AD 98-16-18

This amendment adopts a new airworthiness directive (AD) that is applicable to certain Learjet Model 60 airplanes. This action requires repetitive measurements of the brake wear dimension between the housing subassembly and the pressure plate that is adjacent to the top pistons of the brake assembly; and follow-on corrective actions, if necessary. This amendment is prompted by reports of abnormal (uneven) brake wear. The actions specified in this AD are intended to detect and repair an abnormal brake wear condition, which could result in loss of brake effectiveness and cause the airplane to leave the runway surface.

Final rule; request for comments

98-16-18 LEARJET INC.: Amendment 39-10694. Docket 98-NM-227-AD.

Applicability: Model 60 airplanes equipped with Aircraft Braking Systems (ABS) brake assemblies having part number 5003096-7, certificated in any category.

NOTE 1: This AD applies to each airplane identified in the preceding applicability provision, regardless of whether it has been modified, altered, or repaired in the area subject to the requirements of this AD. For airplanes that have been modified, altered, or repaired so that the performance of the requirements of this AD is affected, the owner/operator must request approval for an alternative method of compliance in accordance with paragraph (c) of this AD. The request should include an assessment of the effect of the modification, alteration, or repair on the unsafe condition addressed by this AD; and, if the unsafe condition has not been eliminated, the request should include specific proposed actions to address it.

Compliance: Required as indicated, unless accomplished previously.

To detect and repair an abnormal (uneven) brake wear condition, which could result in loss of brake effectiveness and cause the airplane to leave the runway surface, accomplish the following:

(a) Within 10 flight hours after the effective date of this AD, measure the brake wear dimension between the housing subassembly and the pressure plate that is adjacent to the top pistons of the brake assembly, in accordance with ABS Service Bulletin LEAR 60-32-03, dated March 5, 1998.

(1) If the dimension is less than 0.359 inch (9.12 mm), thereafter repeat the measurement at intervals not to exceed 25 flight cycles.

(2) If the dimension is equal to or greater than 0.359 inch (9.12 mm) and less than 0.464 inch (11.79 mm), prior to further flight, perform a visual inspection to detect abnormal wear of the friction mix on the rotating disks, in accordance with the service bulletin.

(i) If the friction mix is not worn to the diskcores on either disk, thereafter repeat the measurement at intervals not to exceed 25 flight cycles.

(ii) If the friction mix is worn to the disk core on either disk, replace both rotating disks with new disks in accordance with the service bulletin. Thereafter, repeat the measurement at intervals not to exceed 25 flight cycles.

(3) If the dimension is greater than or equal to 0.464 inch (11.769 mm), replace the disk stack with a new disk stack or overhaul it, in accordance with the service bulletin. Thereafter, repeat the measurement at intervals not to exceed 25 flight cycles.

(b) As of the effective date of this AD, no person shall install on any airplane a used ABS brake assembly, part number 5003096-7, unless it has been inspected and applicable corrective actions have been performed in accordance with the requirements of this AD.

(c) An alternative method of compliance or adjustment of the compliance time that provides an acceptable level of safety may be used if approved by the Manager, Wichita Aircraft Certification Office (ACO), FAA, Small Airplane Directorate. Operators shall submit their requests through an appropriate FAA Principal Maintenance Inspector, who may add comments and then send it to the Manager, Wichita ACO.

NOTE 2: Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the Wichita ACO.

(d) Special flight permits may be issued in accordance with sections 21.197 and 21.199 of the Federal Aviation Regulations (14 CFR 21.197 and 21.199) to operate the airplane to a location where the requirements of this AD can be accomplished.

(e) The actions shall be done in accordance with Aircraft Braking Systems Corporation Service Bulletin LEAR 60-32-03, dated March 5, 1998. This incorporation by reference was approved by the Director of the Federal Register in accordance with 5 U.S.C. 552(a) and 1 CFR part 51. Copies may be obtained from Learjet, Inc., One Learjet Way, Wichita, Kansas 67209-2942. Copies may be inspected at the FAA, Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, Washington; or at the FAA, Small Airplane Directorate, Wichita Aircraft Certification Office, 1801 Airport Road, Room 100, Mid-Continent Airport, Wichita, Kansas; or at the Office of the Federal Register, 800 North Capitol Street, NW., suite 700, Washington, DC.

(f) This amendment becomes effective on August 24, 1998.

The FAA has received reports from Learjet of an abnormal brake wear condition on certain Learjet Model 60 airplanes. Subsequent investigation, conducted by Aircraft Braking Systems Corporation (ABS) (the manufacturer of the brakes), revealed an abnormal (uneven) brake wear condition of the friction material (friction mix) on the rotating disks. The uneven wear has been attributed to thermal gradients within the brake stack of the ABS brake assembly. Such abnormal brake wear, if not corrected, could result in loss of brake effectiveness, which could cause the airplane to leave the runway surface.

Explanation of Relevant Service Information
The FAA has reviewed Aircraft Braking Systems Service Bulletin LEAR 60-32-03, dated March 5, 1998, which describes procedures for repetitive measurements of the brake wear dimension between the housing subassembly and the pressure plate that is adjacent to the top pistons of the brake assembly; and follow-on corrective actions, if necessary. These follow-on actions include performing a visual inspection to detect abnormal wear of the friction mix on the rotating disks, and replacing both rotating disks with new disks, if necessary; and replacing the disk stack with a new disk stack or overhauling it. Accomplishment of certain actions specified in the service bulletin is intended to adequately address the identified unsafe condition.

Explanation of the Requirements of the Rule
Since an unsafe condition has been identified that is likely to exist or develop on other airplanes of the same type design, this AD is being issued to detect and repair an abnormal (uneven) brake wear condition, which could result in loss of brake effectiveness and cause the airplane to leave the runway surface. This AD requires accomplishment of certain actions specified in the service bulletin described previously.

Operators should note that the service bulletin lists other actions in addition to those described previously. The FAA considers these additional actions to be routine maintenance and therefore has not specified their performance in this AD.

Determination of Rule's Effective Date
Since a situation exists that requires the immediate adoption of this regulation, it is found that notice and opportunity for prior public comment hereon are impracticable, and that good cause exists for making this amendment effective in less than 30 days.

Comments Invited
Although this action is in the form of a final rule that involves requirements affecting flight safety and, thus, was not preceded by notice and an opportunity for public comment, comments are invited on this rule. Interested persons are invited to comment on this rule by submitting such written data, views, or arguments as they may desire. Communications shall identify the Rules Docket number and be submitted in triplicate to the address specified under the caption "ADDRESSES." All communications received on or beforethe closing date for comments will be considered, and this rule may be amended in light of the comments received. Factual information that supports the commenter's ideas and suggestions is extremely helpful in evaluating the effectiveness of the AD action and determining whether additional rulemaking action would be needed.

Comments are specifically invited on the overall regulatory, economic, environmental, and energy aspects of the rule that might suggest a need to modify the rule. All comments submitted will be available, both before and after the closing date for comments, in the Rules Docket for examination by interested persons. A report that summarizes each FAA-public contact concerned with the substance of this AD will be filed in the Rules Docket.

Commenters wishing the FAA to acknowledge receipt of their comments submitted in response to this rule must submit a self-addressed, stamped postcard on which the following statement is made: "Comments to Docket Number 98-NM-227-AD." The postcard will be date stamped and returned to the commenter.

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.

The FAA has determined that this regulation is an emergency regulation that must be issued immediately to correct an unsafe condition in aircraft, and that it is not a "significant regulatory action" under Executive Order 12866. It has been determined further that this action involves an emergency regulation under DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979). If it is determined that this emergency regulation otherwise would be significant under DOT Regulatory Policies and Procedures, a final regulatory evaluation will be prepared and placed in the Rules Docket. A copy of it, if filed, 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: