The FAA has been advised that certain engine mounts on affected airplanes have developed cracks. One operator discovered cracking during a routine inspection on the aft flange of the left engine forward carry-through mount bracket. Additional airplanes were subsequently inspected, and cracking was discovered in the same location on four airplanes. At the time of the crack findings, all of those airplanes had accumulated between 2,000 and 3,000 total flight hours, and all were equipped with thrust reversers. The cracks originate in the radius of the cutout of the aft flange of the engine mount brackets. The purpose of the cutout is to provide clearance for certain engine components. Because all of these airplanes were equipped with thrust reversers, it was initially determined that the condition would be found only on airplanes with thrust reversers. However, similar cracking was later discovered on a number of airplanes without thrust reversers. The cause ofthe cracking has not been determined. This condition, if not corrected, could result in failure of the engine mount and possible loss of the engine, and consequent loss of control of the airplane.
Explanation of Relevant Service Information
The FAA has reviewed and approved Raytheon Safety Communique No. 189, Revision 1, dated January 2002, which describes procedures for a one-time visual inspection to detect evidence of cracking of the left engine forward carry-through mount bracket, and a subsequent one-time fluorescent penetrant inspection to detect cracking in the same area. The communique recommends immediate replacement of any cracked bracket with a new bracket and fitting.
Explanation of the Requirements of the Rule
Since an unsafe condition has been identified that is likely to exist or develop on other Raytheon Model Beech 400, 400A, and 400T series airplanes; Model Beech MU-300-10 airplanes; and Model Mitsubishi MU-300 airplanes of the same type design, thisAD is being issued to prevent failure of the engine mount and possible loss of the engine, and consequent loss of control of the airplane. This AD requires repetitive inspections to detect cracking in the radius of the cutout of the aft flange of the left engine forward carry-through mount bracket, and replacement with a new bracket and fitting if necessary. The actions are required to be accomplished in accordance with the service information described previously, except as discussed below.
Requirements for Ferry Flight Permit
The FAA has determined that a ferry flight permit, if granted, must include certain limitations for airplanes equipped with thrust reversers, due to the increased loads and vibration levels associated with thrust reverser operation.
Differences Between AD and Relevant Service Information
The applicability of this AD and the manufacturer's Safety Communique No. 189 are identical with the exception of one serial number. For Beech MU-300-10 airplanes, the communique specifies serial numbers A1001SA through 1010SA inclusive. The type certification data sheet for this model specifies A1011SA as the last serial number. The FAA assumes serial number A1011SA may have been converted to a different model and reidentified and therefore has determined that it is necessary to include serial number A1011SA in the applicability of this AD to ensure the inclusion of all airplanes subject to the identified unsafe condition.
In addition, Safety Communique No. 189 recommends inspection of the subject area via a one-time visual inspection within 25 flight hours (for airplanes with more than 1,500 total flight hours) and a one-time fluorescent penetrant inspection within 50 flight hours. However, in light of the potential severity of the unsafe condition and the uncertainty of the cause of the premature cracking, the FAA finds these recommendations inadequate to address the identified unsafe condition in a timely manner. The FAA has determined that a fluorescent penetrant inspection could detect cracking that a visual inspection might miss. Also, the FAA has determined that the initial inspection must be performed at the earlier of 14 days or 25 flight hours, and that the inspections must be repetitively performed, to timely detect cracking that could contribute to the unsafe condition.
In developing appropriate actions and compliance times for this AD, the FAA considered not only the manufacturer's recommendations, but the availability of parts, the average utilization of the affected fleet, the time necessary to perform an inspection (2 work hours), and the degree of urgency associated with addressing the identified unsafe condition. In light of all of these factors, the FAA finds initial and repetitive fluorescent penetrant inspections to be warranted, in that they will provide more detailed data, allow operators to detect cracking before it becomes a hazard to the structure, and provide the necessary continuedoperational safety for the fleet.
Interim Action
This is considered to be interim action until final action is identified, at which time the FAA may consider further rulemaking.
Determination of Rule's Effective Date
Since 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.
Comments Invited
Although 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.
Submit comments using the following format:
Organize comments issue-by-issue. For example, discuss a request to change the compliance time and a request to change the service bulletin reference as two separate issues.
For each issue, state what specific change to the AD is being requested.
Include justification (e.g., reasons or data) for each request.
Comments 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.
Commenters 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-382-AD." The postcard will be date-stamped and returned to the commenter.
Regulatory Impact
The 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.
The 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.
List of Subjects in 14 CFR Part 39
Air transportation, Aircraft, Aviation safety, Incorporation by reference, Safety.
Adoption of the Amendment
Accordingly, 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:
PART 39--AIRWORTHINESS DIRECTIVES
1. The authority citation for part 39 continues to read as follows:
Authority: 49 U.S.C. 106(g), 40113, 44701.
Sec. 39.13 [Amended]
2. Section 39.13 is amended by adding the following new airworthiness directive: