanded thread pitch and shrink bad diameters previously 

calculated as well as information presented in Tables 19 and 20. Tables 28 and 29 present results of 

the removal force estimates for each condition. Table 30 summarizes the contact pressure estimates. 

Attachment 6 presents a graphical summary of the thread and shrink band contribution to removal 

force for the nominal, maximum, and minimum press fit conditions. Figures 25 and 26 graphically 

summarize these results. Modification N+004 at minimum fit condition will begin transferring

0

10,000

20,000

30,000

40,000

50,000

60,000

70,000

80,000

90,000

100,000

110,000

50 100 150 200 250 300 350 400 450

Removal Force (lb)

Interface Temperature (F)

N Temperature - Force Relationship

Nom. Total C1 Total C2 Total C3 Total C4 Total
Report 1102-13

Page 56

combustion load into the threads at 350F. Modification N+009 will not transfer load using any fit 

condition through 425F interface temperature. 

Using minimum fit condition total resistance force for conditions N, N+004, and N+009 from Tables 26 

and 28 we constructed Figure 27 to permit estimation of the adjustment necessary to avoid transfer of 

load to the threads for various head - barrel interface temperatures. Our estimates show that 

adjusting interference fit by 0.007-inch will avoid combustion load transfer to the threads up to a head 

- barrel interface temperature of 425F. Table 30 shows modification N+009 will result in contact 

pressures approximately 14% of the published yield strength of the aluminum head alloy. Taking 

safety, operational, and mechanical factors into consideration, we recommend AE consider 

implementing an adjustment to increase assembly interference fit by 0.007-inch.

TABLE 27. INTEFERENCE SETTINGS FOR GROUP N+004 AND N+009

Fit Condition Description Shrink Band 

Interference (in.)

Thread Pitch Diameter 

Interference (in.)

N+004

Nominal Nominal interference settings 0.0215 0.0175

1 Maximum interference 0.024 0.020

2 Minimum Interference 0.019 0.015

3 Minimum band, maximum thread 

interference

0.019 0.020

4 Maximum band, minimum thread 

interference

0.024 0.015

N+009

Nominal Nominal interference settings 0.0265 0.02225

1 Maximum interference 0.029 0.025

2 Minimum Interference 0.024 0.020

3 Minimum band, maximum thread 

interference

0.024 0.025

4 Maximum band, minimum thread 

interference

0.029 0.020

TABLE 28. GROUPS N+004 AND N+009 REMOVAL FORCE ESTIMATES 

Interface Temperature (F) Force Shrink Band (lb) Force Threads (lb) Total Force (lb)

N+004 Nominal

68 46,838 81,202 128,040

375 12,275 12,664 24,939

400 10,707 10,451 21,158

425 9,553 7,785 17,338

N+004 Condition 1 (maximum)

68 57,526 103,719 161,245
Report 1102-13

Page 57

Interface Temperature (F) Force Shrink Band (lb) Force Threads (lb) Total Force (lb)

375 18,501 23,329 41,830

400 16,586 19,917 36,503

425 14,666 15,649 30,315

N+004 Condition 2 (minimum)

68 35,262 59,933 26,620

375 7,668 5,754 8,609

400 6,423 3,850 7,248

425 5,249 2,366 6,191

N+004 Condition 3

68 35,262 59,933 138,981

375 7,668 5,754 30,997

400 6,423 3,850 26,340

425 5,249 2,366 20,898

N+004 Condition 4

68 57,526 59,933 117,459

375 18,501 5,754 24,255

400 16,586 3,850 20,436

425 14,666 2,366 17,032

N+009 Nominal

68 69,871 129,670 199,541

375 25,630 36,596 62,226

400 23,105 31,933 55,038

425 20,959 27,688 48,647

N+009 Condition 1 (maximum)

68 82,849 159,037 241,886

375 34,151 53,124 87,275

400 31,043 47,557 78,600

425 28,606 41,182 69,788

N+009 Condition 2 (minimum)

68 55,118 103,336 158,454

375 18,464 23,526 41,990

400 16,307 19,756 36,063

425 14,461 16,283 30,744

N+009 Condition 3

68 55,118 159,037 214,155

375 18,464 53,124 71,588

400 16,307 47,557 63,864

425 14,461 41,182 55,643

N+009 Condition 4

68 82,849 103,336 186,185

375 34,151 23,526 57,677
Report 1102-13

Page 58

Interface Temperature (F) Force Shrink Band (lb) Force Threads (lb) Total Force (lb)

400 31,043 19,756 50,799

425 28,606 16,283 44,889

TABLE 29. SUMMARY OF TOTAL REMOVAL FORCES FOR CYLINDER GROUPS N+004 AND N+009

Interface 

Temperature (F)

Total Estimated Removal Force (lb)

Nominal Condition 1 

(maximum)

Condition 2 

(minimum)

Condition 3 Condition 4

N+004

68 128,040 161,245 95,195 138,981 117,459

375 24,939 41,830 13,422 30,997 24,255

400 21,158 36,503 10,273 26,340 20,436

425 17,338 30,315 7,615 20,898 17,032

N+009

68 199,541 241,886 158,454 214,155 186,185

375 62,226 87,275 41,990 71,588 57,677

400 55,038 78,600 36,063 63,864 50,799

425 48,647 69,788 30,744 55,643 44,889

TABLE 30. CONTACT PRESSURE FOR N+004 AND N+009 AT MAXIMUM INTEFERENCE FIT

Temperature (F) Shrink Band (psi) Thread Pitch Diameter (psi)

N+004

68F 3,286 3,192

375 1,797 1,426

400 1,699 1,312

425 1,590 1,143

N+009

68F 3,970 3,990

375 2,488 2,228

400 2,373 2,108

425 2,273 1,941
Report 1102-13

Page 59

FIGURE 25. TOTAL REMOVAL FORCE FOR GROUP N+004

0

20,000

40,000

60,000

80,000

100,000

120,000

140,000

160,000

50 100 150 200 250 300 350 400 450

Removal Force (lb)

Interface Temperature (F)

N+004 Temperature Force Relationship

Nom. Total C1 Total C2 Total C3 Total C4 Total
Report 1102-13

Page 60

FIGURE 26. TOTAL REMOVAL FORCE FOR GROUP N+009

20,000

40,000

60,000

80,000

100,000

120,000

140,000

160,000

180,000

200,000

220,000

240,000

260,000

50 100 150 200 250 300 350 400 450

Removal Force (lb)

Interface Temperature (F)

N+009 Temperature - Force Relationship

Nom. Total C1 Total C2 Total C3 Total C4 Total
Report 1102-13

Page 61

FIGURE 27. EFFECT OF INTERFERENCE CHANGES ON TOTAL REMOVAL FORCE FOR GROUP N 

0

5,000

10,000

15,000

20,000

25,000

30,000

35,000

40,000

45,000

-0.002 0.000 0.002 0.004 0.006 0.008 0.010

Total Removal Force (lb)

Assembly Interference Changes, Diametrical (in.)

Rev. N Modifications: Force-Interference Change

375F-Min. 400F-Min. 425F-min.

MINIMUM INTERFERNCE FIT

0.000 = Baseline AEC631399 Rev. N
Report 1102-13

Page 62

FINDINGS AND RECOMMENDATIONS

Findings

1. The production run of AEC631397 replacement cylinders for TCM 520/550 series engines fall 

into population groups defined by two critical service bulletins:

a. Group SB4-1

b. Group SB6-2

c. Group Post SB6-2

d. Group Post SB6-2 with improved interference and intake valve seats with an Allison 

style back

2. AE has not implemented sequential serialization of cylinder shipments requiring use of both 

shipping dates and serial numbers to determine population groups. This introduces some 

uncertainty in determining configuration of cylinders in service, resulting in less than desirable 

precision in identifying cylinders subject to specific service bulletins.

3. Based on production and warranty return information, we established total production and 

recorded failures for each identified population group as follows:

a. Group SB4-1: 2,572 total, 4 recorded failures plus 31 failures reported to FAA

b. Group SB6-2: 13,615 total, 21 failures, 756 warranty removals

c. Group Post SB6-2: 20,937 total, 8 failures, 40 warranty removals

d. Group Post SB6-2-INT-A: 6,643 total, no failures 

4. Service Bulletin MSB4-1 mandated inspection for cracks at fin 9 - 10 counting from the bottom 

and inspection by AE for proper heat treatment

5. Service Bulletin MSB6-2 mandated repetitive inspection for cracks each 50-hours at fin 17 on 

the exhaust side.

6. Introducing head casting AEC65385 Rev. D minimized exhaust port side cracks.

7. Critical features of barrel design AEC634501 affecting interference fit did not change 

significantly over the production run.

8. Critical choke and barrel inside diameter dimensions defined by AE65041 did not change over 

the production run.

9. AEC631399 Rev. H set the shrink band to dome transition fillet radius at 0.035/0.025-inch, 

which applied to cylinder groups SB4-1, SB6-2, and Post SB6-2.

10. Beginning with group Post SB6-2, AEC631399 Rev. J set the shrink band to dome transition 

radius at 0.050/0.040-inch.

11. Cylinder groups SB4-1, SB6-2, and Post SB6-2 were produced with diametrical interference fits 

defined by AEC6312399 Rev. H through L at 0.014/0.009-inch.

12. Cylinders produced from October 13, 2009 incorporated an increased diametrical interference 

fit of 0.020-inch nominal at the shrink band and 0.015-inch nominal in the threads. 

13. Visual examination confirmed three failure modes:

a. Transition shrink band to dome fillet radius fatigue cracking

b. Fatigue cracking of the first loaded head thread

c. Thread stripping of repaired cylinder assemblies
Report 1102-13

Page 63

14. We found no effective correlation between reported time in service and computed standard 

time in service for this population group. 

15. Lack of correlation between actual and standard time in service will introduce statistical error in 

Weibull plots

16. Statistical analysis determined three failure modes within group SB4-1:

a. Shrink band to dome transition fillet radius failure on improperly heat treated cylinders

b. Shrink band to dome transition fillet radius failure on correctly heat treated cylinders

c. First load thread fatigue crack failures on correctly heat treated cylinders

17. Statistical analysis of group MSB4-1 strongly suggested fillet radius failure of the population 

remaining in service is unlikely.

18. Statistical analysis of Group MSB4-1 projected 10 additional failures over the next five years.

19. Consolidated Weibull plot of Group MSB6-2 showed clear evidence of multiple failure modes, 

which were confirmed by visual examination of units in storage at AE.

20. Risk projection calculations for Group MSB6-2 suggest only 250 to 260 cylinders remain at risk 

of fatigue cracking in the head shrink band to dome transition fillet radius.

21. Projected risk for MSB6-2 indicates 19 failures will occur in the head fillet radius over the next 

24 months for this population group. In the same period, only 8 failures are projected in the 

first loaded head thread. 

22. Population Group Post MSB6-2 has not exhibited transition radius fatigue cracks.

23. Several reported separations in the Post MSB6-2 population exceed fleet standard time in 

service by more than 60%, weighting the cumulative distribution function.

24. The consolidated Weibull plot for the Post MSB6-2 population showed a characteristic shape 

factor significantly greater that previously reported for the other populations experiences 

thread fatigue failures.

25. For Post MSB6-2 population, factors contributing to the altered cumulative distribution 

function include:

a. Incorrect reporting of the time in service for separated cylinders

b. Revised cylinder head casting with altered wall configuration

c. Variable and unknown field operating conditions resulting in the head barrel interface 

temperature exceeding the maximum design temperature limit of 375F

26. Risk calculations for the Post MSB6-2 population suggest only 5% of the population is at 

significant risk of fatigue cracking in the head threads.

27. Post MSB6-2 population risk projections indicate 26 cylinder assemblies could fail over the next 

twenty-four months

28. Cylinders shipped through October 2009 assembled at design nominal interference will 

experience loss of all interference at the design maximum temperature of 375F.

29. Cylinders shipped through October 2009 assembled at design minimum interference will 

experience loss of all interference at an interface temperature of 325F

30. Cylinders shipped through October 2009 assembled at design maximum interference will retain 

positive interference through 425F
Report 1102-13

Page 64

31. Current production cylinder assemblies assembled at design nominal or maximum will retain 

positive interference through 425F

32. Current production cylinder assemblies assembled at design minimum interference will 

experience loss of all interference at the design maximum temperature of 375F

33. Press fit removal force estimates for cylinders shipped through October 2009 show:

a. Cylinders produced with maximum interference fit will carry about 75% of the 

combustion force load at 300F and 25% of the combustion force load at 375F.

b. Cylinders produced with the nominal interference fit will carry about 28% of the 

combustion force load at 300F and 10% of the combustion force load at 350F.

c. Cylinders produced with minimum interference fit will transfer most of the combustion 

load to the threads at a head-barrel interface temperature of 300F and peak pressure of 

900 psi.

34. Press fit removal force estimates for current production cylinders show:

a. Press fit conditions nominal, maximum, C3, and C4 will carry at least 50% of the 

combustion load through 375F.

b. The minimum fit condition will carry 20% of the combustion force load at 350F and 10% 

of the load at 375F.

35. A suggested increase of assembly interference fit by 0.007-inch shows all maximum, nominal, 

and minimum interference fit will withstand combustion loads through 425F.

36. Maximum contact pressure at maximum interference fit for the modified interface design do 

not exceed 14% of the yield stress of aluminum for between room temperature and 425F.

37. The statistical data and mechanical force calculations suggest head - barrel interface 

temperature is less than 375F and/or peak combustion pressure is below 900 psi.

38. The preliminary Weibull cumulative distribution function for the repaired cylinder stripped 

thread failure mode resembles the cumulative distribution function for fatigue failure in the 

shrink band to dome transition radius. An in depth study of repaired cylinders will be required 

to make risk projections.

Recommendations

1. We recommend establishing a system that would assign a sequential serial number to each 

cylinder assembly and other products that directly affect operational safety at the point of 

shipping. Under this recommendation, each serialized component or assembly would link to a 

product management database holding complete information on materials, processes, and 

inspections, complete information on all sub-components used, and complete service history

information.

2. For those cylinders in population group SB4-1 remaining in service, continue repetitive 

inspections as mandated by MSB6-2.

3. Remove remaining group SB4-1 cylinder assemblies in service at the next engine tear down or 

scheduled overhaul interval, whichever comes first.

4. For cylinder group SB6-2 we recommend continuing the MSB6-2 inspection program.
Report 1102-13

Page 65

5. We suggest amending MSB6-2 to include visual inspections at fins 9 - 10 and 5 - 7 in addition to 

fin 17.

6. We suggest amending MSB6-2 to require removal of these cylinders at the next engine teardown or published limits for time between overhauls, whichever is first.

7. We recommend including a clear statement in MSB6-2 precluding any repair and return to 

service of cylinders affected by this service bulletin.

8. For population group Post SB6-2 we suggest Issuing a mandatory service bulleting calling for 

repetitive inspections of cylinders beginning at 250 hours.

9. We recommend issuing a service bulletin for the Post SB6-2 group to include inspection for 

cracks at fin 5 - 7 as well as fin 17.

10. We recommend removal all Pot MSB6-2 cylinders at the next engine teardown.

11. If records are available, we recommend identifying those Post MSB6-2 cylinders produced at 

the minimum interference fit and require their removal within the next 200-hours. 

12. Require removal of Post MSB6-2 cylinders consuming excessive oil for rehoning, reinstallation, 

and break-in to prevent excessive cylinder interface temperature.

13. .Conduct tests to directly measure head - barrel interface temperature and peak combustion 

pressure of an operating TSIO-520NB at these suggested conditions:

a. Maximum manifold pressure, rated maximum cylinder head temperature

b. Maximum manifold pressure, rated maximum cylinder head temperature plus 25F

c. Maximum manifold pressure, rated maximum cylinder head temperature plus 50F

14. If measured head - barrel interface temperature exceeds 300F at maximum head temperature, 

consider issuing a service bulletin call for removal of current production cylinders produced at 

minimum interference after 84 months or 700-hours in service, replacing them with cylinders 

having greater assembly interference.

15. Adjust assembly interference fit requirements to avoid transferring cyclic load into the threads 

at a head - barrel interface temperature corresponding to rated maximum head temperature 

plus 50F

16. As a precaution, AE should produce current production cylinders with interference fit levels set 

at nominal or above.

17. Pending definitive determination of the head - barrel interface temperature corresponding to 

head temperatures up to 50F above maximum limit, AE should consider the feasibility of

increasing assembly interference fit, preferably by 0.007-inch, to avoid load transfer to the 

threads up to 425F head - barrel interface temperature.

18. Consider issuing a service guideline bulletin to all ECi customers explaining the necessity for: 

a. proper break-in of cylinders 

b. inspection for and removal of cylinders incorrectly broken in

c. Inspection and restoration of all cooling baffles and devices to their properly certified 

configuration to minimize heat stress on the cylinder joints 
Report 1102-13

Page 66

ATTACHMENT 1. FAA MDR AS OF 1/13/04, AEC631397 SEPARATIONS
Report 1102-13

Page 67

ATTACHMENT 2. TENSILE STRENGTH - TEMPERATURE GRAPH FOR A242.0

0

5,000

10,000

15,000

20,000

25,000

30,000

35,000

50 100 150 200 250 300 350 400 450 500 550 600 650

Strength (psi)

Temperature (F)

Cast Alloy A242 T77 Tensile and Yield Strength

Ultimate

Yield
Report 1102-13

Page 68

ATTACHMENT 3. THERMAL EXPANSION COEFFICIENT FOR SAE4140 STEEL

7.05

7.10

7.15

7.20

7.25

7.30

7.35

7.40

7.45

7.50

7.55

7.60

7.65

7.70

200250300350400450500550600650700750800

Expansion Coefficient E

-06 

(in/in/F)

Temperature Limit (F)

SAE 4140 Average Thermal Expansion 

Coefficient from 68F
Report 1102-13

Page 69

ATTACHMENT 4. COMPUTATION OF THE EFFECTIVE FRICTION COEFFICIENT

Push-Off Test Data Provided by Airmotive Engineering

Characteristic Data Input

Head Configuration AEC631399 Rev. L

Barrel Configuration AEC634501 Rev. V

Machined Head Shrink Band Diameter Nominal Interference (in.) 5.458

Machined Head Shrink Band Diameter Maximum Interference (in.) 5.457

Machined Barrel Shrink Band Diameter Nominal Interference (in.) 5.4695

Machined Barrel Shrink Band Diameter Maximum Interference (in.) 5.472

Shrink Band contact Length (in.) 0.348

Interference, Diametrical (in) Interference, Radial (in.) Push-Off Pressure (psi)

0.0115 0.0575 660

0.015 0.0075 1090

Calculations for Friction Coefficient

HKL Nominal Interference Test - Contact Pressure Calculation

Inner Modulus - psi E1 = 29000000

Inner Tensile Strength - psi TS = 158700

Inner Yield Strength - psi YS1 = 142300

Inner Poisson's Ratio ν1 = 0.3

Outer Modulus - psi E2 = 10300000

Outer Tensile Strength - psi TS2 = 30000

Outer Yield Strength - psi TS2 = 23000

Outer Poisson's Ratio ν2 = 0.33

Contact Length - in L = 0.348

Nominal Radius - in r = 2.73475 Common Radius

Outer Radius - in ro = 3.375 Outer Radius of Outer Tube

Outer Opening - in rh = 2.729 Inner Radius of Outer Tube
Report 1102-13

Page 70

Inner Surface - in rs = 2.73475 Outer Radius of Inner Tube

Inner Opening - in ri = 2.626 Inner Radius of Inner Tube

Radial Interference - in δ = 0.00575

Contact Pressure - lbs / sq in σ = 1,569

HKL Maximum Interference Test - Contact Pressure Calculation

Inner Modulus - psi E1 = 29000000

Inner Tensile Strength - psi TS1 = 158700

Inner Yield Strength - psi YS1 = 142300

Inner Poisson's Ratio ν1 = 0.3

Outer Modulus - psi E2 = 10300000

Outer Tensile Strength - psi TS2 = 30000

Outer Yield Strength - psi TS2 = 23000

Outer Poisson's Ratio ν2 = 0.33

Contact Length - in L = 0.348

Nominal Radius - in r = 2.736

Outer Radius - in ro = 3.375

Outer Opening - in rh = 2.7285

Inner Surface - in rs = 2.736

Inner Opening - in ri = 2.626

Radial Interference - in δ = 0.0075

Contact Pressure - lbs / sq in σ = 2058

Convert Push-Off Pressure to Force

Nominal Diametrical Interference (0.011 in.)

Piston diameter (in) D = 5.25

Piston Area (sq. in.) A = 21.6754

Pressure (0.0115-inch) P = 660

Force (lb) F = 14,287

Maximum Diametrical Interference (0.015 in.)

Piston diameter (in) D = 5.25

Piston Area (sq. in.) A = 21.647540

Pressure (0.0115-inch) P = 1090

Force (lb) F = 23,596

=

δ

r / E2[{ro

2

 + r2} / {ro

2

 - r2} + ν2] + r / E1[{r2 + ri

2

} / {r2 - ri

2

} - ν1]

= D2 / 4 = PA 
Report 1102-13

Page 71

Friction Coefficient Calculation

Nominal Diametrical Interference (0.0115-inch)

Contact Pressure (psi) σ = 1,569 From contact pressure calc's

Engaged Length (inch) L = 0.3480

Insertion/Removal Force (lbs) F= 14,287

Nominal Radius (inch) r = 2.73475.

Friction Coefficient μ = 1.523065

Radial Interference (inch) δ = 0.00575

Maximum Diametrical Interference (0.015-inch)

Contact Pressure (psi) σ = 2,058

Engaged Length (inch) L = 0.3480

Insertion/Removal Force (lbs) F= 23,596

Nominal Radius (inch) r = 2.73600

Friction Coefficient μ = 1.916263

Radial Interference (inch) δ = 0.00750

= F / (σ · 2rL) 
Report 1102-13

Page 72

ATTACHMENT 5. THERMAL EXPANSION COMPUTATIONS

Note: All dimensions in inches.

Group Characteristic Temperature (F

68 300 350 375 400 425

H-J-K-L Nominal: Nominal Interference Fit Thread Pitch and Shrink Band Diameters

Jnom 5.5530 5.5715 5.5743 5.5762 5.5781 5.5800

Jnom 5.5530 5.5715 5.5743 5.5762 5.5781 5.5800

Xnom 5.5645 5.5722 5.5757 5.5767 5.5777 5.5787

Ith 0.0115 0.0007 0.0014 0.0005 -0.0004 -0.0012

Hnom 5.4580 5.4742 5.4789 5.4808 5.4826 5.4845

Ynom 5.4695 5.4800 5.4805 5.4815 5.4824 5.4835

Isb 0.0115 0.0058 0.0015 0.0007 -0.0002 -0.0010

Δ 0.0000 0.0052 0.0002 0.0002 0.0002 0.0002

H-J-K-L Condition 1: Maximum Interference Fit Thread Pitch and Shrink Band Diameters

Jmin 5.5520 5.5695 5.5733 5.5752 5.5771 5.5790

Xmax 5.5660 5.5752 5.5772 5.5782 5.5792 5.5801

Ith 0.0140 0.0057 0.0039 0.0030 0.0021 0.0012

Hmin 5.4570 5.4742 5.4779 5.4798 5.4816 5.4835

Ymax 5.4710 5.4800 5.4820 5.4830 5.4839 5.4850

Isb 0.0140 0.0058 0.0041 0.0032 0.0023 0.0015

Δ 0.0000 0.0001 0.0002 0.0002 0.0002 0.0003

H-J-K-L Condition 2: Minimum Interference Fit thread Pitch and Shrink Band Diameters

Jmax 5.5540 5.5715 5.5753 5.5772 5.5791 5.5810

Xmin 5.5630 5.5722 5.5742 5.5752 5.5762 5.5772

Ith 0.0090 0.0007 -0.0011 -0.0020 -0.0029 -0.0037

Hmax 5.4590 5.4762 5.4799 5.4818 5.4836 5.4855

Ymin 5.4680 5.4770 5.4790 5.4800 5.4809 5.4820

Isb 0.0090 0.0008 -0.0010 -0.0018 -0.0027 -0.0035

Δ 0.0000 0.0001 0.0002 0.0002 0.0002 0.0002

Group Characteristic Temperature (F)

68 350 375 400 425

H-J-K-L Condition 3: Max. Interference Fit Thread Pitch Dia. With Min. Interference Fit Shrink Band Dia

Jmin 5.5520 5.5733 5.5752 5.5771 5.5790

Xmax 5.5660 5.5772 5.5782 5.5792 5.5802

Ith 0.0140 0.0039 0.0030 0.0021 0.0013

Hmax 5.4590 5.4799 5.4818 5.4836 5.4855

Ymin 5.4680 5.4790 5.4800 5.4809 5.4820

Isb 0.0090 -0.0010 -0.0018 -0.0027 -0.0035

Δ -0.0050 -0.0048 -0.0048 -0.0048 -0.0048

H-J-K-L Condition 4: Min. Interference Fit Thread Pitch Dia. with Max. Interference Shrink Band Dia

Jmax 5.5540 5.5753 5.5772 5.5791 5.5810
Report 1102-13

Page 73

Xmin 5.5630 5.5742 5.5752 5.5762 5.5772

Ith 0.0090 -0.0011 -0.0020 -0.0029 -0.0037

Hmin 5.4570 5.4779 5.4798 5.4816 5.4835

Ymax 5.4710 5.4820 5.4830 5.4839 5.4850

Isb 0.0140 0.0041 0.0032 0.0023 0.0015

Δ 0.0050 0.0052 0.0052 0.0052 0.0052

Group Characteristic Temperature (F)

68 350 375 400 425

Group N Nominal: Nominal Interference Fit Thread Pitch and Shrink Band Diameters

Jnom 5.5510 5.5723 5.5742 5.5761 5.5780

Xnom 5.5645 5.5757 5.5767 5.5777 5.5787

Ith 0.0135 0.0034 0.0025 0.0016 0.0008

Hnom 5.4520 5.4729 5.4748 5.4766 5.4785

Ynom 5.4695 5.4805 5.4815 5.4824 5.4835

Isb 0.0175 0.0076 0.0067 0.0058 0.0050

Δ 0.0040 0.0042 0.0042 0.0042 0.0042

Group N Condition 1: Maximum Interference Fit Thread Pitch and Shrink Band Diameters

Jmin 5.5500 5.5713 5.5732 5.5751 5.5769

Xmax 5.5660 5.5772 5.5782 5.5792 5.5802

Ith 0.0160 0.0059 0.0050 0.0041 0.0033

Hmin 5.4510 5.4719 5.4738 5.4756 5.4775

Ymax 5.4710 5.4820 5.4830 5.4839 5.4850

Isb 0.0200 0.0101 0.0092 0.0083 0.0075

Δ 0.0040 0.0042 0.0042 0.0042 0.0042

Group N Condition 2: Minimum Interference Fit thread Pitch and Shrink Band Diameters

Jmax 5.5520 5.5733 5.5752 5.5771 5.5790

Xmin 5.5630 5.5742 5.5752 5.5762 5.5772

Ith 0.0110 0.0009 0.0000 -0.0009 -0.0017

Hmax 5.4530 5.4739 5.4758 5.4776 5.4795

Ymin 5.4680 5.4790 5.4800 5.4809 5.4820

Isb 0.0150 0.0051 0.0042 0.0033 0.0025

Δ 0.0040 0.0042 0.0042 0.0042 0.0042

Group N Condition 3: Max. Interference Fit Thread Pitch Dia. With Min. Interference Fit Shrink Band Dia

Jmin 5.5500 5.5713 5.5732 5.5751 5.5769

Xmax 5.5660 5.5772 5.5782 5.5792 5.5802

Ith 0.0160 0.0059 0.0050 0.0041 0.0033

Hmax 5.4530 5.4739 5.4758 5.4776 5.4795

Ymin 5.4680 5.4790 5.4800 5.4809 5.4820

Isb 0.0150 0.0051 0.0042 0.0033 0.0025

Δ -0.0010 -0.0008 -0.0008 -0.0008 -0.0008

Group N Condition 4: Min. Interference Fit Thread Pitch Dia. with Max. Interference Shrink Band Dia

Jmax 5.5520 5.5733 5.5752 5.5771 5.5790
Report 1102-13

Page 74

Xmin 5.5630 5.5742 5.5752 5.5762 5.5772

Ith 0.0110 0.0009 0.0000 -0.0009 -0.0017

Hmin 5.4510 5.4719 5.4738 5.4756 5.4775

Ymax 5.4710 5.4820 5.4830 5.4839 5.4850

Isb 0.0200 0.0101 0.0092 0.0083 0.0075

Δ 0.0090 0.0092 0.0092 0.0092 0.0093

Group Characteristic Temperature (F)

68 350 375 400 425

N+004 Nominal: Nominal Interference Fit Thread Pitch and Shrink Band Diameters

Jnom 5.54700 5.57016 5.57205 5.57393

Xnom 5.56450 5.57666 5.57765 5.5787

Ith 0.01750 0.00650 0.00561 0.00481

Hnom 5.44800 5.47075 5.47260 5.47445

Ynom 5.46950 5.48146 5.48243 5.4835

Isb 0.02150 0.01071 0.00983 0.00905

Δ 0.00400 0.00421 0.00422 0.00424

N+004 Condition 1: Maximum Interference Fit Thread Pitch and Shrink Band Diameters

Jmin 5.54600 5.56916 5.57104 5.57293

Xmax 5.56600 5.57820 5.57920 5.5802

Ith 0.02000 0.00904 0.00816 0.00727

Hmin 5.44700 5.46974 5.47159 5.47345

Ymax 5.47100 5.48296 5.48393 5.48500

Isb 0.02400 0.01322 0.01234 0.01156

Δ 0.00400 0.00417 0.00418 0.00428

N+004 Condition 2: Minimum Interference Fit thread Pitch and Shrink Band Diameters

Jmax 5.54800 5.57116 5.57305 5.57494

Xmin 5.56300 5.57520 5.57620 5.57724

Ith 0.01500 0.00404 0.00315 0.00230

Hmax 5.44900 5.47175 5.47360 5.47546

Ymin 5.46800 5.47995 5.48093 5.481996

Isb 0.01900 0.00820 0.00732 0.00654

Δ 0.00417 0.00417 0.00424

Group Characteristic Temperature (F)

68 350 375 400 425

N+009 Nominal: Nominal Interference Fit Thread Pitch and Shrink Band Diameters

Jnom 5.54200 5.56514 5.56702 5.56891

Xnom 5.56450 5.57666 5.57765 5.57874

Ith 0.02250 0.01152 0.01063 0.00984

Hnom 5.44300 5.46573 5.46758 5.46943

Ynom 5.46950 5.48146 5.48243 5.48350

Isb 0.02650 0.01573 0.01485 0.01407

Δ 0.00400 0.00421 0.00422 0.00424

N+009 Condition 1: Maximum Interference Fit Thread Pitch and Shrink Band Diameters
Report 1102-13

Page 75

Jmin 5.54100 5.56413 5.56602 5.56790

Xmax 5.56600 5.57820 5.57920 5.5802

Ith 0.02500 0.01407 0.01318 0.01230

Hmin 5.44200 5.46472 5.46657 5.46842

Ymax 5.47100 5.48300 5.48390 5.485

Isb 0.02900 0.01828 0.01733 0.01658

Δ 0.00400 0.00421 0.00415 0.00428

N+009 Condition 2: Minimum Interference Fit thread Pitch and Shrink Band Diameters

Jmax 5.54300 5.56614 5.56803 5.56991

Xmin 5.56300 5.57520 5.57620 5.57724

Ith 0.02000 0.00906 0.00817 0.00733

Hmax 5.44400 5.46673 5.46858 5.47043

Ymin 5.46800 5.47995 5.48093 5.481996

Isb 0.02400 0.01322 0.01234 0.01156

Δ 0.00400 0.00417 0.00417 0.00424
Report 1102-13

Page 76

ATTACHMENT 6. REMOVAL FORCE GRAPHICAL SUMMARY NOMINAL,

MAXIMUM, AND MINIMUM FIT CONDITONS

0

5,000

10,000

15,000

20,000

25,000

30,000

35,000

40,000

45,000

50,000

50 100 150 200 250 300 350 400 450

Removal Force (lb)

Interface Temperature (F)

HJKL Nominal Inerferference Fit

Force SB Force Threads Total force
Report 1102-13

Page 77

0

10,000

20,000

30,000

40,000

50,000

60,000

70,000

50 100 150 200 250 300 350 400 450

Removal Force (lb)

Interface Temperature (F)

HJKL Condition 1 - Maximum Interference Fit

Force SB Force Threads Total force
Report 1102-13

Page 78

0

4,000

8,000

12,000

16,000

20,000

24,000

28,000

32,000

50 100 150 200 250 300 350 400 450

Removal Force (lb)

Interface Temperature (F)

HJKL Conditon 2 - Minimum Interference Fit

Force SB Force Threads Total force
Report 1102-13

Page 79

0

10,000

20,000

30,000

40,000

50,000

60,000

70,000

80,000

50 100 150 200 250 300 350 400 450

Removal Force (lb)

Interface Temperature (F)

N Nominal Interference

Force SB Force Threads Total Force
Report 1102-13

Page 80

0

10,000

20,000

30,000

40,000

50,000

60,000

70,000

80,000

90,000

100,000

110,000

50 100 150 200 250 300 350 400 450

Remvoal Force (lb)

Interface Temperature (F)

N Condition 1 - Maximum Interference

Force SB Force Threads Total Force
Report 1102-13

Page 81

0

10,000

20,000

30,000

40,000

50,000

60,000

50 100 150 200 250 300 350 400 450

Removal Force (lb)

Interface Temperature (F)

N Condition 2 - Minimum Interference

Force SB Force Threads Total Force
Report 1102-13

Page 82

0

20,000

40,000

60,000

80,000

100,000

120,000

140,000

50 100 150 200 250 300 350 400 450

Removal force (lb)

Interface Temperature (F)

N+004 Nominal Interference

Force SB Force Threads Total Force
Report 1102-13

Page 83

0

20,000

40,000

60,000

80,000

100,000

120,000

140,000

160,000

50 100 150 200 250 300 350 400 450

Removal Force (lb)

Inteface Temperature (F)

N+004 Condition C1 - Maximum Interference

Force SB Force Threads Total Force
Report 1102-13

Page 84

0

10,000

20,000

30,000

40,000

50,000

60,000

70,000

80,000

90,000

100,000

50 100 150 200 250 300 350 400 450

Removal force (lb)

Interface Temperature (F)

N+004 Condition 2 - Minimum Interference

Force SB Force Threads Total Force
Report 1102-13

Page 85

0

20,000

40,000

60,000

80,000

100,000

120,000

140,000

160,000

180,000

200,000

220,000

240,000

50 100 150 200 250 300 350 400 450

Removal Force (lb)

Interface Temperature (F)

N+009 Nominal Interference

Force SB Force Threads Total Force
Report 1102-13

Page 86

0

20,000

40,000

60,000

80,000

100,000

120,000

140,000

160,000

180,000

200,000

220,000

240,000

260,000

50 100 150 200 250 300 350 400 450

Removal Force (lb)

Interface Temperature (F)

N+009 Condition 1 - Maximum Interference

Force SB Force Threads Total Force
Report 1102-13

Page 87

0

20,000

40,000

60,000

80,000

100,000

120,000

140,000

160,000

50 100 150 200 250 300 350 400 450

Removal Force (lb)

Interface Temperature (F)

N+009 Condition 2 - Minimum Interference

Force SB Force Threads Total Force
Report 1102-13

Page 88

REFERENCES

1

Abernethy, Robert B., The New Weibull handbook, Fifth Edition, ©2004

2

Kenton, D. Airmotive engineering Report 0905-1, AEL65102 Cylinder Weibull Analysis, 5/19/09

3

Excelcalcs, PressFits.xls, downloaded from ExcelCalcs.com 2/28/11

4

Private communication, David Shear, Precision Machined Airparts Subsidiary of Danbury Aerospace, January 

25, 2011

5

Private communication, Pete Hakala, ASW-190, February, 16, 2011

6

Type Certificate E8CE Rev. 21, Teledyne Continental Motors, Mobile, Alabama

7

Al-202, Aluminum 242.0 Alloy T77 Condition, Alloy Digest, ASM International, ©2002

8

Al-25, Aluminum 4032 Alloy, Alloy Digest, ASM International, ©2002

9

SA371, ESR4140 Steel, Alloy digest, ASM International ©2002

10 Private communication, Bob Carlton, Danbury Aerospace, March 28,2011

11 Private communication, Jimmy Tubbs, Danbury Aerospace, February 28, 2011

12 Kaufnab, J. Gilber, and Rooy, Elvin L., Aluminum Alloy Castings, ASM International ©2005