Airworthiness Directives; Boeing Model 737 Series Airplanes

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

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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.

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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.

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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