[Federal Register Volume 64, Number 193 (Wednesday, October 6, 1999)]
[Proposed Rules]
[Pages 54229-54230]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 99-25935]



[[Page 54229]]

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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 99-NM-248-AD]
RIN 2120-AA64


Airworthiness Directives; Boeing Model 747-400 Series Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: This document proposes the adoption of a new airworthiness 
directive (AD) that is applicable to certain Boeing Model 747-400 
series airplanes. This proposal would require removal of existing 
inertial reference units (IRU) and installation of modified IRU's. This 
proposal is prompted by a report of the failure of the left and center 
IRU's on a single flight. The actions specified by the proposed AD are 
intended to prevent loss of multiple IRU's in flight, which could 
result in the loss of navigation data during flight. This could 
compromise the ability of the flight crew to maintain the safe flight 
and landing of the airplane.

DATES: Comments must be received by November 22, 1999.

ADDRESSES: Submit comments in triplicate to the Federal Aviation 
Administration (FAA), Transport Airplane Directorate, ANM-114, 
Attention: Rules Docket No. 99-NM-248-AD, 1601 Lind Avenue, SW., 
Renton, Washington 98055-4056. Comments may be inspected at this 
location between 9:00 a.m. and 3:00 p.m., Monday through Friday, except 
Federal holidays.
    The service information referenced in the proposed rule may be 
obtained from Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, 
Washington 98124-2207. This information may be examined at the FAA, 
Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, 
Washington.

FOR FURTHER INFORMATION CONTACT: Jay G. Yi, Aerospace Engineer, Systems 
and Equipment Branch, ANM-130S, FAA, Transport Airplane Directorate, 
Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, 
Washington 98055-4056; telephone (425) 227-1013; fax (425) 227-1181.

SUPPLEMENTARY INFORMATION:

Comments Invited

    Interested persons are invited to participate in the making of the 
proposed rule by submitting such written data, views, or arguments as 
they may desire. Communications shall identify the Rules Docket number 
and be submitted in triplicate to the address specified above. All 
communications received on or before the closing date for comments, 
specified above, will be considered before taking action on the 
proposed rule. The proposals contained in this notice may be changed in 
light of the comments received.
    Comments are specifically invited on the overall regulatory, 
economic, environmental, and energy aspects of the proposed 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 summarizing each FAA-public contact concerned with 
the substance of this proposal will be filed in the Rules Docket.
    Commenters wishing the FAA to acknowledge receipt of their comments 
submitted in response to this notice must submit a self-addressed, 
stamped postcard on which the following statement is made: ``Comments 
to Docket Number 99-NM-248-AD.'' The postcard will be date stamped and 
returned to the commenter.

Availability of NPRMs

    Any person may obtain a copy of this NPRM by submitting a request 
to the FAA, Transport Airplane Directorate, ANM-114, Attention: Rules 
Docket No. 99-NM-248-AD, 1601 Lind Avenue, SW., Renton, Washington 
98055-4056.

Discussion

    The FAA has received a report indicating that the left and center 
inertial reference units (IRU) failed during a single flight on a 
Boeing Model 747-400 series airplane. A short circuit in the brake 
system control unit (BSCU) connected to the left IRU caused the left 
IRU to fail. The pilot then selected the center IRU to monitor the 
BSCU. The same short circuit also caused the center IRU to fail. Such 
failure of multiple IRU's in flight, if not corrected, could result in 
the loss of navigation data during flight. This could compromise the 
ability of the flight crew to maintain the safe flight and landing of 
the airplane.

Explanation of Relevant Service Information

    The FAA has reviewed and approved Boeing Alert Service Bulletin 
747-34A2638, Revision 1, dated April 8, 1999, which describes 
procedures for removal of the left, right, and center IRU's, and 
replacement with modified IRU's. The modified IRU's are redesigned to 
prevent failure caused by an electrical short circuit in equipment 
connected to the IRU. Accomplishment of the actions specified in the 
alert service bulletin is intended to adequately address the identified 
unsafe condition.

Explanation of Requirements of Proposed Rule

    Since an unsafe condition has been identified that is likely to 
exist or develop on other products of this same type design, the 
proposed AD would require accomplishment of the actions specified in 
the alert service bulletin described previously, except as discussed 
below.

Differences Between Proposed Rule and Alert Service Bulletin

    Operators should note that, although the service bulletin 
recommends accomplishing the replacement of the IRU's with modified 
IRU's at the earliest opportunity when manpower, parts, and facilities 
are available, the FAA has determined that such a compliance time would 
not address the identified unsafe condition in a timely manner. In 
developing an appropriate compliance time for this AD, the FAA 
considered not only the manufacturer's recommendation, but the degree 
of urgency associated with addressing the subject unsafe condition, the 
average utilization of the affected fleet, and the time necessary to 
perform the replacement (one hour). In light of all of these factors, 
the FAA finds a compliance time of 12 months after the effective date 
of this AD for completing the required actions to be warranted, in that 
it represents an appropriate interval of time allowable for affected 
airplanes to continue to operate without compromising safety.

Cost Impact

    There are approximately 429 airplanes of the affected design in the 
worldwide fleet. The FAA estimates that 50 airplanes of U.S. registry 
would be affected by this proposed AD, that it would take approximately 
1 work hour per airplane to accomplish the proposed replacement, and 
that the average labor rate is $60 per work hour. Required parts would 
be supplied by the parts manufacturer at no cost to the operators. 
Based on these figures, the cost impact of the proposed AD on U.S. 
operators is estimated to be $3,000, or $60 per airplane.
    The cost impact figure discussed above is based on assumptions that 
no operator has yet accomplished any of the proposed requirements of 
this AD action, and that no operator would

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accomplish those actions in the future if this AD were not adopted.

Regulatory Impact

    The regulations proposed herein would 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 
proposal would not have sufficient federalism implications to warrant 
the preparation of a Federalism Assessment.
    For the reasons discussed above, I certify that this proposed 
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) if promulgated, 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. A copy of the draft 
regulatory evaluation prepared for this action is contained in the 
Rules Docket. A copy of it may be obtained by contacting the Rules 
Docket at the location provided under the caption ADDRESSES.

List of Subjects in 14 CFR Part 39

    Air transportation, Aircraft, Aviation safety, Safety.

The Proposed Amendment

    Accordingly, pursuant to the authority delegated to me by the 
Administrator, the Federal Aviation Administration proposes to amend 
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.


Sec. 39.13  [Amended]

    2. Section 39.13 is amended by adding the following new 
airworthiness directive:

    Boeing: Docket 99-NM-248-AD.

    Applicability: Model 747-400 series airplanes, having line 
numbers 696 through 1187 inclusive, certificated in any category; 
equipped with Honeywell inertial reference units (IRU).

    Note 1: This AD applies to each airplane 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 airplanes 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 (c) 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 loss of multiple IRU's in flight, which could result 
in the loss of navigation data, and compromise the ability of the 
flight crew to maintain the safe flight and landing of the airplane, 
accomplish the following:

Replacement

    (a) Within 12 months after the effective date of this AD, remove 
the left, center, and right IRU's, and install modified IRU's, in 
accordance with Boeing Alert Service Bulletin 747-34A2638, Revision 
1, dated April 8, 1999.

    Note 2: Removal of existing left, center, and right IRU's and 
replacement with modified IRU's in accordance with Boeing Alert 
Service Bulletin 747-34A2638, dated January 29, 1999, is considered 
acceptable for compliance with paragraph (a) of this AD.

Spares

    (b) As of the effective date of this AD, no person shall install 
an IRU having Boeing part number S242T101-110, S242T101-111, or 
S242T101-112, on any airplane.

Alternative Methods of Compliance

    (c) 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, Seattle Aircraft Certification 
Office (ACO), FAA, Transport Airplane Directorate. Operators shall 
submit their requests through an appropriate FAA Principal Avionics 
Inspector, who may add comments and then send it to the Manager, 
Seattle ACO.

    Note 3: Information concerning the existence of approved 
alternative methods of compliance with this AD, if any, may be 
obtained from the Seattle ACO.

Special Flight Permits

    (d) Special flight permits may be issued in accordance with 
sections 21.197 and 21.199 of the Federal Aviation Regulations (14 
CFR 21.197 and 21.199) to operate the airplane to a location where 
the requirements of this AD can be accomplished.

    Issued in Renton, Washington, on September 29, 1999.
D.L. Riggin,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 99-25935 Filed 10-5-99; 8:45 am]
BILLING CODE 4910-13-U