AD 99-25-08

This document publishes in the Federal Register an amendment adopting Emergency Priority Letter Airworthiness Directive (AD) 99-25-08, which was sent previously to all known U.S. owners and operators of MD Helicopters Inc. (MDHI) Model 500N and 600N helicopters by individual letters. This AD requires, within the next 5 hours time-in-service (TIS) or before further flight after December 31, 1999, whichever occurs first, inspecting the thruster control cable conduit cap (cap) for corrosion or a crack. This AD also requires, within the next 100 hours TIS or before further flight after February 19, 2000, whichever occurs first, inspecting the cap at a specified area of the forward and center thruster cables for corrosion or a crack. If an unacceptable crack is found, replacing the unairworthy thruster cable with an airworthy thruster cable is required. This amendment is prompted by the discovery of stress corrosion cracks on an MDHI Model 500N helicopter. The actions specified by this AD are intended to prevent failure of the cap causing a fixed thruster condition and subsequent loss of normal anti-torque directional control of the helicopter.

Final rule; request for comments

99-25-08 MD HELICOPTERS INC.: Amendment 39-11564. Docket No. 99-SW-71-AD.

Applicability: Model 500N helicopters, serial numbers (S/N) 001 through 099 with a prefix of "LN", and Model 600N helicopters, S/N 003 through 074 with a prefix of "RN", certificated in any category.

NOTE 1: This AD applies to each helicopter identified in the preceding applicability provision, regardless of whether it has been otherwise 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 request approval for an alternative method of compliance in accordance with paragraph (e) of this AD. The request should include an assessment of the effect of the modification, alteration, or repair on the unsafe condition addressed by this AD; and, if the unsafe condition has not been eliminated, the request should include specific proposed actions to address it.

Compliance: Required as indicated, unless accomplished previously.

To prevent failure of the thruster control cable conduit cap (cap) at the telescopic swivel end or relieved area and subsequent loss of normal anti-torque directional control of the helicopter, accomplish the following:

(a) Within 5 hours time-in-service (TIS) or before further flight after December 31, 1999, whichever occurs first, inspect the forward and center thruster control cables, part number (P/N) 500N7201-5, -7, -37, -45, or -51, installed in affected helicopters, for a crack, corrosion, or damage in the cap at the telescopic swivel end in accordance with the following paragraphs of the Accomplishment Instructions, Section 2, of MD Helicopters Inc. (MDHI) Service Bulletin SB500N-021 SB600N-028, dated November 19, 1999 (SB 021/028).

(1) Inspect the forward thruster control cables in accordance with paragraphs A.(1) through (5) of SB 021/028. Install safety wire in accordance with paragraph A.(7) of SB 021/028.

(2) Inspect the center thruster control cable in accordance with paragraphs B.(1) through (4) and (6) of SB 021/028.

(3) If an unacceptable crack or ball separation from the cap is found, remove and replace the unairworthy forward or center thruster control cable with an airworthy cable prior to further flight.

(b) Within 100 hours TIS or before further flight after February 19, 2000, whichever occurs first, inspect the forward and center thruster control cables, P/N 500N7201-5, -7, -37, -45, or -51, installed in affected helicopters in the cap relieved area for a crack, corrosion, or damage in accordance with the Accomplishment Instructions, Section 2, of MDHI SB SB500N-020R1 SB600N-027R1, dated November 24, 1999 (SB 020/027).

(1) Inspect the forward thruster control cable for a crack or corrosion in accordance with paragraphs B.(1) through (5) and (7) of SB 020/027.

(2) Inspect the center thruster control cable for a crack or corrosion in accordance with paragraphs C.(1) through (4), (6), and (for Model 600N only) (7) of SB 020/027.

(3) If an unacceptable crack is found, remove and replace the unairworthy forward or center thruster control cable with an airworthy cable prior to further flight.

(c) Repeat the inspections of paragraphs (a) and (b) of this AD at intervals not to exceed 100 hours TIS or 3 calendar months, whichever occurs first.

(d) On or before December 1, 2000, replace the forward and center thruster control cables, part number (P/N) 500N7201-5, -7, -37, and -45, and -51, with P/N 500N7201-55 and -57 on the MDHI Model 500N or P/N 500N7201-55 and -59 on the MDHI Model 600N. Accomplishment of the requirements of this paragraph is terminating action for the requirements of this AD.

(e) 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, LosAngeles 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 2: 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.

(f) Special flight permits will not be issued.

(g) The inspections required within 5 hours time-in-service or before further flight after December 31, 1999, whichever occurs first, shall be done in accordance with the following paragraphs of the Accomplishment Instructions, Section 2, of MD Helicopters Inc. Service Bulletin SB500N-021 SB600N-028, dated November 19, 1999:

Paragraphs A.(1) through (5);
Paragraph A.(7);
Paragraphs B.(1) through (4) and (6).

The inspections required within 100 hours time-in-service shall be done in accordance with the following paragraphs of the Accomplishment Instructions, Section 2, of MDHI SB SB500N-020R1 SB600N-027R1, dated November 24, 1999:

Paragraphs B.(1) through (5) and (7);
Paragraphs C.(1) through (4),(6), and (for Model 600N only) (7).

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 MD Helicopters Inc., Attn: Customer Support Division, 5000 E. McDowell Rd., Mail Stop M615-GO48, Mesa, Arizona 85215-9797, telephone 1-800-388-3378 or 480-891-6342, fax 480-891-6782. Copies may be inspected 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.

(h) This amendment becomes effective on March 1, 2000, to all persons except those persons to whom it was made immediately effective by Emergency Priority Letter AD99-25-08, issued November 26, 1999, which contained the requirements of this amendment.

On November 26, 1999, the FAA issued Emergency Priority Letter AD 99-25-08, applicable to MDHI Model 500N and 600N helicopters, which requires, within the next 5 hours time-in-service (TIS) or before further flight after December 31, 1999, inspecting the cap for corrosion or a crack. The emergency priority letter AD also requires, within the next 100 hours TIS or before further flight after February 19, 2000, inspecting the cap for corrosion or a crack. If an unacceptable crack is found, replacing the unairworthy thruster cable with an airworthy thruster cable is required. That action was prompted by the discovery of stress corrosion cracks in the forward cap at the telescopic swivel end and the relieved area on an MDHI Model 500N helicopter. The forward thruster control cable in conjunction with the center thruster control cable simultaneously control the NOTAR directional control thruster and the left vertical stabilizer. This condition, if not corrected, could result in failure of the cap causing a fixed thruster condition and subsequent loss of normal anti-torque directional control of the helicopter.

The FAA has reviewed MDHI Service Bulletin (SB) SB500N-021 SB600N-028, dated November 19, 1999, and SB500N-020R1 SB600N-027R1, dated November 24, 1999, which describe procedures for inspecting the cap telescopic swivel end and the cap relieved area for corrosion or a crack and repairing or replacing the forward and center thruster control cables as specified.

Since the unsafe condition described is likely to exist or develop on other MDHI Model 500N and 600N helicopters, which use the same forward thruster cable, the FAA issued Emergency Priority Letter AD 99-25-08 to prevent failure of the cap causing a fixed thruster condition and subsequent loss of normal anti-torque directional control of the helicopter. The AD requires, within the next 5 hours TIS or before further flight after December 31, 1999, whichever occursfirst, inspecting the cap at the telescopic swivel end of the forward and center thruster cables, part number (P/N) 500N7201-5, -7, -37, -45, or -51, for corrosion or a crack in accordance with SB500N-021 SB600N-028, dated November 19, 1999. This AD also requires, within the next 100 hours TIS or before further flight after February 19, 2000, whichever occurs first, inspecting the cap at the relieved area of the forward and center thruster cables, part number (P/N) 500N7201-5, -7, -37, -45, or -51, for corrosion or a crack in accordance with SB500N-020R1 SB600N-027R1, dated November 24, 1999. If an unacceptable crack is found, replacing the unairworthy thruster cable with an airworthy thruster cable is required. The actions must be accomplished in accordance with the SB's described previously. The short compliance time involved is required because the previously described critical unsafe condition can adversely affect the controllability of the helicopter. Therefore, inspecting the cap for corrosion or a crack is required before further flight and inspecting the cap at a specified area is required within 100 hours TIS or before further flight after February 19, 2000, whichever occurs first, and this AD must be issued immediately.

Since it was found that immediate corrective action was required, notice and opportunity for prior public comment thereon were impracticable and contrary to the public interest, and good cause existed to make the AD effective immediately by individual letters issued on November 26, 1999, to all known U.S. owners and operators of MDHI Model 500N and 600N helicopters. These conditions still exist, and the AD is hereby published in the Federal Register as an amendment to section 39.13 of the Federal Aviation Regulations (14 CFR 39.13) to make it effective to all persons.

The FAA estimates that 89 helicopters of U.S. registry will be affected by this AD, that it will take approximately 6 work hours per helicopter, per inspection, and 8 work hours to replace a thruster cable, if necessary. The average labor rate is $60 per work hour. Required parts will cost approximately $1,000 for each thruster cable replaced. Based on these figures, the total cost impact of the AD on U.S. operators is estimated to be $67,040, assuming 2 inspections per helicopter, per year, and replacement of 2 thruster cables.

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 maybe 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. 99-SW-71-AD." The postcard will be date stamped and returned to the commenter.

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.

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