This amendment adopts a new airworthiness directive (AD) that is applicable to Enstrom Model F-28A, F-28C, F-28C2, F-28F, 280, 280C, 280F, and 280FX series helicopters. Field reports indicate that several failures of the main rotor feathering elastomeric Lamiflex bearings (Lamiflex bearings), part numbers (P/N) 28-14320-12 or 28-14320-15, have occurred in which the Lamiflex bearings have partially delaminated and extruded rubber and brass. This delamination and extrusion caused a significant loss in flight control system feedback dampening and resulted in a sudden increase in flight control system feedback, rotorcraft vibration, and degradation in flying qualities. Continued operation of the helicopters resulted in complete delamination of the Lamiflex bearings. The exact cause of the bearing delaminations is under investigation; however, both grease contamination and main rotor overspeeds may have contributed to the reported premature failures. The reported Lamiflex bearing delaminations occurred between 200 and 400 hours' total time-in-service (TIS). The Lamiflex bearing, located in the main rotor retention system, allows the blades to change pitch, or angle of attack. Although delamination and degradation of the Lamiflex bearing occurs slowly, once complete delamination has occurred, flying conditions could rapidly deteriorate. This condition, if not corrected, could result in failure of the Lamiflex bearing, abnormal vibrations in the airframe and flight control systems, and subsequent loss of control of the helicopter.
The FAA has reviewed The Enstrom Helicopter Corporation Service Directive Bulletin (SDB) No. 0081, Revision A, dated November 16, 1992, which describes procedures for performing a visual inspection of the Lamiflex bearing for delamination within the next 5 hours' TIS or whenever: 1) there is a significant deterioration in ride quality during flight; 2) a smooth rotor system suddenly loses track and/or experiences difficulty in maintaining a smooth track; 3) a trimmable aircraft becomes untrimmable, or develops high cyclic stick forces; or 4) there is any sudden abnormal feedback from the cyclic or collective controls, followed by a moderate to severe one-per-rev vibration. The SDB also describes procedures for performing repetitive visual inspections of the Lamiflex bearing for delamination at each 100 hours' TIS or at the annual inspection, whichever occurs first. The FAA has also reviewed Enstrom Helicopter Corporation Service Information Letter (SIL) No. 0097, dated July 1, 1980, that provides information on replacement of the Lamiflex bearing no later than 5 years from the date of manufacture. Since 1975, the date of manufacture has been stamped or etched on the end plate of each Lamiflex bearing to assist in complying with the SIL.
Since an unsafe condition has been identified that is likely to exist or develop on other Enstrom Model F-28A, F-28C, F-28C2, F-28F, 280, 280C, 280F, and 280FX series helicopters of the same type design, this AD is being issued to prevent failure of the Lamiflex bearing, abnormal vibrations in the airframe and flight control system, and subsequent loss of control of the helicopter. This AD requires initial and repetitive visual inspections of the Lamiflex bearing for delamination within the next 5 hours' TIS; whenever main rotor tracking and balancing procedures are required more than once within a 5 hours' TIS period; or, whenever abnormal airframe or flight control system vibrations exist; and, replacement with an airworthy part if delamination is found. The AD also requires replacement of the Lamiflex bearing not later than 5 years after the date of manufacture of the Lamiflex bearing. The actions would be required to be accomplished in accordance with the SDB described previously and the applicable maintenance manual. Due to the critical need for the Lamiflex bearing to ensure the continued safe flight of the affectedhelicopters, and the necessary short compliance time that requires an inspection for delamination of the Lamiflex bearing be conducted upon the occurrence of specified conditions or within the next 5 hours' TIS, this rule must be issued immediately to correct an unsafe condition in the affected helicopters.
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 should identify the Rules Docketnumber 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.
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 No. 94-SW-09-AD." The postcard will be date stamped and returned to the commenter.
The 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.
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 regulationunder 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. App. 1354(a), 1421 and 1423; 49 U.S.C. 106(g); and 14 CFR 11.89.
39.13 -[Amended]
2. Section 39.13 is amended by adding a new airworthiness directive to read as follows: