A proposal to amend part 39 of the Federal Aviation Regulations (14 CFR part 39) to include an airworthiness directive (AD) that is applicable to certain Fokker Model F-28 Mark 1000, 2000, 3000, and 4000 series airplanes was published in the Federal Register on April 5, 1994 (59 FR 15875). That action proposed to require a one-time inspection to detect cracking in the area of the side stay attachment lugs of the fitting subassembly of the main landing gear (MLG), and replacement of cracked subassemblies with new or serviceable subassemblies.
Interested persons have been afforded an opportunity to participate in the making of this amendment. Due consideration has been given to the comments received.
One commenter supports the proposal.
One commenter requests that the proposed rule be withdrawn and that a supplemental notice be issued that would propose the accomplishment of a "refurbishment" program developed by the commenter. This commenterindicates that the inspection and rework proposed in the notice may actually aggravate, rather than prevent, damage to the subject fitting assemblies. This commenter reports that, within several days after reworking the lugs in accordance with the method proposed in the notice, corrosion damage indications reappeared. In order to ensure that all evidence of corrosion was removed, the commenter had to accomplish an intensive refurbishment of the main landing gear side stay attachment lugs. It is this refurbishment process that the commenter requests to be required by the proposed rule.
The FAA does not agree with the commenter's request. The commenter did not provide sufficient data to establish that the procedure required by this rule (namely, a cleaning procedure that is necessary to remove surface corrosion in order to obtain an adequate eddy current inspection) contributes to any aggravation of a corrosion condition. The FAA has determined that the cleaning and eddy currentinspection are sufficient, if no cracks are detected, to allow the main fitting sub-assembly to remain on the airplane until the next overhaul, when a thorough inspection, corrosion removal, and corrosion control process can be accomplished.
This same commenter requests that the proposed AD be revised to provide "credit" for inspections accomplished during overhaul procedures that were performed prior to the effective date of the final rule. The commenter points out that Revision 2 of Fokker F28 Service Experience Digest 32-10, Subject No. 008, states that, if the inspection and restoration of the protective finish on the subject assembly are accomplished, as is recommended during the inspections called out in the referenced service bulletin or during normal overhaul, no repetitive inspections will be necessary between overhaul periods. The commenter considers that this implies that the damage to the anodic film is an isolated occurrence, and that stress corrosion cracking willnot occur if the anodic film is intact with the unit enters service. The commenter states that, compared to a specialized shop environment, field inspections and rework operations (as proposed in the notice) are less likely to ensure that all corrosion is detected and removed. Further, rework that exposes end grains and increases stress levels can aggravate, rather than arrest, the propensity for further corrosion. In this commenter's overhaul shop, corrosion removal is verified after machining by a process beginning with a chemical etch treatment that removes the surfaced layer of metal smeared by machining, followed by a high-sensitivity fluorescent penetrant inspection.
The FAA concurs in part. Although the Fokker F28 Service Experience Digest referenced by the commenter does state that accomplishment of normal overhaul "will ensure that no repetitive inspections are required between overhaul periods," the overhaul instructions provided may not be entirely adequate to support that statement. Therefore, the FAA agrees with the commenter's suggestion to provide credit to operators for inspections that were accomplished during overhaul prior to the effective date of the AD, but only provided that:
1. the overhaul was accomplished within the normal overhaul period (12,000 cycles or 12 years, whichever comes first); and
2. the overhaul was accomplished in accordance with Dowty Aerospace Landing Gear (DALG) Component Maintenance Manual (CMM), dated September 1977 or later; and
3. any resulting repairs were accomplished in accordance with the DALG CMM, dated November 25, 1992, or later; or, if repairs were accomplished after September 1977 but before November 25, 1992, they were performed with concurrence (concession) from DALG.
The FAA has revised paragraph (a) of the final rule, to provide such "credit" to operators who have performed this procedure.
One commenter requests that the proposed rule be revised to permit the installation of uninspected (non-identified) subassemblies after the effective date of the AD and until the compliance time for inspection, which is 3 months after the effective date. This commenter points out that the proposal would require that, as of the effective date of the final rule, no operator could install any subassembly that had not been previously inspected and identified in accordance with the requirements of proposed paragraph (a). The commenter is concerned that this would not allow the installation of an uninspected serviceable part during maintenance that was not related to the AD itself. The commenter states that this does not appear to be consistent with previous AD's that have dealt with affected parts not installed on an airplane.
The FAA does not concur with the commenter's request. Neither does the FAA agree that this is "not consistent with previous AD's." The FAA has issued numerous AD's over the past years that have called for the removal of discrepant parts that havebeen determined to create an unsafe condition; those AD's normally contain a statement indicating that none of those discrepant-type parts may be installed on any airplane in the future. Such statements are necessary in order to prohibit the installation of spares of the discrepant part. In general, once an unsafe condition has been determined to exist with regard to a part, it is the FAA's normal policy not to allow that condition -- or that part --to be re-introduced into the fleet.
Further, in developing the technical information on which every AD is based, one of the important considerations is the availability of parts that the AD will require to be installed. When it is determined that ample numbers of those (safe) parts are immediately available to operators, it is the FAA's policy to prohibit installation of the "unsafe" parts after the effective date of the AD. Removing an unsafe condition that already exists on an airplane necessarily involves performing maintenance on the airplane, and the FAA always provides some kind of "grace period" in order to minimize disruption of operations. On the other hand, prohibiting installation of spares that have been determined to create an unsafe condition does not require any additional maintenance activity; it simply requires use of one part rather than another.
Put in other terms, the purpose of the AD's compliance time is to give the operators time to get the discrepant parts off the airplane. The time interval selected takes into account not only safety implications, but the size of the fleet and convenient maintenance schedules. However, the compliance time is not meant as a time for operators to put discrepant parts on the airplane in the meantime.
Further, the FAA considers that the period of time between publication of the final rule in the Federal Register and the effective date of the final rule (usually 30 days) is sufficient to provide operators with an opportunity to determine their immediate need for modified spares and to obtain them. Of course, in individual cases where this is not possible, every AD contains a provision that allows an operator to obtain an extension of compliance time based upon a specific showing of need.
In light of these issues, the FAA finds that prohibiting installation of uninspected (non-identified) subassemblies on an airplane as of the effective date of this final rule does increase safety and does not impose undue burdens on operators.
As a result of recent communications with the Air Transport Association (ATA) of America, the FAA has learned that, in general, some operators may misunderstand the legal effect of AD's on airplanes that are identified in the applicability provision of the AD, but that have been altered or repaired in the area addressed by the AD. The FAA points out that all airplanes identified in the applicability provision of an AD are legally subject to the AD. If an airplane has been altered or repaired in the affected area in such a way as to affect compliance with the AD, the owner or operator is required to obtain FAA approval for an alternative method of compliance with the AD, in accordance with the paragraph of each AD that provides for such approvals. A note has been added to the final rule to clarify this requirement.
The FAA has recently reviewed the figures it has used over the past several years in calculating the economic impact of AD activity. In order to account for various inflationary costs in the airline industry, the FAA has determined that it is necessary to increase the labor rate used in these calculations from $55 per work hour to $60 per work hour. The economic impact information, below, has been revised to reflect this increase in the specified hourly labor rate.
After careful review of the available data, including the comments noted above, the FAA has determined that air safety and the public interest require the adoption of the rule with the changes previously described. The FAA has determined that these changes will neither increase the economic burden on any operator nor increase the scope of the AD.
The FAA estimates that 42 airplanes of U.S. registry will be affected by this AD, that it will take approximately 14 work hours per airplane to accomplish the required actions, and that the average labor rate is $60 per work hour. Based on these figures, the total cost impact of the AD on U.S. operators is estimated to be $35,280, or $840 per airplane.
The total cost impact figure discussed above is based on assumptions that no operator has yet accomplished any of the requirements of this AD action, and that no operator would accomplish those actions in the future if this AD were not adopted.
The regulations adopted herein will not have substantial direct effects on the States, on the relationship between the national government and the States, or on the distribution of power and responsibilities among the various levels of government. Therefore, in accordance with Executive Order 12612, it is determined that this final rule does not have sufficient federalism implications to warrant the preparation of a Federalism Assessment.
For the reasons discussed above, I certify that this action (1) is not a "significant regulatory action" under Executive Order 12866; (2) is not a "significant rule" under DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979); and (3) will not have a significant economic impact, positive or negative, on a substantial number of small entities under the criteria of the Regulatory Flexibility Act. A final evaluation has been prepared for this action and it is contained in the Rules Docket. A copy of it may be obtained from the Rules Docket at the location provided under the caption "ADDRESSES."
List of Subjects in 14 CFR Part 39
Air transportation, Aircraft, Aviation safety, Incorporation by reference, Safety.
Adoption of the Amendment
Accordingly, pursuant to the authority delegated to me by the Administrator, the Federal Aviation Administration amends part 39 of the Federal Aviation Regulations (14 CFR part 39) as follows:
PART 39 - AIRWORTHINESS DIRECTIVES
1. The authority citation for part 39 continues to read as follows:
Authority: 49 U.S.C. App. 1354(a), 1421 and 1423; 49 U.S.C. 106(g); and 14 CFR 11.89.
39.13 - [Amended]
2. Section 39.13 is amended by adding the following new airworthiness directive: