[Federal Register Volume 62, Number 50 (Friday, March 14, 1997)]
[Proposed Rules]
[Pages 12121-12123]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 97-6436]


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DEPARTMENT OF TRANSPORTATION
14 CFR Part 39

[Docket No. 97-NM-28-AD]
RIN 2120-AA64


Airworthiness Directives; Boeing Model 737-100, -200, -300, -400, 
and -500 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 all Boeing Model 737-100, -200, -
300, -400, and -500 series airplanes. This proposal would require 
installation of a newly designed rudder-limiting device and yaw damper 
system. This proposal is prompted by a report indicating that a full 
rudder input, either commanded or uncommanded, could result in a rapid 
roll upset; and by reports of malfunctions of the yaw damper system. 
The actions specified by the proposed AD are intended to prevent 
excessive rudder authority and consequent reduced controllability of 
the airplane; and malfunctions of the yaw damper system, which could 
result in sudden uncommanded yawing of the airplane and consequent 
injury to passengers and crewmembers.

DATES: Comments must be received by April 23, 1997.

ADDRESSES: Submit comments in triplicate to the Federal Aviation 
Administration (FAA), Transport Airplane Directorate, ANM-103, 
Attention: Rules Docket No. 97-NM-28-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.

FOR FURTHER INFORMATION CONTACT: T. Tin Truong, 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 (206) 227-2552; fax (206) 
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 97-NM-28-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-103, Attention: Rules 
Docket No. 97-NM-28-AD, 1601 Lind Avenue, SW., Renton, Washington 
98055-4056.

[[Page 12122]]

Discussion

    In September 1994, an accident involving a Boeing Model 737-300 
series airplane occurred near Pittsburgh, Pennsylvania. The National 
Transportation Safety Board (NTSB) has not yet determined the cause of 
that accident. However, the FAA has received a report indicating that 
piloted computer simulations of the accident revealed that a full 
rudder input, either commanded or uncommanded, could result in a rapid 
roll upset similar to the aircraft responses recorded on the flight 
data recorder of the accident airplane. Investigation revealed that, 
during certain combinations of flap settings and airspeeds, the amount 
of rudder deflection available is greater than needed for control of 
the airplane. A full rudder deflection (hardover) with such excessive 
rudder authority can result in a rolling moment due to sideslip that 
exceeds the maximum rolling moment available by control wheel inputs. 
This condition, if not corrected, could result in reduced 
controllability of the airplane unless the flight crew takes prompt and 
appropriate action. [In this regard, the FAA issued AD 96-26-07, 
amendment 39-9871 (62 FR 15, January 2, 1997) to amend the Airplane 
Flight Manual to provide the flight crew with the proper control 
techniques in the event of such an occurrence.]
    Additionally, the FAA has received a number of reports of 
malfunctions of the yaw damper system. These malfunctions may have been 
caused by failure of the rate gyroscope of the yaw damper coupler as a 
result of wear of the rotor bearing, and contamination and shorting of 
the electrical connectors or surface position sensors in the area of 
the yaw damper servo-actuator. Such malfunctions of the yaw damper 
system, if not corrected, could result in sudden uncommanded yawing of 
the airplane and consequent injury to passengers and crewmembers.
    Boeing has advised the FAA that it has designed a rudder-limiting 
device and a new yaw damper for installation on the latest versions of 
Model 737 series airplanes currently undergoing certification. Both of 
these systems are capable of being installed on the existing fleet of 
Model 737 series airplanes. Boeing has not yet released a service 
bulletin reflecting these changes.

FAA's Determinations

    In light of this information, the FAA finds that installation of a 
newly designed rudder-limiting device and yaw damper system are 
required to ensure the safety of the affected fleet. Installation of a 
rudder-limiting device is necessary to reduce the rudder authority at 
altitudes above 1,500 feet above ground level (AGL) so that, if any 
inadvertent hardover occurs, the resultant roll upset can be controlled 
with control wheel inputs. Installation of a new yaw damper system is 
necessary to improve the reliability of the system and its fault 
monitoring capability, which will prevent uncommanded yawing of the 
airplane.

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 installation of a newly designed rudder-
limiting device and yaw damper system. The actions would be required to 
be accomplished in accordance with a method approved by the FAA.

Cost Impact

    There are approximately 2,900 Model 737 series airplanes of the 
affected design in the worldwide fleet. The FAA estimates that 1,350 
airplanes of U.S. registry would be affected by this proposed AD.
    The FAA estimates that it would take approximately 87 work hours 
per airplane to accomplish the proposed installation of a newly 
designed rudder-limiting device, and that the average labor rate is $60 
per work hour. Required parts would be supplied by the manufacturer at 
no cost to operators. Based on these figures, the cost impact of the 
proposed AD on U.S. operators is estimated to be $7,047,000, or $5,220 
per airplane.
    The FAA also estimates that it would take approximately 20 work 
hours per airplane to accomplish the proposed installation of a newly 
designed yaw damper system, and that the average labor rate is $60 per 
work hour. Required parts would be supplied by the manufacturer at no 
cost to operators. Based on these figures, the cost impact of the 
proposed AD on U.S. operators is estimated to be $1,620,000, or $1,200 
per airplane.
    The cost impact figures discussed above are based on assumptions 
that no operator has yet accomplished any of the proposed requirements 
of this AD action, and that no operator would accomplish those actions 
in the future if this AD were not adopted.
    The FAA recognizes that the obligation to maintain aircraft in an 
airworthy condition is vital, but sometimes expensive. Because AD's 
require specific actions to address specific unsafe conditions, they 
appear to impose costs that would not otherwise be borne by operators. 
However, because of the general obligation of operators to maintain 
aircraft in an airworthy condition, this appearance is deceptive. 
Attributing those costs solely to the issuance of this AD is 
unrealistic because, in the interest of maintaining safe aircraft, 
prudent operators would accomplish the required actions even if they 
were not required to do so by the AD.
    A full cost-benefit analysis has not been accomplished for this 
proposed AD. As a matter of law, in order to be airworthy, an aircraft 
must conform to its type design and be in a condition for safe 
operation. The type design is approved only after the FAA makes a 
determination that it complies with all applicable airworthiness 
requirements. In adopting and maintaining those requirements, the FAA 
has already made the determination that they establish a level of 
safety that is cost-beneficial. When the FAA, as in this proposed AD, 
makes a finding of an unsafe condition, this means that the original 
cost-beneficial level of safety is no longer being achieved and that 
the proposed actions are necessary to restore that level of safety. 
Because this level of safety has already been determined to be cost-
beneficial, a full cost-benefit analysis for this proposed AD would be 
redundant and unnecessary.

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.

[[Page 12123]]

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 97-NM-28-AD.

    Applicability: All Model 737-100, -200, -300, -400, and -500 
series airplanes, certificated in any category.

    Note 2: 1: This AD applies to each airplane 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 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 (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 as indicated, unless accomplished 
previously.
    To prevent excessive rudder authority and consequent reduced 
controllability of the airplane; and malfunctions of the yaw damper 
system, which could result in sudden uncommanded yawing of the 
airplane and consequent injury to passengers and crewmembers; 
accomplish the following:
    (a) Within 3 years after the effective date of this AD, 
accomplish paragraphs (a)(1) and (a)(2) of this AD in accordance 
with a method approved by the Manager, Seattle Aircraft 
Certification Office (ACO), FAA, Transport Airplane Directorate.
    (1) Install a newly designed rudder-limiting device that reduces 
the rudder authority at altitudes above 1,500 feet above ground 
level (AGL).
    (2) Install a newly designed yaw damper system that improves the 
reliability and fault monitoring capability.
    (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, Seattle ACO. 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.

    (c) 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 March 7, 1997.
Ronald T. Wojnar,
Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 97-6436 Filed 3-13-97; 8:45 am]
BILLING CODE 4910-13-P