AD 2000-23-34

[Federal Register Volume 65, Number 233 (Monday, December 4, 2000)]
[Rules and Regulations]
[Pages 75595-75597]
From the Federal Register Online via the Government Publishing Office [<a href="http://www.gpo.gov">www.gpo.gov</a>]
[FR Doc No: 00-30319]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 2000-NM-107-AD; Amendment 39-12007; AD 2000-23-34]
RIN 2120-AA64


Airworthiness Directives; Boeing Model 737-300, -400, and -500 
Series Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Final rule.

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SUMMARY: This amendment adopts a new airworthiness directive (AD), 
applicable to all Boeing Model 737-300, -400, and -500 series 
airplanes, that requires replacement of the existing autothrottle 
computer with a new, improved autothrottle computer. This amendment is 
prompted by reports of asymmetric thrust conditions during flight 
caused by irregular autothrottle operation in which the thrust levers 
slowly move apart causing the airplane to bank excessively and go into 
a roll. The actions specified by this AD are intended to prevent such 
conditions, which could result in loss of control of the airplane.

DATES: Effective January 8, 2001.
    The incorporation by reference of certain publications listed in 
the regulations is approved by the Director of the Federal Register as 
of January 8, 2001.

ADDRESSES: The service information referenced in this AD may be 
obtained from Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, 
Washington 98124-2207. This information may be examined at the Federal 
Aviation Administration (FAA), Transport Airplane Directorate, Rules 
Docket, 1601 Lind Avenue, SW., Renton, Washington; or at the Office of 
the Federal Register, 800 North Capitol Street, NW., suite 700, 
Washington, DC.

FOR FURTHER INFORMATION CONTACT: Thanh Truong, Aerospace Engineer, 
Systems and Equipment Branch, ANM-130S, FAA, Seattle Aircraft 
Certification Office, 1601 Lind Avenue, SW., Renton, Washington 98055-
4056; telephone (425) 227-2552; fax (425) 227-1181.

SUPPLEMENTARY INFORMATION: A proposal to amend part 39 of the Federal 
Aviation Regulations (14 CFR part 39) to include an airworthiness 
directive (AD) that is applicable to all Boeing Model 737-300, -400, 
and -500 series airplanes was published in the Federal Register on June 
12, 2000 (65 FR 36803). That action proposed to require replacement of 
the existing autothrottle computer with a new, improved autothrottle 
computer.

Comments

    Interested persons have been afforded an opportunity to participate 
in the making of this amendment. Due consideration has been given to 
the comments received.

Support for the Proposal

    Two commenters state no objection to the proposed rule and indicate 
that the proposed replacements are already in progress on their fleets.

Request to Increase Compliance Time

    Three commenters request an increase in the compliance time above 
the proposed one year after the effective date of this AD. One 
commenter suggests a compliance time of 18 months, but states no reason 
for its request. A second commenter suggests a compliance time of two 
years, to account for the amount of time necessary for a particular 
repair station to accomplish the modification. A third commenter does 
not make a specific suggestion for a compliance time, though it states 
that it will need four years to complete the proposed replacement using 
existing spares, considering the amount of time necessary for the 
repair station (the same one referenced by the second commenter) to 
modify existing autothrottle computers.
    The FAA concurs that the compliance time for the requirements of 
this AD may be extended. To assist in determining an appropriate 
compliance time, the FAA contacted the manufacturer of the autothrottle 
computers to determine the number of authorized repair facilities and 
the manpower available. The FAA also obtained data on the number of 
autothrottle computers manufactured, the number of units already 
converted, and the number of airplanes that are affected. Based on this 
information, the FAA finds that an extension of the compliance time to 
18 months will be sufficient to allow accomplishment of this AD on all 
affected airplanes. The FAA also finds that such an extension of the 
compliance time will not adversely affect the continued safety of the 
airplane fleet. Therefore, paragraph (a) of this AD has been revised to 
state a compliance time of 18 months after the effective date of this 
AD.

Request to Remove ``Spares'' Requirement

    One commenter requests that the FAA revise the proposed AD to 
remove paragraph (b), the ``Spares'' paragraph. That paragraph states, 
``As of the effective date of this AD, no person shall install on any 
airplane, an autothrottle computer having part number 10-62017-1, -2, -
3, -4, -5, -11, -21, -23, -25, or -27.'' The commenter's request was 
based on the length of time necessary for modification of the existing 
autothrottle computers by an authorized repair facility.
    The FAA does not concur with the commenter's request to delete the 
``Spares'' requirement. As stated previously, the FAA finds that 
extension of the compliance time for this AD from one year to 18 months 
after the effective date of this AD will allow adequate time for 
autothrottle computers to be modified by an authorized repair facility 
and for operators to comply with the requirements of this AD, without 
compromising safety. No change to the final rule is necessary in this 
regard.

Request to Reduce Compliance Time and Consider Interim Actions

    One commenter states that there is an inconsistency between the 
urgency of the unsafe condition, as explained in the proposal, and the 
length of the compliance time. The commenter points to the statement in 
the ``Differences Between Proposed Rule and Alert Service Bulletin'' 
section of the proposed AD, which reads, ``The FAA

[[Page 75596]]

also finds that such a compliance time will not adversely affect the 
safety of the affected airplanes.'' The commenter states that it does 
not understand ``an `unsafe condition' that has already been identified 
that does not come into effect until 6th June 2001'' and requests an 
explanation. The commenter also notes that the proposed AD does not 
contain any interim actions to be undertaken to ensure safety of the 
airplane fleet prior to accomplishment of the proposed replacement.
    While the commenter makes no specific request for a change to the 
proposed AD, the FAA infers that the commenter is requesting that the 
FAA reduce the compliance time and include revisions to the flight 
procedures in this AD. The FAA does not concur with the commenter's 
request. As explained in the proposed AD, in developing an appropriate 
compliance time for the proposed replacement, the FAA considered not 
only the degree of urgency associated with addressing the subject 
unsafe condition, but also the number of proposed requirements and the 
availability of required parts. As stated previously in this AD, since 
the issuance of the proposed rule, the FAA has received information 
indicating that 18 months is an appropriate compliance time wherein all 
of these actions can be accomplished during scheduled airplane 
maintenance and an ample number of required parts will be available for 
modification of the U.S. fleet within the compliance period. The FAA 
also finds that such a compliance time will not adversely affect the 
safety of the affected airplanes.
    With regard to the lack of interim actions in this AD, the FAA 
provides the following explanation. In 1994, the airplane manufacturer 
issued a Flight Operations Procedure to advise operators of an anomaly 
related to asymmetric thrust lever settings occurring during 
autothrottle operation. Such a procedure, if followed, adequately 
addresses the unsafe condition identified in this AD. However, this 
procedure does not take into account human factors that may result in 
the flightcrew failing to recognize an abnormality that develops over 
an extended period of time, resulting in an excessive bank angle for 
the airplane. There have been eight reported incidents of asymmetric 
thrust that occurred with delayed intervention by the pilots. Six of 
these eight incidents resulted in a bank angle of more than 30 degrees. 
In two incidents, airplanes have rolled more than 40 degrees before the 
flightcrew recognized the condition. For this reason, revisions to 
flight procedures are not considered adequate to provide the degree of 
safety assurance necessary for the transport airplane fleet. 
Consideration of these factors has led the FAA to mandate the 
replacement required by this AD. No change to the final rule is 
necessary in this regard.

Conclusion

    After careful review of the available data, including the comments 
noted above, the FAA has determined that air safety and the public 
interest require the adoption of the rule with the change previously 
described. The FAA has determined that this change will neither 
increase the economic burden on any operator nor increase the scope of 
the AD.

Cost Impact

    There are approximately 1,974 Model 737-300, -400, and -500 series 
airplanes of the affected design in the worldwide fleet. The FAA 
estimates that 799 airplanes of U.S. registry will be affected by this 
AD, that it will take approximately 1 work hour per airplane to 
accomplish the required replacement, and that the average labor rate is 
$60 per work hour. Required parts will cost between $1,400 and $4,200 
per airplane. Based on these figures, the cost impact of the AD on U.S. 
operators is estimated to be between $1,460 and $4,260 per airplane.
    The cost impact figure discussed above is based on assumptions that 
no operator has yet accomplished any of the requirements of this AD 
action, and that no operator would accomplish those actions in the 
future if this AD were not adopted. The cost impact figures discussed 
in AD rulemaking actions represent only the time necessary to perform 
the specific actions actually required by the AD. These figures 
typically do not include incidental costs, such as the time required to 
gain access and close up, planning time, or time necessitated by other 
administrative actions.

Regulatory Impact

    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.
    For the reasons discussed above, I certify that this action (1) is 
not a ``significant regulatory action'' under Executive Order 12866; 
(2) is not a ``significant rule'' under 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. A final evaluation has been prepared for this action 
and it is contained in the Rules Docket. A copy of it 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.


Sec. 39.13  [Amended]

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

2000-23-34 Boeing: Amendment 39-12007. Docket 2000-NM-107-AD.

    Applicability: All Model 737-300, -400, and -500 series 
airplanes; certificated in any category.

    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 a severe asymmetric thrust condition during flight 
which could result in loss of control of the airplane, accomplish 
the following:

Replacement

    (a) Within 18 months after the effective date of this AD: 
Replace the existing autothrottle computer with a new, improved 
autothrottle computer in accordance with

[[Page 75597]]

Boeing Alert Service Bulletin 737-22A1130, dated September 24, 1998.

Spares

    (b) As of the effective date of this AD, no person shall install 
on any airplane, an autothrottle computer having part number 10-
62017-1, -2, -3, -4, -5, -11, -21, -23, -25, or -27.

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. Operators shall submit their requests through an 
appropriate FAA Principal Maintenance Inspector, who may add 
comments and then send it to the Manager, Seattle ACO.

    Note 2: 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.

Incorporation by Reference

    (e) The replacement shall be done in accordance with Boeing 
Alert Service Bulletin 737-22A1130, including Appendix A, dated 
September 24, 1998. 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 Boeing 
Commercial Airplane Group, P.O. Box 3707, Seattle, Washington 98124-
2207. Copies may be inspected at the FAA, Transport Airplane 
Directorate, 1601 Lind Avenue, SW., Renton, Washington; or at the 
Office of the Federal Register, 800 North Capitol Street, NW., suite 
700, Washington, DC.

Effective Date

    (f) This amendment becomes effective on January 8, 2001.

    Issued in Renton, Washington, on November 16, 2000.
Donald L. Riggin,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 00-30319 Filed 12-1-00; 8:45 am]
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