Discussion \n\n\n\tWe issued a notice of proposed rulemaking (NPRM) to amend 14 CFR part 39 by adding an AD that would apply to all The Boeing Company Model MD-90-30 airplanes. The NPRM published in the Federal Register on June 13, 2016 (81 FR 38113) (''the NPRM''). The NPRM was prompted by reports of stick shaker activation at airspeeds that were above the stall protection system's stick shaker schedule. The NPRM proposed to require installing AOA sensor external case heaters on the existing AOA sensors, installing additional wires, and doing a functional test and applicable corrective actions. We are issuing this AD to prevent ice formation between the AOA sensor vane and face plate, which could cause both vanes to become immobilized. If both vanes become immobilized, the stall protection system could become unreliable or non-functional, which could result in loss of control of the airplane. \n\nComments \n\n\n\tWe gave the public the opportunity to participate in developing this AD. The following presents the comments received on the NPRM and the FAA's response to each comment. \n\nSupport of the NPRM \n\n\n\tThe Air Line Pilots Association, International provided comments that supported the intent of the NPRM. \n\nRequest To Change Boeing Address Identified in the NPRM \n\n\n\tBoeing asked that we change its mailing address for obtaining copies of service information as specified in the NPRM to the following: Boeing Commercial Airplanes, Attention: Contractual & Data Services (C&DS), 2600 Westminster Blvd., MC 110-SK57, Seal Beach, CA 90740-5600; telephone 562-797-1092; Internet https://www.myboeingfleet.com. Boeing stated that this address is valid for this and all future ADs affecting Boeing airplanes. \n\tWe agree with the commenter's request. We have updated the contact information accordingly. However, we have corrected the telephone number; it should be 562-797-1717. We have changed this AD to include this new mailing address forBoeing service information. \n\nRequest To Clarify Certain Language in the NPRM \n\n\n\tBoeing asked that we clarify the language specifying what prompted the AD action, and the description of the unsafe condition, as specified in the SUMMARY section. Boeing stated that the reported incident occurred ''on Model 717-200 airplanes'' and included further description of what prompted the AD action. Boeing also stated that including this description clarifies the airplane model on which the safety issue was identified. Boeing also asked that we revise the description of the unsafe condition, which stated that ''the vane'' could become immobilized. Boeing noted that the safety issue is a common cause failure (both vanes could become immobilized) due to an external threat (i.e., weather). \n\tWe agree to add ''both vanes'' to the Discussion section and paragraph (e) of this AD for clarification. Information concerning the origin of the safety issue on Model 717-200 airplanes was included in theDiscussion section of the NPRM. Since the information in the Discussion section of the NPRM does not reappear in the final rule, we have not changed this AD in this regard. In addition, we do not agree that the requested changes are necessary in the SUMMARY section, which merely provides a high-level description of the relevant information. Details concerning the unsafe condition that appeared in the SUMMARY section of the NPRM have been removed from this final rule in response to new guidance from the Office of the Federal Register. \n\tBoeing also asked that we clarify the AD requirements by specifying ''installing additional wires'' in lieu of ''changing wires'' and installing AOA sensor external case heaters ''on the AOA sensors'' in lieu of ''and AOA sensors.'' Delta Air Lines (Delta) asked that we change ''and AOA sensors'' to \n\n((Page 95858)) \n\n''and existing AOA sensors'' since they are not new sensors. \n\tWe agree to make the requested changes in the SUMMARY section, the Discussion and the Related Service Information under 1 CFR part 51 sections of this final rule, and in paragraph (g) of this AD for clarification. \n\tDelta asked that we remove the references to ''water intrusion'' from the NPRM related to the description of the unsafe condition. Delta stated that the referenced service information does not address water intrusion. Delta added that the installation of the external case heater only prevents the existing water from freezing and rendering the vane immobilized. UTC Aerospace Systems (UTC) also asked that we remove the reference to moisture (water) intrusion since the referenced service information does nothing to reduce or eliminate the problem; it simply keeps the water from freezing. UTC also asked that we add to the description of the unsafe condition that the AD is intended to reduce or eliminate ice formation between the AOA sensor vane and face plate. \n\tWe partially agree with the commenters' requests. Water intrusion is addressed inthe referenced service information since it contributes to ice formation between the AOA sensor vane and face plate. However, water intrusion is not corrected by this AD. Therefore, we have revised the Discussion section and paragraph (e) of this AD to state ''We are issuing this AD to prevent ice formation between the angle-of-attack (AOA) sensor vane and face plate.'' \n\nRequest To Clarify Corrective Actions \n\n\n\tUTC asked that we re-identify the corrective actions in the SUMMARY and Discussion sections of the NPRM as removing and replacing the existing AOA unit having part number (P/N) 0861EW1 with a certified AOA, or installing a new AOA in accordance with the instructions specified in Boeing Alert Service Bulletin MD90-30A029, dated November 25, 2015. UTC stated that this would clarify the potential cause of the problem as related to the subject AOA and provide another choice for operators to comply with the proposed AD. UTC added that this would also define the AOA replacement as not including the existing AOA unit having P/N 0861EW1. \n\tWe agree that clarification is necessary; however, we do not agree that this clarification should be included in the SUMMARY section and the Discussion section of this final rule. The purpose of the language in the SUMMARY section is to provide a high-level description of the relevant information, and the information in the Discussion section of the NPRM does not reappear in the final rule. Therefore, we have revised the description of the required actions in the Related Service Information under 1 CFR part 51 section of this final rule, as specified by the commenter, to provide clarification to operators. We have also included the correct part number for the existing AOA unit in paragraph (g) of this AD. \n\nRequest To Update Referenced Service Information To Include the Correct Part Number \n\n\n\tUTC asked that Boeing Alert Service Bulletin MD90-30A029, dated November 25, 2015, be updated to correct the part number for the AOA sensor identified therein. UTC stated that the service information identifies replacing any AOA sensor having P/N ''081EW1,'' but the correct part number is ''0861EW1.'' \n\tWe acknowledge the commenter's concern; however, Boeing Alert Service Bulletin MD90-30A029, dated November 25, 2015, has not yet been revised by the airplane manufacturer. We have confirmed that this part number does not exist, and have clarified the correct part number for the existing AOA sensor in paragraph (g) of this AD. \n\nRequest To Change the Costs of Compliance Section \n\n\n\tBoeing asked that we change the Costs of Compliance section of the NPRM to include the parts cost for the external case heaters, as provided by the supplier. Boeing stated that the supplier of these heaters has received FAA parts manufacturer approval (PMA), which allows operators to go directly to the supplier to procure the parts. Boeing noted that the parts cost for two heaters is $2,389 each, for a total of $4,778 (operators are required to purchase two external case heaters for installation). \n\tWe agree with the commenter's request for the reason provided. We have changed the Costs of Compliance section in this final rule accordingly. \n\nConclusion \n\n\n\tWe reviewed the relevant data, considered the comments received, and determined that air safety and the public interest require adopting this AD with the changes described previously and minor editorial changes. We have determined that these minor changes: \n\tAre consistent with the intent that was proposed in the NPRM for correcting the unsafe condition; and \n\tDo not add any additional burden upon the public than was already proposed in the NPRM. \n\tWe also determined that these changes will not increase the economic burden on any operator or increase the scope of this AD. \n\nRelated Service Information Under 1 CFR Part 51 \n\n\n\tWe reviewed Boeing Alert Service Bulletin MD90-30A029, dated November 25, 2015. The service information describes procedures for installing AOA sensor external case heaters on the existing AOA sensors, installing additional wires, and doing a functional test and applicable corrective actions. The applicable corrective actions include removing and replacing the existing AOA unit (P/N 0861EW1) with a certified AOA, or installing a new AOA. This 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\tWe estimate that this AD affects 95 airplanes of U.S. registry. \n\tWe estimate the following costs to comply with this AD: \n\n\n\tEstimated Costs ---------------------------------------------------------------------------------------------------------------- \n\tCost on U.S. \n\tAction Labor cost Parts cost Cost per product operators ---------------------------------------------------------------------------------------------------------------- Installation of AOA sensor Up to 44 work- Up to $5,998 Up to $9,738 Up to $925,110 \n\texternal case heaters on the hours (depending (depending on the (depending on the (depending on the \n\tAOA sensors, installation of on the group group number). group number). group number). \n\tadditional wires, and a number) x $85 per \n\tfunctional test. hour = $3,740. ---------------------------------------------------------------------------------------------------------------- \n\n\n\n((Page 95859)) \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\tWe are 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\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) Is not a ''significant rule'' under DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979), \n\t(3) Will not affect intrastate aviation in Alaska, and \n\t(4) 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.