On June 13, 2001, the FAA issued emergency AD 2001-12-51, which is applicable to all Boeing Model 737-800 series airplanes. \n\nBackground \n\n\tThe FAA has received a report indicating that severe vibration of the horizontal stabilizer occurred on a Boeing Model 737-800 series airplane. The airplane was operating at an altitude of 23,000 feet and an airspeed of 320 knots indicated airspeed (KIAS). This high frequency vibration was initiated by deployment of the speedbrakes during flight; it continued unabated for approximately 40 seconds, even though the speedbrakes were retracted. \n\n\tResults of post-event analysis and investigation indicate that the type of vibration of the elevator and elevator tab assembly following deployment of the speedbrakes, if not corrected, could result in severe damage to the horizontal stabilizer, followed by loss of controllability of the airplane. \n\nFAA's Conclusions \n\n\tIn light of this information, the FAA finds that certain new limitations should be included in the FAA-approved Airplane Flight Manual (AFM) for Model 737-800 series airplanes to prohibit operating the airplane at speeds in excess of 300 KIAS with speedbrakes extended. The FAA has determined that an airspeed of 300 KIAS provides an acceptable safety margin compared to the 320-KIAS airspeed at which the severe vibration occurred. \n\nOther Similar Models \n\n\tOperators should note that Model 737-600, -700, -700C, and -900 series airplanes are not included in the applicability of this AD. Existing analysis and flight testing data have not shown that Model 737-600, -700, and -700C series airplanes are subject to this severe vibration. Modified elevator tabs have already been installed on Model 737-900 series airplanes. \n\nExplanation of Requirements of the Rule \n\n\tSince the unsafe condition described is likely to exist or develop on other airplanes of the same type design, the FAA issued emergency AD 2001-12-51 to prevent severe vibration of the elevator and elevator tab assembly following deployment of the speedbrakes, which, if not corrected, could result in severe damage to the horizontal stabilizer, followed by loss of controllability of the airplane. The AD requires revising the AFM to prohibit operating the airplane at speeds in excess of 300 KIAS with speedbrakes extended. The AD also provides for optional terminating action for the AFM revision. \n\n\tSince the issuance of the emergency AD, an issue has been raised about whether this limitation has the effect of prohibiting operation at airspeeds above 300 KIAS in the event of an emergency descent (e.g., necessitated by rapid decompression of the fuselage). It was always the FAA's intent that the pilot would be able to operate as necessary in the event of an emergency as permitted in accordance with 14 CFR 91.3. This AD does not change that authority. \n\nInterim Action \n\n\tThis AD is considered to be interim action. The specific details of the modification discussed previously are being developed, but are not yet available for dissemination to affected operators. Once the modification of the elevator tab assembly discussed previously is developed, approved, and available, the FAA may consider further rulemaking.\n \n\tSince it was found that immediate corrective action was required, notice and opportunity for prior public comment thereon were impracticable and contrary to the public interest, and good cause existed to make the AD effective immediately by individual notices issued on June 13, 2001, to all known U.S. owners and operators of Boeing Model 737-800 series airplanes. These conditions still exist, and the AD is hereby published in the Federal Register as an amendment to section 39.13 of the Federal Aviation Regulations (14 CFR 39.13) to make it effective to all persons. \n\nComments Invited \n\n\tAlthough this action is in the form of a final rule that involves requirements affecting flight safety and, thus, was not preceded by notice and an opportunity for public comment, comments are invited on this rule. Interested persons are invited to comment on this rule by submitting such written data, views, or arguments as they may desire. Communications shall identify the Rules Docket number and be submitted in triplicate to the address specified under the caption ADDRESSES. All communications received on or before the closing date for comments will be considered, and this rule may be amended in light of the comments received. Factual information that supports the commenter's ideas and suggestions is extremely helpful in evaluating the effectiveness of the AD action and determining whether additional rulemaking action would be needed. \n\n\tComments are specifically invited on the overall regulatory, economic, environmental, and energy aspects of the rule that might suggest a need to modify the rule. All comments submitted will be available, both before and after the closing date for comments, in the Rules Docket for examination by interested persons. A report that summarizes each FAA-public contact concerned with the substance of this AD will be filed in the Rules Docket. \n\tCommenters wishing the FAA to acknowledge receipt of their comments submitted in response to this rule must submit a self-addressed, stamped postcard on which the following statement is made: "Comments to Docket Number 2001-NM-193-AD." The postcard will be date stamped and returned to the commenter. \n\nRegulatory Impact \n\n\tThe regulations adopted herein 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. Therefore, it is determined that this final rule does not have federalism implications under Executive Order 13132. \n\n\tThe FAA has determined that this regulation is an emergency regulation that must be issued immediately to correct an unsafe condition in aircraft, and that it is not a "significant regulatory action" under Executive Order 12866. It has been determined further that this action involves an emergency regulation under DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979). If it is determined that this emergency regulation otherwise would be significant under DOT Regulatory Policies and Procedures, a final regulatory evaluation will be prepared and placed in the Rules Docket. A copy of it, if filed, may be obtained from the Rules Docket at the location provided under the caption ADDRESSES. \n\nList of Subjects in 14 CFR Part 39 \n\n\tAir transportation, Aircraft, Aviation safety, Safety. \nAdoption of the Amendment \n\n\n\tAccordingly, pursuant to the authority delegated to me by the Administrator, the Federal Aviation Administration amends part 39 of the Federal Aviation Regulations (14 CFR part 39) as follows: \n\nPART 39--AIRWORTHINESS DIRECTIVES \n\n\t1. The authority citation for part 39 continues to read as follows: \n\n\tAuthority: 49 U.S.C. 106(g), 40113, 44701. \n\n\nSec. 39.13 (Amended) \n\n\n\t2. Section 39.13 is amended by adding the following new airworthiness directive: