In late July, as tens of thousands of GA aircraft owners were converging on Oshkosh for AirVenture 2017, Lycoming published Mandatory Service Bulletin 632 titled “Identification of Connecting Rods with Non-Conforming Small End Bushings.” This was a very nasty service bulletin affecting Lycoming engines of all models that were built, rebuilt, overhauled or repaired during the past two years. Lycoming quickly published two revisions (632A and 632B) in rapid succession.

SB 632B addressed a problem with small-end connecting rod bushings (part number LW-13923) that were used in Lycoming factory new and rebuilt engines and shipped by Lycoming to overhaul shops and mechanics between November 2015 and November 2016. It turns out that there was a quality assurance problem with these bushings, and many of them had an outside diameter that did not conform with specifications. These bushings are pressed into the small end of Lycoming connecting rod assemblies using a hydraulic press. If the bushings are too small in diameter, the press-fit isn’t secure and the bushings can migrate out of the connecting rod when in service. That’s exactly what seems to have happened to a relatively small percentage of these non-conforming bushings, hence the mandatory service bulletin.

Lycoming Rod Bushings: Good vs Bad

Lycoming rod bushings.

Lycoming used these bushings in-house to build connecting rod assemblies, some of which were sold to overhaul shops and mechanics between November 2015 and February 2017, and most of which went into Lycoming factory new and rebuilt engines. Any engine that has these non-conforming bushings, whether built by the factory or overhauled or repaired in the field, are affected by SB 632B.

Why is SB 632B so nasty?

SB 632B requires that all engines that might possibly contain these non-conforming bushings have all their cylinders removed within the next 10 hours. With the cylinders removed, the securing of all small-end connecting rod bushings then must be tested using a special tool (“ST-531 Connecting Rod Bushing Press-Out Verification Tool”) to apply a calibrated force to each bushing to see if it can be displaced. If the bushing moves during this press-out test, then the connecting rod assembly must be removed from the engine and sent to Lycoming, and a new connecting rod assembly with a known-good bushing must be installed. Lycoming initially estimated that the press-out test will have approximately a 20% flunk rate, but from what we’ve been hearing that estimate may turn out to be way too optimistic.

Lycoming ST-531 Connecting Rod Bushing Press-Out Verification Tool

Lycoming ST-531 Connecting Rod Bushing Press-Out Verification Tool

As someone deeply involved in piston GA maintenance, I find what SB 632B requires to be a horrifying prospect. The requirement to remove all cylinders within 10 hours is bad enough; there is a long history of catastrophic engine failure after removal and replacement of all cylinders in the field that I’ve written about extensively. But the prospect of having 20% or 30% or 40% of the connecting rods removed and replaced in the field represents a far greater risk, because the majority of mechanics have never before performed this operation (notably tightening rod bolts to a specified stretch using a special micrometer). The rod bolts are the most highly-stressed component in the entire engine, and tightening them properly is ultra-critical. In my opinion and the opinion of every highly experienced A&P/IA I’ve spoken with, this is NOT work that should be attempted by line mechanics in the field working on engines mounted in airplanes. It really should be done only by an experienced technician in an engine shop with the engine mounted on a stand with unencumbered access.

In short, I quickly concluded that that the cure called for by Lycoming would very likely be worse than the disease, and that it’s likely that there may be more catastrophic engine failures caused by maintenance errors in performing SB 632B than would be caused by the migrating bushing problem that SB 632B addresses. After conferring with a few very experienced A&P/IAs who have much more experience maintaining Lycoming engines than I do, I also concluded that there is a far less invasive and risky and expensive method that would effectively detect bushing migration and mitigate the safety risk without creating a bigger one in the process.

Owner organizations respond

While in Oshkosh, I spoke to several Lycoming executives who indicated that they expected the FAA’s New York Aircraft Certification Office (ACO) to start the wheels in motion to issue an emergency Airworthiness Directive the following week that would mandate compliance with SB 632B. I then sought out AOPA’s David Oord, with whom I’d recently worked so successfully on dealing with the Continental camshaft gear issue. Dave and I discussed that the FAA had not issued an Airworthiness Concern Sheet (ACS) about this Lycoming bushing issue in order to solicit input from the affected aircraft owner associations, something they had promised to do when we met with the FAA Engine and Propeller Directorate at a GA engine summit meeting in 2015. Dave and I agreed that it would be appropriate for AOPA to ask the FAA to do that so we would have a reasonable time to research this issue and provide the FAA with a thoughtful response before their AD process began, and Dave promised he’d make some calls as soon as he returned to his office.

On Tuesday, Dave phoned to tell me that that he’d heard back from the FAA, and that they said they would not be able to issue an ACS because they considered the issue too time-critical. Dave pressed for input to the process from the aircraft owner community, and the FAA agreed to try to set up a conference call between aircraft owner representatives, key FAA personnel, and representatives of Lycoming. That sounded better than nothing.

The next morning, I was awakened by another phone call from Dave, who told me that the FAA was willing to do a conference call, but it had to be TODAY. Yikes! We identified several other qualified aircraft owner representatives to be on the call to represent Cessna and Piper owners, and all agreed to participate.

The call was scheduled for 3 pm Eastern. I spent two hours drafting a bullet-point document containing our questions, concerns, and proposed alternative solution to SB 632B, and emailed it to Dave, who sent it to all the participants expected to be on the call from the FAA, Lycoming, and the owner associations.

Stonewalled!

The conference call took place as scheduled and lasted for an hour. However, Lycoming declined to answer ANY of the questions we posed to them, telling us that the information was proprietary and Lycoming was sharing it solely with the FAA and no one else.

Lycoming would not tell us how many displaced bushings have been found, how many connecting rod failures had occurred due to bushing displacement, what the distribution of engine times was when bushing displacement was detected or connecting rod failure occurred. They would not tell us how many engines they expected to be affected. They would not even tell us how much the special ST-531 press-out tool would cost, or how soon they could get enough of these tools out in the field to perform the required test.

The FAA would not tell us, either, saying that they were not permitted to release any of this information without Lycoming’s permission (which clearly was not forthcoming). We spent the better part of an hour asking questions but got no answers. It was absolutely exasperating.

We spent the rest of the time on the call trying to convince Lycoming and the FAA that there was a far less invasive and risky and costly way to deal with the displaced bushing problem, and we described it to them in detail. But it became clear that Lycoming and the FAA had already decided that SB 632B was necessary, despite the maintenance-induced failure risk, and that they were not interested in considering any alternatives.

As the call concluded, I felt totally disgusted with the total lack of cooperation exhibited by Lycoming and the FAA. I have been involved in working with the FAA on numerous Airworthiness Directives during the past two decades, and this was unquestionably the most unreasonable performance I’ve seen.

Shameful and disturbing

On Thursday, we worked with Dave to create a formal joint letter to the head of the FAA’s New York ACO. In it, we expressed our disappointment in how the FAA seemed to be dealing with this issue, and included the bullet-point document I’d created outlining our questions, concerns, and recommended alternative to SB 632B. In the letter, we specifically asked the FAA to approve our proposed minimally-invasive alternative as an Alternate Means of Compliance (AMOC) as outlined at the end of the document.

Needless to say, the New York ACO convened a Corrective Action Review Board (CARB) that rubber-stamped Lycoming’s requested corrective action in record-breaking time. On August 9, the FAA issued AD 2017-16-11 mandating compliance with SB 632B and putting numerous Lycoming-powered GA aircraft on the ground and their owners in jeopardy both moneywise and (IMHO) safetywise.

I find this whole sorry episode very disturbing for several reasons.

In discussing this situation with companies like Rick Romans and Aircraft Specialties Services and Zephyr Aircraft Engines who are in the business of re-bushing Lycoming connecting rods in the field, it appears that the problem with these loose Lycoming connecting rod bushings has been well-known by industry insiders for more than a year. Several of those firms told me that they stopped installing Lycoming-supplied rod bushings many months ago in favor of PMA-equivalent bushings from Superior Air Parts that fit properly. Given that this problem has been known for quite some time, it seems to me that the FAA could and should have taken a bit more time to solicit and consider input from folks who would be most affected, especially alternative methods of addressing the problem in a less risky fashion, before publishing an emergency AD.

Furthermore, I find it unconscionable for the FAA to justify such a draconian rulemaking action on data that it refuses to disclose to the very people who will bear the burden of that rulemaking. I understand that if a manufacturer provides information to the FAA that the manufacturer identifies as proprietary, the FAA is not permitted to disclose it. But it seems to me that the FAA should be forbidden from using such proprietary data to justify issuing an AD. The federal Administrative Procedure Act (APA) guarantees that members of the public who will be affected by federal rulemaking shall have a say in the rulemaking process. I’m not a lawyer, but clearly rulemaking made in the kind of secret “star chamber” fashion that characterized AD 2017-16-11 makes a mockery of the spirit (and perhaps the letter) of the APA.

Mike Busch is arguably the best-known A&P/IA in general aviation, honored by the FAA in 2008 as National Aviation Maintenance Technician of the Year. Mike is a 7,500-plus hour pilot and CFI, an aircraft owner for 45 years, a prolific aviation author, co-founder of AVweb, and presently heads a team of world-class GA maintenance experts at Savvy Aviation. Mike’s book Manifesto: A Revolutionary Approach to General Aviation Maintenance is available from Amazon.com in paperback and Kindle versions.