Discussion \n\n\tWe issued a notice of proposed rulemaking (NPRM) to amend 14 CFR part 39 to include an airworthiness directive (AD) that would apply to certain Boeing Model 737-300, -400, and -500 series airplanes. That NPRM was published in the Federal Register on January 12, 2009 (74 FR 1153). That NPRM proposed to require modifying the control power wiring of the normal supply fan and the low flow sensor for the equipment cooling system of the electronic flight instrument system (EFIS). \n\nComments \n\n\tWe gave the public the opportunity to participate in developing this AD. We considered the comments received. \n\nSupportive Comments \n\n\tBoeing and Continental Airlines support the actions in the NPRM. \n\nRequest To Add an Alternate Method of Compliance \n\n\tLufthansa German Airlines asks that we add a method acceptable for compliance with the corresponding requirements of the NPRM. Lufthansa notes that, as specified in paragraphs (f), (g)(1), and (g)(2) of the NPRM, actions done in accordance with Boeing Alert Service Bulletin 737-21A1156, Revision 1, dated October 23, 2007; or Boeing Alert Service Bulletin 737-21A1156, dated June 20, 2006; are acceptable for compliance. Lufthansa adds that these actions prevent loss of all attitude indications from both the standby indicator and EFIS displays in case of battery bus failure. (The following is a clarification of the commenter's description of acceptable sources of service information specified in this AD: Boeing Alert Service Bulletin 737- 21A1156, Revision 2, dated December 11, 2008, is the source of service information referred to in the NPRM for accomplishing the specified actions. Actions done previously in accordance with Boeing Alert Service Bulletin 737-21A1156, Revision 1, dated October 23, 2007; or Boeing Alert Service Bulletin \n737-21A1156, dated June 20, 2006 (for Groups 1 and 2 airplanes identified in Boeing Alert Service Bulletin 737-21A1156, Revision 1), are acceptable for compliance with the corresponding requirements of this AD.) \n\tLufthansa asks that we consider another method to address this unsafe condition, which is to append an abnormal procedure task to the flight crew operations manual in case of battery bus failure to specify setting the equipment cooling switch to alternate if the battery bus fails. This would allow the alternate supply fan to still cool the EFIS displays and prevent them from failing. \n\tWe disagree with the commenter's request to add this additional method of compliance to the AD requirements. The identified unsafe condition is loss of all attitude indications from both the standby indicator and EFIS displays, which could decrease the ability of the flightcrew to maintain the safe flight and landing of the airplane. Although we recognize the commenter's suggestion provides some safety mitigation for the unsafe condition, the inherently unsafe design of the EFIS cooling system must be corrected to ensure that flightcrews are equipped with attitude indications. Therefore, after the modification of the control power wiring of the EFIS cooling system is done, revising the flightcrew operations manual is not necessary and is not acceptable as an alternate method of compliance to this AD. We have made no change to the AD in this regard. \n\nConclusion \n\n\tWe reviewed the relevant data, considered the comments received, and determined that air safety and the public interest require adopting the AD as proposed. \n\nCosts of Compliance \n\n\tWe estimate that this AD will affect 263 airplanes of U.S. registry. The following table provides the estimated costs for U.S. operators to comply with this AD. \n\n\tEstimated Costs \n\n\nAction/Airplane group\nWork hours\nAverage labor rate per hour\nParts\nCost per product\nNumber of U.S.-registered airplanes\nFleet cost\nGroups 1 & 2 modification\n3\n$80\n$0\n$240\n153\n$36,720\nGroup 4 modification\n2\n$80\n$0\n$160\n113\n$18,080\n\n\n\tCurrently, there are no Group 3 airplanes on the U.S. Register. However, if an affected airplane is imported and placed on the U.S. Register in the future, the required actions would take about 5 work hours, at an average labor rate of $80 per work hour. Based on these figures, we estimate the cost of this AD for Group 3 airplanes to be $400 per airplane. \n\nAuthority for This Rulemaking \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\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), 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\tYou can find our regulatory evaluation and the estimated costs of compliance in the AD Docket. \n\nList of Subjects in 14 CFR Part 39 \n\n\tAir transportation, Aircraft, Aviation safety, Incorporation by reference, Safety. \n\nAdoption of the Amendment \n\nAccordingly, under the authority delegated to me by the Administrator, the FAA amends 14 CFR part 39 as follows: \n\nPART 39--AIRWORTHINESS DIRECTIVES \n\n1. The authority citation for part 39 continues to read as follows: \n\n\tAuthority: 49 U.S.C. 106(g), 40113, 44701. \n\nSec. 39.13 (Amended) \n\n2. The FAA amends Sec. 39.13 by adding the following new AD: