[Federal Register Volume 62, Number 195 (Wednesday, October 8, 1997)]
[Rules and Regulations]
[Pages 52486-52489]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 97-24334]
=======================================================================
-----------------------------------------------------------------------
DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 39
[Docket No. 96-NM-149-AD; Amendment 39-10116; AD 97-18-06]
RIN 2120-AA64
Airworthiness Directives; Boeing Model 737 Series Airplanes
AGENCY: Federal Aviation Administration, DOT.
ACTION: Final rule.
-----------------------------------------------------------------------
SUMMARY: This amendment adopts a new airworthiness directive (AD),
applicable to all Boeing Model 737 series airplanes, that requires
revising the FAA-approved maintenance program to prohibit the use of
pressure washing within the wheel well or on the landing gear and to
prohibit the use of pumps and/or nozzles for washing wheel wells or the
landing gear; or incorporation of a certain Temporary Revision to the
Boeing Airplane Maintenance Manual into the FAA-approved maintenance
program. This amendment is prompted by a review of the design of the
flight control systems on Model 737 series airplanes. The actions
specified by this AD are intended to prevent corrosion of certain
equipment due to the use of inappropriate pressure washing techniques.
Corrosion of bearings, cables, electrical connectors, or other
equipment in the main wheel well, if not detected and corrected in a
timely manner, could result in reduced controllability of the airplane.
DATES: Effective November 12, 1997.
The incorporation of reference of certain publications listed in
the regulations is approved by the Director of the Federal Register as
of November 12, 1997.
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: David Herron, 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) 227-2672; 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 series
airplanes was published in the Federal Register on August 28, 1996 (61
FR 44239). That action proposed to require revising the FAA-approved
maintenance program to prohibit the use of pressure washing within the
wheel well or on the landing gear and to prohibit the use of pumps and/
or nozzles for washing wheel wells or the landing gear.
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
One commenter supports the proposal.
Request To Revise Statement of Findings of Critical Design Review
Team
One commenter requests the second paragraph of the Discussion
section that appeared in the preamble to the proposed rule be revised
to accurately reflect the findings of the Critical Design Review (CDR)
team. The commenter asks that the FAA delete the one sentence in that
paragraph, which read: ``The recommendations of the team include
various changes to the design of the flight control systems of these
airplanes, as well as correction of certain design deficiencies.'' The
commenter suggests that the following sentences should be added: ``The
team did not find any design issues that could lead to a definite cause
of the accidents that gave rise to this effort. The recommendations of
the team include various changes to the design of the flight control
systems of these airplanes, as well as incorporation of certain design
improvements in order to enhance its already acceptable level of
safety.''
The FAA does not find that a revision to this final rule in the
manner suggested by the commenter is necessary, since the Discussion
section of a proposed rule does not reappear in a final rule. The FAA
acknowledges that the CDR team did not find any design issue that could
lead to a definite cause of the accidents that gave rise to this
effort. However, as a result of having conducted the CDR of the flight
control systems on Boeing Model 737 series airplanes, the team
indicated that there are a number of recommendations that should be
addressed by the FAA for each of the various models of the Model 737.
In reviewing these recommendations, the FAA has concluded that they
address unsafe conditions that must be corrected through the issuance
of AD's. Therefore, the FAA does not concur that these design changes
merely ``enhance [the Model 737's] already acceptable level of
safety.''
Request To Withdraw the Proposal: Existing Procedures Are Adequate
Several commenters request that the proposed rule be withdrawn
since pressure washing procedures exist that adequately clean the wheel
wells and landing gear, yet provide protective shielding for various
components.
The FAA does not concur that this final rule should be withdrawn
for the reason requested by the commenters. Since the issuance of the
proposal, the FAA has reviewed and approved a new Temporary Revision to
the Airplane Maintenance Manual (AMM), Chapter 12-40-0, that lists
specific components that require protection from exposure to moisture.
The Temporary Revision describes procedures to shield and protect these
specific components from moisture during pressure washing. Therefore,
the FAA has revised paragraph (a) of this final rule to provide an
alternative method of compliance for the requirements of this AD by
incorporating the Temporary Revision into the AMM.
Request To Withdraw the Proposal: No Supporting Data
Several commenters contend that there are no data or records of in-
service findings that support the conclusion that corrosion of the
wheel wells or the landing gear is induced by proper pressure washing.
One commenter considers that the improper use of pressure equipment,
lack of protection of critical areas, and improper lubrication
techniques are the more significant and likely causes of any corrosion
occurring in the wheel well. The commenter suggests that the
appropriate action to minimize the possibility of corrosion is: proper
training of cleaning personnel, use of proper equipment, protection of
critical
[[Page 52487]]
areas, and proper lubrication techniques.
The FAA does not concur that the rule should be withdrawn for the
reasons presented by the commenters. The FAA acknowledges that pressure
washing done correctly may not induce corrosion of the wheel wells or
the landing gear. However, incorrect pressure washing techniques of the
bearings, cables, electrical connectors, and other equipment in the
main wheel well can result in fluids (or additives in the fluids) being
forced into these areas. Such retention of fluid in these areas can
result in the development of corrosion. Therefore, the FAA finds that
one method of preventing fluids from being forced into certain areas is
to prohibit the use of pressure washing within the wheel well or
landing gear.
Request To Withdraw the Proposal: Alternative Methods of Washing Are
Unsatisfactory
Several commenters state that methods other than pressure washing
do not clean the area as well. The commenters point out that surfaces
of the wheel wells or the landing gear that are not adequately cleaned
could adversely affect the ability to perform accurate structural
inspections for cracking. The commenters also contend that hand washing
of the wheel wells or the landing gear would take significantly more
work hours to accomplish than pressure washing and, consequently, would
be much more costly to perform. The commenters request that the
proposal be withdrawn since use of alternative methods of washing are
unsatisfactory.
The FAA does not concur that the rule should be withdrawn for the
reasons presented by the commenters. The FAA acknowledges that proper
pressure washing techniques provide adequate cleaning of wheel wells
and landing gears, which enables structural inspections for cracking to
be performed under optimum conditions. As stated previously, the FAA
has revised paragraph (a) of this final rule, which provides for
pressure washing by incorporation of the previously described Temporary
Revision into the AMM as an alternative method of compliance with the
requirements of this AD.
Request to Clarify the Prohibition of Pressure Washing
Several commenters request that the FAA clarify whether the
proposed prohibition of pressure washing would include the use of de-
icing fluids since de-icing fluids are also applied with pressure
equipment. One commenter, an operator, requests that de-icing be
specifically excluded from the requirements of the proposed AD. The
commenter notes that it applies indirect pressure spray to remove rime
ice buildup and other frozen accumulations from the airplane. The
commenter states that there is a high potential for anomalous operation
if ice and grime are not removed from the airplane. Another operator
requests that pressure de-icing fluid be permitted when used with a fan
spray pattern, which the operator asserts will reduce the impact of the
fluid on the airplane structure.
The FAA acknowledges that clarification is appropriate. This AD
addresses procedures and limitations of pressure washing as applicable
only to the cleaning of the airplane prior to repair and inspection.
Since de-icing fluids are generally applied with a lower pressure than
pressure washing, and de-icing normally impacts the ice directly,
rather than the sensitive components, the FAA does not consider de-
icing to be encompassed within this rule. However, if additional
information warrants further consideration of the aspects of de-icing
as related to pressure application, the FAA may consider additional
rulemaking to address that issue.
Request to Revise the Limit of 80 Pounds Per Square Inch, Gauge
(PSIG)
Several commenters suggest that the FAA has not given proper
consideration to the effects of impact pressure (force) or momentum in
determining the need for a prohibition of use of pressure equipment.
One commenter points out that impact pressure is a function of flow
rate and the square root of pressure. This commenter states that
pressure psig is merely one component of the force function. Another
commenter added that the temperature of the spraying fluid should also
be considered since hot water or steam has a much higher capability of
dissolving grease than cold water when applied at the same pressure.
