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 Gates Learjet Model 35 and 36 series airplanes that have been modified in accordance with Raisbeck Supplemental Type Certificate (STC) SA766NW was published in the Federal Register on May 13, 1996 (61 FR 21982). That action proposed to require a reduction of the maximum operating limit speed on the affected airplanes to prevent encountering certain potentially hazardous conditions.
Interested persons have been afforded an opportunity to participate in the making of this amendment. Due consideration has been given to the single comment received.
Request to Require New Part Numbers of Modified Parts
One commenter requests that the proposal be revised to require that, once the overspeed warning switch is recalibrated and the airspeed indicators are modified [in accordance with OPTION I of the proposed AD], new part numbers should be assigned to those items. Additionally, the commenter requests that a parts catalog supplement be issued with the STC, calling out the correct new part number of the devices for future reference by maintenance personnel. The commenter considers that merely ink-stamping these parts once the required actions have been accomplished on them, as the proposed rule specifies, is not generally acceptable practice. The commenter states that, if either of those items is replaced in the future, there is no mechanism in place that would prevent the installation of a standard (unmodified) part number device in the airplane. Therefore, the airplane would no longer be in compliance with the AD, and would not be airworthy.
The FAA does not concur with the commenter s request for two reasons:
1. First, assigning and changing part numbers, and developing a parts catalog supplement, would be more labor-intensive and time consuming than ink-stamping a recalibrated or modified part. Additionally, the FAA is not convinced that the actions suggested by the commenter would be any more effective than the requirements of this AD.
2. Second, to show that actions specified in this AD have been complied with, it is necessary for the operator to make a maintenance log book entry indicating that the modified and ink-stamped warning switch and airspeed indicators are installed. If these items are replaced in the future (with parts that are not modified and not ink-stamped), a review of the log book entry would readily inform the mechanic or inspector that the airplane is not in compliance with the AD. Further, this process for verifying compliance would be identical whether the part is ink-stamped or has a new part number.
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 as proposed.
Petitioning foran Exemption of the Requirements of the Final Rule
Affected operators should note that the aileron instability that is the subject of this AD is a condition affected by the contour of the wing leading edge, which is a function of manufacturing tolerances. In light of this, the FAA recognizes that not all airplanes modified in accordance with Raisbeck STC SA766NW may exhibit the problem of aileron buffet or buzz below .83 Mach. Operators of those airplanes may wish to petition the FAA for an exemption from the requirements of the rule, under the provisions of part 11 of the Federal Aviation Regulations (14 CFR 11), "General Rulemaking Procedures."
Petitioners for such an exemption must provide data that would justify a grant of exemption, including, but not limited to, information concerning:
- the number of flights the airplane has flown in conditions involving high weight, high altitude, and high speed; and
- if any incident of buffet or buzz was observed during flight in those conditions. Based on the data submitted with the petition, the FAA will determine on a case-by-case basis if a flight evaluation or other additional data are necessary to determine if granting the petition would not adversely affect safety, and would be in the public interest.
Cost Impact
There are approximately 29 Gates Learjet Model 35 and 36 series airplanes of the affected design in the worldwide fleet. The FAA estimates that at least 1 airplane of U.S. registry will be affected by this proposed AD.
To accomplish the removal and recalibration of the airspeed indicators and Mach overspeed warning switch, and to revise the AFM Supplement, as provided by "Option I" of the proposed rule, it will take approximately 5 work hours per airplane, at an average labor rate of $60 per work hour. The FAA estimates that it will cost approximately $1,000 per airplane to reset the airspeed indicators and Mach overspeed warning switch. Based on these figures, the cost impact of this action (Option 1 of the AD) on U.S. operators is estimated to be $1,300 per airplane.
To accomplish the removal of the STC modifications, as provided by "Option II" of the rule, it will take approximately 100 work hours per airplane, at an average labor rate of $60 per work hour. Based on these figures, the cost impact of this action (Option II of the AD) on U.S. operators is estimated to be $6,000 per airplane.
The cost impact figures discussed above are 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 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, 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: