AD 95-18-02

This amendment adopts a new airworthiness directive (AD), applicable to certain Boeing Model 757 and 767 series airplanes, that requires replacement of the hydraulic pressure transfer tube of the ram air turbine (RAT) system with a new hose assembly. This amendment is prompted by reports that, during flight tests, the hydraulic pressure transfer tube of the RAT cracked when the RAT was extended on a Model 767 series airplane due to overload of the hydraulic transfer tube. The actions specified by this AD are intended to prevent such overload, which could result in cracking of the hydraulic transfer tube. Such cracking subsequently could lead to the loss of hydraulic fluid of the center system and the inability of the RAT to pressurize the center system; this situation could lead to loss of all hydraulic system power in the event that power is lost in both engines.

Final rule

95-18-02 BOEING: Amendment 39-9350. Docket 95-NM-26-AD. \n\n\tApplicability: Model 757 series airplanes having line positions 1 through 650 inclusive, and equipped with Sundstrand ram air turbine (RAT)/hydraulic pumps having part number (P/N) 730814 series, serial numbers 0001 through 0735 inclusive; and Model 767 series airplanes having line positions 1 through 564 inclusive, and equipped with Sundstrand RAT/hydraulic pumps having P/N 729548 series, serial numbers 0001 through 0620 inclusive; certificated in any category. \n\n\tNOTE 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 use the authority provided in paragraph (b) of this AD to request approval from the FAA. This approval may address either no action, if the current configuration eliminates the unsafe condition; or different actions necessary to address the unsafe condition described in this AD. Such a request should include an assessment of the effect of the changed configuration on the unsafe condition addressed by this AD. In no case does the presence of any modification, alteration, or repair remove any airplane from the applicability of this AD. \n\n\tCompliance: Required as indicated, unless accomplished previously. \n\n\tTo prevent overload of the hydraulic pressure transfer tube, which could result in cracking of the tube of the ram air turbine (RAT), and subsequently could lead to the loss of all center systems hydraulic fluid and the inability of the RAT to pressurize the center hydraulic system, accomplish the following: \n\n\t(a)\tWithin 24 months after the effective date of this AD, replace the hydraulic pressure transfer tube of the RAT system with a new hose assembly, in accordancewith Boeing Alert Service Bulletin 757-29A0046, dated October 6, 1994 (for Model 757 series airplanes); or Boeing Alert Service Bulletin 767-29A0077, dated October 6, 1994, or Revision 1, dated June 8, 1995 (for Model 767 series airplanes); as applicable. \n\n\tNOTE 2: Boeing Alert Service Bulletin 757-29A0046 references Sundstrand Service Bulletin 730814-29-11, dated November 3, 1994, or Revision 1, dated May 3, 1995; and Boeing Alert Service Bulletin 767-29A0077 references Sundstrand Service Bulletin 729548-29-14, dated November 3, 1994, or Revision 1, dated May 3, 1995; as additional sources of service information for procedures to replace the pressure tube. \n\n\tNOTE 3: Modification of the hydraulic pressure transfer tube of the RAT system in accordance with Sundstrand Service Bulletin 730814-29-9, Revision 1, dated November 3, 1994, or Revision 2, dated March 31, 1995 (for Model 757 series airplanes); or Sundstrand Service Bulletin 729548-29-12, Revision 2, dated November 3, 1994, or Revision 3, dated March 31, 1995 (for Model 767 series airplanes); is considered acceptable for compliance with the modification requirements of paragraph (a) of this AD. \n\n\t(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, Seattle Aircraft Certification Office (ACO), FAA, Transport 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, Seattle ACO. \n\n\tNOTE 4: Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the Seattle ACO. \n\n\t(c)\tSpecial 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.(d)\tThe replacement shall be done in accordance with Boeing Alert Service Bulletin 757-29A0046, dated October 6, 1994 (for Model 757 series airplanes); or in accordance with Boeing Alert Service Bulletin 767-29A0077, dated October 6, 1994, or Boeing Alert Service Bulletin 767- 29A0077, Revision 1, dated June 8, 1995 (for Model 767 series airplanes); 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 Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, Washington 98124-2207. Copies may be inspected at the FAA, Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, Washington; or at the Office of the Federal Register, 800 North Capitol Street, NW., suite 700, Washington, DC. \n\n\t(e)\tThis amendment becomes effective on October 10, 1995.

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 Boeing Model 757 and 767 series airplanes was published in the Federal Register on May 1, 1995 (60 FR 21054). That action proposed to require replacement of the hydraulic pressure transfer tube of the ram air turbine (RAT) system with a new hose assembly. \n\n\tInterested persons have been afforded an opportunity to participate in the making of this amendment. Due consideration has been given to the comments received. \n\n\tOne commenter supports the proposed rule. \n\n\tOne commenter notes that the description of the cause of the unsafe condition that appeared in the Discussion section of the preamble to the notice states that ". . . cracking has been attributed to overload due to mishandling or improper installation of the pressure transfer tubes on the strut of the RAT system." The commenter states that this description is inaccurate, since the overload condition could only occur as a result of maintenance action on in-service airplanes. The commenter suggests that a more accurate description would be ". . . cracking has been attributed to overload of the pressure transfer tube due to mishandling or improper installation during in-service RAT maintenance." The FAA concurs that the commenter's wording is more accurate; however, since the Discussion section is not restated in this final rule, no change to the final rule is necessary. \n\n\tThis commenter also provides further clarification of the unsafe condition described throughout the notice. That description states that "cracking of the hydraulic transfer tube, if not corrected, could result in loss of hydraulic fluid . . ." The commenter states that a more complete description of the unsafe condition would be ". . . overload of the hydraulic transfer tube, if not corrected, may cause the tube to crack and could result in lossof hydraulic fluid . . ." The FAA concurs and has revised all references to the unsafe condition accordingly throughout this final rule. \n\n\tThe same commenter further notes that the Discussion section of the preamble to the notice states that "such overloads are likely to have occurred on other tubes . . ." The commenter states that, since only one operator has reported cracking on two pressure transfer tubes, it does not provide a basis to conclude that overload is "likely" to occur on other airplanes. The commenter suggests that a more accurate description of this situation would be, "such overloads may have occurred on other tubes. . ." Further, the commenter states that testing has demonstrated that the RAT transfer tubes performed acceptably during an in-flight RAT deployment when shimmed in accordance with the maintenance manual. The FAA has reviewed the relevant data currently available. The FAA finds no basis to support the commenter's suggestion that the RAT transfer tubes perform acceptably when shimmed. In fact, the testing showed abnormally high stresses in the tube when the tube was shimmed in accordance with the maintenance manual. However, the FAA concurs that the commenter's suggested wording relative to the fact that overload conditions "may have occurred" is more accurate. Since the Discussion section is not restated in this final rule, no change to the final rule is necessary. \n\n\tAdditionally, this commenter points out a statement that appeared in the Discussion section of the preamble to the notice that reads, "since an unsafe condition has been identified that is likely to exist . . ." The commenter suggests that this phrase would be more accurate if it were changed to read, "since an unsafe condition has been identified that may exist. . ." The FAA does not concur. The phrasing used in that particular statement in the preamble is not accidental. Part 39.1, "Applicability," of the Federal Aviation Regulations (FAR) (14 CFR 39.1)states: \n\n\t"This part prescribes airworthiness directives that apply to aircraft . . . when -- \n\n\t\t(a) An unsafe condition exists in a product; and \n\n\t\t(b) That condition is likely to exist or develop in other products of the same type design." Therefore, the finding that the condition "is likely to exist or develop" is necessary to ensure that the AD falls within the scope of part 39; its absence would arguably subject the FAA to legal challenge for inappropriately using the AD process to issue rules that do not meet the criteria for AD's. While it is understandable that a manufacturer would like to minimize any adverse implications regarding the safety of its products, the FAA reiterates that the purpose of an AD is to correct an identified unsafe condition in aircraft, regardless of where it is or what it is caused by. In essence, the AD serves to protect the flying public from the consequences of the unsafe condition. The AD also serves to protect the manufacturer from the liability that would be faced should the unsafe condition not be corrected. \n\n\tTwo commenters request that the compliance time be extended from the proposed 24 months to 36 months. One of these commenters states that such an extension will allow operators to accomplish the replacement during a regularly scheduled heavy maintenance visit and will allow time for procurement of additional parts. \n\n\tThe FAA does not concur with the commenters' request to extend the compliance time. In developing an appropriate compliance time for this action, the FAA considered not only the degree of urgency associated with addressing the subject unsafe condition, but the availability of required parts and the practical aspect of accomplishing the required replacement within an interval of time that parallels normal scheduled maintenance for the majority of affected operators. The manufacturer has advised that an ample number of required parts will be available for modification of the U.S. fleetwithin the proposed compliance period. Further, the FAA estimates that it would take approximately 2 work hours per airplane to accomplish the replacement; therefore, the FAA has determined that a heavy maintenance visit is not required to accomplish the replacement. However, under the provisions of paragraph (b) of the final rule, the FAA may approve requests for adjustments to the compliance time if data are presented to justify such an adjustment. \n\n\tOne commenter requests that the proposed rule be revised to cite the latest revision of Boeing Alert Service Bulletin 767-29A0077. The FAA concurs. Since the issuance of the proposed rule, the FAA has reviewed and approved Revision 1, dated June 8, 1995, of that Boeing alert service bulletin. This revised service bulletin is essentially identical to the original version; the only relevant change in Revision 1 is a revision to the effectivity listing that removes the airplane having serial number 565. The FAA has revised paragraph(a) of the final rule to reflect the latest revision to the alert service bulletin as an additional source of service information. The FAA has also revised the applicability of the final rule to remove serial number 565 from those Model 767 series airplanes that are subject to the AD. \n\n\tThe same commenter requests that NOTE 3 of the proposal be revised to cite the latest revision of Sundstrand Service Bulletins 730814-29-9 and 729548-29-12. The FAA concurs. The FAA has reviewed and approved Sundstrand Service Bulletin 729548-29-12, Revision 3, dated March 31, 1995; and Sundstrand Service Bulletin 730814-29-9, Revision 2, dated March 31, 1995. These revised service bulletins are essentially identical to the corresponding earlier versions, but contain certain minor editorial changes. The FAA has revised NOTE 3 of the final rule to reflect the latest revision to the service bulletins as additional sources of service information. \n\n\tSince issuance of the notice, the FAA also hasreviewed and approved Sundstrand Service Bulletin 729548-29-14, Revision 1, dated May 3, 1995, and Sundstrand Service Bulletin 730814- 29-11, Revision 1, dated May 3, 1995. These revised service bulletins are essentially identical to the corresponding earlier versions, but contain certain minor editorial changes. The FAA has revised NOTE 2 of the final rule to reflect these latest revisions to those service bulletins as additional sources of service information. \n\n\tAfter 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 with the changes previously described. The FAA has determined that these changes will neither increase the economic burden on any operator nor increase the scope of the AD. \n\n\tThere are approximately 1,215 Model 757 and 767 series airplanes of the affected design in the worldwide fleet. The FAA estimates that 582 airplanes of U.S. registry willbe affected by this AD, that it will take approximately 2 work hours per airplane to accomplish the required actions, and that the average labor rate is $60 per work hour. Required parts will be supplied by the manufacturer at no cost to the operators. Based on these figures, the total cost impact of the AD on U.S. operators is estimated to be $69,840, or $120 per airplane. \n\n\tThe total cost impact figure discussed above is 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. \n\n\tThe 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 sufficientfederalism implications to warrant the preparation of a Federalism Assessment. \n\n\tFor 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."\n\n List of Subjects in 14 CFR Part 39 \n\n\tAir transportation, Aircraft, Aviation safety, Incorporation by reference, Safety. \n\nAdoption of the Amendment \n\n\tAccordingly, pursuant to the authority delegated to me by the Administrator, the Federal Aviation Administration amends part 39 of theFederal Aviation Regulations (14 CFR part 39) as follows:\n\n PART 39 - AIRWORTHINESS DIRECTIVES \n\n\t1 The authority citation for part 39 continues to read as follows: Authority: 49 USC 106(g), 40101, 40113, 44701. § 39.13 - (Amended) \n\n\t2. Section 39.13 is amended by adding the following new airworthiness directive: