As the comment period ends on 3 July and no word of an extension has been heard I submitted the following AMOC. I would much prefer to do this after seeing the information that the EAA has requested but given that if an extension is not granted an no AMOC has been submitted we will be stuck with the FAA's proposal. 0Of course there is no guarantee that they will entertain my submission.) If you have not posted a request for an extrension of the comment period please do it now!
Here is a copy of what I submitted:
Aeronca 15AC Wing Spar Proposed AD
Suggested Means of Compliance
The Aeronca model 15AC/S15AC features a main spar composed of extruded aluminum spar cap riveted to an aluminum web. There have been instances where intergranular corrosion has been found in the spar cap extrusion. The exact number is not known but is believed to be very low. Intergranular corrosion is not uncommon in extruded aluminum pieces. It is a result of the grain of the metal and the boundary between the grains interacting with an electrolyte. A corrosive environment, i.e. a salt water/salt air environment, can contribute to the formation of intergranular corrosion. There have been no reported instances of failure of a wing due to spar or spar cap corrosion on the 15ACor S15AC model planes. Only one SDR has been completed for spar cap corrosion. However, there have been some verbal, but undocumented, reports of spar cap corrosion that were found by inspection or when the wing was opened to repair physical damage to the wing.
Experience with the 15AC indicates that this corrosion can be detected by visual inspection which is greatly aided by the use of a borescope. The difficulty lies in the fact that the 15AC has limited access to the wing for an inspection to be conducted. Current openings in the wing such as the inspection ports above and below the aileron bellcrank, the landing light port in the left wing, openings in front of the ailerons, and openings in the wing root allow for the majority of the spar in each wing to be to be inspected with a borescope with a length of 34" or more. This is somewhat variable depending on the equipment in use, technique, etc. Tests have shown that with a six-foot borescope the entire right wing would be able to be inspected with the addition of only one additional inspection hole. Borescope inspections are a normal practice in the industry and have become much more practical for the general aviation fleet as availability of the equipment has gone up and prices have come down.
Based on field experience, corrosion of the spar cap tends to manifest over multiple areas on the spar. The portion of the spar cap aft of the spar is believed to be the area most likely to exhibit corrosion. It is believed that an inspection of 50% or more of the spar would reveal the presence of corrosion in a particular wing.
The intergranular corrosion can be stopped or prevented by the application of a corrosion control substance such as CorrosionX. A substance such as CorrosionX will wick its way between the cap strips and the skins and spar web. It will then work its way into any corroded area where it will stop any existing corrosion by forming a dielectric barrier. It will also prevent any new corrosion from forming. This product will not negatively react with wiring in the wing or with fuel bladders and lines. The wing can probably be treated through the existing openings in the wings with the wings on the airplane. However, it would be far easier, and would only require common corrosion treatment application hardware, if it were permissible to drill two holes in each wingtip so that a standard treatment wand could be inserted along the length of each spar for the purpose of applying the specified corrosion control product to the entire spar and interior of the wing.
This would not only be beneficial for controlling corrosion of the spar but also for preventing and controlling corrosion in the wing itself. A product such as CorrosionX would not hide corrosion or other defects from view as would paint or zinc chromate. Additionally it will creep into current corrosion and stop its progress, something paint cannot do. The holes would only need to be approximately 1/8" to 1/2" in diameter and could be plugged with a standard nylon hole plug, a metal hole plug, or covered with tape or fabric. These holes could also be used for borescope inspection. The CorrosionX treatment would be good for at least two years.
This approach is likely to be more quickly and properly complied with due to its low cost and relative ease of compliance. It will not place undue burden on the aircraft owner and will provide for the continued airworthiness and increased safety of the aircraft while providing for a means to prevent and detect future corrosion of the spar and the wing in general.
To be accomplished within 360 days of this AD being published or at the next annual or 100 hour inspection, whichever comes first. This procedure is in regards to this AD only and does not change any of the requirements from an annual or other required inspection. Definitions of corrosion limits may be found in AC-43-4A, page 151.
A. If no, or only light, corrosion is found by an inspection that looks at 50% or more of the spar, through the existing access points, the wing shall be inspected thereafter at each annual in accordance with this AD. No further action is required although treatment with an approved corrosion preventative treatment is recommended. If no, or only light corrosion, is found and the spar is treated with CorrosionX it will not need to be inspected for two years from the date of the last inspection or retreated for two years from the date of the last treatment.
B. If evidence of more than light corrosion is found during the inspection additional access points may need to be provided so that the remainder of the spar can be inspected (see Para C.). If the corrosion found is more than moderate the wing will have to be removed from service for repair or replacement. If light to moderate corrosion is found document its location in the aircraft logbook. The wing will have to be treated with an approved corrosion treatment product every two years, or as recommended by the products manufacturer. Further reoccurring inspections will be conducted at each subsequent annual to confirm that the corrosion is not increasing. This will be allowed until the corrosion exceeds a moderate amount at which time the wing will have to be removed from service. Any pitting corrosion will have to be cleaned and the depth of the pitting must be less than the definition of moderate corrosion as specified by AC-43-4A.
C. If additional inspection holes are required, or desired, they shall be made in the underside of the wing 3 to 6 inches aft of the main spar and more than three inches from any rib. It is recommended that these holes be placed where they would be removed if the service bulletin method was followed. The diameter of the hole shall be from 1/4" to 1" as required. One hole per bay is allowed. All holes shall be properly deburred on both edges. A Unibit or similar tool is recommended. The diameter, number and location of the holes shall be as required, subject to previous limitations in this paragraph, to inspect and the remainder of the spar. This will vary depending on the borescope in use.
The holes may be plugged with a standard nylon/plastic hole plug, a metal hole plug, or covered with tape or fabric.
Optionally the inspection doublers and covers from Burl's Aircraft P/N 2-1271 and 2-1285 may be installed in one or more of the locations specified by Burl's Aircraft, LLC Mandatory Service Bulletin No. 15AC06-08-10, dated June 8, 2010. A doubler and cover plate may also be fabricated and installed in the locations specified in the previously referenced mandatory service bulletin. See later page for materials and dimensions.
D. If a corrosion treatment is required, or desired, two holes with an approximate diameter of 1/8 to 3/4 inch may be placed in the outboard end of each wing tip, as required, to facilitate corrosion treatment of the spar and wing. Consideration should be taken of the relative location to the spar lightning holes and items such as the aileron bellcrank. The holes may be plugged with a standard nylon/plastic hole plug, a metal hole plug, or covered with tape or fabric. Treatment with any approved solution should cover, at a minimum, the entire aft portion of the spar so that the material can "creep" between the skin of the aircraft, the spar web, and the spar caps. Treatment of both sides of the spar is preferred but not required.
E. Approved corrosion treatments: CorrosionX Aviation, ACF-50 or other products meeting Mil-C-1309E type II, or Mil-C-81309E Amd 3, Type ll and specified for aircraft use.
F. Repairs. If repair of the spar cap is necessarily it shall be done with approved data from a DER or other source acceptable to the administrator. Spar caps shall not be spliced within two feet of the lift strut attach point.
1. The hole plugs are not required for flight but are recommended.
2. The additional holes, if required or desired, are considered a minor alteration.
3. Allow owners to treat aircraft with approved corrosion treatment in accordance with manufactures application instructions.
4. Need a provision for those who have already replaced their spar caps or who have opened their wings for repairs etc and have not found any corrosion.
5. Corrosion definitions and limits are contained in FAA Advisory Circular (AC) 43-4A, paragraph 640 (a) (b) (c).
6. ACF-50 Information. http://acf-50.com/userfiles/ACF-50%20Tech%20Specs.pdf
,http://acf-50.com/userfiles/Product%20S ... ations.pdf
The cost of compliance under this suggested procedure will range from approximately 2 to 4 hours of labor for an inspection where no corrosion is found. If additional, drilled type, inspection or treatment holes are required this will require approximately 1-2 hours of labor to drill and deburr the holes. Installation of original type inspection holes will require approximately 2 hours labor per hole plus parts costs. The cost of the corrosion treatment product will vary with the product used but the amount of CorrosionX required to treat both wings cost approximately 25 dollars. Labor to treat the wings is expected to be 1 to 2 hours.
1. Information provided by Corrosion Technologies Corporation, makers of CorrosionX.
Doubler and inspection hole cover fabrication.
Doubler O.D. 5.00" +.2", -.10", I.D. 3.5" +.10", -.15"
14, -3 2017 "AD" universal head rivets centered on a 4" diameter circle
Doubler fabricated from .063 2024 T3 Alclad. .071 or .050" is acceptable as a substitute.
Fabricate cover plate to fit from .020 or .025 tempered aluminum. Attach flat spring retainer with two
-3 or -4 universal head rivets. Spring can be taken from a standard fabric inspection hole cover.
Use original inspection holes and cover as a pattern. Hole in skin to be 4" +.15", -.20". Deburr and rivet in accordance with ac 43-13-1B chapter 4.