AD 96-23-05

This amendment adopts a new airworthiness directive (AD), applicable to certain Boeing Model 747 series airplanes, that requires repetitive inspections to detect cracks and/or corrosion of the girt bar support fitting at certain main entry doors (MED); and repair or replacement of the support fitting. This amendment also provides for various terminating actions for the repetitive inspections. This amendment is prompted by reports that, during scheduled deployment tests of main entry door slides, corrosion was found on the floor structure supports for the escape slides of the main deck entry doors on these airplanes. The actions specified by this AD are intended to prevent such corrosion, which could result in separation of the escape slide from the lower door sill during deployment, and subsequently prevent proper operation of the escape slides at the main entry doors during an emergency.

Final rule

96-23-05 BOEING: Amendment 39-9810. Docket 94-NM-221-AD. \n\n\tApplicability: Model 747 series airplanes; line numbers 1 through 868 inclusive, excluding freighters and special freighters; certificated in any category. \n\n\tNOTE 1: The requirements of this AD are not applicable to doors where an escape slide or slide/raft is not installed or is not used for passenger egress (such as a deactivated door 3, at doors 4 and/or 5 of an airplane being operated in the "combi" configuration, or any door not used for passenger egress on a convertible). The requirements of this rule become applicable at the time when an escape slide or slide/raft is installed on such doors, or when such doors are activated and/or converted for passenger use. The requirements also become applicable at the time an airplane operating in an all-cargo configuration is converted to a passenger or passenger/cargo configuration. \n\n\tNOTE 2: 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 (n) 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. \n\n\tCompliance: Required as indicated, unless accomplished previously. \n\n\tTo detect and correct corrosion on girt bar support fittings, which could result in separation of the escape slide from the lower door sill during deployment, and subsequently prevent operation of the escape slides at the main entry doors during an emergency, accomplish the following: \n\n\t(a)\tFor airplanes equipped with Main Entry Door (MED) 1: Prior to the accumulation of 16 years of service since date of manufacture of the airplane, or within 18 months after the effective date of this AD, whichever occurs later, perform a detailed visual inspection to detect cracking and/or corrosion of the girt bar support fitting at the left and right MED 1, in accordance with Boeing Service Bulletin 747-53A2378, Revision 1, dated March 10, 1994. \n\n\t(b)\tIf no cracking or corrosion is found during the inspection required by paragraph (a) of this AD, prior to further flight, accomplish either paragraph (b)(1) or (b)(2) of this AD, in accordance with the applicable instructions specified in Boeing Service Bulletin 747-53A2378, Revision 1, dated March 10, 1994. \n\n\t\t(1)\tInstall a new fitting with new fasteners, and reinstall the threshold assembly with new corrosion-resistant fasteners, in accordance with the service bulletin. After these actions are accomplished, no further action is required by paragraph (b) of this AD. Or \n\n\t\t(2)\tReinstall the threshold assembly with corrosion-resistant fasteners, in accordance with the service bulletin. Thereafter, repeat the inspection required by paragraph (a) of this AD at intervals not to exceed 6 years. \n\n\t(c)\tIf any cracking is found during the inspection required by paragraph (a) or (b)(2) of this AD, prior to further flight, install a new fitting with new fasteners, and reinstall the threshold assembly with new corrosion-resistant fasteners, in accordance with Boeing Service Bulletin 747- 53A2378, Revision 1, dated March 10, 1994. After these actions are accomplished, no further action is required by this paragraph. \n\n\t(d)\tIf any corrosion is found during the inspection required by paragraph (a) or (b)(2) of this AD, prior to further flight, accomplish either paragraph (d)(1) or (d)(2) of this AD, in accordance with Boeing Service Bulletin 747-53A2378, Revision 1, dated March 10, 1994.(1)\tInstall a new fitting with new fasteners, and reinstall the threshold assembly with new corrosion-resistant fasteners in accordance with the service bulletin. After these actions are accomplished, no further action is required by this paragraph. Or \n\n\t\t(2)\tBlend out corrosion in accordance with the service bulletin. \n\t\t\t(i)\tIf blend out of corrosion is beyond 10 percent of original thickness or any crack is found during accomplishment of the blend out procedures, install a new fitting with new fasteners, and reinstall the threshold assembly with new corrosion-resistant fasteners, in accordance with the service bulletin. After these actions are accomplished, no further action is required by this paragraph. \n\n\t\t\t(ii)\tIf blend out of corrosion does not exceed 10 percent of original material thickness, accomplish either paragraph (d)(2)(ii)(A) or (d)(2)(ii)(B) of this AD: \n\t\t\t\t(A)\tInstall a new fitting with new fasteners, and reinstall threshold assembly with new corrosion-resistant fasteners, in accordance with the service bulletin. After these actions are accomplished, no further action is required by this paragraph. Or \t\t\n\t\t(B)\tInstall the repaired fitting with new fasteners and reinstall the threshold assembly with corrosion-resistant fasteners, in accordance with the service bulletin. Thereafter, repeat the inspection, and corrective actions as necessary, required by paragraph (a) of this AD at intervals not to exceed 6 years. \n\n\t(e)\tFor airplanes equipped with Main Entry Doors (MED) 2, 4, and/or 5 (MED 2, 3, and/or 4 on Model 747SP series airplanes): Prior to the accumulation of 10 years of service since date of manufacture of the airplane, or within 18 months after the effective date of this AD, whichever occurs later, perform a detailed visual inspection to detect cracking and/or corrosion of the girt bar support fitting at the left and right MED 2, 4, and 5 (MED 2, 3, and 4 on Model 747SP series airplanes), in accordance with Boeing Service Bulletin 747-53A2378, Revision 1, dated March 10, 1994. \n\n\t(f)\tIf no cracking or corrosion is found during the inspection required by paragraph (e) of this AD, prior to further flight, accomplish either paragraph (f)(1) or (f)(2) of this AD, in accordance with the applicable instructions in Boeing Service Bulletin 747-53A2378, Revision 1, dated March 10, 1994. \n\n\t\t(1)\tRemove the inspected fitting and reinstall it with a new coat of primer and new fasteners; and reinstall the threshold assembly with new corrosion-resistant fasteners; in accordance with the service bulletin. After these actions are accomplished, no further action is required by this paragraph. Or \n\n\t\t(2)\tReinstall the serrated plate assembly and the girt bar floor fitting with corrosion- resistant fasteners, in accordance with the service bulletin. Thereafter, repeat the inspection required by paragraph (e) of this AD at intervals not to exceed 6 years. \n\n\t(g)\tIf any cracking is found during the inspection required by paragraph (e) or (f)(2) of this AD, prior to further flight, install a new fitting with new fasteners, and reinstall the threshold assembly with new corrosion-resistant fasteners, in accordance with Boeing Service Bulletin 747- 53A2378, Revision 1, dated March 10, 1994. After these actions are accomplished, no further action is required by this paragraph.\n\n\t(h)\tIf any corrosion is found during the inspection required by paragraph (e) or (f)(2) of this AD, prior to further flight, accomplish either paragraph (h)(1) or (h)(2) of this AD, in accordance with Boeing Service Bulletin 747-53A2378, Revision 1, dated March 10, 1994. \n\n\t\t(1)\tInstall a new fitting with new fasteners, and reinstall the threshold assembly with new corrosion-resistant fasteners, in accordance with the service bulletin. After these actions are accomplished, no further action is required by this paragraph. Or \n\n\t\t(2)\tBlend out corrosion in accordance with the service bulletin. \n\n\t\t\t(i)\tIf blend out of corrosion is beyond 10 percent of original thickness or any crack is found during accomplishment of the blend out procedures, install a new fitting with new fasteners, and reinstall the threshold assembly with new corrosion-resistant fasteners, in accordance with the service bulletin. After these actions are accomplished, no further action is required by this paragraph. \n\n\t\t\t(ii)\tIf blend out of corrosion does not exceed 10 percent of original material thickness, install the repaired fitting with new fasteners, and reinstall the threshold assembly with new corrosion-resistant fasteners, in accordance with the service bulletin. After these actions are accomplished, no further action is required by this paragraph. \n\n\t(i)\tFor airplanes equipped with Main Entry Door (MED) 3 (this paragraph does not apply to Model 747SP series airplanes): Prior to the accumulation of 16 years of service since date of manufacture of the airplane, or within 18 months after the effective dateof this AD, whichever occurs later, perform a detailed visual inspection to detect cracking and/or corrosion of the girt bar support angles at the left and right MED 3, in accordance with Boeing Service Bulletin 747-53A2378, Revision 1, dated March 10, 1994.\n\n\t(j)\tIf no cracking or corrosion is found during the inspection required by paragraph (i) of this AD, prior to further flight, accomplish either paragraph (j)(1) or (j)(2) of this AD in accordance with the applicable instructions in Boeing Service Bulletin 747-53A2378, Revision 1, dated March 10, 1994.\n\n\t\t(1)\tRemove inspected angle and reinstall it with a new coat of primer and new fasteners; and reinstall the threshold assembly with new corrosion-resistant fasteners, in accordance with the service bulletin. After these actions are accomplished, no further action is required by this paragraph. Or \n\n\t\t(2)\tReinstall the corner scuff plate and the threshold apron with corrosion-resistant fasteners, in accordance with the service bulletin. Thereafter, repeat the inspection required by paragraph (i) of this AD at intervals not to exceed 6 years. \n\n\t(k)\tIf any crack common to the support angles is found during the inspection required by paragraph (i) or (j)(2) of this AD, prior to further flight, accomplish the actions specified in paragraph (k)(1) or (k)(2), as applicable, in accordance with Boeing Service Bulletin 747-53A2378, Revision 1, dated March 10, 1994: \n\n\t\t(1)\tInstall the new angles with new fasteners, and reinstall the threshold assembly with new corrosion-resistant fasteners. After these actions are accomplished, no further action is required by this paragraph of this AD. \n\n\t\t(2)\tFor any cracking found only in the corner casting as specified in the service bulletin, accomplish either paragraph (k)(2)(i) or (k)(2)(ii) prior to further flight: \n\n\t\t\t(i)\tReplace the corner casting in accordance with the service bulletin. Or \n\n\t\t\t(ii)\tRepair the cracked part in accordance with a method approved by the Manager, Seattle Aircraft Certification Office (ACO), FAA, Transport Airplane Directorate. Refer to paragraph (n) of this AD for the appropriate procedure for seeking such an approval. (This option is provided in order to give operators time to obtain a replacement corner casing without grounding an airplane.) This repair is considered temporary action only; replacement of the corner casting eventually must be accomplished in accordance with a schedule prescribed by the Manager, Seattle ACO. \n\n\t(l)\tIf any corrosion is found during the inspection required by paragraph (i) of this AD, prior to further flight, accomplish either paragraph (l)(1) or (l)(2) of this AD, in accordance with Boeing Service Bulletin 747-53A2378, Revision 1, dated March 10, 1994. \n\n\t\t(1)\tInstall the new angles with new fasteners, and reinstall the threshold assembly with new corrosion-resistant fasteners, in accordance with the service bulletin. After these actions are accomplished, no furtheraction is required by this paragraph. Or\n \n\t\t(2)\tBlend out corrosion in accordance with the service bulletin. \n\n\t\t\t(i)\tIf blend out of corrosion is beyond 10 percent of original thickness, or if any crack common to the support angles is found during accomplishment of the blend out procedures, install the new angles with new fasteners, and reinstall the threshold assembly with new corrosion- resistant fasteners, in accordance with the service bulletin. After these actions are accomplished, no further action is required by this paragraph. \n\n\t\t\t(ii)\tIf blend out of corrosion does not exceed 10 percent of original material thickness, install the repaired angles with new fasteners, and reinstall the threshold assembly with new corrosion-resistant fasteners, in accordance with the service bulletin. After these actions are accomplished, no further action is required by this paragraph. \n\n\t(m)\tInstallation of a girt bar support fitting in accordance with Boeing Service Bulletin 747-25A2831, dated August 29, 1991, is considered acceptable for compliance with the requirements of this AD for each affected fitting location. \n\n\t(n)\tAn 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 request through an appropriate FAA Principal Maintenance Inspector, who may add comments and then send it to the Manager, Seattle ACO. \n\n\tNOTE 3: 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(o)\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. \n\n\t(p)\tThe actions shall be done in accordance with Boeing Service Bulletin 747-53A2378, Revision 1, dated March 10, 1994. 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(q)\tThis amendment becomes effective on December 16, 1996.

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 747 series airplanes was published in the Federal Register on February 8, 1995 (60 FR 7482). That action proposed to require repetitive detailed visual inspections to detect cracks and/or corrosion of the girt bar support fitting at MED's 1 through 5, inclusive; repair or replacement of the support fitting; and reinstallation of the threshold assembly. The action also proposed to require, under certain conditions, replacing the support fittings with new support fittings having new fasteners; refinishing uncorroded support fittings; and removing the corrosion and refinishing corroded support fittings. When accomplished, these latter actions will constitute terminating action for the repetitive visual inspections. \n\n\tInterested persons have been afforded an opportunity to participate in the making of this amendment. \n\n Due consideration has been given to the comments received.\n\nSupport for the Proposal \n\n\tOne commenter supports the proposal. \n\nRequest for Clarification of Requirements for Different Configurations of Airplanes \n\n\tOne commenter requests that the proposed rule be revised to clarify the actions that are required for variously configured airplanes. The FAA has considered each of the commenter's requests, which are iterated below: \n\n\tDoors with Escape Slide/Raft Not Installed or Deactivated. This commenter requests that the proposal clarify instructions for addressing airplanes having doors where an escape slide or slide/raft is not installed or is not being used for passenger egress, such as a deactivated door 3, at doors 4 and/or 5 of an airplane being operated in the "combi" configuration, or any door not used for passenger egress on a convertible. The commenter suggests that, for these airplanes, the proposed requirements of the rule be "postponed" until such time that any door was reactivated for passenger egress use. \n\n\tThe FAA concurs with the commenter's suggestion, and has added a NOTE in the final rule to indicate this. \n\n\tAirplanes with Improved Door Fittings Installed. This commenter requests that the proposal be revised to indicate that airplanes on which support fittings have been replaced in accordance with Boeing Alert Service Bulletin 747-25A2831, dated August 29, 1991, require no further action at the replaced fitting locations. \n\n\tThe FAA concurs. The service bulletin mandated by this AD replaces Boeing Alert Service Bulletin 747-25A2831. The FAA has determined that the modifications specified in Alert Service Bulletin 747-25A2831 are acceptable for compliance with this AD. This AD requires no further action on fittings that were replaced or modified in accordance with that service bulletin. This final rule has been revised to include a new paragraph (m), which clarifies this issue. \n\n\tAirplanes with Main Entry Door (MED) 1 Fittings. This commenter states that proposed paragraph (b) should be more specific as to the requirements for certain airplanes with Main Entry Door 1. As proposed, that paragraph would require that, if no corrosion or cracking was found during the initial inspection, operators may accomplish either one of two actions: \n\n\t1. install a new fitting with new fasteners and reinstall the threshold assembly with new corrosion-resistant fasteners; or \n\n\t2. reinstall the threshold assembly with new corrosion-resistant fasteners and, thereafter, repetitively inspect the girt bar support fittings. \n\n\tHowever, this commenter points out that for certain airplanes, line numbers 12 through 36, with MED 1 support fittings specified in Figure 3, Details II, III, or IV, of Boeing Service Bulletin 747-53A2378, the instructions in the service bulletin specify that these fittings can only be replaced (per item 1, above). \n\n\tThe FAA acknowledges that the commenter is correct with regard to these airplanes, and that the wording of the notice was not clear. By referring to Boeing Service Bulletin 747-53A2378, Revision 1, the FAA intended that operators follow the appropriate actions specified in it. The FAA intended that, based on the configuration of the airplane, operators would accomplish the actions that are applicable to their airplanes, as defined in the service bulletin. To make this eminently clearer, the FAA has revised paragraph (b) of the final rule to clarify that operators are to accomplish the action in accordance with the "applicable instruction" in the service bulletin; by doing so, operators will be directed to that portion of the service bulletin that contains the instructions applicable for their specific airplanes. \n\n\tDifferent Configurations of Airplanes Have Different MED Numbers. This commenter requests that the proposal be revised to clarify the fact that: \n\n\t\tModel 747 airplanes that are not "SP's" have MED 1, 2, 3, 4, and 5; \n\t\tModel 747SP airplanes have MED 1, 2, 3, and 4. \n\n\tHowever, MED 3 and 4 on the Model 747SP correspond in their configuration to MED 4 and 5 on the non-SP models. In light of this, the commenter requests that the proposed requirements of paragraph (e) be clarified to account for these various configurations. Additionally, proposed paragraph (i), which relates to MED 3, should be revised to indicate that its requirements are applicable only to non-SP airplanes. In addition, the commenter points out that the referenced Boeing Service Bulletin makes this differentiation in its relevant instructions. \n\n\tThe FAA concurs and has revised paragraphs (e) and (i) of the final rule to specify the model and corresponding door number of those airplanes subject to the requirements of those paragraphs. \n\n\tAirplanes with Different Configuration at MED 5. This commenter states that Boeing Service Bulletin 747-53A2378, Revision 1, does not address the configuration of some airplanes at MED 5 where the support fitting is more like that at MED 1 than at MED 2 and 4. The commenter states that the service bulletin is being revised to contain instructions that will address the access, inspection, removal, and replacement of this different type of MED 5 fitting. The commenter requests that the proposed rule be revised to contain those new instructions. \n\n\tThe FAA concurs that some additional procedures may be necessary for those airplanes. However, at this time, the revised service bulletin referred to by the commenter has not been approved and is not available. When it is available, the FAA may consider requests for approval of the use of it as an alternative method of compliance with the requirements of this AD, as provided by paragraph (n).\n\nRequest to Make AD Requirements Parallel to Service Bulletin Instructions \n\n\tOne commenter suggests that, if the requirements of the AD are identical to the instructions of the Boeing Service Bulletin 747-53A2378,Revision 1, then the AD should merely state this, instead of reiterating each requirement. Another commenter, the airframe manufacturer, requests that, if the intent of the proposed AD is to mandate the same actions described in that service bulletin, then the wording of certain portions of the proposal must be clarified. \n\n\tIn general, the FAA responds by stating that it did not intend for requirements of this AD to deviate significantly from the service bulletin instructions. However, certain portions of the AD, such as the initial compliance time and other items explained elsewhere in this preamble, do differ from the service bulletin. In light of this, a statement indicating that the "AD is identical to the service bulletin" would be incorrect. As for the suggested wording changes relative to this issue, each is discussed below: \n\n\tActions When Little Corrosion is Found. The commenter requests that paragraph (d)(2)(ii) be clarified by reordering the required steps to match what is specified in the referenced service bulletin. As written, the proposed paragraph could be interpreted to mean that operators must first reinstall a repaired fitting, and then immediately follow that step by installing a new fitting (as specified in proposed paragraph (d)(2)(ii)(A)). The commenter points out that, if the intent of the paragraph is to follow the logical sequence of steps as defined in the service bulletin, paragraph (d)(2)(ii) should be changed as follows: \n\n\t"(ii) If blend out of corrosion does not exceed 10 percent of original material thickness, accomplish either paragraph (d)(2)(ii)(A) or (d)(2)(ii)(B) of this AD: \n\n\t(A) Install a new fitting with new fasteners, and reinstall threshold assembly with new corrosion-resistant fasteners, in accordance with the service bulletin. After these actions are accomplished, no further action is required by paragraph (d) of this AD. Or \n\n\t(B) Install the repaired fitting with new fasteners and reinstall thethreshold assembly with corrosion-resistant fasteners, in accordance with the service bulletin. Repeat the inspection required by paragraph (a) of this AD thereafter at intervals not to exceed 6 years." \n\n\tThe FAA concurs. The intent of the requirements of that paragraph was that operators would follow the procedures specified in the referenced service bulletin. The FAA finds that the change in wording suggested by the commenter's suggestion will help to clarify these instructions. The final rule has been revised accordingly. \n\n\tInstalling New Fasteners after Primer Application. The commenter points out that proposed paragraph (f) would require removal of the inspected fitting and reinstallation of it with a new coat of primer. Likewise, proposed paragraph (j) would require the removal of the inspected girt bar support angle, and reinstallation of it with a new coat of primer. However, the commenter requests that these paragraphs be clarified to state that when the fitting or angle is reinstalled, new fasteners must be used. This is specified in the service bulletin, but is not called out precisely in the proposed rule; therefore, the commenter considers that operators may be unsure as to whether or not new fasteners must be used. \n\n\tThe FAA concurs that clarification is necessary. As stated previously, the intent of this AD is to parallel the actions described in the service bulletin. In the particular case of proposed paragraphs (f) and (j), the FAA assumed that operators would use new fasteners when reinstalling the subject components since that action is specified in the instructions laid out in the service bulletin, and since those paragraphs state that the required actions are to be accomplished "in accordance with" that service bulletin. However, the FAA acknowledges that this may not be clear to affected operators. Therefore, the FAA has revised the two paragraphs to include a statement indicating the installation of new fasteners is a necessary part of the process of reinstalling the components. \n\n\tCorrect Terminology of Inspection Item. The commenter requests that proposed paragraph (i) be corrected to indicate that the inspection is required to be performed on the "girt bar support angles," not the "girt bar support fitting." The follow-on corrective actions specified in proposed paragraph (j) and (k) correctly refer to the "support angles." \n\n\tThe FAA acknowledges this error and has corrected the terminology in paragraph (i) accordingly. \n\n\tAddressing Cracking at Support Angles. This commenter requests that proposed paragraph (k) be revised to clarify that the cracking that is to be addressed is any that is found "common to the support angles." Additionally, proposed paragraph (l)(2)(i), which is a follow-on action to paragraph (k), should be revised to specify this same language. The commenter points out that this language is used in the referenced Boeing service bulletin and likewise should be used in the AD to avoid confusion for operators. \n\n\tThe FAA concurs, and has revised paragraph (k) and (l)(2)(i) of the final rule accordingly. \n\n\tInspections of the Support Angles Corner Castings. The commenter requests that paragraph (k) be clarified to include the instructions for addressing cracking that is found in the corner casting of the support angles during the inspection required by proposed paragraph (i). The commenter points out that special instructions are contained in the referenced Boeing service bulletin to address this cracking, but these instructions were not specified in the proposal. The service bulletin provides for repair of cracks found in corner castings, rather than the immediate installation of new angles and fasteners if such cracking is found, as would be required by the proposal. The commenter maintains that allowing operators to repair these cracks rather than replace the components would provide operators with time to obtain the replacement corner castingwithout having to ground the airplane. A repaired corner casting would be structurally acceptable, since it is not primary load carrying structure. \n\n\tThe FAA concurs that this repair action should be provided as an option to replacement in cases of cracking in the corner casting. However, the service bulletin does not sufficiently describe all of the actions that are necessary to repair the part. The FAA considers that cracked corner castings should be addressed on a case-by-case basis. Therefore, operators that prefer to repair a cracked corner casting, as an option to replacing it, should request an alternative method of compliance with this portion of the AD, as provided by paragraph (n). Paragraph (k)(2) of this final rule has been revised accordingly. \n\nRequests to Extend the Compliance Time \n\n\tSeveral commenters request that the proposal be revised to require operators to perform the initial visual inspections prior to an airplane accumulating 16 years of service or18 months -- rather than the proposed 15 months -- after the effective date of the final rule, whichever is later: \n\n\t1. One of these commenters states that the Corrosion Prevention and Control Program, which was mandated by AD 90-25-05 (amendment 39-6790, (55 FR 31401, November 27, 1990)), already requires inspections in this area at 18-month intervals. Allowing the proposed inspections to be accomplished at this same interval would reduce the economic burden on affected operators, since they would not have to special schedule airplanes for those inspections. \n\n\t2. Another commenter states that some of the proposed inspections will necessarily require that the galley be removed from the airplanes. This removal activity is so extensive that it is normally accomplished at main base locations when airplanes are undergoing their regularly scheduled 18-month "C" check activity. By extending the proposed compliance time to correspond with this activity, operators would not be required to schedule special times for the accomplishment of this inspection, at considerable additional expense. Additionally, it will allow the inspections and any necessary installation or repair to be performed at a main maintenance base where special equipment and trained maintenance personnel will be available, if necessary. \n\n\t3. Finally, another commenter points out that the lead time for obtaining some of the parts that may be necessitated by the proposed actions may take as long as 37 months; the proposed 15- month compliance time would make it very difficult to place a parts order in time to comply with the AD.\n\n\tThe FAA concurs that the compliance time may be extended to 18 months. In consideration of all of the factors raised by the commenters, as well as the demonstrated reliability and safety features of the Model 747, and the likelihood of having to perform an emergency evacuation during the compliance period, the FAA finds that extending the compliance time by a modest 3 additional months will have an insignificant effect on safety, while significantly reducing the burden on the affected operators.\n\nRequest to Shorten the Compliance Time \n\n\tOne commenter supports the proposal, but requests that it be revised to require operators to perform the initial visual inspections prior to an airplane accumulating 16 years of service or 6 months -- rather than the proposed 15 months -- after the effective date of the final rule, whichever is later. The commenter provided no technical justification for this request, but indicated that it was based on its general feeling that the proposed AD is vital to the safety and well-being of the traveling public. This commenter considers the problem addressed to be an extremely hazardous situation that could endanger the lives of both passengers and cabin crew. \n\n\tThe FAA does not concur with this commenter's request. While the FAA does not intend in any way to depreciate the commenter's statements relative tothe unsafe condition, as discussed previously, the FAA is obligated to weigh many other factors in addition to safety when developing an appropriate compliance time. In the case of this AD, the FAA considered not only the safety implications, but normal maintenance schedules for timely accomplishment of the actions, parts availability, recommendations of the airframe manufacturer based on crack analysis and service reports, the reliability of the affected fleet, and the probability of an incident occurring that is associated with the problem addressed by the AD. In light of all of these factors, the FAA has determined that a reduction of the compliance time is not warranted. \n\nRequest to Clarify Replacement Requirements \n\n\tOne commenter requests that the proposal be revised to clarify that the replacement of fittings or fasteners is required only if cracking or corrosion is found. The commenter states that, as the proposal is written, if an inspection shows that no cracking or corrosion is present, an operator may accomplish one of two possible actions: \n\n\t1. install a new fitting with new fasteners in the cracking location; or \n\t2. reinstall corrosion-resistant fasteners in the threshold assembly and repeat the inspection thereafter every 6 years. \n\n\tThe commenter states that one could conclude from the wording of this second option that the operators would have to install corrosion-resistant fasteners every six years, regardless of whether or not corrosion was present. If this is not the FAA's intent, the commenter requests that this requirement be clarified. \n\n\tThe FAA concurs that clarification is necessary. It is not the FAA's intent that fasteners be replaced at every inspection, regardless of whether corrosion is present or not. The only time that the replacement must be accomplished is if corrosion is detected during the inspection. \n\nThe FAA has added wording to the appropriate portions of the final rule to clarify this requirement.Conclusion\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 not increase the economic burden on any operator. Additionally, these changes do not increase the scope of the AD, and are a logical outgrowth of the notice that does not necessitate providing an additional opportunity for public comment.\n\n Cost Impact \n\n\tThere are approximately 868 Boeing Model 747 series airplanes of the affected design in the worldwide fleet. The FAA estimates that 169 airplanes of U.S. registry will be affected by this AD. \n\n\tThe inspection of MED 1 will take approximately 81 work hours per door to accomplish, at an average labor rate of $60 per work hour. Based on these figures, the cost impact of this required inspection on U.S. operators is estimated to be $4,860 per door.The inspection of MED's 2, 4, and 5 (MED 2, 3, and 4 on Model 747 SP series airplanes) will take approximately 7 work hours per door to accomplish, at an average labor rate of $60 per work hour. Based on these figures, the cost impact of this required inspection on U.S. operators is estimated to be $420 per door. \n\n\tThe inspection of MED 3 would take approximately 13 work hours per door to accomplish, at an average labor rate of $60 per work hour. \n\nBased on these figures, the cost impact of this required inspection on U.S. operators is estimated to be $780 per door. \n\n\tThe replacement of both support fittings will take approximately 37 work hours per door to accomplish, at an average labor rate of $60 per work hours. Based on these figures the cost impact of the required replacement on U.S. operators is estimated to be $2,200 per door. \n\n\tThe cost impact figures discussed above is based on assumptions that no operator has yet accomplished any of the requirements of this ADaction, 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 sufficient federalism 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 the Federal 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 U.S.C. 106(g), 40113, 44701. § 39.13 - (Amended) \n\t2. Section 39.13 is amended by adding the following new airworthiness directive: