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###### Department of Transportation

###### Federal Aviation Administration 

          - 14 CFR Part 39 
          - [Docket No. FAA-2007-27343; Directorate Identifier 2007-SW-05-AD; Amendment 39-15030; AD 2007-05-51] 
          - RIN 2120-AA64 

# AGENCY:

Federal Aviation Administration, DOT. 

# ACTION:

Final rule; request for comments. 

# SUMMARY:

                        This document publishes in the                         **Federal Register**                         an amendment adopting Airworthiness Directive (AD) 2007-05-51, which was sent previously to all known U.S. owners and operators of MDHI Model MD600N helicopters by individual letters. This AD requires, before further flight, a visual and eddy current inspection of each lateral mixer output link assembly (mixer link) and replacing any cracked mixer link. This AD also requires performing an eddy current inspection on each mixer link before installing it on any helicopter. This amendment is prompted by the discovery of 3 cracked mixer links. The actions specified by this AD are intended to detect a crack in the mixer link, which could result in failure of the mixer link and subsequent loss of control of the helicopter.                     

# DATES:

Effective May 7, 2007, to all persons except those persons to whom it was made immediately effective by Emergency AD 2007-05-51, issued on February 17, 2007, which contained the requirements of this amendment. 

Comments for inclusion in the Rules Docket must be received on or before June 19, 2007. 

# ADDRESSES:

Use one of the following addresses to submit comments on this AD: 
      -  DOT Docket Web site:                          Go to                          http://dms.dot.gov                          and follow the instructions for sending your comments electronically;                     
      -  Government-wide rulemaking Web site:                          Go to                          http://www.regulations.gov                          and follow the instructions for sending your comments electronically;                     
      -  Mail:                          Docket Management Facility; U.S. Department of Transportation, 400 Seventh Street, SW., Nassif Building, Room PL-401, Washington, DC 20590;                     
      -  Fax:                          (202) 493-2251; or                     
      -  Hand Delivery:                          Room PL-401 on the plaza level of the Nassif Building, 400 Seventh Street, SW., Washington, DC, between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays.                     

                        You may get the service information identified in this AD from MD Helicopters Inc., Attn: Customer Support Division, 4555 E. McDowell Rd., Mail Stop M615, Mesa, Arizona 85215-9734, telephone 1-800-388-3378, fax 480-346-6813, or on the Web at                         *http://www.mdhelicopters.com.*

### Examining the Docket 

                    You may examine the docket that contains the AD, any comments, and other information on the Internet at                     *http://dms.dot.gov,*                     or in person at the Docket Management System (DMS) Docket Offices between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays. The Docket Office (telephone (800) 647-5227) is located on the plaza level of the Department of Transportation Nassif Building at the street address stated in the                     **ADDRESSES**                     section. Comments will be available in the AD docket shortly after the DMS receives them.                 

# FOR FURTHER INFORMATION CONTACT:

Jon Mowery, Aviation Safety Engineer, FAA, Los Angeles Aircraft Certification Office, Airframe Branch, 3960 Paramount Blvd., Lakewood, California 90712, telephone (562) 627-5322, fax (562) 627-5210. 

# SUPPLEMENTARY INFORMATION:

                    On February 17, 2007 we issued Emergency AD 2007-05-51 for MDHI Model MD600N helicopters, which requires, before further flight, a visual and eddy current inspection of each mixer link and replacing any cracked mixer link.                           ( print page 19789)                        The Emergency AD also requires performing an eddy current inspection on each mixer link before installing it on any helicopter. That action was prompted by the discovery of a cracked mixer link, part number (P/N) 600N7636-1, on an in-service MDHI Model MD600N helicopter. Cracks were also found on two additional mixer links, P/N 600N7636-3, which were being held as spares. The cracks on all three mixer links run through the bearing end area of the mixer link and emanate from staking marks in the mixer link. Cracks in the mixer link, if not detected, could result in failure of the mixer link and subsequent loss of control of the helicopter.                 

We have reviewed MDHI Service Bulletin No. SB600N-044, dated February 16, 2007 (SB), which describes procedures for a one-time visual inspection and an eddy current inspection of the mixer link. The SB includes only P/Ns 600N7636-1, and -3 in its effectivity, however, because the exact cause of the cracks is unknown, and the -9 and -11 are similar designs, we have included them in the applicability of this AD. We are also requiring an eddy current inspection of each affected mixer link before installing it on any helicopter. 

Since the unsafe condition described is likely to exist or develop on other MDHI Model MD600N helicopters of the same type design, we issued Emergency AD 2007-05-51 to detect a crack in the mixer link, which could result in failure of the mixer link and subsequent loss of control of the helicopter. The AD requires, before further flight, the following for each mixer link, P/N 600N7636-1, -3, -9, and -11: 
    - Removing each mixer link, and visually inspecting, with a bright light and a 10x or higher magnifying glass, the areas on the ends of the mixer link on both sides around the bearing bore for any crack,
    - Performing an eddy current inspection of each mixer link in the bearing end areas, and
    - Replacing any cracked mixer link with an airworthy mixer link on which an eddy current inspection has been performed.

The AD also requires performing an eddy current inspection on each mixer link before installing it on any helicopter. 

The short compliance time involved is required because the previously described critical unsafe condition can adversely affect the structural integrity and controllability of the helicopter. Therefore, the actions described previously are required before further flight, and this AD must be issued immediately. 

A one-time flight permit is allowed for flying the helicopter to a location where the eddy current inspection can be performed, provided that no crack is found during the visual inspection required in paragraph (a) of this AD and that the helicopter's airspeed does not exceed 100 knots. 

The requirements of this AD are interim actions; the manufacturer continues to investigate the cause of the cracks and, based on that investigation, we will determine either follow-on actions or a terminating action for the requirements of this AD. 

                    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 February 17, 2007 to all known U.S. owners and operators of MDHI Model MD600N helicopters. These conditions still exist, and the AD is hereby published in the                     **Federal Register**                     as an amendment to 14 CFR 39.13 to make it effective to all persons.                 

We estimate that this AD will affect 26 helicopters of U.S. registry. It will take approximately: 
    - 2 work hours to remove, inspect, and replace both mixer links on each helicopter,
    - 5 work hours for an eddy current inspection of both mixer links,
    - $80 per work hour, and
    - $865 for a mixer link, if necessary.

Based on these figures, we estimate the total cost impact of the AD on U.S. operators to be $18,885, assuming that a visual and eddy current inspection are performed on each mixer link installed on a helicopter and that 5 of the 52 mixer links are cracked and need to be replaced. 

## Comments Invited 

                    This AD is a final rule that involves requirements that affect flight safety and was not preceded by notice and an opportunity for public comment; however, we invite you to submit any written data, views, or arguments regarding this AD. Send your comments to an address listed under                     **ADDRESSES**                    . Include “Docket No. FAA-2007-27343; Directorate Identifier 2007-SW-05-AD” at the beginning of your comments. We specifically invite comments on the overall regulatory, economic, environmental, and energy aspects of the AD. We will consider all comments received by the closing date and may amend the AD in light of those comments.                 

                    We will post all comments we receive, without change, to                     *http://dms.dot.gov,*                     including any personal information you provide. We will also post a report summarizing each substantive verbal contact with FAA personnel concerning this AD. Using the search function of our docket web site, you can find and read the comments to any of our dockets, including the name of the individual who sent the comment. You may review the DOT's complete Privacy Act Statement in the                     **Federal Register**                     published on April 11, 2000 (65 FR 19477-78), or you may visit                     *http://dms.dot.gov*.                 

## Regulatory Findings 

We have determined that this AD will not have federalism implications under Executive Order 13132. This AD 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. 

For the reasons discussed above, I certify that the regulation:

1. Is not a “significant regulatory action” under Executive Order 12866; 

2. Is not a “significant rule” under the DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979); and 

3. Will not have a significant economic impact, positive or negative, on a substantial number of small entities under the criteria of the Regulatory Flexibility Act. 

We prepared an economic evaluation of the estimated costs to comply with this AD. See the DMS to examine the economic evaluation. 

## Authority for This Rulemaking 

Title 49 of the United States Code specifies the FAA's authority to issue rules on aviation safety. Subtitle I, Section 106, describes the authority of the FAA Administrator. Subtitle VII, Aviation Programs, describes in more detail the scope of the Agency's authority. 

We are issuing this rulemaking under the authority described in Subtitle VII, Part A, Subpart III, Section 44701, “General requirements.” Under that section, Congress charges the FAA with promoting safe flight of civil aircraft in air commerce by prescribing regulations for practices, methods, and procedures the Administrator finds necessary for safety in air commerce. This regulation is within the scope of that authority because it addresses an unsafe condition that is likely to exist or develop on products identified in this rulemaking action. 

      ( print page 19790)    

# List of Subjects in 14 CFR Part 39

      - Air transportation
      - Aircraft
      - Aviation safety
      - 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 

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

**2007-05-51 MD Helicopters Inc. (MDHI):**                             Amendment 39-15030. Docket No. FAA-2007-27343; Directorate Identifier 2007-SW-05-AD.                         

*Applicability:*                             Model MD600N helicopters, with a lateral mixer output link assembly (mixer link), part number (P/N) 600N7636-1, -3, -9, or -11 installed, certificated in any category.                         

*Compliance:*                             Required as indicated, unless accomplished previously.                         

To detect a crack in the mixer link, which could result in failure of the mixer link and subsequent loss of control of the helicopter, accomplish the following: 

(a) Before further flight: 

(1) Remove each mixer link and visually inspect, with a bright light and a 10x or higher magnifying glass, the shaded areas around the bearing bore for any crack as depicted in the following Figure 1: 

(2) Perform an eddy current inspection of each mixer link in the bearing end areas. 

(3) Replace any cracked mixer link with an airworthy mixer link on which an eddy current inspection has been performed. 

# Note:

MDHI Service Bulletin No. SB600N-044, dated February 16, 2007, pertains to the subject of this AD.

(b) Perform an eddy current inspection on each mixer link before installing it on any helicopter. 

(c) To request a different method of compliance or a different compliance time for this AD, follow the procedures in 14 CFR 39.19. Contact the Manager, Los Angeles Aircraft Certification Office, FAA, ATTN: Jon Mowery, Aviation Safety Engineer, Airframe Branch, 3960 Paramount Blvd., Lakewood, California 90712, telephone (562) 627-5322, fax (562) 627-5210, for information about previously approved alternative methods of compliance. 

(d) A one-time special flight permit may be issued in accordance with 14 CFR 21.197 and 21.199 to operate the helicopter to a location where the eddy current inspection requirements of this AD can be accomplished provided that no crack is found during the visual inspection required in paragraph (a) of this AD and that the helicopter's airspeed does not exceed 100 knots. 

(e) This amendment becomes effective on May 7, 2007, to all persons except those persons to whom it was made immediately effective by Emergency AD 2007-05-51, issued February 17, 2007, which contained the requirements of this amendment. 

Issued in Fort Worth, Texas, on April 5, 2007. 

Mark R. Schilling, 

Acting Manager, Rotorcraft Directorate,  Aircraft Certification Service.

[FR Doc. E7-7438 Filed 4-19-07; 8:45 am] 

BILLING CODE 4910-13-P