Discussion \n\n\n\tThe FAA issued a notice of proposed rulemaking (NPRM) to amend 14 CFR part 39 by adding an AD that would apply to certain The Boeing Company Model 727 airplanes, Model 757 airplanes, and Model 767-200, - 300, -300F, and -400ER series airplanes. The NPRM published in the Federal Register on July 9, 2019 (84 FR 32667). The NPRM was prompted by reports of nuisance stick shaker activation while the airplane accelerated to cruise speed at the top of climb. The NPRM was also prompted by an investigation of those reports that revealed that the AOA sensor vanes could not prevent the build-up of ice, causing the AOA sensor vanes to become immobilized, which resulted in nuisance stick shaker activation. The NPRM proposed to require a general visual inspection of the AOA sensors for certain AOA sensors, and replacement of affected AOA sensors. \n\tThe FAA is issuing this AD to address ice build-up in the AOA sensor faceplate and vane, which may immobilize the AOA sensor vanes, and could result in inaccurate or unreliable AOA sensor data being transmitted to airplane systems and consequent loss of controllability of the airplane. \n\nChanges Since the NPRM Was Issued \n\n\n\tThe FAA has reviewed Boeing Alert Service Bulletin 727-34A0247, Revision 1, dated October 1, 2019 (the FAA referred to Boeing Alert Service Bulletin 727-34A0247, dated January 2, 2019, as an appropriate source of service information for accomplishing the actions specified in the NPRM) and have revised this AD to refer to Boeing Alert Service Bulletin 727-34A0247, Revision 1, dated October 1, 2019. This service information adds airplanes to the effectivity, but specifies that no additional work is needed if the actions in Boeing Alert Service Bulletin 727-34A0247, dated January 2, 2019, have been accomplished. The FAA has added paragraph (i) to this AD to provide credit for actions done prior to the effective date of this AD using Boeing Alert Service Bulletin 727-34A0247, dated January 2, 2019. Subsequent paragraphs have been redesignated accordingly. \n\tAlthough Boeing Alert Service Bulletin 727-34A0247, Revision 1, dated October 1, 2019, adds airplanes to the effectivity, the FAA has not added those airplanes to the applicability of this AD. In paragraph (c) of this AD, the FAA refers to the airplanes identified in Boeing Alert Service Bulletin 727-34A0247, Revision 1, dated October 1, 2019, except for the additional airplanes (variable numbers QB065, QD191, QD192, QD402, QD403, QD407, and QD410). Adding airplanes to the applicability of this AD would necessitate (under the provisions of the Administrative Procedure Act) reissuing the notice, reopening the comment period, considering additional comments subsequently received, and eventually issuing a final rule. In consideration of the urgency of the unsafe condition identified in this final rule, the FAA has determined that delay of this final rule is not appropriate. However, the FAA might consider further rulemaking on this issue to address the additional airplanes. \n\nComments \n\n\n\tThe FAA gave the public the opportunity to participate in developing this final rule. The following presents the comments received on the NPRM and the FAA's response to each comment. \n\nEffect of Winglets on Accomplishment of the Proposed Actions \n\n\n\tAviation Partners Boeing (APB) stated that they have reviewed the NPRM and have determined that the installation of winglets per Supplemental Type Certificate (STC) ST01518SE (for Model 757 airplanes) and STC ST01920SE (for Model 767 airplanes) do not affect the accomplishment of the manufacturer's service instructions. \n\tThe FAA agrees with the commenter that STC ST01518SE and STC ST01920SE do not affect the accomplishment of the manufacturer's service instructions. Therefore, the installation of STC ST01518SE or STC ST01920SE does not affect the ability to accomplish the actions required by this AD. The FAA has not changed this AD in this regard. \n\nRequest To Reduce Compliance Time \n\n\n\tThe Air Line Pilots Association, International (ALPA) requested the compliance time in the proposed AD be shortened from within 36 months after the effective date of this AD to within 24 months after the effective date of this AD for all airplanes. The ALPA stated that it agrees with the intent of the proposed AD, but does not agree that a 36-month compliance time is sufficient when considering the publication dates of the service information, the low estimated time to complete the repairs, and the high risk associated with inaccurate AOA readings and nuisance stick shaker indications. \n\tThe FAA does not agree with the request. The FAA has determined that the compliance time specified in this AD for each airplane model will accommodate the time necessary to accomplish the actions required by this AD and maintain an adequate level of safety. In addition, the commenter did not provide adequate data to justify a shortened compliance time. Lastly, the suggested compliance time change would alter the requirements of this AD to be more restrictive, so additional rulemaking would be required, ultimately delaying issuance of the AD. The FAA finds that delaying this action is inappropriate in light of the identified unsafe condition. However, if additional data are presented that would justify a shorter compliance time, the FAA may consider further rulemaking on this issue. The FAA has not changed this AD in this regard. \n\nRequest To Extend Compliance Time \n\n\n\tAmerican Airlines (AAL) and United Airlines (UAL) requested that the FAA extend the compliance time for the Boeing Model 767 fleet from within 36 months or 3,470 flight hours (FH) after the effective date of this AD, whichever occurs first, to match the compliance time of the Boeing Model 757 fleet, which is within 36 months or 9,960 FH after the effective date of this AD, whichever occurs first. AAL reasoned that the Boeing Model 757 and 767 fleets share the same parts for both the AOA sensors and air data computers and operate similar missions with similar cold-soak times on the AOA vanes, and argued that the risk should be the same. AAL asserted that matching the FH compliance times will ensure that accomplishing this proposed AD can be effectively and economically planned, while allowing for the components to be handled the same regardless of fleet. AAL concluded this \n\n((Page 71780)) \n\nmethod would maintain an equivalent level of safety. \n\tUAL also pointed out that UAL's Boeing Model 757 and 767 fleets are equipped with equivalent AOA sensors and air data computers, and the operation and cold-soak times of the AOA sensors are the same. UAL argued that changing the FH compliance time for Model 767 airplanes to match the FH compliance time for Model 757 airplanes would provide an equivalent level of safety, stating that the AOA sensors of both airplane models are exposed to the same adverse conditions in the air and on the ground. \n\tThe FAA does not agree with the request. The FAA has determined that the flight-hour compliance times identified in the service information, without a time threshold, will not ensure that the identified unsafe condition is addressed in a timely manner. In developing an appropriate compliance time for this AD, the FAA considered the degree of urgency associated with addressing the subject unsafe condition, the average utilization of the affected fleet, and the time necessary to perform the modifications. In light of all of these factors, the FAA finds the compliance times specified in the applicable service information, or within 36 months after the effective date of this AD, whichever occurs first, represents an appropriate interval of time for affected airplanes to continue to operate without compromising safety. However, under the provisions of paragraph (j) of this AD, the FAA will consider requests for approval of an extension of the compliance time if sufficient data are submitted to substantiate that the new compliance time would provide an acceptable level of safety. The FAA has not changed the AD in this regard. \n\nRequest To Include Records Review \n\n\n\tAll Nippon Airways (ANA) requested that the FAA add a statement to the proposed AD that allows a review of the airplane maintenance records for the part number (P/N) of the AOA sensor, if the P/N of the AOA sensor can be conclusively determined from that review. ANA stated that they have installed AOA sensor P/N 0861FL1 (new Boeing P/N S233T913-5) on their Boeing Model 767 fleet because it began accomplishing Boeing Alert Service Bulletin 767-34A0828, dated December 6, 2018, since the issue date of the service information. ANA argued that the proposed AD would require them to repeat accomplishment of Boeing Alert Service Bulletin 767-34A0828, dated December 6, 2018. ANA stated that it manages the P/N of the AOA sensor within its airplane maintenance records, and the installation of the new AOA sensor P/N 0861FL1 (new Boeing P/N S233T913-5) on each airplane can be traced by reviewing its airplane maintenance records. \n\tThe FAA agrees with the commenter's request to add a records review. The FAA has added paragraph (h)(2) to this AD to allow a review of airplane maintenance records in lieu of the inspections for the AOA sensor P/Ns. The FAA also notes that paragraph (f) of this AD states to accomplish the required actions within the compliance times specified, ''unless already done.'' Therefore, if operators have accomplished the actions required for compliance with this AD before the effective date of this AD and have records that show the actions were done as specified in the AD, no further action is necessary. \n\nRequest To Reference Later Revisions of Service Information \n\n\n\tAAL requested that the applicability, required actions, and exceptions to service information in the proposed AD be revised to include any future FAA approved revisions of service information. AAL requested that the FAA add the phrase ''or later FAA approved revisions'' to Boeing Alert Service Bulletin 757-34A0611, Revision 1, dated March 22, 2019; and Boeing Alert Service Bulletin 767-34A0828, dated December 6, 2018. AAL suggested that any requirement that references service information would state, for example, ''Boeing Alert Service Bulletin 757-34A0611, Revision 1, dated March 22, 2019, or later FAA approved revisions.'' AAL argued that allowing later FAA approved revisions of service information would avoid extra work and delays in implementation required for an alternative method of compliance (AMOC) approval should either service information require a revision due to an error or omission of data. \n\tThe FAA does not agree with the request. The FAA may not refer to any document that does not yet exist. In general terms, the FAA is required by Office of the Federal Register (OFR) regulations for approval of materials incorporated by reference, as specified in 1 CFR 51.1(f), toeither publish the service document contents as part of the actual AD language; or submit the service document to the OFR for approval as referenced material, in which case the FAA may only refer to such material in the text of an AD. The AD may refer to the service document only if the OFR approved it for incorporation by reference. See 1 CFR part 51. \n\tTo allow operators to use later revisions of the referenced document (issued after publication of the AD), either the FAA must revise the AD to reference specific later revisions, or operators must request approval to use later revisions as an AMOC with this AD under the provisions of paragraph (j) of this AD. \n\nRequest To Clarify the Impact of Case Heaters on Unsafe Condition \n\n\n\tThe commenter, Alan Peterson, FedEx, stated that the proposed AD does not address the possibility that the case heaters within the AOA sensor may be contributing to the unsafe condition, noting specifically that the proposed AD does not address the case heaters within the AOA sensors for Captain and First officer positions on FedEx's large fleet of Boeing Model 757 and 767 airplanes. The commenter pointed out that the case heaters keep the dampening fluid inside the body of the AOA sensor from getting cold-soaked in flight and on the ground. The commenter explained that the wiring of the case heater is in parallel with the AOA vane heater, so in a scenario where the case heater fails, the AOA sensor vane would continue working, but the AOA sensor would become slow to move once it becomes cold-soaked due to the lack of heat from the case heater within the AOA sensor. The commenter described this as a critical oversight in the proposed AD because both the case heater and the AOA vane heater must work correctly for the AOA vanes to function properly. \n\tThe commenter stated that, in his experience, an operator may check the resistance of the case heater wiring on both AOA sensor vanes to verify that it is within the tolerance specifiedby the component maintenance manual (CMM) and verify the wiring is not burnt due to an open circuit. The commenter stated that this check was accomplished on the Boeing Model 757 and 767 fleet, and, if a discrepancy was discovered during the resistance check or revealed evidence of an open circuit in the case heater, the AOA vane would then be replaced. The commenter noted that a malfunction with the case heater would not be registered by the engine-indicating and crew-alerting system (EICAS) because the system only monitors the AOA vane heaters, and suggested that a malfunctioning case heater could affect reactive windshear, reduced vertical separation minimum (RVSM), and stall warning. The FAA infers that the commenter is requesting that the FAA clarify the impact of case heaters within the AOA sensors on the unsafe condition. \n\n((Page 71781)) \n\n\n\tThe FAA agrees to clarify. One of the specific mitigating design changes in this AD is the position of the case heater. Although thecase heaters in the AOA vane assembly are not specifically mentioned in the preamble of the proposed AD, the new AOA sensors with supplier P/N 0861FL1 (new Boeing P/N S233T913-5) have a repositioned case heater specifically designed to mitigate the unsafe condition of moisture build-up and freezing. AOA sensors with supplier P/N 2566A-21 (new Boeing P/N 10-60878-3), 2566A-30 (new Boeing P/N 10-60878-4), and 0861FL (new Boeing P/N S233T913-4), mitigate the unsafe condition using an improved vane design. The FAA has not changed the AD in this regard. \n\nConclusion \n\n\n\tThe FAA reviewed the relevant data, considered the comments received, and determined that air safety and the public interest require adopting this final rule with the changes described previously and minor editorial changes. The FAA has determined that these minor changes: \n\tAre consistent with the intent that was proposed in the NPRM for addressing the unsafe condition; and \n\tDo not add any additional burden upon the public than was already proposed in the NPRM. \n\tThe FAA also determined that these changes will not increase the economic burden on any operator or increase the scope of this final rule. \n\nRelated Service Information Under 1 CFR Part 51 \n\n\n\tThe FAA reviewed Boeing Alert Service Bulletin 727-34A0247, Revision 1, dated October 1, 2019; Boeing Alert Service Bulletin 757- 34A0611, Revision 1, dated March 22, 2019; and Boeing Alert Service Bulletin 767-34A0828, dated December 6, 2018. The service information describes procedures for a general visual inspection of the AOA sensors for certain AOA sensors, and replacement of affected AOA sensors. These documents are distinct since they apply to different airplane models. \n\tThis service information is reasonably available because the interested parties have access to it through their normal course of business or by the means identified in the ADDRESSES section. \n\nCosts of Compliance \n\n\n\tThe FAA estimates that this AD affects 1,287airplanes of U.S. registry. The FAA estimates the following costs to comply with this AD: \n\n\n\tEstimated Costs for Required Actions ---------------------------------------------------------------------------------------------------------------- \n\tCost on U.S. \n\tAction Labor cost Parts cost Cost per product operators ---------------------------------------------------------------------------------------------------------------- Inspection................... 1 work-hour x $0.................... $85................... $109,395. \n\t$85 per hour = \n\t$85. Replacement.................. Up to 3 work- Up to $54,000......... Up to $54,255......... Up to \n\thours x $85 per $69,826,185. \n\thour = Up to \n\t$255. ---------------------------------------------------------------------------------------------------------------- \n\nAuthority for This Rulemaking \n\n\n\tTitle 49 of the United States Code specifies the FAA's authority to issue rules on aviation safety. Subtitle I, section 106, describes the authority of the FAA Administrator. Subtitle VII: Aviation Programs, describes in more detail the scope of the Agency's authority. \n\tThe FAA is issuing this rulemaking under the authority described in Subtitle VII, Part A, Subpart III, Section 44701: ''General requirements.'' Under that section, Congress charges the FAA with promoting safe flight of civil aircraft in air commerce by prescribing regulations for practices, methods, and procedures the Administrator finds necessary for safety in air commerce. This regulation is within the scope of that authority because it addresses an unsafe condition that is likely to exist or develop on products identified in this rulemaking action. \n\tThis AD is issued in accordance with authority delegated by the Executive Director, Aircraft Certification Service, as authorized by FAA Order 8000.51C. In accordance with that order, issuance of ADs is normally a function of the Compliance and Airworthiness Division, but during this transition period, the Executive Director has delegated the authority to issue ADs applicable to transport category airplanes and associated appliances to the Director of the System Oversight Division. \n\nRegulatory Findings \n\n\n\tThis AD will not have federalism implications under Executive Order 13132. This AD will not have a substantial direct effect 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. \n\tFor the reasons discussed above, I certify that this AD: \n\t(1) Is not a ''significant regulatory action'' under Executive Order 12866, \n\t(2) Will not affect intrastate aviation in Alaska, and \n\t(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. \n\nList of Subjects in 14 CFR Part 39 \n\n\n\tAir transportation, Aircraft, Aviation safety, Incorporation by reference, Safety.