May 23, 2011

This survey is a consolidation of survey results obtained from our club (CAAC) and The American Bonanza Society and Cirrus Owners and Pilots Association. We would like to thank the three hundred (plus) club members from our club (CAAC), The American Bonanza Society (ABS) and Cirrus Owners and Pilots Association (COPA) who participated in the survey.

The survey was not intended to be scientific. Why, most owners do not have the necessary information. What we did hope to address were perceptions of component performance and overall engine reliability. The end goal was to increase awareness in order to make a more informed decision if/when a significant maintenance issue developed.

“Failure Rate” will denote how many of a given population of similar parts has failed. (This is a snapshot in time. If conducted again next year the results may or may not be similar.) All we expected from this short, non-technical survey was to determine which items are failing, whether the failure rates seemed acceptable or not, and ask what can be done to be better prepared if a failure occurs on their engine.

Using this approach, several items are above reasonable failure rates. Starter adapters, starters and exhaust valves are the top three. The big weaknesses in the first two have resulted in change and understanding. Time will tell if the changes prove to be the correct ones. Exhaust valves are under a needed discussion now on the CAAC thread but it is to early to determine the outcome of the conversation.

Some observations can also be made – and argued/discussed. The fuel expense between LOP and ROP is widely discussed. Some of the failure data suggests ROP does not result in a lower failure rate. (I’m ignoring the requirement for ROP operations at higher altitudes.) Some engine configurations have very high cylinder failure rates. Why? And, I’m not sure failures only occur early in the engine life as I’ve heard from a variety of sources. Data suggests failures are in sync with engine hours! What may cut down on failures as engine hours grow is a smarter operation. (Change nothing and get the same outcome. If you don’t like the outcome, change something.)

A couple notes to make: This survey only shows the questions that were common across each club. Example: Columbia offered Platinum. We didn’t ask this question of the other two clubs so it wasn’t included in this consolidation. The order of one or two minor questions is slightly different. Comments on particular questions are addressed to all three clubs. I do not plan to rewrite this for each club.

The IO-550 appears to be a highly reliable engine as most problems are discovered on the ground. I believe this is critical as it indicates the items with higher failure rates occur over time.

Going forward, our energies will be to find improvement opportunities and pursue them when feasible. AND, only do so in a positive and productive fashion. More comments on this at the end.

I have been mixing tense between I/My and We. I would like to give my sincere thanks to Darryl Taylor for his participation. Darryl is my maintenance management consultant (Evolution Aviators – www.flyevolution.com) and took the lead in crafting this survey.

To the Survey!

Question 1: How many hours do you have on your motor?

This by itself isn’t very valuable but will prove useful when combined with later questions.


Question 2: How many hours per year do you fly?

Nothing earth shattering in this data. Bonanza flies, on average, the lowest hours per year with Cirrus flying the highest.


Question 3: Have you made any engine modifications?

GAMI injectors and modified baffling are huge interest areas in the Bonanza group. Sixty four percent of Cessna aircraft were purchased with a “Platinum” engine which included TCM’s tuned injectors.

All Cirrus aircraft, until last year, were delivered as Normally Aspirated as it has been explained to me. The TAT turbo, sponsored by Cirrus is an after-market option available in the last 2 to 4 years. (This short life suggests failure rate data may not be fully represented yet.) I also understand Cirrus buyers are shifting their preference to the recently introduced turbo option. If correct, those considering the turbo option should make sure to evaluate the Cessna turbo information.

Question 4 (CAAC Survey only): Is your engine Platinum?

64% were yes.

36% were no.


Question 6: We asked which engine oil everyone used.

We looked at the data to see if there was a correlation between engine oil and failure rates – no conclusion.


Question X: asked Cirrus (only) which starter was installed on your aircraft. All Cessna aircraft have been delivered with Iskra starters. CAAC has done an informal review of starters and starter adapters and is making two suggestions to club members. One, if the starter fails also install a new/rebuilt starter adapter. Our experience suggests that failing to do so will result in a 90+% chance of failure of the old starter adapter within 20 starts. Second, if the starter adapter fails, do not reinstall an Iskra starter. I understand all Cirrus aircraft are now delivered with SkyTec starters. And believe (correction if necessary) that Continental is delivering all engines with a SkyTec starter.

C 1DATA PAUL Aviation CIRRUS Engine Survey Q5 jpg

Question 7: This question was intended to get your memory working in preparation for the next several questions. We asked whether you had a problem with you motor - or not. If yes, which areas did you have a problem. This only provided the overall failure rate for all components in each fleet. It does not provide details for each component as it did not take into account the number of failures.

The overall failure rate for each group is:

Bonanza = 65%

Cessna = 77%

Cirrus = 76%

The next several questions allowed us to determine how severe the failure rates were for each item and when they occurred.

Question 8: asked you to detail engine problems by clock hours. This data is presented two ways. The first view is tabular.

C 1DATA PAUL Aviation BONANZA Survey Q8 jpg

I graphed each of the hourly groups divided by the last line – Percent Total Problems.


I then compared this graph it to the graph of Percent of all Aircraft versus their Current Engine Hours.

I have heard from several sources that the greatest exposure for failures occurs in the first 200 to 400 hours. These two graphs suggest the frequency of component failures will track accumulated engine hours – if nothing is changed. The information is not suggesting every engine will have every problem.

In Question 7 we were able to determine the overall probability of a problem occurring and we get a peak where the problems were. In Question 9, we fine tune this by asking how many failures occurred and at what engine hours. The following two tables are for Normally Aspirated and Turbo (both TAT and TT).

Each group has something to smile about. But be fair, each has questions to ask as well.

Number ONE: starter adapters. Cirrus Aircraft (along with COPA?) did a study of the failure rate of the starter and starter adapter that resulted in Cirrus specifying all future engines come equipped with a SkyTec, rather than Iskra, starter. I heard (but have not verified) the Cirrus failure rate was approximately 25% for the Iskra starters but their survey data shows double the study amount. This gives an indication that failure rates (as defined and applied to all items) could by 100% in error – not good for confidence!

Exhaust valves were the third highest failure item but don’t look that bad when evaluated across the graph. Focus on just this item (or any item) and there is a factor difference. Cirrus is low at 2% followed by Cessna at 6% and Bonanza at 12% for Normally Aspirated engines. The trend suggests Bonanza is twice as bad as Cessna and 6X worse than Cirrus. A possible contributing factor: Cessna and Cirrus operate LOP while a large majority of Bonanza’s are operated ROP. Does this suggest LOP is not only more fuel efficient but also less damaging to the motor?

Another trend, why does the Bonanza turbo engine have so many cylinder problems? Nine out of 22 reported cylinder problems. Five of the nine showed all 6 being repaired at the same time. Another 2 showed 4 being repaired. Where these all damaged? Perhaps this included overly cautious pilots/owners or service center issues?

Another trend, why does Cessna have so many starter problems than the others? A number of owners (8) pulled their Iskra starter as part of an informal ‘study’ to see if other starters were more effective. Several other owners, at their own cost, also changed. In every case but one, the starter adapter failed. So, the starters look bad and the starter adapters look worse. I looked at that data and could make an argument the CAAC failure rate was possibly as low as 15% and high as 40%. The higher rate correlates with the completed surveys. The lower failure rate applies when I pulled out the owners who didn’t participate in the informal tests and opted to change their starters. IE., many failures were induced by a change. Not normal wear and tear.

Another trend, Cirrus Turbo has an ignition problem. One owner reported 3 Ignition problems. Remove this one and it looks less problematic but still high.

According to the survey data, the average hours per year is 150ish. In my airplane, the difference between LOP and ROP for the same HP is ~5 GPH. Assume fuel is $5/G. That equates to an increment of $3,800 per year in fuel expense. I lose 2-3% TAS flying LOP but reduce fuel consumption by 20%. Add additional savings due to lower component failures and I’m a happy camper flying LOP. We are having a very interesting and challenging conversation on how to most effectively fly LOP. An agreement on this could enhance LOP operations even further.

There are other benefits: My CHTs are lower by 15 – 20 dF when flying LOP vs ROP at the same power setting and the delta between my highest and lowest CHT is smaller when flying LOP.

Question 10: asked you where and how your problems were discovered.

The overwhelming outcome was during inspections.

The last questions asked about spark plugs.

Champion dominates both NA and Turbo aircraft. I don’t know all of the reasons Cessna owners changed. I know why I changed. The Massive plugs have to be pulled and inspected every 100 hours. The fine wire plugs do not! There is also the savings in shop time from not needing to remove both intercoolers every 100 hours which you have to do to properly pull/install the #1 and #2 cylinder plugs. There was a lot of discussion at one time on our forum about chipped ceramic but I haven’t heard much lately. I suspect many inexperienced shops were not completely removing the intercoolers. If not removed, two failure opportunities are created.

One is to crack the intercooler attachment flange. If not fully removed, the tech WILL have to use a pry bar to push the intercooler out of the way to insert the socket/extension to remove and reinstall the plugs on #1 and #2 cylinders. This prying action places a lot of stress on the attachment flange.

The second failure opportunity is the potential to crack the ceramic when the plug is removed or replaced. If the intercooler is not fully removed the socket and extension is under a slight sideways pressure which can cause the unsuspecting tech to let the tip of the plug knock against the cylinder.


The following table is the same data graphically presented in Question 7 above. Shown are the reported failure rates for Normally Aspirated and Turbo airplanes and by manufacturer.

NA / NA / NA / IO-360 / TAT / TAT / TT
Exhaust Valve / 12% / 3% / 6% / 0% / 7% / 2% / 10%
Intake Valve / 1% / 0% / 0% / 0% / 0% / 0% / 0%
Piston/Rings/Rods / 3% / 4% / 2% / 0% / 5% / 0% / 0%
Cylinder / 12% / 6% / 6% / 0% / 31% / 11% / 7%
Cam/Lifters / 21% / 14% / 6% / 0% / 5% / 0% / 0%
Crankshaft / 1% / 0% / 0% / 0% / 0% / 0% / 0%
Turbo Charger / 0% / 0% / 0% / 0% / 0% / 13% / 5%
Exhaust System / 14% / 16% / 6% / 14% / 18% / 31% / 25%
Starter / 11% / 46% / 12% / 14% / 0% / 38% / 27%
Starter Adapter / 17% / 61% / 47% / 14% / 14% / 56% / 41%
Ignition/Fuel / 8% / 16% / 6% / 14% / 5% / 50% / 0%

A good next step is searching for a WIN/WIN opportunity so that all contributors to our engine health are working as a team.

This survey looks at data from only one perspective – the owner operator. It ignores others involved in the maintenance chain. This includes the aircraft manufacturer, engine manufacturer, service center, technician and maintenance manager (if you use one). My conversations about engine longevity with fellow aviators, maintenance managers and others always open a flood gate of knowledge and exasperations. Critical to these, and readily viewed in CAAC threads, are a lack of communication, information and standards. What can be done to have a positive impact?