The FAA has received reports of erroneous airspeed readings, including those from the airspeed indicator and Machmeter, after a McDonnell Douglas Model DC-8 series airplane had flown through visible moisture. The original airplane design included a turbo compressor system. The turbo compressors generated enough heat to prevent freezing of any trapped moisture in the lines running from the pitot tubes. The turbo compressors were removed during installation of Supplemental Type Certificate (STC) ST466CH, which incorporated a flow control system that uses bleed air from the engines. However, the flow control system did not generate enough heat in the area of the pitot tube lines to prevent freezing. Frozen pitot lines could generate erroneous or total loss of airspeed indications to the flight crew, which could result in loss of control of the airplane \n\n\tA modification to positively address this unsafe condition was subsequently developed, and applicable parts and procedures were provided to operators of the affected airplanes. However, a recent fleetwide inspection revealed that not all of those airplanes had been modified. \n\nExplanation of Relevant Service Information \n\tNational Aircraft Service, Inc., issued Service Bulletin SB-98-01R1, dated January 26, 1999, which the FAA reviewed and approved. The service bulletin describes procedures to modify the flow control system by rerouting the bleed air ducts to warm the pitot tube lines. Accomplishment of the actions specified in the service bulletin is intended to adequately address the identified unsafe condition. \n\nExplanation of the Requirements of the Rule \n\tSince an unsafe condition has been identified that is likely to exist or develop on other airplanes of the same type design, this AD is being issued to prevent the pitot lines from freezing, which could result in erroneous or total loss of airspeed indications to the flight crew, and consequent loss of control of the airplane. This AD requires accomplishment of the actions specified in the service bulletin described previously, except as discussed below. \n\nDifference Between AD and Service Bulletin \n\tThe service bulletin recommends the modification within 500 flight hours after March 1, 1999; this AD requires the modification within 30 days after the effective date of this AD. In light of the urgency of the unsafe condition and the fact that the revised service bulletin has been available to affected operators for nearly two years, the FAA finds that the required compliance time represents an appropriate interval of time allowable for affected airplanes to continue to operate without compromising safety. \n\nDetermination of Rule's Effective Date \n\tSince a situation exists that requires the immediate adoption of this regulation, it is found that notice and opportunity for prior public comment hereon are impracticable, and that good cause exists for making this amendment effective in less than 30 days. \n\nComments Invited \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\tSubmit comments using the following format: \n\nOrganize comments issue-by-issue. For example, discussa request to change the compliance time and a request to change the service bulletin reference as two separate issues. \n\nFor each issue, state what specific change to the AD is being requested. \n\nInclude justification (e.g., reasons or data) for each request. \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 2001-NM-26-AD." The postcard will be date stamped and returned to thecommenter. \n\nRegulatory Impact \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\tAir transportation, Aircraft, Aviation safety, Incorporation by reference, Safety. \n\nAdoption of the Amendment \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\t1. The authority citation for part 39 continues to read as follows: \n\tAuthority: 49 U.S.C. 106(g), 40113, 44701. \n\n§ 39.13 (Amended) \n\t2. Section 39.13 is amended by adding the following new airworthiness directive: