December 26, 1996 Who Benefits from Airworthiness Directives?

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by	Mike Busch

About the Author ... Mike Busch is editor-in-chief of AVweb, a member of the technical staff at Cessna Pilots Association, and in a prior lifetime was a contributing editor for The Aviation Consumer and IFR Magazine. A 6,000-hour commercial pilot and CFI with airplane, instrument and multiengine ratings, Mike has been flying for 36 years and an aircraft owner for 33. For the past 14 of those years, he's owned and flown a Cessna T310R turbocharged twin, which he maintains himself. In his never-ending quest to become a true renaissance man of aviation, Mike's on the verge of earning his A&P mechanic certificate. Mike and his wife Jan reside on the central coast of California in a semi-rural area where he can't get DSL or cable TV.

Airworthiness Directives have been with us since the 1940's, but it seems as if the industry's attitude toward them has changed dramatically in recent years. Twenty years ago, manufacturers would often brag in their sales literature that their airplanes or engines "have never had an AD issued against them." Issuance of an AD was considered a black mark against a manufacturer, suggesting that the firm's engineering or quality control was not up to par.

In the last decade, that attitude appears to have made a 180-degree turn. Nowadays, it seems as if most ADs that come out of the FAA are being issued at the request of the manufacturers. Sometimes firms ask the FAA to issue an AD at the advice of their lawyers in an effort to limit their liability exposure. In other instances, their requests are prompted by honest-to-goodness safety concerns.

But we're troubled by an increasing incidence of manufacturer requests for ADs that look suspiciously as if they're intended to enhance the company's revenues and/or hurt their competition. And what's really disturbing is that the FAA seems to be going along with these requests, issuing ADs without first doing independent due-diligence to establish that they are justified by the facts.

That's what apparently occurred with two recently-proposed crankshaft ADs. In two rulemaking actions last year, the FAA declares that they've identified an "unsafe condition" affecting the crankshafts of 60,000 TCM and Lycoming engines in many of the world's most popular light airplanes, and says it wants at least 20,000 of those crankshafts to be scrapped and replaced, at a cost to owners of $50 to $100 million. Ouch!

Now, before taking this kind of drastic action, you'd think the FAA would need to be pretty doggone sure that there is a real safety problem with the existing crankshafts and that the replacement cranks actually solve the problem. But it sure looks to us as if the FAA simply took the word of TCM and Lycoming that there is a problem...and that neither the FAA's own statistics on crankshaft failures nor independent studies support the manufacturer's claims. To make matters worse, we don't think it's an accident that TCM and Lycoming have adopted pricing policies on replacement crankshafts that will compel most affected owners to exchange their engines for factory remans, to the severe detriment of field overhaul shops who nowadays are the principal competitors of TCM and Lycoming. In short, we smell a rat.

TCM crank history

TCM has used two different processes to cast the steel billets used in forging their crankshafts. For decades, the cranks were manufactured using a conventional "airmelt" process. But in the late 1970s, TCM became concerned about metallurgical "inclusions"-tiny air bubbles trapped inside the steel as the billet is poured-which cannot be detected through ordinary magnaflux inspection and which might weaken the cranks. So between 1978 and 1980, TCM gradually switched over to a different process called "vacuum arc remelt" (VAR) to eliminate the possibility of inclusions. They also increased the crankshaft diameter slightly on their 520-series engines. However, they continued to re-use serviceable airmelt crankshafts in their factory-rebuilt engines.

It is very rare for a crankshaft to fail because of a material or manufacturing defect. According to FAA Advisory Circular AC20-103, the vast majority of crankshaft fractures are the result of undetected or unreported prop-strike damage, out-of-balance propellers, spun bearings, excessive oil temperatures, contaminated oil, and other lubrication failure situations.

Nevertheless, TCM became convinced that a small number of crankshaft failures in their 360- and 520-series engines were due to "unexplained subsurface origin fatigue cracks initiating below the intermediate main bearing fillets" which could not be detected through magnaflux inspection. So in 1987, TCM issued Service Bulletin M87-5 which recommended (but did not require) that crankshafts be inspected at overhaul using ultrasonic test equipment capable of detecting subsurface cracks. Magnaflux inspection continued to be required.

TCM also persuaded the FAA to issue an Airworthiness Directive, AD 87-23-08, requiring ultrasonic inspection of IO-520 and TSIO-520 crankshafts to detect subsurface cracks, and replacement of the crankshaft if a crack is found. The impact of this AD was relatively small: the extra inspection added about $200 to the cost of a major overhaul or post-prop-strike teardown inspection, but fewer than 1% of the crankshafts flunked the ultrasonic exam.

TCM: scrap all airmelt cranks!

Five years later, TCM decided they wanted to get all the older airmelt cranks out of the system. In September, 1992, they issued Mandatory Service Bulletin M92-16 which required that all airmelt cranks (or cranks whose manufacturing process could not be determined) be scrapped and replaced with a VAR crankshaft at the next major overhaul or teardown. About 25,000 airmelt-crank engines were affected. They also announced that all factory-new and factory-rebuilt engines would be equipped with VAR cranks.

New VAR crankshafts have list prices which vary from $6,700 to $8,200. However, TCM announced a special exchange program whereby old airmelt cranks could be traded for brand new VAR cranks for a mere $2,200. This was presumably TCM's way of trying to persuade overhaul shops to comply with M92-16.

But then a funny thing happened. TCM quietly established a policy of accepting runout airmelt-crank engines as cores in exchange for factory-rebuilt engines with no up-charge. This meant that the owner of an airmelt-crank engine would pay a penalty of at least $2,200 on a field overhaul, but no penalty at all on a factory reman. Needless to say, the overhaul shops and their trade association, the Aeronautical Repair Station Association (ARSA), cried "foul!"

TCM responded by going to the FAA and asking them to put "teeth" into M92-16 by turning it into an Airworthiness Directive. The FAA agreed, and in June 1993 issued a proposed AD (58 FR 39748) that would supersede AD 87-23-08, eliminate its ultrasonic inspection requirements, and mandate replacement of airmelt crankshafts with VAR cranks anytime the case was split. The proposed AD would also expand the affected population of engines to include 360-series engines as well as 520-series.

The FAA was inundated by negative responses to its NPRM, mostly attacking the FAA's lack of data justifying the need for the AD and disputing the FAA's estimate of economic impact as unrealistically low. The principal commenter was ARSA, who claimed the FAA's crankshaft failure data was anecdotal and not representative of the entire fleet.

The wheels of FAA rulemaking grind slowly. Two years later in August, 1995, the FAA issued a supplemental NPRM (60 FR 43995) to address the criticisms by ARSA and others by publishing additional data in support of the proposed AD. In the supplemental notice, the FAA dismissed its own Service Difficulty Report (SDR) database as inaccurate and elected to rely on TCM-supplied failure analysis. According to this analysis, there are approximately 18,000 airmelt and 25,000 VAR cranks in service in 520-series engines as of 1994, and that between 1986 and 1994 there were 40 failures of airmelt crankshafts but only 3 failures of VAR cranks. The implication was that airmelt cranks were 15 times more likely to fail than VAR cranks. For 360-series engines, the numbers quoted were 5,000 airmelt cranks and 10,800 VAR cranks in service, and 8 airmelt failures but only 1 VAR failure during the same period. Again, a failure ratio of more than 15 to 1. Pretty convincing, wouldn't you say?

Damned lies and statistics

Not so fast, said ARSA. Two weeks after the supplemental notice issued, ARSA submitted a Freedom of Information Act request to the FAA, asking for the source information (primarily TCM warranty claims) on which the FAA justification was based. The FAA declined to provide this data, indicating that it was proprietary to TCM.

In October, 1995, ARSA joined forces with three other alphabet groups (the Aircraft Owners and Pilots Association, the Cessna Pilots Association, and the National Air Transportation Association) to file a response in opposition to the supplemental NPRM. They criticized the FAA for relying on data that has not been made available for public scrutiny, and suggested that TCM's data might be "presented in such a way as to favor the commercial goals of the party that compiles it (such as selling more crankshafts)."

They also pointed out that the FAA elected to ignore its own SDR database (which did not support the need for the proposed AD), and also ignored the analysis submitted by ARSA in February, 1994. ARSA's analysis was based on the results of ultrasonic testing of crankshafts required by AD 87-23-08 by TCM-authorized inspection facilities throughout the U.S. The ARSA data showed that companies had detected 27 subsurface fatigue failures out of 3,821 airmelt crankshafts subjected to ultrasonic test, for a failure rate of .707%, and had detected 5 failures out of 488 VAR cranks tested, for a failure rate of 1.025%. ARSA pointed out that these failure rates are statistically equivalent.

Furthermore, the joint Association response points out that the FAA's own supplemental notice "exhibits a lack of confidence in the superiority of VAR crankshafts." The proposed AD requires that VAR crankshafts undergo ultrasonic testing at every removal, so that "clearly the FAA recognizes that VAR crankshafts are subject to the same unsafe condition as airmelt crankshafts. The FAA has offered no evidence to conclude that unsafe conditions exist in airmelt crankshafts that do not exist in VAR crankshafts. The two types of crankshafts should be treated in a comparable fashion."

The Cessna Pilots Association (well known for its activism in opposing oppressive ADs) analyzed Cessna production figures, and determined that Cessna delivered aircraft with approximately 30,000 airmelt crankshafts versus only about 8,500 VAR crankshafts. Assuming that roughly the same percentages hold true for Beech aircraft, CPA concluded that the TCM-supplied population estimates that the FAA relied upon (18,000 airmelt vs. 25,000 VAR) "are either greatly in error or indicate that the airmelt crank will disappear without the need of regulatory action."

That's where things stand as this article is being written. The next move is up to the FAA. They may issue an AD, issue yet another NPRM, or drop the matter altogether.

Realistically, what the FAA does may not make any real difference. TCM's Mandatory Service Bulletin M92-16 already has the force of law on Part 135 operators. Furthermore, no reputable engine shop would fail to comply with such a mandatory service bulletin because of potential liability concerns. So with the AD or without it, airmelt crankshafts are going on the scrap heap.

TCM has no obligation to hold the line on its $2,200 special trade-in price, and in fact has already increased it once to $2,330. TCM continues to accept airmelt cores in exchange for factory remans with no up-charge, making the field overhaul shops the big losers in this affair.

The Lycoming Crank Situation

A strikingly similar scenario is now playing out with respect to four-cylinder Lycoming engines that drive fixed-pitch props. At Lycoming's request, the FAA has proposed an Airworthiness Directive that would require the inspection and possible replacement of the crankshafts in an estimated 46,000 U.S. aircraft.

The story began in October 1993, when the British CAA received a report of a Piper PA-28-161 Warrior that made a forced landing due to a crankshaft failure that caused the propeller to separate from the aircraft. Analysis of the crankshaft indicated that the failure was caused by "a high cycle reverse torsional fatigue mechanism that had initiated from a number of corrosion pits in the crankshaft bore." Ya just gotta love those Brit engineers! The Warrior's Lycoming O-320-D3G engine had 1,950 hours SMOH and the crankshaft had 4,429 hours and 15 years since new.

In plain (American) English, here's what investigators discovered. Crankshafts designed for use with constant-speed propellers are hollow in the front, allowing oil pressure from the governor to reach the propeller hub and adjust the blade pitch. Lycoming elected to use the same sort of hollow-front crankshaft for most of its fixed-pitch prop installations, simply installing an expansion plug in the front of the crankshaft to retain the oil. That's apparently where the problem lies: in engines with the plug installed, the oil in the crankshaft hollow is stagnant, and crankshaft rotation centrifuges this trapped oil and can create a buildup of acid-rich sludge on the inner surface of the crankshaft bore. The sludge promotes internal corrosion, and the corrosion pits can become stress-risers that ultimately lead to crankshaft fracture near the propeller flange.

As a result of the British Warrior incident and several other reports, Lycoming issued Mandatory Service Bulletin 505A in October, 1994, affecting all Lycoming 235- and 290-series engines and most Lycoming 320- and 360-series engines with fixed-pitch propellers. The SB requires inspection of the plugged-up crankshafts immediately if they are more than ten years old, or within ten years of ship date if they are recent-vintage. The mechanic must remove the prop and the plug, clean the forward four inches of the crankshaft bore, and inspect the surface for corrosion. Surface corrosion may be removed, but only if the inner diameter of the crankshaft remains 1.91" or less. If further corrosion or pitting is found, the SB calls for the crankshaft to be removed from service immediately (which would require a preemptive engine teardown). New crankshafts for these engines cost between $4,500 and $6,500 apiece.

Lycoming also asked the FAA to issue an Airworthiness Directive against the crankshafts in these engines. The FAA agreed, and published a proposed AD (60 FR 58580) in November, 1995. The proposed AD is somewhat more lenient that Lycoming's SB, allowing crankshafts to remain in service for five years after pitting is found, provided repeated fluorescent penetrant inspections reveal no cracks. But five years after pitting is detected, or anytime FPI reveals cracks, the AD would require that the crankshaft be replaced.

The proposed AD requires initial inspection within six months or 100 hours for engines with at least 1,000 hours, or within ten years if that is reached first. Thereafter, visual inspections are required every five years if no pitting is found, or FPI every 100 hours after pitting is detected.

How many crankshafts will exhibit pitting and need to be replaced? It depends who you ask. In the cost analysis portion of the proposed AD, the FAA estimates that 10% of the cranks will be pitted and require replacement at each overhaul. But the Lycoming factory claims that most of the cranks they see coming back as cores are pitted and need to be scrapped. If Lycoming is right, then the cost impact of the proposed AD will be an order of magnitude bigger than what the FAA claims it is.

No supporting data

For rulemaking action with a potential cost impact of $15 to $50 million (depending on whom you believe), the proposed AD is shockingly devoid of supporting data. The only justification cited by the FAA is the British Warrior forced landing, plus ten additional reports allegedly received by the FAA but about which absolutely no details are offered.

The proposed AD is opposed by AOPA and Cessna Pilots Association, among other commenters. AOPA filed a FOIA request demanding to know what data the FAA used to justify the five-year limitation on crankshafts which are found to be pitted but not cracked. Failing to get a substantive response, AOPA requested a two-month extension to the original January 29, 1996, deadline for public comments.

The Cessna Pilots Association (CPA) got involved because the Cessna 152s and 172s represent the single largest group of aircraft that would be affected by this AD. CPA filed a FOIA request asking for details of the "ten additional reports" that the FAA says they used to determine that an unsafe condition exists that justifies the AD. The FAA replied that they could not provide this information because it was proprietary to Lycoming! (Sound familiar?)

CPA also asked the FAA to provide SDR reports filed during the past five years that involved flange-end crankshaft failures in Lycoming O-235 and O-320 engines (as used in the C152 and C172, respectively), and the FAA did so. The SDR database revealed some interesting facts. There was not a single report of a flange-end crankshaft failure in O-235 engines, although there were some fractures back in the solid portion of the cranks (probably due to lubrication failure).

For O-320 engines, there were five reports of flange-end crankshaft problems in five years, a very modest number. Only three of those reports involved actual crankshaft failures; the other two involved oil leaks that were ultimately traced to crankshaft cracks. One of the three crankshaft failures involved an aircraft that had obviously had a prop strike. In a second failure report, the reporting A&P stated that he could not rule out the possibility that the aircraft had an unreported prop strike (making it sound as if he suspected as much). Even discounting all of this, five reports of failures in five years from a population of more than 20,000 engines would make the O-320 crankshafts among the least failure-prone in the fleet.

Most significantly to CPA, not one of the five SDRs involved Cessnas! Three involved Piper PA-28-161 Warriors just like the British aircraft that started the whole thing, one involved a Piper PA-18 Super Cub, and the last one involved a Socata TB-9 Tobago. Yet the largest group of owners that would be affected by the proposed AD are Cessna owners.

Keep in mind that Lycoming is not offering a redesigned solid crankshaft to replace the hollow ones that they claim are corroding away from the inside. The new cranks will be subject to the same corrosion problem as the ones they replace. Also, Lycoming is offering no "special deal" on crankshafts. Owners who need a new crank will have to pay $4,500 or more to get one. But just as with the TCM situation, Lycoming is not charging any up-charge for pitted-crank cores that are exchanged for Lycoming factory remans. So it would appear once again that the field overhaul shops are the big losers here, and Lycoming stands to be the big winner.

Final thoughts

When the general aviation market imploded in the early 1980s, both TCM and Lycoming went through a period of denial, waiting for their OEM market to come back to life. But by 1990, both companies recognized that this just wasn't going to happen. They realized that they were now basically in the overhaul business, and that their competition was the field overhaul shops.

Both companies responded to this revelation by slashing the prices of factory-rebuilt engines while simultaneously hiking parts prices, putting field overhaulers at a tremendous disadvantage and driving many of them (including such well-known names as Mid-States, Schneck, and Western Skyways) out of business. The overhaul shops that managed to survive reacted by buying cylinder assemblies and everything else they could get from PMA firms like Superior and ECI, and by reducing their need for new parts by reworking old ones whenever possible.

All of this is arguably in the great American tradition of a laissez-faire free-market economy. But when manufacturers like TCM and Lycoming start using a government agency like the FAA as a weapon to gain commercial advantage over their competition, it's time to blow the whistle. Perhaps you can't blame the manufacturer's for trying. But the FAA has an obligation not to issue an AD without first independently verifying that there's a genuine threat to safety that the AD will rectify. From what we see, the FAA isn't doing its job. Toot toot!