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 F28 Mark 0100 series airplanes was published in the Federal Register on March 17, 1995 (60 FR 14395). That action proposed to require repetitive checks to detect backlash in the elevator mechanical control system, and various follow-on actions. That action also proposed an optional terminating action for the repetitive check requirements.
Interested persons have been afforded an opportunity to participate in the making of this amendment. Due consideration has been given to the comments received.
Request to Defer Release of Final Rule
One commenter requests that the FAA defer the release of the final rule until a bolt replacement program can be developed to satisfactorily address the problems with corrosion. This commenter asserts that the proposed rule goes beyond what is needed to address the stated safety concern. Further, this commenter considers that, since both U.S. operators affected by this proposed rule already have instituted a maintenance program that includes applying corrosion inhibitor to the subject bolts, the FAA s interim safety objectives are being met. The commenter also notes that a similar problem of bolt corrosion occurred on the same system on a Fokker Model F28 series airplane, and the manufacturer simply recommended that a corrosion-resistant bolt be installed. The commenter maintains that, if the proposed rule is adopted without change, then the FAA will be mandating a very complex inspection program at operators "B"-check intervals, with little thought to actually correcting the unsafe condition. If there is a simple, cost-effective terminating action that could be introduced -- other than the replacement of the elevator booster control unit (BCU) with an improved unit -- then it should be considered prior to going forward with this AD.
The FAA does not concur with the commenter s request to delay the issuance of this AD until a "bolt replacement program" is developed, because such a "program" is already included in the AD as an optional terminating action. This AD provides for two optional actions, either of which could be accomplished in order to terminate the required repetitive inspections:
1. modification of the affected BCU by replacing the currently installed bolts with improved bolts that are corrosion-resistant; or
2. replacement of the currently installed BCU with a unit that already has the improved, corrosion-resistant bolts installed.
The FAA has provided the terminating actions as optional to operators, since the accomplishment of either terminating action is far more complicated and time-consuming than performing the required repetitive operational checks and inspections. For example, because it is physically impossible to replace one of the affected bolts while the BCU is still installed on the airplane, in order to perform either terminating action, the BCU must be removed; this procedure in itself is more labor-intensive than performing the required checks and inspections. However, the FAA maintains that the accomplishment of either action provided for in this AD -- repetitive checks/inspections or terminating action -- will adequately address the unsafe condition presented by corrosion.
The FAA cannot concur with the commenter s suggestion that the FAA s "interim safety objectives are being met" by operators current practice of applying a corrosion inhibitor to the suspect bolts. The commenter provided no data to substantiate that the procedure will provide a level of safety equivalent to that provided by the actions required by this AD. However, under the provisions of paragraph (e) of the final rule, the FAA may approve requests for use of alternative methods of compliance if data are submitted to substantiate that such a method would providean acceptable level of safety.
Request to Add Intermediate Step in Operational Check
One commenter requests that the proposal be revised to include the "intermediate" step of checking the position of the backlash remover lever, which is specified in the referenced Fokker Service Bulletin SBF100-27-052. This commenter notes that proposed paragraph (b), as written, would require an inspection of the elevator BCU backlash remover bolts for freedom of movement and corrosion if any backlash is detected during the operational check required by proposed paragraph (a). However, the referenced Fokker service bulletin specifies an intermediate step to inspect the position of the backlash remover to determine whether the bolt inspection is even necessary, or if troubleshooting for some other cause of the problem is necessary.
The FAA concurs with the commenter s request. While this "intermediate" step was not specified in the proposal, the FAA s intent was to require operators to accomplish all of the check and inspection procedures specified in Fokker Service Bulletin SBF100-27-052. The final rule has been revised to indicate that operators are to perform this intermediate step to determine if the bolt inspection is necessary, rather than immediately performing the bolt inspection in all cases. Since this addition to the final rule is relieving in nature (i.e., operators may not have to accomplish a more complicated inspection immediately, as was proposed), it will not increase the economic burden on any operator, nor will it increase the scope of the AD.
Request to Allow Deferment of BCU Replacement Requirement
One commenter requests that the proposal be revised to include the option to defer the replacement of the elevator BCU prior to further flight if the backlash remover bolts are found to be frozen or corroded. The commenter states that the backlash remover bolts are neither torqued nor subjected to high shear loads; therefore, operators should not be required to remove the BCU prior to further flight, provided that the bolts can be freed and lubricated, and the backlash operational check is subsequently accomplished successfully. If removal and modification of the BCU (in accordance with Fokker Service Bulletin SBF100-27-061) could be deferred so that operators could schedule it during a regular maintenance interval, the amount of downtime and additional expenses could be minimized.
The FAA concurs with the commenter s request. If the bolt having part number NAS6204C22D can be freed so that it rotates and slides freely, and is lubricated; and if the backlash operational check is subsequently accomplished and is successful; then the FAA agrees that the replacement of the elevator BCU can be deferred somewhat. The FAA considers an appropriate deferral interval to be 10 days. Paragraph (b) of the final rule has been revised to specify this deferral provision.
However, for the bolt having part number NAS6204C13D, the FAAhas determined that its replacement cannot be deferred if it does not rotate and slide freely, or if there are any signs of corrosion; under those conditions, that bolt must be replaced prior to further flight. The FAA considers this action both appropriate and warranted, since that bolt is readily accessible on the airplane.
Request to Add Optional Repetitive Inspections
One commenter requests that the proposal be revised to include the option to conduct periodic inspections of the backlash remover mechanism and to apply corrosion preventative lubrication on the subject backlash remover bolts at 1,800-flight cycle intervals. The commenter requests that operators be permitted to accomplish these actions in lieu of the proposed operational checks to detect backlash. This commenter does not consider the proposed backlash check from the flight deck to be a good solution to the problem of corroded or frozen backlash remover lever bolts because:
1. the check is subjective, sinceit requires a sense of feel that may vary from person to person; and
2. the check procedures are ill-defined in the referenced Fokker Service Bulletin SBF100-27-052.
In addition, this commenter states that the Fokker service bulletin does not provide any instructions that will prevent the existing bolts from corroding.
This commenter, a U.S. operator, indicates that it already has implemented a program that includes periodic inspection and lubrication of the subject bolts at 1,800-flight cycle intervals; the commenter considers its program to be a more proactive approach to addressing the unsafe condition.
The FAA does not concur with the commenter s request. In consultation with Fokker and the Netherlands airworthiness authority (RLD), the FAA has determined that the operational check is not subjective, as suggested by the commenter: there will be a clear indication of backlash if the mechanism is stuck, and the referenced Fokker service bulletin provides objective standards of approximately 2 inches of freeplay. In addition, the commenter has not provided any technical data to prove that inspection and lubrication of the bolts at 1,800-flight cycle intervals will provide at least the same level of safety as that provided by the operational check at 500-flight cycle intervals. While an inspection and lubrication may help to prevent sticking of the mechanism, it may not provide the necessary safety margins. Paragraph (e) of the final rule, however, does provide for the use of alternative methods of compliance with the AD, provided that sufficient justification is presented to the FAA.
Further, the FAA agrees that Fokker Service Bulletin SBF100-27-052 does not provide instructions to prevent corrosion, other than inspection and lubrication of the bolts whenever backlash is detected during the operational check. However, this AD provides for two optional terminating actions for the checks: either modification of the existing BCU by replacing the currently-installed bolts with corrosion-resistant bolts (as described in Fokker Service Bulletin SBF100-26-061); or by replacement of the affected elevator BCU with a unit that already has corrosion-resistant bolts installed. Such replacement of the bolts positively addresses the problem of galvanic corrosion.
Conclusion
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.
Cost Impact
The FAA estimates that 112 Fokker Model F28 Mark 0100 series airplanes of U.S. registry will be affected by this AD, that it will take approximately 1 work hour per airplane to accomplish the required actions, and that the average labor rate is $60 per work hour. Required parts will be suppliedby the manufacturer at no cost to the operators. Based on these figures, the cost impact of the AD on U.S. operators is estimated to be $6,720, or $60 per airplane.
The 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.
Regulatory Impact
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 ExecutiveOrder 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. 106(g), 40113, 44701. 39.13 - [Amended]
2. Section 39.13 is amended by adding the following new airworthiness directive: