AD 97-02-19 ACTIVE

This amendment adopts a new airworthiness directive (AD), applicable to certain Boeing Model 757 and 767 series airplanes, that requires replacement of the thrust management computer (TMC) with a new TMC. This amendment is prompted by reports indicating that an uncommanded advancement of the throttle levers occurred; this condition was apparently due to a high impedance connection to the excitation phase of the servo motor. The actions specified by this AD are intended to prevent an uncommanded runaway of the autothrottle during flight or ground operations as a result of problems associated with the TMC, which could distract the crew from normal operation of the airplane or lead to an unintended speed or altitude change.

Final rule

97-02-19 BOEING: Amendment 39-9904. Docket 96-NM-125-AD. \n\n\tApplicability: Model 757 series airplanes, having line positions 001 through 716, inclusive; and Model 767 series airplanes having line positions 001 through 556 inclusive, 558 through 587 inclusive, and 589 through 615 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 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 (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. \n\n\tCompliance: Required as indicated, unless accomplished previously. \n\n\tTo prevent runaway of the autothrottle during flight or ground operations, which could distract the crew from normal operation of the airplane or lead to an unintended speed or altitude change, accomplish the following: \n\n\t(a)\tWithin 18 months after the effective date of this AD, replace the thrust management computer (TMC) with a new TMC in accordance with Boeing Alert Service Bulletin 757-22A0052, dated May 30, 1996 (for Model 757 series airplanes); or Boeing Alert Service Bulletin 767-22A0097, dated May 30, 1996 (for Model 767 series airplanes); as applicable.\n\n\t(b)\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 requests through an appropriate FAA Principal Maintenance Inspector, who may add comments and then send it to the Manager, Seattle ACO. \n\n\tNOTE 2: 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. \n\n\t(d)\tThe replacement shall be done in accordance with Boeing Alert Service Bulletin 757- 22A0052, dated May 30, 1996 (for Model 757 series airplanes); or Boeing Alert Service Bulletin 767- 22A0097, dated May 30, 1996 (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 March 4, 1997.

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 August 29, 1996 (61 FR 45373). That action proposed to require replacement of the thrust management computer (TMC) with a new TMC in the main equipment center. \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\nRequest to Clarify Description of Problem Addressed \n\n\tOne commenter requests that references in the proposal to the problems prompting the AD action be clarified. The commenter points out that the "Discussion" section of the preamble to the notice makes reference to a "defective relay within the TMC" as being the cause of the uncommanded advancement of the autothrottle lever. However, the commenter considers that statement to be inaccurate. Instead, the commenter suggests that the statement be changed to indicate that the cause is due to "high impedance connection to the excitation phase of the servo motor. The impedance can be internal to the TMC or the result of an external condition." \n\n\tThe FAA concurs that the commenter's suggested wording is more accurate. The pertinent portions of this final rule have been revised to incorporate that wording. \n\nRequest to Extend Compliance Time \n\n\tSeveral commenters request that the proposal be revised to extend the compliance time for the TMC replacement from the proposed 6 months to as much as 24 months. These commenters are concerned that there will be a problem with the availability of ample parts to retrofit the affected U.S. fleet within the proposed compliance time. \n\n\tThe FAA concurs that the compliance time can be extended somewhat. Input from the TMC vendor indicates that there are 1,800 units that will need to be modified and the turn-around time for doing that is 45 days for each unit; based on current production rates, it will be logistically impossible for the vendor to meet a 6-month schedule. In light of this information, the FAA has determined that the compliance time can be extended to 18 months without adversely compromising safety. Paragraph (a) of the final rule has been revised accordingly. \n\nRequest to Clarify References to E1-3 Shelf \n\n\tOne commenter, Boeing, points out that the references in the proposal to the TMC being located in the "E1-3 shelf of the main equipment center" are incorrect with regard to the Model 757. Further, this commenter states that the Boeing service bulletins referenced in the proposal adequately describe the correct replacement instructions for TMC's in both the Model 757 and 767, including the location of the TMC; therefore, any reference to the specific shelf number is not needed. The commenter suggests that those references be deleted from the final rule. \n\n\tThe FAA concurs. To avoid any confusion on the part of affected operators, the FAA has deleted all references to the "E1-3 shelf" from the final rule. \n\nRequest to Revise Cost Impact Information \n\n\tSeveral commenters request that the cost impact information, which appeared in the preamble to the proposal, be revised. These commenters point out that the cost figures presented did not include the per-unit modification cost changed by the manufacturer or approved repair station for modification of the TMC. One commenter, Lockheed-Martin, indicates that some operators, if they have the tooling capability, can perform the modification themselves with a $104 kit obtained from the TMC manufacturer; Lockheed-Martin charges $1,000 per unit to modify the TMC. Other commenters present cost estimates per airplane that range from $1,780 to $2,400. Two commenters also factor in the cost of purchasing an additional new TMC unit as a "seed unit" for implementing the change in their fleets, resulting in cost estimates ranging from $45,530 to $60,000. \n\n\tThe FAA concurs that the cost impact information should be revised to reflect more up-to- date and accurate information. While any operator certainly has the option to purchase new TMC's to meet the intent of this AD, the FAA does not consider that to be economically feasible for the majority of the affected fleet. However, based on figures provided by the commenters, the FAA finds that an appropriate estimate of costs is $2,400 per airplane; this represents 3 work hours to replace the unit (at an average labor charge of $60 per work hour) and an average of $2,220 for the required (modified) replacement parts. The cost impact information, below, has been revised accordingly. \n\nConclusion \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\nCost Impact \n\n\tThere are approximately 1,339 Boeing Model 757 and 767 series airplanes of the affected design in the worldwide fleet; this number represents 716 Model 757 series airplanes and 623 Model 767 series airplanes. Of the total number, the FAA estimates that 558 airplanes of U.S. registry will be affected by this AD; this number represents 356 Model 757 series airplanes and 202 Model 767 series airplanes.\n\n\tThe required replacement will take approximately 3 work hours per airplane to accomplish, at an average labor rate of $60 per work hour. The cost of the required (modified) replacement units would differ depending upon whether the operator, airframe manufacturer, repair station, or TMC manufacturer performs the modification of the TMC; in any case, the FAA estimates that the average cost for these replacement units will be $2,220 per airplane. Based on these figures, the cost impact of the AD on U.S. operators is estimated to be $1,339,200, or $2,400 per airplane. \n\n\tThe 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\nRegulatory Impact \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. \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:

The service information referenced in this AD may be obtained from Boeing\nCommercial Airplane Group, P.O. Box 3707, Seattle, Washington 98124-2207. This information may be examined at the Federal Aviation Administration (FAA), Transport Airplane Directorate, Rules Docket, 1601 Lind Avenue, SW., Renton, Washington; or at the Office of the Federal Register, 800 North Capitol Street, NW., suite 700, Washington, DC.

Forrest Keller, Senior Aerospace Engineer, Systems and Equipment Branch, ANM-130S, FAA, Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, Washington; telephone (206) 227-2790; fax (206) 227-1181.