A new engine is only as good as the cylinders the shop or owner picks and cylinders have, episodically, proved problematic. As we go to press in early September, this is indeed the case with an extensive manufacturing run of Engine Components International cylinders that the FAA proposes to remove from service via a massive AD. At issue are about 30,000 ECI cylinders for Continental O-520- and O-550-series engines manufactured between 2002 and 2012. According to the FAA’s proposed rulemaking notice for the AD, more than 30 of these cylinders have suffered head-to-barrel separations due to two unique types of cracking. Although the FAA can’t explain the reason for these failures, it wants the affected cylinders removed from service via a complex, hour-based metric that it estimates would cost owners as much as $82.6 million, making the proposed AD one of the largest on record.
Not surprisingly, ECI is opposing the AD as being far too broad and unsupported by accurate data. It says the FAA has overestimated the number of true head/barrel separations and it believes the ones that have occurred were due to severe overheating caused by pilots mismanaging leaning. In response to the FAA’s shotgun approach, ECI would like to stick with a 2008 bulletin it issued against a smaller population of cylinders requiring inspection at 50-hour intervals and removal at TBO.
As of press time in early September, the FAA’s docket for the proposed AD remained open and was gathering overwhelmingly negative comments.
Background
Problems with ECI cylinders date as far back as 2004, but the incidents that led to the AD proposal result from what the FAA says are multiple reports of cylinder failures.
Technically, these cylinders are identified under the Airmotive Engineering Corp. flag, the ECI sister entity that owns the approved parts manufacturing authority. These cylinders are marketed by ECI under the Titan brand name.
The FAA has been somewhat vague about how many failures have occurred and, in any case, ECI doesn’t agree that all of the cylinders the FAA has flagged qualify as head/barrel separations. The FAA claims more than 30 and possibly as many as 39 head/barrel failures, while ECI counters it has verified 19 head/barrel separations since about 2002. When we visited ECI’s San Antonio, Texas, factory in August, we were told that the company hasn’t examined all of the cylinders that the FAA claimed failed, if these are even available for analysis.
The proposed AD names two failure modes, although neither it nor the docket filed in support of the NPRM offers an explanation or mechanism for the failures. One type of separation, says the NPRM, is a shrink-band failure, while the other is cracking in the dome of the cylinder head above the combustion chamber.
Aircraft cylinders of the type in question consist of two components, a finned steel barrel and an aluminum head. The load surface—the part that actually carries the stress of containing combustion pressures—is called the shrink band and cylinder assemblies are held together via a precision interference fit between band surfaces on both parts. Threads on both the barrel and the head serve only as a means of assembling the two parts; they’re not intended to carry combustion loads, since threads in the aluminum head lack the yield strength.
Prior to assembly, the head is heated and screwed onto the barrel while hot, driving the expanded shrink band into an interference fit on the barrel. If the band fails, either due to cracking or loss of interference, all of the combustion loads are transferred to the uppermost thread in the assembly. It’s likely to fail, resulting in head/barrel separation.
ECI concedes that it has had issues with head/barrel separations in the past, due either to a slightly out-of-tolerance shrink band fit or improper heating during assembly. But Ty Stoller, who is president of ECI’s parent, Danbury Aerospace, told us those issues have been addressed and don’t have any bearing on the 30,000 cylinders the FAA has named in its recent NPRM.
Although the dome cracking is a fundamentally different process, ECI and the FAA still consider these to be head/barrel separations. ECI has identified one other mode of separation which it calls a “slip off.” They showed us one cylinder which appeared to have an intact shrink band, but little evidence of thread damage. ECI doesn’t have an explanation for this type of failure.
No Agreement
ECI and the FAA don’t agree on the actual number of separations that have occurred in the identified cylinder population. We’re told that most of the data for both ECI’s and the FAA’s analysis comes from service difficulty reports (SDRs) which are problematical on several counts. They don’t necessarily sweep up all the cylinder failures and many that are identified may not be accurately reported as head/barrel separations.
When we asked if ECI’s research had also included a look at Continental OEM head/barrel separations during a comparable period, ECI told us that it found 21, a number comparable to ECI’s failures, if you accept 19 as an accurate claim. However, Continental’s failures are among a much larger population of cylinders—about five times larger, according to Continental’s estimates of its cylinder production.
Jimmy Tubbs, ECI’s vice president of engineering, concedes that Continental cylinders have had a lower rate of failure. “There’s no question they’ve done we’ll with their cylinders,” Tubbs said of Continental’s OEM cylinders.
Asked why this is so, Tubbs explained that ECI believes Continental cylinders are more likely to be installed in newer or more sophisticated aircraft equipped with electronic engine monitoring equipment that makes it less likely that a pilot would inadvertently overtemp the cylinders. “We’ve seen some of the older, single-probe CHTs that haven’t been calibrated in years and can be 50 degrees in error,” Stoller told us.
ECI argues that all of the failures it has seen are due to overheated cylinders caused by improper leaning or poor baffling and not detectable problems in manufacturing quality. When we visited ECI, the company showed us a couple of cylinders with signs of thermal stress and possibly detonation. ECI is arguing for a requirement for datalogging digital engine monitors as both a safety-of-flight instrument and a means for tracking engine health.
Low Numbers, Low Risk?
The FAA’s NPRM docket doesn’t offer much in the way of risk analysis to back up its claims of a safety issue requiring the removal of 30,000 cylinders. But it’s not hard to run some basic numbers. Accepting the FAA’s higher failure numbers, the percentage of cylinders that have had head/barrel separations is 0.116 percent. At ECI’s lower number, it’s 0.06 percent. On a per-engine basis, 30,000 cylinders represents 5000 engines for a per-engine failure rate of one in 263 engines using ECI’s figures or one 147 engines using the FAA’s higher claims. However, the affected engine population might be larger, since not all cylinders will be installed in a complete set.
Furthermore, says ECI, a head/barrel separation doesn’t necessarily result in a catastrophic engine failure because with five remaining good cylinders, the engine should continue to produce usable power for an emergency landing. ECI also claims there have been no accidents or injuries as a result of head/barrel separations. (We’re unable to confirm this independently and a sweep of the NTSB records as far back as 1995 revealed just a handful of accidents related to head/barrel separations for both Lycoming and Continental engines. If head/barrel separations are more numerous, they don’t seem to cause many accidents.)
ECI also challenges the FAA’s claims on predicting future failures in the affected cylinder population. ECI told us to support the AD’s breadth, the FAA appears to have used two statistical models, one called Weibull and the other Crow-AMSAA. Taken together, the two models predicted 15 to 35 head-barrel separations between 2011 and 2013 in the two cylinder populations. But ECI says there have been no separations during that period and none in ECI cylinders manufactured since 2008.
What Shops Say
We canvassed six respected engine shops about their experiences with ECI cylinders. Although reaction to the AD was mixed, none of these shops reported any head/barrel separations in ECI cylinders. Two shops, Penn Yan Aero in Penn Yan, New York, and Poplar Grove Airmotive in Popular Grove, Illinois, told us they’ve stopped recommending ECI cylinders because of a perceived higher rate of cracking not related to head/barrel separations. But Penn Yan’s Bill Middlebrook said he thought the proposed AD was far too broad and an FAA overreach.
“It appears to us to be excessive and over burdensome on aircraft owners, ECI and the industry as a whole. It is already having an effect on our business in that we are flooded with panicked customers who may or may not have ECI product on their engines,” Middlebrook said.
Zephyr Engine’s Herman Vollrath echoed the sentiment, but in descriptive prose too harsh to print. Only one shop, Certified Engines in Opa-Locka, Florida, thought the AD was justified. Said Certified’s Allen Weiss, “Are the cylinders unsafe? I don’t know about that word, but we’ve seen plenty of cracking of cylinders outside the applicable serial numbers,” he adds. Weiss says Certified has had “moderate success” with the ECI Titan line, with issues no different than other shops may have experienced. When asked if the AD is justified, Weiss said: “My answer is yes. I wish it was no. This could potentially put them out of business and that’s very bad for our industry. I want them to win their appeal because I need them to stay afloat. On the other hand, safety has got to be number one.”
Recommendations
As we go to press in early September, the FAA was at least a month away from closing the comment period on the proposed ECI AD and we can’t predict which way it will go. The NPRM has attracted widespread opposition, including from AOPA, EAA and scores of owners and shops.
In the meantime, should you buy ECI cylinders for an overhaul? As recently as 2008, Aviation Consumer’s cylinder and engine customer satisfaction surveys have revealed favorable results with ECI cylinders. Since then, we haven’t seen a notable uptick in complaints about ECI cylinders, so our recommendation is to consult with the overhaul shop before making a decision.
At least two of the shops we interviewed—Zephyr and America’s Engines in Tulsa, Oklahoma, both well-known shops—report no problems with ECI cylinders and either use them exclusively or don’t steer customers away from them. Although our shop poll didn’t reveal a universal ringing endorsement for ECI cylinders, we haven’t seen enough convincing data from the FAA (or anyone else) to advise avoiding these cylinders. As for the AD, we’re withholding judgment until we’ve seen more data.
