AD 98-15-26

This amendment supersedes an existing priority letter Airworthiness Directive (AD) 98-03-15, applicable to McDonnell Douglas Helicopter Systems (MDHS) Model 369, 369A, 369D, 369E, 369F, 369FF, 369H, 369HE, 369HM, 369HS, 500N, 600N, and OH-6 helicopters that currently requires an inspection for main rotor blade (blade) cracks and for missing or cracked adhesive or paint. This amendment requires the same inspections required by the existing priority letter AD but deletes the Model 369 (Army YOH-6A), specifies recording torque events (TE), and establishes a shorter retirement life for certain blades. This amendment is prompted by an accident in which a blade failed on a Model 369D helicopter due to fatigue cracks. The actions specified by this AD are intended to detect cracks that could lead to failure of the blade and subsequent loss of control of the helicopter.

Final rule; request for comments

98-15-26 MCDONNELL DOUGLAS HELICOPTER SYSTEMS: Amendment 39-10675. Docket No. 98-SW-22-AD. Supersedes Priority Letter AD 98-03-15, Docket No. 98-SW-06-AD which Supersedes Priority Letter AD 98-01-13, Docket No. 97-SW-68-AD.

Applicability: Model 369A, 369D, 369E, 369F, 369FF, 369H, 369HE, 369HM, 369HS, 500N, 600N, and OH-6A helicopters with main rotor blades Part Number (P/N) 369A1100-507 with Serial Number (S/N) D139 through D203, D209 through D223; P/N 369D21100-517 with S/N H664, H665, H667, H669, H671, H672, H674, H676, H679, H680, H683 through H724, H726 through H999, J000 through J039, J041 through J055; or P/N 369D21102-517 with S/N 1976 through 2100, 2106 through 2115, installed, certificated in any category.

NOTE 1: This AD applies to each helicopter identified in the preceding applicability provision, regardless of whether it has been modified, altered, or repaired in the area subject to the requirements of this AD. For helicopters that have been modified, altered, or repaired so that the performance of the requirements of this AD is affected, the owner/operator must use the authority provided in paragraph (f) to request approval from the FAA. This approval may address either no action, if the current configuration eliminates the unsafe condition, or different actions necessary to address the unsafe condition described in this AD. Such a request should include an assessment of the effect of the changed configuration on the unsafe condition addressed by this AD. In no case does the presence of any modification, alteration, or repair remove any helicopter from the applicability of this AD.

Compliance: Required as indicated, unless accomplished previously.

(a) For Model 369A, 369D, 369E, 369F, 369FF, 369H, 369HE, 369HM, 369HS, 500N, and OH-6A helicopters with any affected main rotor blade (blade) that has 600 or more hours time-in-service (TIS), to detect cracks that could lead to failure of the blade and subsequent loss of control of the helicopter, before further flight and thereafter at intervals not to exceed 25 hours TIS, accomplish the following:

(1) With each blade lifted off the droop stop, using a 10X or higher magnifying glass, visually inspect the blade for any chordwise cracking starting at the root fitting edge on the blade lower surface doubler and skin or cracks on the doubler adjacent to the root end fitting (Figure 1). If any cracking is discovered, remove the blade and replace it with an airworthy blade.

NOTE 2: Boeing McDonnell Douglas Helicopter Systems Service Bulletin No. SB369H-243R3, SB369E-088R3, SB500N-015R3, SB369D-195R3, SB369F-075R3, SB600N-007R2, dated July 13, 1998 (SB), pertains to the subject of this AD.
(2) With each blade lifted off the droop stop, inspect the lower surface for missing or cracked adhesive or paint at the root end fitting-to-doubler bond line (Figure 1). If any missing or cracked adhesive or paint is discovered, remove and inspect the bladein accordance with paragraph 3E of Part II of the Accomplishment Instructions in McDonnell Douglas Helicopter Systems Service Information Notice No. HN-239, DN-188, EN-81, FN-67, NN-008, dated October 27, 1995. If there is any disbonding in excess of the allowable margins specified in paragraph 3E of Part II of the service information notice, replace the blade with an airworthy blade.

(b) For the Model 600N helicopters, before further flight, remove any affected blade from service and replace it with an airworthy blade not listed in the applicability section of this AD. Blades removed from the Model 600N helicopters are not eligible for use on any rotorcraft.

NOTE 3: The recurring inspection requirements, contained in paragraph (a) of this AD, DO NOT apply to the Model 600N helicopters.

(c) Affected blades are to be removed from service on or before reaching either of the applicable new life limits. The new life limits are determined by hours TIS or number of torque events (TE). A torque event is defined as the transition to a hover from forward flight. For this definition of TE, forward flight is considered to be flight at any airspeed after attaining translational lift.

(1) For blades that do not have TE logged, prior to further flight, log the TE in the rotorcraft log or equivalent record as follows:

(i) Log the number of TE, if known.

(ii) For noncargo hook operations, if the number of TE is unknown, log 6 TE for each hour TIS.

(iii) For cargo hook (external load) operations, or for any combination of noncargo hook operations and cargo hook (external load) operations, if the number of TE is unknown, log 20 TE for each hour TIS.

(2) Make an entry into the component record or equivalent record to reflect new life limits for blade P/N's as follows.

(i) For P/N 369A1100-507, Models 369A, 369H, 369HE, 369HM, 369HS, and OH-6A, enter 1,750 hours TIS or 10,600 TE, whichever occurs first.

(ii) For P/N 369D21100-517, Models 369D and 369E, enter 2,500 hours TIS or 15,000 TE, whichever occurs first.

(iii) For P/N 369D21102-517, Model 369F, 369FF, and 500N, enter 2,500 hours TIS or 15,000 TE, whichever occurs first.

(d) After compliance with paragraph (c) of this AD, during each operation thereafter, maintain a count of TE performed and additional hours TIS accumulated, and, at the end of each day's operations, add those counts to the accumulated number of TE and hours TIS on the rotorcraft log or equivalent record.

(e) The blades are no longer retired based upon only hours TIS. This AD revises the Airworthiness Limitations Section of the maintenance manual by establishing a new retirement life for certain blade P/N's based on hours TIS or a number of TE, whichever occurs first.

(f) An alternative method of compliance or adjustment of the compliance time that provides an acceptable level of safety may be used if approved by the Manager, Los Angeles 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, Los Angeles Aircraft Certification Office.

NOTE 4: Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the Los Angeles Aircraft Certification Office.

(g) Special flight permits will not be issued.

(h) The inspection required by paragraph (a)(2) of this AD shall be done in accordance with McDonnell Douglas Helicopter Systems Service Information Notice No. HN-239, DN-188, EN-81, FN-67, NN-008, dated October 27, 1995. 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 McDonnell Douglas Helicopter Systems, Commercial Technical Publications, Bldg. M615/G048, 5000 E. McDowell Road, Mesa, Arizona 85215-9797, telephone (602)891-3667, fax (602) 891-6522. Copies may be examined at the FAA, Office of the Regional Counsel, Southwest Region, 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.

(i) This amendment becomes effective on August 3, 1998.

On January 29, 1998, the FAA issued Priority Letter AD 98-03-15, applicable to Boeing MDHS Model 369, 369A 369D, 369E, 369F, 369FF, 369H, 369HE, 369HM, 369HS, 500N, 600N, and OH-6 helicopters, which requires an inspection for blade cracks and for missing or cracked adhesive or paint. That priority letter AD was prompted by an accident in which a blade failed on a Boeing MDHS Model 369D helicopter due to cracks. The blade that failed had accumulated over 2,300 hours time-in-service (TIS). Subsequent investigation revealed cracks in two other blades on the same helicopter. Additionally, an operator reported finding a blade crack as a result of complying with AD 98-01-13. The cracks had initiated in the lower doubler and propagated in a chordwise direction through the blade skin and spar. These fatigue cracks may have been caused by residual stresses induced by nonconforming doublers used to construct the blade. A fatigue crack in a blade creates anunsafe condition. That condition, if not detected, could result in failure of the blade and subsequent loss of control of the helicopter.

The FAA previously issued AD 95-03-13, effective March 21, 1995, Docket No. 94-SW-05-AD; AD 96-10-09, effective May 29, 1996, Docket No. 96-SW-02-AD; Priority Letter AD 98-01-13, issued December 31, 1997, Docket No. 97-SW-68-AD, and Priority Letter AD 98-03-15 issued January 29, 1998, Docket No. 98-SW-06-AD, all of which mandate inspections in the same general area. Priority Letter AD 98-03-15 superseded Priority Letter AD 98-01-13. This AD supersedes Priority Letter AD 98-03-15. This AD does not supersede AD 95-03-13 or AD 96-10-09.

Since the issuance of AD 98-03-15, the FAA has determined the need for establishing and recording of torque events (TE) plus the lowering of the limit lives of the main rotor blades. The FAA has reviewed Boeing McDonnell Douglas Helicopter Systems Service Bulletin No. SB369H-243R3, SB369E-088R3, SB500N-015R3, SB369D-195R3, SB369F-075R3, SB600N-007R2, dated July 13, 1998 (SB). The SB describes procedures for a visual inspection of certain main rotor blades using a 10X magnifying glass. The inspections are intended to detect cracking of the lower surface of each blade starting at the root fitting and the doubler at the inboard end of the blade and to detect debonding between the blade root end fitting and doubler if missing or cracked adhesive or paint is observed. For all affected helicopters except the Model 600N, with blades installed that have 600 or more hours TIS, the SB provides that these inspections are to be accomplished prior to further flight, and thereafter at intervals not to exceed 25 hours TIS. For Model 600N helicopters, the SB provides, prior to further flight, removal of affected blades due to higher blade stresses on this model as compared to other affected models. Additionally, this SB introduces flight hour factoring as a means of addressing certain low cycle fatigue by providing an alternate retirement life for the affected blades based on TE. The manufacturer has determined that this action would not affect any Model 369 (Army YOH-6A) helicopters. There are no known Model 369 helicopters in the U.S. fleet. Further, there were only two Model 369 helicopters produced as prototype Army YOH-6A. Therefore, the Model 369 helicopter is deleted from the SB. The FAA has also reviewed McDonnell Douglas Helicopter Systems Service Information Notice No. HN-239, DN-188, EN-81, FN-67, NN-008, dated October 27, 1995, which describes procedures for an inspection for debonding between the blade root end fitting and doubler if missing or cracked adhesive or paint is observed.

Since an unsafe condition has been identified that is likely to exist or develop on other MDHS Model 369A, 369D, 369E, 369F, 369FF, 369H, 369HE, 369HM, 369HS, 500N, 600N, and OH-6A helicopters of the same type design, this AD requires, before further flight, and thereafter at intervals not to exceed 25 hours TIS, for affected blades that have 600 or more hours TIS, a visual inspection for cracks in the lower surface of the blade root fitting and doubler at the inboard end of the blade and for missing or cracked adhesive or paint at the root end-to-doubler bonding line. The inspections will be accomplished using a 10X or higher magnifying glass. Blades will be removed from service before or upon the accumulation of a specified number of TE or hours TIS, whichever occurs first. Since this same unsafe condition is likely to exist on MDHS Model 600N helicopters and develop at a faster rate because of higher blade stresses, this AD requires removal of certain main rotor blades prior to further flight and replacement with airworthy blades.

The short compliance time involved is required because the previously described critical unsafe condition can adversely affect the controllability and structural integrity of the helicopter. Therefore, inspecting for blade cracks and missing or cracked adhesive or paint, removing certain MDHS Model 600N helicopter blades, and reducing the service life for the blades are required prior to further flight, and this AD must be issued immediately.

Since issuance of Priority Letter 98-03-15, the FAA has evaluated additional data and has determined that the reduction of the service life of the affected blades is appropriate. The actions are required to be accomplished in accordance with this AD and Service Information Notice No. HN-239, DN-188, EN-81, FN-67, NN-008, dated October 27, 1995, described previously.

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.

The FAA estimates that 1,030 helicopters of U.S. registry will be affected by this AD, and it will take approximately 0.5 hours perhelicopter to determine whether an affected blade is installed, 1 work hour per helicopter with an affected blade for the initial inspection, and 2.5 hours to replace a blade at a rate of $60 per work hour. Required parts will cost approximately $6200 per blade. Based on these figures, the total cost impact of the proposed AD on U.S. operators is estimated to be $3,799,980 to inspect the blades for cracks and to replace 588 affected blades.

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 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.

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. 98-SW-22-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 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.

39.13 [Amended]
2. Section 39.13 is amended by adding a new airworthiness directive (AD) to read as follows: