AD 99-16-03

This amendment adopts a new airworthiness directive (AD), applicable to certain Learjet Model 23, 24, 25, 28, 29, 31, 55, and 60 series airplanes, that requires a one-time detailed visual inspection of the electrical wire leads of the horizontal stabilizer anti-ice system to verify that the numbers on the wire leads correctly correspond to the numbers on the connected airframe wiring; installation of a wire ID strap on the left- and right-hand sides of each terminal block; and installation of a warning placard. This amendment is prompted by a report of severe flight control buffeting of a Learjet Model 55 series airplane due to a malfunction of the horizontal stabilizer anti-ice system. The actions specified by this AD are intended to prevent undetected accretion of ice on the leading edge of the horizontal stabilizer, which could result in the loss of pitch control and consequent reduced controllability of the airplane.

Final rule

99-16-03 LEARJET: Amendment 39-11238. Docket 98-NM-372-AD.

Applicability: Model 23, 24, 25, 28, 29, 31, 55, and 60 series airplanes; as listed in Learjet Service Bulletins SB 23/24/25-30-3, SB 28/29-30-3, SB 31-30-05, SB 55-30-3, and SB 60-30-4, all dated October 27, 1998; 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 (b) 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 prevent undetected accretion of ice on the leading edge of the horizontal stabilizer, which could result in the loss of pitch control and consequent reduced controllability of the airplane, accomplish the following:

One-Time Inspection
(a) Within 100 flight hours after the effective date of this AD: Perform a one-time detailed visual inspection of the electrical wire leads of the horizontal stabilizer anti-ice system to verify that the numbers on the wire leads correctly correspond to the numbers on the connected airframe wiring, in accordance with Learjet Service Bulletins SB 23/24/25-30-3, (for Model 23, 24, and 25 series airplanes), SB 28/29-30-3 (for Model 28 and 29 series airplanes), SB 31-30-05 (for Model 31 series airplanes), SB 55-30-3 (for Model 55 series airplanes), or SB 60-30-4 (for Model 60 series airplanes); all dated October 27, 1998; as applicable.

NOTE 2: For the purposes of this AD, a detailed inspection is defined as: "An intensive visual examination of a specific structural area, system, installation or assembly to detect damage, failure or irregularity. Available lighting is normally supplemented with a direct source of good lighting at intensity deemed appropriate by the inspector. Inspection aids such as mirror, magnifying lenses, etc. may be used. Surface cleaning and elaborate access procedures may be required."

Corrective Action
(1) If no discrepancy is detected during the inspection required by paragraph (a) of this AD: Concurrent with the inspection, install a wire ID strap on the left- and right-hand sides of each terminal block, and install a warning placard on each terminal block, in accordance with the applicable service bulletin.

(2) If any discrepancy is detected during the inspection required by paragraph (a) of this AD: Prior to further flight, repair the discrepancyin accordance with the procedures specified in Chapter 30 of the Learjet Airplane Wiring Manual. Concurrent with the repair, install a wire ID strap on the left- and right-hand sides of each terminal block, and install a warning placard on each terminal block; in accordance with the applicable service bulletin.

Alternative Methods of Compliance
(b) 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 3: Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the Wichita ACO.

Special Flight Permits
(c) 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.

Incorporation by Reference
(d) Except as provided by paragraph (a)(2) of this AD, the actions shall be done in accordance with Learjet Service Bulletin SB 23/24/25-30-3, dated October 27, 1998; Learjet Service Bulletin SB 28/29-30-3, dated October 27, 1998; Learjet Service Bulletin SB 31-30-5, dated October 27, 1998; Learjet Service Bulletin SB 55-30-3, dated October 27, 1998; or Learjet Service Bulletin SB 60-30-4, dated October 27, 1998, as applicable. 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; orat 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.

(e) This amendment becomes effective on September 7, 1999.

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 Learjet Model 23, 24, 25, 28, 29, 31, 55, and 60 series airplanes was published in the Federal Register on May 17, 1999 (64 FR 26703). That action proposed to require a one-time detailed visual inspection of the electrical wire leads of the horizontal stabilizer anti-ice system to verify that the numbers on the wire leads correctly correspond to the numbers on the connected airframe wiring; installation of a wire ID strap on the left- and right-hand sides of each terminal block; and installation of a warning placard.

Comments
Interested persons have been afforded an opportunity to participate in the making of this amendment. No comments were submitted in response to the proposal or the FAA s determination of the cost to the public.

Conclusion
The FAA has determined that air safety and the public interest require the adoption of the rule as proposed.

Cost Impact
There are approximately 1,010 airplanes of the affected design in the worldwide fleet. The FAA estimates that 806 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 inspection and installations, and that the average labor rate is $60 per work hour. Required parts will be provided by the manufacturer at no cost to the operators. Based on these figures, the cost impact of the required AD on U.S. operators is estimated to be $48,360, or $60 per airplane.

The cost impact figure discussed above is based on assumptions that no operator has yet accomplished any of the proposed 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, 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: