AD 94-17-15 ACTIVE

This amendment adopts a new airworthiness directive (AD) that is applicable to The Enstrom Helicopter Corporation (Enstrom) Model F-28A, F-28C, F-28C2, F-28F, 280, 280C, 280F, and 280FX series helicopters. This action requires initial and repetitive inspections for delamination of the main rotor feathering elastomeric Lamiflex bearing (Lamiflex bearing). This amendment is prompted by several reported failures of the Lamiflex bearing. The actions specified in this AD are intended to prevent failure of the Lamiflex bearing, abnormal vibrations in the airframe and flight control system, and subsequent loss of control of the helicopter.

Final rule; request for comments

94-17-15 THE ENSTROM HELICOPTER CORPORATION: Amendment 39-9010. Docket No. 94-SW-09-AD.
Applicability: Model F-28A, F-28C, F-28C2, F-28F, 280, 280C, 280F, and 280FX series helicopters, equipped with main rotor feathering elastomeric Lamiflex bearing (Lamiflex bearing), part numbers (P/N) 28-14320-12 or 28-14320-15, certificated in any category.

Compliance: Required as indicated, unless accomplished previously.

To prevent failure of the Lamiflex bearing, abnormal vibrations in the airframe and flight control system, and subsequent loss of control of the helicopter, accomplish the following:

(a) Within the next 5 hours' time-in-service (TIS) or whenever main rotor tracking and balancing procedures are required more than once in 5 hours' TIS, or abnormal airframe or flight control system vibrations exist, remove and visually inspect the Lamiflex bearing for evidence of delamination in accordance with the Inspection Criteria of paragraph 5.2 in The Enstrom Helicopter Corporation Service Directive Bulletin No. 0081, Revision A, dated November 16, 1992.

(b) Repeat the inspections of paragraph (a) at intervals not to exceed 100 hours' TIS since the last inspection or during each annual inspection, whichever occurs first.

(c) If Lamiflex bearing delamination is found during the inspections required by paragraph (a) or (b) of this AD, replace the Lamiflex bearing with an airworthy Lamiflex bearing before further flight.

(d) If any Lamiflex bearing is found that has no date stamped or etched on an end plate, remove and replace it with an airworthy Lamiflex bearing before further flight.

(e) No later than 5 years from the date of manufacture of the Lamiflex bearing, remove and replace the Lamiflex bearing with an airworthy Lamiflex bearing.

(f) This AD establishes a retirement life of 5 years for the Lamiflex bearing.

NOTE: The Enstrom Helicopter Corporation Service Information Letter No. 0097, dated July 1, 1980, pertainsto the replacement of the Lamiflex bearing.

(g) An alternative method of compliance or adjustment of the compliance time that provides an acceptable level of safety may be used when approved by the Manager, Chicago Aircraft Certification Office, FAA. Operators shall submit their requests through an FAA Principal Maintenance Inspector, who may concur or comment and then send it to the Manager, Chicago Aircraft Certification Office.

NOTE: Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the Chicago Aircraft Certification Office.

(h) Special flight permits may be issued in accordance with sections 21.197 and 21.199 of the Federal Aviation Regulations (14 CFR 21.197 and 21.199) to operate helicopters that do not have abnormal vibrations to a location where the requirements of this AD can be accomplished.

(i) The inspection, removal, and replacement shall be done in accordance with The Enstrom Helicopter Corporation Service Directive Bulletin No. 0081, Revision A, dated November 16, 1992. This incorporation by reference was approved by the Director of the Federal Register in accordance with 5 U.S.C. 552(a) and 1 CFR part 51. Copies may be obtained from The Enstrom Helicopter Corporation, Twin County Airport, P.O. Box 490, Menominee, Michigan 49858. Copies may be inspected at the FAA, Office of the Assistant Chief Counsel, 2601 Meacham Blvd., Room 663, Fort Worth, Texas; or at the Office of the Federal Register, 800 North Capitol Street, NW., suite 700, Washington, DC.

(j) This amendment becomes effective on September 15, 1994.

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:

Submit comments in triplicate to the Federal Aviation Administration (FAA), Office of the Assistant Chief Counsel, Attention: Rules Docket No. 94-SW-09-AD, 2601 Meacham Blvd., Room 663, Fort Worth, Texas 76137.
The service information referenced in this AD may be obtained from The Enstrom Helicopter Corporation, Twin County Airport, P.O. Box 490, Menominee, Michigan 49858. This information may be examined at the FAA, Office of the Assistant Chief Counsel, 2601 Meacham Boulevard, Room 663, Fort Worth, Texas; or at the Office of the Federal Register, 800 North Capitol Street, NW., suite 700, Washington, DC.

Mr. Joe McGarvey, Aerospace Engineer, Chicago Aircraft Certification Office, Airframe Branch, FAA, Small Airplane Directorate, 2300 East Devon Avenue, Room 232, Des Plaines, Illinois 60018, telephone (708) 294-7136, fax (708) 294-7834.