AD 97-24-02

This amendment adopts a new airworthiness directive (AD) that is applicable to certain Bombardier Model CL-600-1A11, -2A12, and -2B16 series airplanes. This action requires repetitive inspections to detect cracks of a certain bulkhead web of the fuselage at certain locations, and repair, if necessary. This amendment is prompted by issuance of mandatory continuing airworthiness information by a foreign civil airworthiness authority. The actions specified in this AD are intended to detect and correct cracking in the pressure bulkhead at frame station (FS) 409.00, which could result in uncontrolled depressurization of the airplane and/or reduced structural integrity of the fuselage.

Final rule; request for comments

97-24-02 BOMBARDIER, INC.: Amendment 39-10209. Docket 97-NM-285-AD.
Applicability: Model CL-600-1A11 (CL-600) series airplanes, serial numbers 1004 through 1085 inclusive; Model CL-600-2A12 (CL-601) series airplanes, serial numbers 3001 through 3066 inclusive; Model CL-600-2B16 (CL-601-3A/-3R) series airplanes, serial numbers 5001 through 5194 inclusive; Model CL-600-2B16 (CL-604) series airplanes, serial numbers 5301 through 5352 inclusive; certificated in any category.

NOTE 1: This AD applies to each airplane identified in the preceding applicability provision, regardless of whether it has been otherwise 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 correct fatigue cracking in the underfloor pressure bulkhead of the fuselage, which could result in uncontrolled depressurization of the airplane and/or reduced structural integrity of the fuselage, accomplish the following:

(a) For Model CL-600-1A11 (CL-600) airplanes: Prior to the accumulation of 1,900 total landings, or within 100 landings after the effective date of this AD, whichever occurs later, perform a detailed visual inspection to detect cracks at frame station (FS) 409 of the bulkhead web [part number (P/N) 600-32014-71/-95/-105], in accordance with Canadair Challenger Service Bulletin 600-0679, dated September 12, 1997.

(1) If no crack is detected, repeat the detailed visual inspection thereafter at intervals not to exceed 600 landings.

(2) If any crack is detected and if all three of the conditions specified in paragraphs (a)(2)(i), (a)(2)(ii), and (a)(2)(iii) of this AD are met, within 600 landings or 12 months after the crack is detected, whichever occurs first, repair the cracking in accordance with a method approved by the Manager, New York Aircraft Certification Office (ACO), FAA, Engine and Propeller Directorate. Until the repair is accomplished, repeat the detailed visual inspection at intervals not to exceed 100 landings.

(i) No more than one crack exists at each corner radius, as specified in the service bulletin; and

(ii) No crack extends under the angles having P/N 600-32014-13 and P/N 600-32014-15 on the aft side of the bulkhead web; and

(iii) No crack exists in angles having P/N 600-32014-13 and P/N 600-32014-15 on the aft side of the bulkhead web.

(3) If any cracking other than that identified in paragraph (a)(2) of this AD is detected, prior to further flight, repair it in accordance with a method approved by the Manager, New York ACO.

(b) For Model CL-600-2A12 (CL-601), CL-600-2B16 (CL-601-3A/-3R), and CL-600-2B16 (CL-604) series airplanes: Prior to the accumulation of 1,100 total landings, or within 100 landings after the effective date of this AD, whichever occurs later, perform a detailed visual inspection to detect cracks at FS 409 of the bulkhead web (P/N 600-32014-105/-137), in accordance with Canadair Challenger Service Bulletin 601-0501, dated September 12, 1997 [for Model CL-600-2A12 (CL-601) and CL-600-2B16 (CL-601-3A/-3R) series airplanes); or Canadair Challenger Service Bulletin 604-53-007, dated September 30, 1997 [for Model CL-600-2B16 (CL-604) series airplanes]; as applicable.

(1) If no crack is detected, repeat the detailed visual inspection thereafter at intervals not to exceed 600 landings.

(2) If any crack is detected and if allthree of the conditions specified in paragraphs (b)(2)(i), (b)(2)(ii), and (b)(2)(iii) of this AD are met, within 600 landings or 12 months after the crack is detected, whichever occurs first, repair the cracking in accordance with a method approved by the Manager, New York ACO. Until the repair is accomplished, repeat the detailed visual inspection at intervals not to exceed 100 landings.

(i) No more than one crack exists at each corner radius, as specified in the service bulletin; and

(ii) No crack extends under the angles having P/N 600-32014-113 and P/N 600-32014-115 on the aft side of the bulkhead web; and

(iii) No crack exists in angles having P/N 600-32014-113 and P/N 600-32014-115 on the aft side of the bulkhead web.

(3) If any cracking other than that identified in paragraph (b)(2) of this AD is detected, prior to further flight, repair it in accordance with a method approved by the Manager, New York ACO.

(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, New York ACO. Operators shall submit their requests through an appropriate FAA Principal Maintenance Inspector, who may add comments and then send it to the Manager, New York ACO.

NOTE 2: Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the New York 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 inspections shall be done in accordance with Canadair Challenger Service Bulletin 600-0679, dated September 12, 1997; Canadair Challenger Service Bulletin 601-0501, dated September 12, 1997; or Canadair Challenger Service Bulletin 604-53-007, dated September 30, 1997; 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 Bombardier, Inc., Canadair, Aerospace Group, P.O. Box 6087, Station Centre-ville, Montreal, Quebec H3C 3G9, Canada. Copies may be inspected at the FAA, Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, Washington; or at the FAA, Engine and Propeller Directorate, New York Aircraft Certification Office, 10 Fifth Street, Third Floor, Valley Stream, New York; or at the Office of the Federal Register, 800 North Capitol Street, NW., suite 700, Washington, DC.

NOTE 3: The subject of this AD is addressed in Canadian airworthiness directive CF-97-16, dated September 25, 1997.

(f) This amendment becomes effective on December 3, 1997.

Transport Canada Aviation (TCA), which is the airworthiness authority for Canada, recently notified the FAA that an unsafe condition may exist on certain Bombardier Model CL-600-1A11, -2A12, and -2B16 series airplanes. TCA advises that the structural configuration of these airplanes at frame station (FS) 409.00 is similar to that of Bombardier Model CL-600-2B19 (Regional Jet Series 100 and 200) series airplanes, which was shown to have a pressurization problem caused by fatigue cracking in the underfloor pressure bulkhead of the fuselage. TCA has received several reports of cracking at this same location on Bombardier Model CL-600-1A11, -2A12, and -2B16 series airplanes. This condition, if not corrected, could result in uncontrolled depressurization of the airplane and/or reduced structural integrity of the fuselage.

Other Relevant Rules
The FAA previously issued AD 97-14-11, amendment 39-10082 (62 FR 38206, July 17, 1997), which requires repetitive inspections to detect cracks of a certain bulkhead web of the fuselage at certain locations, and repair, if necessary. That AD applies to certain Bombardier Model CL-600-2B19 (Regional Jet Series 100 and 200) series airplanes.

Explanation of Relevant Service Information
The manufacturer has issued Canadair Challenger Service Bulletin 601-0501, dated September 12, 1997 [for Model CL-600-2A12 (CL-601) and CL-600-2B16 (CL-601-3A/-3R) series airplanes]; Service Bulletin 604-53-007, dated September 30, 1997 [for Model CL-600-2B16 (CL-604) series airplanes]; and Service Bulletin 600-0679, dated September 12, 1997 [for Model CL-600-1A11 (CL-600) series airplanes]. These service bulletins describe procedures for repetitive detailed visual inspections to detect fatigue cracking of the underfloor pressure bulkhead at FS 409.00, and repair, if necessary. TCA classified these service bulletins as mandatory and issued Canadian airworthiness directive CF-97-16, dated September 25, 1997, inorder to assure the continued airworthiness of these airplanes in Canada.

FAA's Conclusions
These airplane models are manufactured in Canada and are type certificated for operation in the United States under the provisions of section 21.29 of the Federal Aviation Regulations (14 CFR 21.29) and the applicable bilateral airworthiness agreement. Pursuant to this bilateral airworthiness agreement, TCA has kept the FAA informed of the situation described above. The FAA has examined the findings of TCA, reviewed all available information, and determined that AD action is necessary for products of this type design that are certificated for operation in the United States.

Explanation of Requirements of Rule
Since an unsafe condition has been identified that is likely to exist or develop on other airplanes of the same type design registered in the United States, this AD requires accomplishment of the inspections specified in the service bulletins described previously. In addition,this AD requires repair, if necessary, in accordance with a method approved by the FAA.

Operators should note that, while it is not the FAA s normal policy to allow flight with known cracks, this AD does permit further flight with cracking within certain limits. The results of a review, conducted by the manufacturer, revealed that cracking in the underfloor pressure bulkhead of the fuselage will not result in rapid decompression of the airplane. Therefore, according to the review, if the crack size limits are strictly observed and if repetitive inspections are performed at the required intervals, cracks that grow beyond the limits will be detected, and corrective action taken, before they can grow to a size that would create an unacceptable risk of structural failure. Transport Canada Aviation concurs with the findings of this review. In consideration of these findings and based on the FAA s criteria for flight with known cracking, the FAA has determined that further flight with cracking within certain limits in the center pressure bulkhead is permissible for an interim period.

This is considered to be interim action. The manufacturer has advised that it currently is developing a modification that will positively address the unsafe condition addressed by this AD. Once this modification is developed, approved, and available, the FAA may consider additional rulemaking.

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 15 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 ruleby 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 before the 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 willbe 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 97-NM-285-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: