AD 2004-03-08

This amendment adopts a new airworthiness directive (AD), applicable to certain Learjet Model 31, 31A, 35, 35A (C-21A), 36, and 36A airplanes, that requires modification of the drag angles of the fuselage and engine pylons to gain access to the shear webs of the forward engine beams; repetitive inspections of the shear webs of the forward engine beams for cracks; follow-on actions; and modification/repair of the shear webs of the forward engine beams, as necessary, which terminates the repetitive inspections. This action is necessary to prevent significant structural damage to the engine pylons, possible separation of the engines from the fuselage, and consequent reduced controllability of the airplane. This action is intended to address the identified unsafe condition.

Final rule.

2004-03-08 Learjet: Amendment 39-13452. Docket 2001-NM-366-AD.

Applicability: The following airplanes, certificated in any category, as applicable:

Table 1.-Applicability

Model-
As Listed in Bombardier Service Bulletin-
31 and 31A Airplanes
31-51-2, dated February 1, 2001; and 31-51-3, Revision 1, dated August 2, 2001.
35, 35A (C-21A), 36 and 36A Airplanes
35/36-51-3, dated February 1, 2001; and 35/36-51-4, Revision 1, dated August 2, 2001.

Compliance: Required as indicated, unless accomplished previously.

To prevent significant structural damage to the engine pylons, possible separation of the engines from the fuselage, and consequent reduced controllability of the airplane, accomplish the following:

Inspections

(a) At the later of the times specified in paragraphs (a)(1) and (a)(2) of this AD: Do a detailed inspection (using a probe) and a general visual inspection of the shear webs of the forward engine beams (including modification of the drag angles) for cracking in accordance with the Accomplishment Instructions of Bombardier Service Bulletin 31-51-2 (for Model 31 airplanes) or 35/36-51-3 (for Model 35 and 36 airplanes), both dated February 1, 2001; as applicable.

(1) Prior to the accumulation of 3,000 total flight hours; or

(2) Within 1,200 flight hours or 1 year after the effective date of this AD, whichever occurs first.

Note 1: For the purposes of this AD, a general visual inspection is defined as: "A visual examination of an interior or exterior area, installation, or assembly to detect obvious damage, failure, or irregularity. This level of inspection is made from within touching distance unless otherwise specified. A mirror may be necessary to enhance visual access to all exposed surfaces in the inspection area. This level of inspection is made under normally available lighting conditions such as daylight, hangar lighting, flashlight, or droplight and may require removal or opening of access panelsor doors. Stands, ladders, or platforms may be required to gain proximity to the area being checked."

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."

Detailed Probe Inspection Follow-On Actions

(b) Following the detailed probe inspection required by paragraph (a) of this AD, do the follow-on actions specified in paragraphs (b)(1), (b)(2), or (b)(3) of this AD, as applicable, in accordance with the Accomplishment Instructions of Bombardier Service Bulletin 31-51-2 or 35/36-51-3, both dated February 1, 2001; as applicable.

(1) If the resistance measured during the inspection is less than 0.110 milliohm: Repeat the inspections required by paragraph (a) of this AD thereafter at intervals not to exceed 1,200 flight hours.

(2) If the resistance measured during the inspection is 0.110 milliohm or more, but less than 0.150 milliohm: Within the next 1,200 flight hours, repair and modify the forward engine beam shear web in accordance with the Accomplishment Instructions of Bombardier Service Bulletin 31-51-3, Revision 1 (for Model 31 airplanes) or 35/36-51-4, Revision 1 (for Model 35 and 36 airplanes), both dated August 2, 2001; as applicable.

(3) If the resistance measured during the inspection is 0.150 milliohm or more: Before further flight, repair and modify the forward engine beam shear web in accordance with the Accomplishment Instructions of Bombardier Service Bulletin 31-51-3, Revision 1, or 35/36-51-4, Revision 1; as applicable.

General Visual Inspection Follow-On Actions

(c) Following the general visual inspection required by paragraph (a) of this AD, do all of the applicable follow-on actions at the times specified in the Accomplishment Instructions of Bombardier Service Bulletin 31-51-2 or 35/36-51-3, both dated February 1, 2001; as applicable; except as specified in paragraph (d) of this AD.

(d) If any crack opening is found that is more than 0.03 inch during the general visual inspection required by paragraph (a) of this AD: Before further flight, do the actions specified in paragraphs 2.C.(16)(a) and 2.C.(16)(b) of Bombardier Service Bulletin 31-51-2 or 35/36-51-3, both dated February 1, 2001; as applicable; repair per a method approved by the Manager, Wichita Aircraft Certification Office (ACO), FAA; and do the terminating action specified in paragraph (e) of this AD.

Terminating Action

(e) Modification of the shear webs by accomplishing all of the actions specified in the Accomplishment Instructions of Bombardier Service Bulletin 31-51-3, Revision 1, or 35/36-51-4, Revision 1, both dated August 2, 2001; as applicable; terminates the initial inspections required by paragraph (a) and the repetitive inspections required by paragraph (b)(1) of this AD.

Repair Approval

(f) Where any service bulletin identified in this AD specifies that the manufacturer may be contacted for disposition of certain repair conditions, repair per a method approved by the Manager, Wichita ACO, FAA.

Submission of Inspection Results Not Required

(g) Although the service bulletins identified in this AD specify to submit information to the manufacturer, this AD does not include such a requirement.

Alternative Methods of Compliance

(h) In accordance with 14 CFR 39.19, the Manager, Wichita ACO, is authorized to approve alternative methods of compliance for this AD.

Incorporation by Reference

(i) Unless otherwise specified in this AD, the actions shall be done in accordance with Bombardier Service Bulletin 31-51-2, dated February 1, 2001, and Bombardier Service Bulletin 31-51-3, Revision 1, dated August 2, 2001; or Bombardier Service Bulletin 35/36-51-3, dated February 1, 2001, and Bombardier Service Bulletin 35/36-51-4, Revision 1, dated August 2, 2001; 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; or at the FAA, 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.

Effective Date

(j) This amendment becomes effective on March 15, 2004.

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 31, 31A, 35, 35A (C-21A), 36, and 36A airplanes was published in the Federal Register on November 13, 2003 (68 FR 64283). That action proposed to require modification of the drag angles of the fuselage and engine pylons to gain access to the shear webs of the forward engine beams; repetitive inspections of the shear webs of the forward engine beams for cracks; follow-on actions; and modification/repair of the shear webs of the forward engine beams, as necessary, which would terminate the repetitive inspections.

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

We have determined that air safety and the public interest require the adoption of the rule as proposed.

Cost Impact

There are approximately 893 airplanes of the affected design in the worldwide fleet. We estimate that 673 airplanes of U.S. registry will be affected by this AD.

It will take between 2 and 3 work hours per airplane to accomplish the required modification, at an average labor rate of $65 per work hour. Required parts will cost approximately $243 per airplane. Based on these figures, the cost impact of the required modification on U.S. operators is estimated to be between $251,029 and $294,774, or between $373 and $438 per airplane.

We estimate that it will take 3 work hours to perform the required inspections, and that the average labor rate is $65 per work hour. Based on this figure, the cost impact of the required inspections on U.S. operators is estimated to be $131,235, or $195 per airplane, per inspection cycle.

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. The cost impact figures discussed in AD rulemaking actions represent only the time necessary to perform the specific actions actually required by the AD. These figures typically do not include incidental costs, such as the time required to gain access and close up, planning time, or time necessitated by other administrative actions. The manufacturer may cover the cost of replacement parts associated with this AD, subject to warranty conditions. Manufacturer warranty remedies may also be available for labor costs associated with this AD. As a result, the costs attributable to this AD may be less than stated above.

Regulatory Impact

The regulations adopted herein will not have a substantial direct effect on the States, on the relationship between the national government and the States, or on the distribution ofpower and responsibilities among the various levels of government. Therefore, it is determined that this final rule does not have federalism implications under Executive Order 13132.

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: