We have all seen Airworthiness Directives (ADs) in the past that made us fear the further demise of general aviation. I can think back to 2003 when the outrageous proposal on 400 Cessna series aircraft threatened huge costs regarding wing spar modifications. Costs were estimated to be more than $250 million. Who now knows for sure what AD 2005-12-12 and AD 2005-12-13 has and will cost owners of 400 series aircraft. Of course, we all remember the VAR crankshaft situation that back in 2002 required the removal and/or replacement of allegedly improperly heat-treated crankshafts that were supposed to be subject to failure. That was another huge expense for owners concerned. Now stand by for another one.
The FAA on Aug. 12, 2013, published its Notice of Proposed Rulemaking regarding certain cylinders installed on Continental IO-520, TSIO-520, IO-550 and IOF-550 engines and O-470 models that have been modified to use such cylinders by STC, for use on Continental engines. This proposed AD will be huge. The proposal states that the costs are estimated at more than $82 million (NPRM Docket 2012-02).
The basis for this massive inspection and removal program are random failure reports (they say 30) of ECi (now Danbury Aerospace-Airmotive Engineering Corporation, AEC in San Antonio) PMA cylinder assemblies. These were not ersatz cylinders. They were approved for use by the FAA through the PMA process. The AD applies to certain part number and series cylinders sold by AEC. The proposal describes two cracking characteristics: (1) a crack that starts in the internal dome radius of the cylinder and (2) cracking at the cylinder head to the barrel thread. These are the two most common locations for all cylinder cracks for years, no matter who made them.
The proposed AD goes on to say that these failures could result in head cracks, engine failure, and loss of the aircraft, and the FAA cites no specific example of aircraft loss. The manufacturer stated that no accidents or injuries were reported in any of the 30 incidents, which form the basis for the AD. Note that the proposal says could result. The manufacturer stated that more than 10,000 aircraft would be affected by this AD, and that a number of the damaged cylinders could be traced to improper engine operation not manufacturing defects. There is some dispute over whether these cylinders (ECi) had a lower failure rate than the OEM cylinders sold by Continental. The manufacturer stated further that it could be forced into bankruptcy by this AD, and that this action was a punitive, unnecessary, and inappropriate action against owners of the affected engines.
The proposal allows no repairs to any damaged cylinders that are removed. They must be discarded. Furthermore, with respect to cylinders with no apparent defects … they too must be removed and discarded. That is if they fall into the categories described in the proposed AD. So, even cylinders that appear to be perfectly serviceable must be discarded.
I am pleased my C182 has a low compression O-470 engine. There’s no high compression, no turbo, no fuel injection, and no threat of high cylinder head temps. It even runs fine on car gas. But pity the poor souls who have the T210, 300, and 400 series Cessnas. These owners could be faced with significant cylinder inspection, removal, and possible replacement of all their ECi cylinders if this AD were in fact published. The manufacturer says that 10,000 aircraft are involved. The costs alone would be significant even if there was an initial price adjustment for the cylinders, but the wholesale removal and trashing of hundreds of airworthy cylinders is outrageous. The NTSB never suggested anything of this sort in its analysis of the so-called failures.
Efforts should be taken to remove the AD or change it substantially.
A common repair for years
The repair of cylinders has been going on for years. If you found a crack in one of your cylinders, no matter what engine, you could have it returned to service with weld repairs or parts replacement. Common repair areas included: fuel injector and spark plug hole, intake and exhaust ports, head cooling fins, barrel thread, valve guide bosses, rocker shaft supports, and so on. You can of course have your cylinders rebored oversize if they are worn internally. This has been the repair mode for years.
The cylinders were repaired by certified shops who knew their business and returned your airworthy cylinder to you or an exchange for a modest price that was significantly lower than a new factory cylinder at that time. If the crack returned, it was not life-threatening and cracked cylinders rarely resulted in injuries or crashed aircraft. As in this AD situation, there never was any evidence of an accident or injury in any of the 30 reported incidents.
Pilot operating conditions
Apparently the FAA did not consider the fact that pilots routinely damage cylinders with operations at high cylinder head temperatures. Common errors in the leaning process can cause serious damage to cylinders and valves. Any temp in the vicinity of 400+ degrees is extremely damaging to cylinders. Detonation can also raise temperatures and severely damage or cause cylinder cracks. The cylinders we are concerned with are on high compression, turbo-charged, powerful engines, with high operating temperatures and they are subject to random internal damage and cracks. This has been routine for years.
In fact, Cessna, the manufacturer of most of the aircraft concerned with the proposed AD has advised pilots in a confusing way in some of its Pilot Operating Handbooks. Here it states that the pilot should lean his engine to 50 degrees lean of peak. According to experts in the field, this is where the pilot should not set his mixture. The cylinder is subject to maximum temperature and internal pressure at this setting, and it will ensure that the cylinder will operate at the hottest and most dangerous level. That is not good practice, but reportedly used by many.
Manufacturing flaws have of course been found from time to time on all manufactured cylinders. The heat-treating process has many times produced faulty cylinders. These problems and others are routinely fixed and fortunately there are usually only a small run of cylinders that are affected.
Some alternate proposals
There are many alternate solutions available to mitigate the threat of cracked cylinders causing further damage. The FAA should consider urging the following procedures, which they themselves recommend.
Although used for years, the traditional differential compression check required during all annual inspections is a poor indicator of cylinder condition and fails to detect leaks many times, but it has been used for years. The best use of this test, as suggested by experts in the field, is to keep a record of cylinder readings over several or more annual inspections, or during the year at routine oil changes, showing the relative trend of readings that are observed. This is not perfect, but along with other tests can be very useful.
Continental (now Avic) has provided very specific instruction on the performance of compression checks on its engines. See Service Bulletin SB03-3, which sets out in detail how to perform the check and more importantly how to make a determination on removing cylinders for cause. However, cylinders need not be removed for low compression readings alone. This instruction should be considered along with the “guidance” contained in AC 43-13, (6-15-98) (Reciprocating Engine Power-Loss Accident Prevention and Trend Monitoring).
In the above Service Bulletin, Continental suggests using a borescope, pricey devices that let you look into the interior of a cylinder and examine the condition of cylinder walls, valves, and other parts of the interior. Borescopes are, however, not yet required to be used by regulation like the compression test but they certainly are a useful practice.
Just the simple careful inspection of each of the cylinders is one of the best procedures to detect any cracks in cylinders. Most, if not all, can be detected visually if you are familiar with where to look. I know many times inspectors find cracks by observation, where the working technician missed them. Of course that’s what inspectors are for.
There could be more random inspection of cylinders, during oil changes, compression checks, and borescope inspections.
Engine performance monitors allow pilots to provide the technician with operating data that may be capable of providing real-time data. Historical real-time operating data can lead to detecting cylinder problems.
Spark plugs also can predict cylinder damage. Close examination of plugs can show how the cylinder is performing by indicating hot or cold running characteristics and other indicators of cylinder performance.
Finally, pilots should be urged to discuss their operating techniques, placing emphasis on engine leaning procedures, how they do it and awareness of shock cooling cylinders, the two most common elements involved with pilot-induced cracked cylinders.
What you can do
The NPRM is open for comment through Oct. 11, routinely, however these dates are extended to provide for late comments. File your comment even if it is late, the comments all will be read and hopefully considered. Here is the place to file:
You can comment online at: http://www.regulations.gov/#!docketDetail;D=FAA-2012-0002
You can mail comments to: