Discussion \n\n\n\tThe FAA has received reports involving discrepancies between the airplane FQIS, specifically the CWT fuel quantity, and the refueling truck uploaded fuel amount, followed by a FUEL DISAGREE EICAS message at an early stage of flight (e.g., within 3 hours after take off), and/ or with an INSUFFICIENT FUEL EICAS message. There have been at least 25 in-service events reported by operators. In at least 16 of these events, the airplanes continued with the mission; of those, 6 landed at the destination airport, and 10 had to land at a diversion airport. Insufficient fuel in the CWT as a result of this discrepancy is due to a design flaw in the FQIS in which the FQIS calibrates incorrect velocity of sound in the jet fuel during center tank fueling, which leads to an improper fuel density calculation, and results in the FQIS showing a different fuel amount from the actual fuel quantity in the CWT. In almost all of the events, the FQIS showed morefuel than the actual fuel quantity in the CWT, resulting in less fuel on the airplane than the required fuel load for the mission. Alternatively, the FQIS could show less fuel than the actual fuel quantity in the CWT, resulting in more fuel on the airplane than the required fuel load for the mission. This issue affects only the CWT and not the main tanks. \n\tThere are practical difficulties in comparing the fuel quantity uploaded by the refueling truck or hydrant. The fueling system relies on the airplane FQIS to report the mass (kilograms or pounds) of fuel onboard and stops the fueling process when the requested fuel for the next flight is onboard. The refueling trucks then report the volume (liters or gallons) of fuel that was uploaded because fuel is paid for by a volume measurement. Comparing the fuel volume upload with the final fuel load mass, which also accounts for the remaining fuel in the tanks from previous flight, is not an easy calculation and is prone to significant inaccuracies. The existing airplane maintenance manual and operator fueling procedures require verification that the correct fuel amount required for the current mission has been loaded onto the airplane. The FAA has received reports that verification tasks are either not accomplished or done incorrectly. As a result, the flight crew may be unaware of insufficient fuel loaded in the CWT and the airplane is dispatched for the mission. The airplane onboard fuel management system typically reports fuel quantity anomalies within the first three hours of flight resulting in a FUEL DISAGREE EICAS message and/or an INSUFFICIENT FUEL EICAS message that necessitates fuel check (e.g., leak check) and fuel quantity monitoring. These messages may require the flight crew to take action, such as performing an air turn back or a diversion. \n\tDiscrepancies in the CWT FQIS fuel quantity and the refueling truck uploaded fuel amount could result in an airplane dispatched with insufficient fuel loaded in the CWT and with the flight crew unaware of the insufficient fuel prior to departure. This condition, coupled with continued flight to the destination airport after receiving the EICAS messages while en route to the destination, could result in fuel exhaustion and subsequent power loss of all engines. Thereby, resulting in the inability to land at the destination airport or at a diversion airport, possibly leading to uncontrolled flight into terrain. \n\nFAA's Determination \n\n\n\tThe FAA is issuing this AD because the agency evaluated all the relevant information and determined the unsafe condition described previously is likely to exist or develop in other products of the same type design. \n\nAD Requirements \n\n\n\tThis AD requires a repetitive check of the FQIS fuel quantity calculation and display of the CWT fuel quantity through a new procedure, Refueling Station Door Cycling Procedure, developing a process to provide documentation to the flight crew that this check was done, and revising the existing AFM to incorporate verification procedures for flight crew awareness. \n\nInterim Action \n\n\n\tThe FAA considers this AD interim action. The FAA has been coordinating with Boeing in the development of a modification that will address the unsafe condition identified in this AD. However, due to the urgency of the unsafe condition and due to additional time needed for Boeing to develop the modification, the FAA has determined that interim action is necessary. Once the modification is developed, approved, and available, the FAA might consider additional rulemaking. \n\nFAA's Justification and Determination of the Effective Date \n\n\n\tAn unsafe condition exists that requires the immediate adoption of this AD without providing an opportunity for public comments prior to adoption. The FAA has found that the risk to the flying public justifies waiving notice and comment prior to adoption of this rule because discrepancies in the CWT FQIS fuel quantity and the refueling truck uploaded fuel amount could result in an airplane dispatched with insufficient fuel loaded in the CWT and with the flight crew unaware of the insufficient fuel prior to departure. This condition, coupled with continued flight to the destination airport after receiving the EICAS messages while en route to the destination, could result in fuel exhaustion and subsequent power loss of all engines. Thereby, resulting in the inability to land at the destination airport or at a diversion airport, possibly leading to uncontrolled flight into terrain. Additionally, the compliance time for the required action is shorter than the time necessary for the public to comment and for publication of the final rule. Therefore, the FAA finds good cause that notice and opportunity for prior public comment are impracticable. In addition, for the reasons stated above, the FAA finds that good cause exists for making this amendment effective in less than 30 days. \n\nComments Invited \n\n\n\tThis AD is a final rule that involves requirements affecting flight safety and was not preceded by notice and an opportunity for public comment. However, the FAA invites you to send any written data, views, or arguments about this final rule. Send your comments to an address listed under the ADDRESSES section. Include the docket number FAA-2020- 0461 and Product Identifier 2020-NM-065-AD at the beginning of your comments. The FAA specifically invites comments on the overall regulatory, economic, environmental, and energy aspects of this final rule. The FAA will consider all comments received by the closing date and may amend this final rule because of those comments. \n\tThe FAA will post all comments received, without change, to https://www.regulations.gov, including any personal information you provide. The \n\n((Page 34092)) \n\nFAA will also post a report summarizing each substantive verbal contact received about this final rule. \n\nRegulatory Flexibility Act (RFA) \n\n\n\tThe requirements of theRFA do not apply when an agency finds good cause pursuant to 5 U.S.C. 553 to adopt a rule without prior notice and comment. Because the FAA has determined that it has good cause to adopt this rule without notice and comment, RFA analysis is not required. \n\nCosts of Compliance \n\n\n\tThe FAA estimates that this AD affects 255 airplanes of U.S. registry. The FAA estimates 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 ---------------------------------------------------------------------------------------------------------------- Refueling Station Door Cycling 1 work-hour x $85 $0 $85 per check...... $21,675 per check. \n\tProcedure. per hour = $85 per \n\tcheck. AFM revision..................... 1 work-hour x $85 0 $85................ $21,675. \n\tper hour = $85. ---------------------------------------------------------------------------------------------------------------- \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\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, and \n\t(2) Will not affect intrastate aviation in Alaska. \n\nList of Subjects in 14 CFR Part 39 \n\n\n\tAir transportation, Aircraft, Aviation safety, Incorporation by reference, Safety.