Presented to: By: Date: **Federal Av**  **iation Ad**  **ministration**

**Federal Av**  **iation Ad**  **ministration** 

# ECi **Cylinder Risk Analysis** 

**NTSB An**  **n A zevedo, F** 

**AA C**  **ST A,**  **S afety** 

**An aly** **sis June 9, 2015** **Federal Av** **iation Ad**  **ministration** 

# 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 Av** **iation Ad**  **ministration** 

# Risk Analysis **– Specifics** 

• **Analy sis**  **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 Av** **iation Ad**  **ministration** 

# Risk Analysis **– Assumptions** 

• **No differentiation by**  **s erial**  **numbers (S/Ns). In other**  **wo rds,**  **all parts**  **equally suspect**  • **28,800 P/N 631397**  **ECi cy**  **linders installed in Continental**  **engines are subject to this risk analy** **sis. This is the estimated total**  **at the time of current**  **AD preparation (September**  **2014 )**  • **Av erage fleet**  **utilization: Average airplane**  **utilization (normalized**  **across tw in**  **- and single**  **- engine**  **airplanes by**  **percentage) is rounded to 140 hours/y** **ear** • **Parts advanced 140 hours per y** **ear for 3.75 y ears 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 cy**  **linders per engine**  4**Federal Av** **iation Ad**  **ministration** 

# Risk Analysis **– Assumptions (cont.)** 

• **74 %**  **engines installed on**  **tw ins**  • **The recommended**  **overhaul interval varies from 1200 hours to 2400 hours depending upon engine ty** **pe, but the average interval is assumed to be 1700**  **hours** • **2 fatal accidents**  **involving P/N 631397**  **ECi cy**  **linders cracking or separation**  **on Continental engines**  • **Maximum allow** **ed time**  **for each category (no credit**  **for removal for cause**  **)** • **Zero risk for replacement parts.**  **In other wo**  **rds, parts**  **produced in the future wi**  **ll not be suspect**  **of having the safety issue**  • **No credit taken**  **in the risk analy** **sis for inspection** 

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

– Considerable uncertainty about the value of the available inspection 5**Federal Av** **iation Ad**  **ministration** 

# 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 analy** **sis allows**  **considerable relief to**  **the original version of the AD, released for Public Comment**  **on August 12,**  **2013** 6**Federal Av**  **iation Ad**  **ministration** 

# Single Engine **Recip vs Class I** 

7 SARA (Class I) EPD (single engine recip ) Uncorrected Risk (long term) - ECi**Federal Av**  **iation Ad**  **ministration** 

# Twin Engine **Recip vs Class II** 

8 SARA (Class II) EPD (twin engine recip ) Uncorrected Risk (long term) - ECi