AOPA response to American Champion wing spar NPRM

Federal Aviation Administration
Central Region
Office of the Regional Counsel
Attn: Rules Docket No. 97-CE-79-AD
601 East 12th Street
Kansas City, MO 64106

Gentlemen:

The Aircraft Owners and Pilots Association (AOPA), representing the aviation interests of more than 340,000 pilots and aircraft owners, submits the following comments to the proposed airworthiness directive (AD) on American Champion Aircraft Corporation 7, 8, and 11 series aircraft wing spars. AOPA has examined the available accident and service histories of these aircraft, and has conducted interviews with numerous owners, maintenance professionals, and type association personnel in an effort to gain a complete picture of the service history of American Champion Aircraft. In addition, two of the affected aircraft are currently owned by staff members of AOPA. Tragically, the only AOPA staff member ever to be involved in a fatal aircraft accident in the association’s 57-year history fell victim to a wing spar failure in one of the affected aircraft. It is with this balanced background that we submit our comments to the docket on behalf of our members who own nearly 85 percent of the general aviation aircraft in this country.

The American Champion product line covers a broad base of aircraft who’s production spanned many decades by several manufacturers. Over the years, the type certificate was amended to permit the production of aircraft spanning a wide range of weight, horsepower, and performance capabilities. Early Aeronca aircraft were produced with a 65-horsepower engine and a gross weight of 1,220 pounds. The later examples produced by Bellanca, Champion, and American Champion dramatically increased performance by including engines up to 180 horsepower and gross weights as high as 2,150 pounds. Many of the later examples of these aircraft were also certificated for aerobatic maneuvers. During the course of the product upgrades to the 7, 8, and 11 series aircraft, few if any changes were made to the original wing spar. The nearly doubling of gross weight and tripling of engine power output coupled with the addition of high-stress aerobatic maneuvers on the basic wing spar clearly points out that all not American Champion wing spars are stressed in the same manner.

The obvious differences in stress imposed on the American Champion wing spars is borne out by a close examination of the available service data. While there have been a number of cracked wing spars reported on the lighter, less powerful aircraft, nearly all of these can be attributed to some prior damage to the wing. This damage includes taxiing incidents, ground loops, landing incidents, and other instances of the wing striking an immovable object. Compression cracks resulting from in-flight over-stress conditions are not evident on the non-aerobatic and lower gross weight aircraft. This is supported not only by the service data but also by the experience of numerous maintenance professionals with extensive experience in wood spar replacement and repair. Bearing this in mind, it is not appropriate to subject these aircraft to a cookie-cutter approach in the proposed AD.

Based on the service experience of the 7, 8, and 11 series aircraft, AOPA does not believe there is sufficient justification for an AD against the low gross weight, non-aerobatic aircraft in the product line. AOPA urges the FAA to remove the following Aeronca and early Champion aircraft from the applicability section of the proposed AD:

AOPA recognizes that Federal Aviation Administration (FAA) has a secondary concern over pulled nails and loose ribs that is demonstrably common to the entire line of American Champion aircraft. This condition is widely recognized by the general aviation community and has been reported numerous times in the FAA service and difficulty database. However, we do not believe that this airworthiness issue requires AD action since the condition is readily detectable during the course of normal inspections and in fact has been detected and reported on numerous occasions. The fact that there have never been any incidents attributable to the pulled nails or loose ribs indicates that the condition is being detected, corrected, and reported during the normal course of maintenance. If the FAA still believes it is necessary to heighten awareness of this issue in the owner and maintenance communities, AOPA would suggest that an airworthiness alert letter be issued to registered owners of the entire American Champion product line specifically addressing this issue. This would raise the awareness of the problem without mandatory inspection intervals. Again, we reiterate that this issue does not warrant AD action.

After removing the models listed above from the proposed AD, AOPA is prepared to accept that there is sufficient justification to require some form of inspection for compression cracks on the wing spars of the remaining models of American Champion aircraft. These aircraft models represent the segment of the product line that are of a higher gross weight and horsepower, and/or are certificated for aerobatic maneuvers. We have identified the following aircraft models as being most likely to suffer from compression cracks based on the service history of cracks or the similarity of certain models to those that have shown a propensity for wing spar cracking.

While we maintain that some action should be taken on these aircraft, we have serious concerns about the proposed method of compliance and frequency of inspection. The remaining comments in this response are intended to address modifications to the proposed compliance for the aircraft models that we believe warrant some form of inspection listed above.

One universal comment that has been made to AOPA in recent months regarding the proposed method of compliance for inspecting the wing spars on the 7 and 8 series aircraft concerns the top inspection panels. Nearly everyone involved with American Champion aircraft believes that the proposed inspection panels on the top surface of the wing will likely lead to future airworthiness problems stemming from water damage to the spar. We support this concern and maintain that water damage to the spar and doubler plates could cause an airworthiness problem far more severe than any current reported problems with compression cracks. Based on this, AOPA proposes that a nylon reinforced fabric patch be used in place of the two metal inspection panels proposed in the AD and accompanying service letter. These pinked fabric patches would maintain a greater water-tight integrity than any removable panel and could be softened and removed for inspection, then reinstalled with dope as necessary.

Similar comments have been expressed to AOPA concerning the addition of numerous removable under-wing inspection panels. The fabric covering on American Champion wings undergoes significant flutter and flexing both on the ground and in flight. It is very common to see the fabric panels between the wing ribs flutter up and down especially during taxi operations. This causes some stretching of the fabric and can increase with the aging of the fabric and the passage of time. Adding dozens of inspection access holes with “bubble patches” will greatly exacerbate this action especially in light of the additional mass introduced by the patches themselves. Further, the factory original “bubble patches” covering existing inspection access holes are notorious for movement, sliding fore and aft in flight and chafing the fabric. The addition of dozens more of these patches will clearly damage the wing fabric over time. Based on this, AOPA would recommend that the under-wing inspection patches also be fabricated with a nylon reinforced pinked fabric patch similar to our proposal for the top inspection panels. Again, these patches could be softened and removed for future inspections.

Obviously, there is a significant penalty in proposing fabric patches in place of the removable panels in the form of cosmetic damage that would be incurred with each softening and removal of the patches for inspection. Most of the owners we discussed this with feel that this is an acceptable penalty on the condition that the inspection interval would be significantly lengthened. Both owners and maintenance professionals feel so strongly that the removable panels would cause future airworthiness problems that they are willing to expend the resources to repair the cosmetic damage at each inspection rather than suffer the fabric damage and possible reduction in wing strength that could be caused by the proposed removable panels. Again, this is contingent upon a lengthened inspection interval.

After reviewing the service history of the American Champion aircraft, AOPA believes that the inspection interval could successfully be lengthened particularly as it relates to calendar time. We would propose that the 500-hour inspection interval remain in effect as proposed in the AD, however, we do not believe there is sufficient justification for requiring inspections be conducted on an annual basis. The wing spars on the affected aircraft have been in successful service for many years, and compression cracks are a function of operating time or over-stress conditions rather than calendar time. Based on this, we would urge FAA to extend the repetitive inspection interval to five years or 500 hours, whichever occurs first. This would maintain the maximum operating time between inspections proposed by the FAA while minimizing the penalty on private, non-commercial operators who generally do not accumulate a large number of operating hours in a given year. This repetitive compliance time would make the concept of nylon-reinforced fabric patches worthwhile and acceptable from a cost perspective.

AOPA is concerned with the impact of the proposed initial inspection interval on aircraft that have recently been recovered. The FAA proposal does not give consideration to owners who have recently recovered the wings of their American Champion and thus have thoroughly inspected the wing structure. We recommend that the initial inspection interval be predicated on the last recovering of the wing consistent with our proposal for a five-year inspection interval. For example, we recommend that the initial inspection be conducted within five years or 500 operating hours of the last recovering of the wings. Clearly, the majority of aircraft would already exceed the five-year, 500-hour interval upon the effective date of the AD. In those instances, initial compliance and inspection would be required at the next annual inspection that occurs three calendar months or more after the effective date of the AD or within 15 calendar months, whichever occurs first. This follows the initial compliance time outlined in the proposed AD.

AOPA firmly maintains that the proposals in these comments would significantly reduce the cost impact of the AD on American Champion aircraft owners, while thoroughly addressing the legitimate airworthiness concerns. In several instances, we believe that our proposals would enhance safety above and beyond that proposed in the AD by heading off some future airworthiness problems resulting from the proposed methods of compliance. AOPA looks forward to working with the FAA in resolving the concerns of American Champion aircraft owners, and we stand ready to assist in any manner possible.

Respectfully,

Douglas C. Macnair
Director
Aviation Standards

December 31, 1997