Recently, the FAA has received reports of damage to the high pressure compressor (HPC) of the engines on several Boeing Model 757 series airplanes equipped with Pratt & Whitney Model PW2000 series engines. Investigation into the cause of this damage revealed that, during prolonged ground operation in icing conditions, ice can accumulate on the first stage of the low pressure compressor (LPC) stator. Subsequent acceleration to high thrust levels releases this ice, which travels through the LPC and into the HPC, where blade damage may occur. \n\n\tDuring ground operation in icing conditions, ice may build up on the first stage of the LPC stator of the engines. The engine anti-ice system will not remove or prevent the formation of ice on this component; it only protects the inlet cowl. Ice accumulation on the first stage of the LPC stator is an urgent safety concern since it may be ingested into the core of the compressor, which can cause damage to the engine. If the ice accumulation is sufficiently large and is subsequently shed and ingested, the resulting damage to the engine may lead to surges in or loss of power from the affected engine. \n\n\tThe FAA has determined that periodic engine run-ups will shed the ice from the first stage of the LPC stator before it accumulates in sufficiently large quantities that, when shed, may result in damage to the engine. Ice shedding occurs when the air loads exceed the adhesion force between the ice and the stator. However, the quantity of ice that is shed is not proportional to rotor speed. The FAA finds that a minimum of 50 percent rotation speed of the engine fan (N1) is necessary to shed ice; power settings below 50 percent N1 are ineffective for ice removal. In addition, the FAA has determined that these engine run-ups should be based on temperature and visible moisture, rather than on icing indications on the airframe of the airplane. \n\n\tIce accumulation, if not detected and removed, can be ingested into the compressor and cause damage to the engine, which could result in the loss of power from the affected engine. \n\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 damage to these engines due to ice ingestion into the compressor, which may result in the loss of power from the affected engine. This AD requires revising the Limitations Section of the FAA-approved Airplane Flight Manual (AFM) to include procedures that will ensure that during inclement weather, periodic engine run-ups will shed ice before it accumulates and causes damage to the engine. \n\n\tThis action also provides procedures for a visual check to detect ice build-up on the first stage of the LPC stator and removal of any ice, if necessary. The FAA has determined that these visual checks may be properly performed by pilots because the checks do not require the use of tools, precision measuring equipment, training, pilot logbook endorsements, or the use of or reference to technical data that are not contained in the body of the AD. \n\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\n Comments 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 beconsidered, 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\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 94-NM-231-AD." The postcard will bedate stamped and returned to the commenter. \n\n\tThe regulations adopted herein will not have substantial direct effects 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, in accordance with Executive Order 12612, it is determined that this final rule does not have sufficient federalism implications to warrant the preparation of a Federalism Assessment. \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 Policiesand 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\n List of Subjects in 14 CFR Part 39 \n\nAir 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.\tThe authority citation for part 39 continues to read as follows: Authority: 49 U.S.C. App. 1354(a), 1421 and 1423; 49 U.S.C. 106(g); and 14 CFR 11.89. § 39.13 - (Amended) \n\n\t2.\tSection 39.13 is amended by adding the following new airworthiness directive: