ECi 470/520/550 Dome and First Thread Separations Summary (FAA Assessed)

Separation S/N

Assembly

Assembly

Date

Date of

Failure

TIS

(Hrs.)

Aircraft

Make/Model

Failure

Location

1 4360‐32 01/15/2003 12/02/2008 218.1 Cessna 340A dome radius

2 4464‐24 01/20/2003 03/31/2003 87 Cessna 207A dome radius

3 5482‐19 02/14/2003 09/03/2003 283 Not Reported Not Reported

4 7141‐16 04/14/2003 11/15/2003 269 Not Reported Not Reported

5 7819‐23 05/23/2003 04/23/2004 204 Cessna 414 Not Reported

6 8013‐28 05/19/2003 08/12/2009 960 Not Reported dome radius

7 12612‐5 10/10/2003 04/28/2004 200 Cessna 414 Not Reported

8 13515‐11 01/05/2004 06/15/2010 360 Cessna 340A thread

9 13515‐26 02/05/2004 08/12/2008 338 Cessna 182 thread

10 13670‐3 01/22/2004 04/18/2006 1301 Beech 58P thread

11 16757‐6 04/01/2004 03/18/2005 475 Cessna T310R Not reported

12 18700‐1 06/17/2004 05/01/2009 663 Cessna U206F Not reported

13 19441‐28 07/23/2004 06/05/2007 290 Not reported Not reported

14 20940‐22 08/19/2004 12/12/2005 89 Cessna U206F Not reported

15 21327‐19 09/10/2004 02/07/2005 721 Cessna 401 Not reported

16 21432‐10 08/31/2004 10/14/2008 355 Beech A36 Not reported

17 21590‐14 09/10/2004 04/27/2009 150 Beech A36 dome radius

18 21994‐21 09/16/2004 05/11/2006 330 Cessna 414 Not reported

19 22241‐24 10/11/2004 07/14/2010 264 Cessna 340A Not reported

20 22389‐9 10/05/2004 05/03/2006 170 Beech A36 Not reported

Table 1:  FAA Confirmed ECi Separations Assessed by FAA to be Either Dome Radius or First Thread
ECi 470/520/550 Dome and First Thread Separations Summary (FAA Confirmed)

(Continued)

Separation S/N

Assembly

Assembly

Date

Date of

Failure

TIS

(Hrs.)

Aircraft

Make/Model

Failure

Location

21 22537‐24 10/05/2004 05/03/2006 172 Beech A36 Not specified

22 22838‐19 10/20/2004 03/11/2009 390 Beech 58P dome radius

23 23217‐13 10/19/2004 12/30/2008 257 Cessna 340A dome radius

24 23343‐15 10/26/2004 08/01/2005 505 Not reported Not reported

25 23258‐14 11/01/2004 05/18/2008 424 Cessna 414 dome radius

26 33947‐29 11/22/2005 11/20/2008 210 Beech A36 thread

27 34684‐13 11/06/2005 10/01/2010 1061 Cessna 310R thread

28 35955‐22 01/06/2006 05/20/2009 1163 Cessna 414 thread

29 45312‐15 03/02/2007 09/12/2009 1095 Cessna T207A thread

30 50785‐26 11/20/2007 04/03/2009 196 Beech 58P thread

31 51847‐12 01/23/2008 07/30/2010 71 Cessna 414A thread

32 51973‐08 01/28/2008 08/04/2009 835 Cessna 414 Not reported

33 52884‐22 06/04/2008 11/13/2008 416 Cessna P206 thread

            

Table 1:  FAA Confirmed ECi Separations Assessed by FAA to be Either Dome Radius or First Thread
Figure 1:  Scatter plot of FAA known ECi 470/520/550 separation events assessed by FAA to have originated in

the dome radius or first thread of the head‐to‐barrel interface.

The data points listed in Table 1 above were then summarized in the form of a scatter plot of time‐in‐service

(TIS) ~ hrs. vs. cylinder assembly serial number ~ S/N to better identify what segment of production was at risk

for separation for each failure mode.

