Presented to:

By:

Date:

Federal Aviation

Administration

Federal Aviation

Administration

ECi Cylinder 

Risk Analysis

NTSB

Ann Azevedo, FAA CSTA, Safety Analysis 

June 9, 2015
Federal Aviation

Administration

ECi Cylinders Risk Analysis

• Risk evaluated for fatal accidents

– Suspected under-reporting of base events (cracks 

and possibly separations)

– Risk guidelines are for high-severity events, so 

whether we start with base event and multiply by 

conditional probability of fatal accident, or use fatal 

accidents, we get to the same value

• Existing part population estimated from 

production records, reporting, utilization 

and retirement rates, and prior AD’s

2
Federal Aviation

Administration

Risk Analysis – Specifics

• Analysis of the basic cracks and 

separations indicates random failure mode, 

which means MTBF can be used to predict 

risk

• Fatal accident experience not significantly

different between single- and twin-engine 

airplanes

3
Federal Aviation

Administration

Risk Analysis – Assumptions

• No differentiation by serial numbers (S/Ns). In other words, all 

parts equally suspect

• 28,800 P/N 631397 ECi cylinders installed in Continental 

engines are subject to this risk analysis. This is the estimated 

total at the time of current AD preparation (September 2014)

• Average fleet utilization: Average airplane utilization 

(normalized across twin- and single-engine airplanes by

percentage) is rounded to 140 hours/year 

• Parts advanced 140 hours per year for 3.75 years from 

histogram established for prior ADs

• 35% of produced parts retired (based on production rates and 

the number of parts affected by the prior ADs)

• 6 cylinders per engine

4
Federal Aviation

Administration

Risk Analysis – Assumptions (cont.)

• 74% engines installed on twins

• The recommended overhaul interval varies from 1200 hours to 

2400 hours depending upon engine type, but the average 

interval is assumed to be 1700 hours

• 2 fatal accidents involving P/N 631397 ECi cylinders cracking 

or separation on Continental engines 

• Maximum allowed time for each category (no credit for 

removal for cause) 

• Zero risk for replacement parts. In other words, parts 

produced in the future will not be suspect of having the safety

issue

• No credit taken in the risk analysis for inspection

– Part 91 operators do not have a required 100-hour inspection

– Considerable uncertainty about the value of the available inspection

5
Federal Aviation

Administration

Risk Analysis – Results

• 0.31 expected fatal accidents

– 0.23 twin-engine airplanes

– 0.08 on single-engine airplanes

• 0.31 fatal accidents equates to a 27%

chance that one or more fatal accidents will 

occur during the AD period while the 

suspect parts are removed from service

• Risk analysis allows considerable relief to 

the original version of the AD, released for 

Public Comment on August 12, 2013

6
Federal Aviation

Administration

Single Engine Recip vs Class I

7

SARA (Class I)

EPD (single engine recip)

Uncorrected Risk (long term) - ECi
Federal Aviation

Administration

Twin Engine Recip vs Class II

8

SARA (Class II)

EPD (twin engine recip)

Uncorrected Risk (long term) - ECi