Two other commenters suggested the following procedures to establish an
appropriate pressure limit: One procedure is to use an equation that
would establish an impact pressure, and the other procedure is to base
the pressure limit upon the pain threshold of impact on the human hand.
The FAA does not concur that the proposed pressure limit (80) psig
should be revised. The FAA established a conservative figure based on
water tap pressure with an upper limit of 80 psig, as provided by some
municipalities. The FAA has determined that with a limitation of 80
psig during washing, water and other contaminates such as dirt are not
likely to be driven into close tolerance areas such as sealed bearings.
Therefore, if an operator elects to eliminate pressure washing in order
to comply with the requirements of this AD, 80 psig is an appropriate
pressure limit, since fluid would still be needed to clean the wheel
wells or landing gear.
Additionally, the FAA does not concur with the commenters'
suggested means of establishing a pressure limit. The methods suggested
by the commenters provide no documentation as to whether or not a
pressure limit established by either method proposed would provide
protection against water and other contaminates such as dirt from being
driven into close tolerance areas.
Request to Clarify Design Consideration
One commenter requests clarification of the statement in the
preamble of the proposal indicating that ``the FAA concludes that these
aircraft were designed to operate with contaminate buildup in the wheel
wells and landing gears.'' The FAA concurs that clarification of the
impact of design considerations is necessary. The manufacturer has
advised the FAA that certain elements of the airplane design are not
readily changed. For example, the feel and centering mechanism of the
aileron system has bearings that must be oriented horizontally. That
orientation results in a pool of water/solvent and debris accumulating
on the top of certain component equipment within the wheel well.
Another commenter states that pressure washing is comparable to the
airplane design to withstand the momentum of rain droplets hitting
gears at 200 knots (which may be expected with a Boeing Model 737
series airplane during final approach). This commenter further states
that, while intense gear and wheel well washing of the type done during
a C-check normally occurs only once a year, airplanes could be expected
to fly through precipitation with gear extended fifty or more times a
year.
The FAA does not concur that the impact of rain is analogous to
pressure washing. While the design of the airplane provides for the
landing gear to withstand the impact of rain, the wheel well is located
outside the streamline flow. Consequently, rain pellets entering the
wheel well would be well below the streamline velocity of the flow
field around the airplane. Therefore, the FAA considers a certain
amount of contaminate buildup in the wheel wells
[[Page 52488]]
and landing gears to be an inherent consideration of the design.
Request to Revise Estimated Cost
Several commenters (operators) state that the estimated cost impact
information presented in the proposal is clearly understated. These
operators all state, that instead of the estimated 5 work hours
specified in the proposal to perform the wheel well washings, it would
be more accurate and realistic to estimate 40 or 50 work hours per
airplane for methods other than pressure washing. The commenters state
that the expense of implementing this type of corrective action is
inappropriate since pressure cleaning done properly is, in itself, not
a cause of corrosion.
The FAA concurs that the cost impact information, below, should be
revised based on information received from the commenters. The FAA has
revised this information to specify 40 work hours to perform the wheel
well washings by means other than pressure washing. Additionally, the
FAA has included cost impact information of one work hour for
incorporating the Temporary Revision into the AMM for those operators
who elect to accomplish this method of complying with the requirements
of this AD.
Request to Clarify How Restricting Pressure Washing Impacts
Controllability of the Airplane
One commenter requests clarification on how pressure washing
affects the controllability of the airplane. The operator points out
that, in its experience, no incidents have occurred where the
controllability of the airplane has been compromised due to washing of
the landing gear.
The FAA acknowledges that clarification is necessary. Corroded or
contaminated joints of the landing gear could cause an increase in
forces that could adversely affect the actuation/retraction of the
landing gear or movement of flight control surfaces during flight.
Additionally, damage such as weakened seals due to erosion or abrasion
to hydraulic hoses or other elements located on the landing gear could
further contribute to an adverse effect on the controllability of the
airplane during flight and/or landing. Therefore, the FAA finds that
the failure of bearings, cables, electrical connectors, or other
equipment in the main wheel well, if not detected and corrected in a
timely manner, could result in reduced controllability of the airplane.
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 changes previously
described. The FAA has determined that these changes will neither
significantly increase the economic burden on any operator nor increase
the scope of the AD.
Cost Impact
There are approximately 2,463 Model 737 series airplanes of the
affected design in the worldwide fleet.
The FAA estimates that 1,040 airplanes of U.S. registry will be
affected by this AD, that it will take approximately 40 work hours per
airplane to accomplish washing of the wheel wells and landing gear by
means other than pressure washing, and that the average labor rate is
$60 per work hour. If operators choose to comply with this AD by
prohibiting pressure washing, the cost impact of the AD on U.S.
operators is estimated to be $2,400 per airplane, per washing.
If operators choose to comply with this AD by incorporating a
certain Temporary Revision into the AMM, it will take approximately 1
work hour per airplane, at an average labor rate of $60 per work hour.
Based on these figures, the cost impact of U.S. operators is estimated
to be $60 per airplane.
The cost impact figures discussed above are 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.
Regulatory Impact
The regulations adopted herein will 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 final
rule does not have sufficient federalism implications to warrant the
preparation of a Federalism Assessment.
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:
97-18-06 Boeing: Amendment 39-10116. Docket 96-NM-149-AD.
Applicability: All Model 737 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 (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 corrosion in the bearings, cables, electrical
connectors, or other equipment in the main wheel well, which could
result in reduced controllability of the airplane, accomplish the
following:
(a) Within 90 days after the effective date of this AD, perform
the requirements of either paragraph (a)(1) or (a)(2) of this AD.
(1) Incorporate a revision into the FAA-approved maintenance
program that prohibits the use of pressure washing within the wheel
well or on the landing gear, and that prohibits the use of pumps
and/or nozzles for washing wheel wells or the landing gear. Pressure
washing is defined as the use of any fluid under pressure greater
[[Page 52489]]
than 80 pounds per square inch, gauge (psig); or
(2) Incorporate the following Temporary Revision(s) to Chapter
12 of the Boeing Model 737 Airplane Maintenance Manual (AMM), all
dated February 7, 1997; as applicable; into the FAA-approved
maintenance program.
------------------------------------------------------------------------
Temporary
Airplane model revision
No.
------------------------------------------------------------------------
737-100/200.................................................. 12-368
12-369
12-370
12-371
12-372
12-373
737-300/-400/-500............................................ 12-85
------------------------------------------------------------------------
Note 2: Once an operator has incorporated the above procedures
into its maintenance program, this AD does not require that the
operator subsequently record accomplishment each time the wheel well
is cleaned. Future changes to the above maintenance program require
prior approval of an appropriate FAA Principal Maintenance Inspector
(PMI).
(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 Aircraft Certification
Office (ACO), FAA, Transport Airplane Directorate. Operators shall
submit their requests through an appropriate FAA PMI, 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.
(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.
(d) Except as specified in paragraph (a)(1) of this AD, the
actions shall be done in accordance with the following Temporary
Revisions to Chapter 12 of the Boeing Model 737 Airplane Maintenance
Manual.
------------------------------------------------------------------------
Temporary
Airplane model revision Dated
No.
------------------------------------------------------------------------
737-100/200........................ 12-368 Feb. 7, 1997.
12-369 Feb. 7, 1997.
12-370 Feb. 7, 1997.
12-371 Feb. 7, 1997.
12-372 Feb. 7, 1997.
12-373 Feb. 7, 1997.
737-300/-400/-500.................. 12-85 Feb. 7, 1997.
------------------------------------------------------------------------
The 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.
(e) This amendment becomes effective on November 12, 1997.
Issued in Renton, Washington, on August 25, 1997.
James V. Devany,
Acting Manager, Transport Airplane Directorate, Aircraft Certification
Service.
[FR Doc. 97-24334 Filed 10-7-97; 8:45 am]
BILLING CODE 4910-13-U
