[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]


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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.

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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.

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                                     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