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###### Department of Transportation

###### Federal Aviation Administration 

          - 14 CFR Part 39 
          - [Docket No. 2001-SW-51-AD; Amendment 39-12559; AD 2001-25-06] 
          - RIN 2120-AA64 

# AGENCY:

Federal Aviation Administration, DOT. 

# ACTION:

Final rule; request for comments. 

# SUMMARY:

This amendment adopts a new airworthiness directive (AD) for Sikorsky Aircraft Corporation (Sikorsky) Model S-76B and S-76C helicopters. This action requires modifying the electrical power distribution system to change the source of the 28 volts supplied to Nos. 1 and 2 attitude and heading reference (AHRS) WARN circuits. This amendment is prompted by a ground test simulating loss of the essential bus by pulling both bus tie circuit breakers and switching off both batteries. As a result of this action, both autopilots went off-line. The actions specified in this AD are intended to prevent an AHRS fail signal to both autopilots due to a failure of the essential bus, loss of autopilot functions, and subsequent loss of control of the helicopter. 

# DATES:

Effective January 4, 2002. 

The incorporation by reference of certain publications listed in the regulations is approved by the Director of the Federal Register as of January 4, 2002. 

Comments for inclusion in the Rules Docket must be received on or before February 19, 2002. 

# ADDRESSES:

                        Submit comments in triplicate to the Federal Aviation                               ( print page 65630)                            Administration (FAA), Office of the Regional Counsel, Southwest Region, Attention: Rules Docket No. 2001-SW-51-AD, 2601 Meacham Blvd., Room 663, Fort Worth, Texas 76137. You may also send comments electronically to the Rules Docket at the following address:                         *9-asw-adcomments@faa.gov*.                     

The service information referenced in this AD may be obtained from Sikorsky Aircraft Corporation, Attn: Manager, Commercial Tech Support, 6900 Main Street, Stratford, Connecticut 06614, phone (203) 386-3001, fax (203) 386-5983. This information 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. 

# FOR FURTHER INFORMATION CONTACT:

Solomon Hecht, Aviation Safety Engineer, Boston Aircraft Certification Office, 12 New England Executive Park, Burlington, MA 01803, telephone (781) 238-7159, fax (781) 238-7199. 

# SUPPLEMENTARY INFORMATION:

This amendment adopts a new AD for Sikorsky Model S-76B and S-76C helicopters. This action requires modifying the electrical power distribution system by changing the source of the 28 volts electrical power supplied to Nos. 1 and 2 AHRS WARN circuits. This amendment is prompted by ground testing of a Sikorsky Model S-76B helicopter which simulated loss of the essential bus by pulling both bus tie circuit breakers and switching off both batteries. As a result of this action, both autopilots went off-line. This condition, if not corrected, could result in an unintended AHRS fail signal to both autopilots due to failure of the essential bus, loss of autopilot functions, and subsequent loss of control of the helicopter. 

The FAA has reviewed Sikorsky Alert Service Bulletin No. 76-34-7A (320A), Revision A, dated September 17, 2001 (ASB). The ASB describes procedures for modifying the electrical power distribution system to prevent an AHRS fail signal to the autopilots by changing the source of the 28 volts supplied to Nos. 1 and 2 AHRS WARN circuits. The essential bus currently supplies both Nos. 1 and 2 AHRS WARN circuits. If this essential bus failed, the AHRS WARN circuits would generate an AHRS fail signal which would cause both autopilots to go off-line. The modification specified in the ASB changes the 28 volt electrical power source to the AHRS WARN circuits so that one of the two autopilots will remain on-line after an essential bus failure. 

We have identified an unsafe condition that is likely to exist or develop on other Sikorsky Model S76-B and S-76C helicopters of this same type design. Therefore, this AD is being issued to prevent an AHRS fail signal to both autopilots, loss of autopilot functions, and subsequent loss of control of the helicopter. This AD requires modifying the AHRS WARN circuits so that one of the two autopilots will remain on-line should the essential bus fail. The actions must be accomplished in accordance with the ASB 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, modifying the AHRS is required within 30 days and this AD must be issued immediately. 

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 20 of the helicopters affected by this AD are on the U.S. register, that it will take approximately 5 work hours to install the modification kit, and that the average labor rate is $60 per work hour. The manufacturer states in the ASB that the required modification kit will be provided at no cost. Based on these figures, the total cost impact of the AD on U.S. operators is estimated to be $6000. 

## 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 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. 2001-SW-51-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: 

      ( print page 65631)    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: 

**2001-25-06 Sikorsky Aircraft Corporation:**                             Amendment 39-12559. Docket No. 2001-SW-51-AD.                        

*Applicability:*                             Model S-76B helicopters, serial numbers (S/N) 760430, 760441 through 760445, 760448 through 760452, 760454, 760455, 760458, 760462, and 760465, and Model S-76C helicopters, S/N 760420, 760436, 760438, 760440, 760453, 760456, 760457, 760459, 760460, 760461 760463, 760464, 760466 through 760487, 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 (b) 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 within 30 days after the effective date of this AD, unless accomplished previously.                         

To prevent an attitude and heading reference (AHRS) fail signal to both autopilots due to a failure of the essential bus, loss of both autopilot functions, and subsequent loss of control of the helicopter, accomplish the following: 

(a) Modify Nos. 1 and 2 AHRS WARN circuits in accordance with the Accomplishment Instructions, paragraphs 3.A. through 3.D, of Sikorsky Aircraft Corporation Alert Service Bulletin No. 76-34-7A (320A), Revision A, dated September 17, 2001. 

(b) 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, Boston 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, Boston 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 Boston Aircraft Certification Office.

(c) Special flight permits may be issued in accordance with 14 CFR 21.197 and 21.199 to operate the helicopter to a location where the requirements of this AD can be accomplished. 

(d) The modification shall be done in accordance with the Accomplishment Instructions, paragraphs 3.A. through 3.D., of Sikorsky Aircraft Corporation Alert Service Bulletin No. 76-34-7A (320A), Revision A, dated September 17, 2001. 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 Sikorsky Aircraft Corporation, Attn: Manager, Commercial Tech Support, 6900 Main Street, Stratford, Connecticut 06614, phone (203) 386-3001, fax (203) 386-5983. 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. 

(e) This amendment becomes effective on January 4, 2002. 

Issued in Fort Worth, Texas, on November 29, 2001. 

David A. Downey, 

Manager, Rotorcraft Directorate, Aircraft Certification Service. 

[FR Doc. 01-31039 Filed 12-19-01; 8:45 am] 

BILLING CODE 4910-13-U