The scatter plot data indicates that separations originating in the dome radius were primarily associated with

cylinders manufactured prior to S/N 33696.  Sharp radii have the direct effect of increasing the local stress

concentration factor in structural elements, which in turn decreases the fatigue life.  ECi increased the design

dome radius around that S/N and those failures have been drastically reduced since that design change,

although a small number may still have occurred since then.   Cylinders that failed in the dome radius were

shown to most likely occur within 500 hrs. TIS and such failures were documented as low as 87 hrs. TIS.  The FAA

views the dome radius issue as an “infant mortality” failure mode where if it does not fail by 500 hrs. TIS, it

probably was manufactured to the upper tolerance of the dome radius and most likely will not separate in this

location while in continued service.  However, since the actual dome radius for a given cylinder was not

recorded at the time of manufacture and cannot be determined in service, cylinders manufactured prior to S/N

33696 that currently have less than 500 hrs. TIS remain at risk for separation due to this failure mode and they

must be removed within the next 25 hrs.  

The data also indicates that the thread fatigue failures that are associated with insufficient head‐to‐barrel

design interference fit occur later in the life of the cylinders, but almost always before 1,000 hrs. TIS.  There are,
however, a few possible outliers above 1,000 TIS.  The FAA has since discovered that ECi has incrementally

increased the design head‐to‐barrel interference fit multiple times while these failures were occuring, in most

cases without notification to the FAA.  The most recent such increase was at S/N 61176.  The FAA therefore

established a 1,000 hr. life limit on such cylinders manufactured before S/N 61176 because we have

documented separations due to this failure mode prior to the latest increase in interference fit, but no

documented failures after implementation of the most recent change to the interference fit at S/N 61176.

It should be noted that the 25 hr. repetitive inspection interval prescribed in the scatter plot has since been

changed to 50 hrs.  However, the FAA is aware of at least two instances where these cylinders had passed

compression tests and then separated within 50 hrs., in one instance at 23 hrs.  Some operators have also

reported that such inspections have revealed some partially separated cylinders which were intercepted before

total separation.  For that reason, the FAA included the 50 hr. repetitive visual and compression test inspection

in the proposed AD.

The FAA conducted an exhaustive three year review of all available data sources and determined that the

subject ECi cylinders separate at a much higher rate than the OEM cylinders (TCM).  Our data indicates that ECi

has experienced 104 known head‐to‐barrel separations since their introduction into the market (after PMA

issuance in 1999), while TCM experienced 13 (Figure 2).  The data shown starts in 2001 because ECi had

insignificant market share before that and very little time on the initial cylinders before that.   

The degree of the disparity in rate of separation (ECi vs. TCM) is significantly further magnified by the

recognition that ECi only has one‐quarter of the number of cylinders in service that TCM has.   

Figure 2:  Comparison of documented separations for ECi and TCM since 2001.
Figure 3:  Comparison of documented separations for ECi and TCM since 2001 normalized to reflect

differences in annual production.  TCM produces approximately 4x the number of cylinders that ECi

produces in an average year.

Figure 4:  Since 2005, ECi has continued to have higher numbers of separations every year, despite the

lower production rate.  Note:  The 23 separations listed on this graph differs from the 33 separations

listed in Table 1 above.  This is because the FAA had assessed some separations in the 2003 and 2004

time frame as being due to the thin‐wall design problem that was addressed by an earlier FAA AD.  We

subsequently learned that some of those prior failures were actually dome radius or thread failures.
Figure 5:  When we normalize the actual number of known separations for production rate, we note

that ECi continues to experience separations at a much higher rate than the OEM.  Note:  the FAA

estimates that the ECi cylinders separate at a rate that is (32)times higher than that of the OEM

cylinders.

Figure 6:  The FAA obtained approximate annual production data from both ECi and TCM during the

2001 through 2012 time frame.  This data showed that TCM has approximately four times the

production rate as ECi and at least four times the total number of cylinders in the field.