On April 11, 2002, the FAA issued emergency AD 2002-08-52, which is applicable to all Boeing Model 737-600, -700, and -700C series airplanes. \n\nBackground \n\n\tThe FAA received a report indicating that severe vibration of the horizontal stabilizer occurred on a Boeing Model 737-700 series airplane. The airplane was operating at an altitude of 19,500 feet and an airspeed of 315 knots indicated airspeed (KIAS). The high frequency vibration was initiated by deployment of the speedbrakes during descent of the airplane. The vibration continued until the airspeed was reduced to 285 KIAS, even though the speedbrakes were retracted. The airplane landed without further incident. The FAA and the manufacturer have determined that the vibration was due to a "limit cycle oscillation" of the elevator and elevator tab assembly attached to the horizontal stabilizer. Such oscillation was caused by a buffeting flow over the surface of the horizontal stabilizer, which occurred following deployment of the speedbrakes. \n\n\tResults of post-event analysis and investigation indicate that severe 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 possible loss of controllability of the airplane. \n\nOther Similar Models \n\n\tThe elevator tabs on Model 737-600 and -700C series airplanes are identical to those on Model 737-700 series airplanes. Therefore, those Model 737-600 and -700C series airplanes may be subject to the same unsafe condition revealed on Model 737-700 series airplanes. \n\n\tIn addition, operators should note that modified elevator tabs have already been installed on Model 737-900 series airplanes. \n\nOther Relevant Rulemaking \n\n\tThe FAA previously issued AD 2001-12-51, amendment 39-12294 (66 FR 34094, June 27, 2001), applicable to all Boeing Model 737-800 series airplanes. That AD was issued to ensure that theflight crew is advised of the potential hazard associated with extending the speedbrakes at speeds in excess of 300 KIAS. That AD requires revising the Airplane Flight Manual to prohibit operating the airplane at speeds in excess of 300 KIAS with speedbrakes extended. That AD also provides for optional terminating action for the AFM revision. \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 737-600, -700, and -700C 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 315-KIAS airspeed at which the severe vibration occurred. \n\nExplanation of the Requirements of the Rule \n\n\tSince an unsafe condition has been identified that is likely to exist or develop on other airplanes of this same type design,this airworthiness directive is issued to require revising the AFM to prohibit operating the airplane at speeds in excess of 300 KIAS with speedbrakes extended. This AD also provides for optional terminating action for the AFM revision. \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 April 11, 2002, to all known U.S. owners and operators of Boeing Model 737-600, -700, and -700C 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 ADaction 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\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 2002-NM-109-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 andthe 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. \n\nAdoption of the Amendment \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\nSec. 39.13 (Amended) \n\n\t2. Section 39.13 is amended by adding the following new airworthiness directive: