Background \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 all GE CF6-80C2A5F, - 80C2B1F, -80C2B2F, -80C2B4F, -80C2B5F, -80C2B6F, -80C2B6FA, -80C2B7F, - 80C2B8F, -80C2D1F, -80C2K1F, -80C2L1F, -80E1A2, -80E1A3, -80E1A4, and - 80E1A4/B model turbofan engines with a certain HMU installed. The NPRM published in the Federal Register on September 6, 2019 (84 FR 46896). The NPRM was prompted by a report of fuel coking of the HMU FMV EHSV resulting in tailpipe fire. The NPRM proposed to require the removal of the HMU and its replacement with a part eligible for installation. The FAA is issuing this AD to address the unsafe condition on these products. \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\nRequest To Update Applicability To Exclude Engines With Updated Electronic Control Unit (ECU) Software \n\n\n\tGE requested that the FAA update paragraph (c), Applicability, of this AD, to include ''For CF6-80E engines that have complied with (GE Service Bulletin (SB)) CF6-80E1 SB 73-0129 'Introduction of ECU Software Version E.1.Q' no action is required.'' GE reasoned that CF6- 80E1 ECU Software Version E.1.Q was designed to avoid tailpipe fires caused by the malfunction of the HMU FMV EHSV. There have been no reported tailpipe fires on GE CF6-80E1 model turbofan engines that have installed ECU Software Version E.1.Q. \n\tThe FAA disagrees with updating the applicability of this AD to exclude engines with updated ECU Software Version E.1.Q. Although GE CF6-80E1 ECU Software Version E.1.Q addresses the known sequence of tailpipe fires by monitoring the HMU FMV position at low N2 speeds, which may relate to the unsafe condition in this AD, the FAA would need additional data that shows how the ECU software update addresses the potential for this failure to occur at other phases of flight. If the data reveal information relevant to this unsafe condition, the FAA will consider future rulemaking. The FAA did not change this AD. \n\nRequest To Allow Modification of the HMU as an Alternative Method of Compliance (AMOC) \n\n\n\tAn anonymous commenter requested that the FAA consider whether the \n\n((Page 68432)) \n\nmodification of the HMU using GE CF6-80C2 SB 73-0378 R00, dated July 14, 2010 (''GE SB 73-0378''), is an AMOC (alternative method of compliance) to this AD. The commenter reasoned that the modification results in an HMU FMV EHSV with a new part number (P/N). \n\tThe FAA disagrees. GE SB 73-0378 introduces material properties to the HMU that improves corrosion resistance. GE SB 73-0378 does not, however, require the installation of a new or overhauled HMU FMV EHSV. The HMU with improved corrosion resistance introduced by GE SB 73-0378 is not related to the unsafe condition of this AD. Additionally, although GE SB 73-0378 results in a new HMU P/N after modification of the HMU, this AD still applies to this new P/N. \n\nRequest To Change the Compliance Time \n\n\n\tHoneywell requested that the FAA reduce the compliance time of paragraph (g), Required Actions, of this AD from 40,000 to 20,000 flight hours (FHs) since new or since last overhaul. \n\tThe FAA disagrees. The FAA does not have data to support reducing the removal and replacement of the HMU from 40,000 FHs to 20,000 FHs. According to reports from GE, which were considered by the FAA when preparing the NPRM, the related tailpipe fire incidents occurred in engines with HMUs exceeding 40,000 FHs since new or since the last overhaul. The FAA did not change this AD. \n\tDelta Air Lines (DAL) requested that the FAA increase the initial compliance time to remove and replace the HMU from 180 days to 12 months or to a number of hours or cycles greater than 40,000 FHs, based on the level of risk. DAL stated that they have attempted to purchase additional units to support the compliance time of 40,000 FHs or 180 days proposed in the NPRM; however, there are few spares on the market. Additionally, DAL reasoned that the turnaround time for an overhaul of the HMU has not allowed DAL to progress as fast as required to meet the expected compliance deadline for units in their fleet. \n\tAtlas Air Inc. (Atlas Air) also indicated that the volume of HMUs wherein operators will be unable to determine HMU FMV EHSV compliance will exceed the available compliant spares in the market. The lack of available HMUs will cause the grounding of a significant number of aircraft unless the AD allows for the completed overhaul to count as evidence of compliance (EoC) as documented by FAA Form 8130-3, Authorized Release Certificate, Airworthiness Approval Tag. \n\tThe FAA disagrees with increasing the compliance time for the required actions of this AD. The FAA infers that DAL's and Atlas Air's request to increase the compliance time of this AD,while mentioning the lack of spares and delays with the overhaul of the HMU, is the result of the definition of ''an overhaul of the HMU'' in paragraph (h)(2), Definitions, in the NPRM. The concern is that operators do not track usage time on the HMU FMV EHSV separately from the HMU and, therefore, would need to replace the complete HMU in all scenarios within 180 days. The FAA changed the definition of ''an overhaul of the HMU'' in this AD to clarify the methods that an HMU may be overhauled. \n\nRequest To Require Complete Overhaul of HMU \n\n\n\tHoneywell requested that the FAA revise the definition of ''an overhaul of the HMU'' in the Definitions, paragraph (h)(2), of this AD, to clarify that an overhaul of the HMU is a ''complete overhaul'' of the HMU rather than just an overhaul of HMU FMV EHSV. \n\tBased on its requested change to the definition, Honeywell also requested that the FAA add additional estimated costs to the Cost of Compliance section of this AD to include the estimated costs of a complete HMU overhaul. \n\tThe FAA agrees that performing a complete overhaul of the HMU addresses the unsafe condition of this AD. The FAA disagrees with requiring a complete overhaul of the HMU as only an overhaul of the HMU FMV EHSV is required to prevent fuel coking or fuel deposits in the HMU FMV EHSV. The FAA, however, changed the definition of ''an overhaul of the HMU'' to include either overhaul of the HMU (complete) or overhaul of the HMU FMV EHSV. The FAA added an estimate for the cost of a complete HMU overhaul since this is an acceptable means of complying with the requirements of this AD. \n\nRequest To Clarify the Definition of an Overhaul of the HMU \n\n\n\tSeveral commenters requested clarification, as described below, of the definition of ''an overhaul of the HMU'' provided in paragraph (h)(2) of this AD. \n\nClarification of Other FAA-Approved Methods \n\n\n\tFedEx Express (FedEx) and United Airlines (UAL) requested that the FAA clarify overhauled by ''other FAA-approved methods.'' FedEx asked what is the intended scope of this phrase and if it includes accomplishment of earlier revisions of GE SB CF6-80C2 SB 73-0436, as well as work performed using the applicable component maintenance manual (CMM) which was classified as an overhaul in block 11 of FAA Form 8130-3, Authorized Release Certificate, Airworthiness Approval Tag (or equivalent). UAL also asked if ''other FAA-approved methods'' included work accomplished using the CMM for the HMU FMV EHSV. \n\tThe FAA agrees ''other FAA-approved methods'' was unclear and has removed it from the definition for ''an overhaul of the HMU.'' The FAA added a credit for previous actions paragraph to provide credit for the initial removal and replacement required actions contained in paragraph (g)(1) of this AD if the HMU FMV EHSV was overhauled before the effective date of this AD using GE SB CF6-80C2 SB 73-0436 R01, dated May 14, 2019, or GE SB CF6-80C2 73-0142 R01, dated May 14, 2019. The FAA also changed the definition of ''an overhaul of the HMU'' in this AD to clarify that an HMU may be overhauled using Honeywell-approved maintenance procedures. \n\nClarification of Approved Facility \n\n\n\tDAL, Kalitta Air Group (Kalitta Air), and United Parcel Service (UPS) requested that an overhaul of the HMU at an FAA or Honeywell- approved facility be considered an overhaul of the HMU that resets the 40,000 FHs requirement. \n\tThe FAA agrees and clarified the definition of ''an overhaul of the HMU'' in this AD to include ''An overhaul of the HMU (complete) using Honeywell-approved maintenance procedures.'' \n\nClarification That HMU Overhaul Includes HMU EHSVs \n\n\n\tAll Nippon Airways (ANA) asked if an overhaul of the HMU includes overhauling all HMU EHSVs. \n\tThe FAA agrees that the overhaul of the HMU includes overhauling all HMU EHSVs. The FAA changed the definition of ''an overhaul of the HMU'' to include either overhaul of the HMU (complete) or overhaul of the HMU FMV EHSV. The FAAnotes, however, that complete overhaul of the HMU is not required by this AD. \n\nClarification of Tracking of HMU FMV EHSVs \n\n\n\tANA, Atlas Air, DAL, FedEx, Kalitta Air, Thai Airways, and UPS stated that the HMU EHSVs are sub-assemblies of the HMU and repair or overhaul of these sub-components is not typically tracked separately from the HMU at an engine shop visit level. Therefore, overhaul of \n\n((Page 68433)) \n\nthe HMU FMV EHSV is not recorded by most operators in a separate maintenance program record. The commenters reasoned that they received FAA Form 8130-3, Authorized Release Certificate, Airworthiness Approval Tag, documenting the HMU approval for return to service, but FAA Form 8130-3 does not include information about the EHSVs within the HMU. Atlas Air suggested that if the time since the most recent replacement of the HMU FMV EHSVs cannot be determined, then the time since overhaul (TSO) based on FAA Form 8130-3 be used as EoC to the AD for HMUs overhauled before theeffective date of this AD. \n\tThe FAA acknowledges that the HMU FMV EHSVs are not typically tracked separately from the HMU. The FAA agrees that in cases where the overhaul of the HMU FMV EHSV cannot be determined, the TSO can be used as EoC to the AD for HMUs overhauled before the effective date of this AD. The FAA changed the definition of ''an overhaul of the HMU'' to include either overhaul of the HMU (complete) or overhaul of the HMU FMV EHSV. \n\nRequest To Clarify Previous Compliance With the AD \n\n\n\tDAL stated that paragraph (f) of this AD states, ''Comply with this AD within the compliance times specified, unless already done.'' Yet, the NPRM does not address what constitutes previous compliance. \n\tThe FAA notes that ''unless already done,'' as used in this AD, means performing the actions in paragraph (g), Required Actions, before the effective date of this AD. \n\nRequest To Clarify if This AD Affects SAIB NE-09-25R2 \n\n\n\tAn anonymous commenter asked if this AD affectsthe following statements in SAIB NE-09-25R2: ''The FAA has determined that the performance properties of aviation turbine fuel are not impacted with up to 50 mg/kg of FAME (fatty acid methyl ester) under continuous usage . . .'' and ''At high enough concentrations, FAME can impact the thermal stability of the fuel that could lead to coke deposits in the fuel system.'' \n\tWhile FAME can impact the thermal stability of the fuel, leading to coke deposits in the fuel system, the HMU FMV EHSV fuel coking and fuel deposits of this AD is not related to FAME. The HMU FMV EHSV fuel coking and fuel deposits unsafe condition of this AD neither substantiates nor refutes SAIB NE-09-25R2. Therefore, this AD does not affect the SAIB guidance. \n\nSupport for the AD \n\n\n\tThe Boeing Company and The Air Line Pilots Association, International, expressed support for the AD as written. \n\tAn anonymous commenter disagreed with Honeywell's suggestion to remove the HMU for a complete overhaul before reaching 20,000 FHs considering the root cause analysis is identified as high-time wear failure of the HMU FMV EHSV. The FAA infers that this comment represents support for the AD as written. \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\nService Information Incorporated by Reference Under 1 CFR Part 51 \n\n\n\tThe FAA reviewed GE SB CF6-80C2 SB 73-0436 R02, dated August 15, 2019, and GE SB CF6-80E1 SB 73-0142 R02, dated August 15, 2019. The SBs provide instructions, differentiated by the turbofan engine model, for repetitive overhauls of the HMU FMV EHSVs. 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\tThe FAA estimates that this AD affects 573 engines installed on airplanes of U.S. registry. \n\tThe FAA estimates the following costs to comply with this AD: \n\n\n\tEstimated Costs ---------------------------------------------------------------------------------------------------------------- \n\tCost per Cost on U.S. \n\tAction Labor cost Parts cost product operators ---------------------------------------------------------------------------------------------------------------- Removal and replacement of HMU...... 5 work-hours x $85 per $0 $425$243,525 \n\thour = $425. ---------------------------------------------------------------------------------------------------------------- \n\n\n\tThe FAA estimates the following costs to do any necessary overhaul. The FAA has no way of determining the number of aircraft that might perform the overhaul of the HMU FMV EHSV or overhaul of the complete HMU: \n\n\n\tOn-Condition Costs ---------------------------------------------------------------------------------------------------------------- \n\tCost per \n\tAction Labor cost Parts cost product ---------------------------------------------------------------------------------------------------------------- Overhaul HMU FMV EHSV......................... 5 work-hours x $85 per hour = $4,000 $4,425 \n\t$425. Overhaul HMU (complete)....................... 25 work-hours x $85 per hour = 92,875 95,000 \n\t$2,125. ---------------------------------------------------------------------------------------------------------------- \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. \n\n((Page 68434)) \n\nThis 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 FindingsThis 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.