Airworthiness Directives; Sikorsky Aircraft Corporation Model S-76B and S-76C Helicopters

[Federal Register Volume 66, Number 245 (Thursday, December 20, 2001)]
[Rules and Regulations]
[Pages 65629-65631]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 01-31039]


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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


Airworthiness Directives; Sikorsky Aircraft Corporation Model S-
76B and S-76C Helicopters

AGENCY: Federal Aviation Administration, DOT.

ACTION: Final rule; request for comments.

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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

[[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: [email protected].
    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:


[[Page 65631]]


    Authority: 49 U.S.C. 106(g), 40113, 44701.


Sec. 39.13  [Amended]

    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

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