Airworthiness Directives; Boeing Model 737-100, -200, -300, -400, and -500 Series Airplanes

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 96-NM-150-AD; Amendment 39-10010; AD 97-09-14]

RIN 2120-AA64

Airworthiness Directives; Boeing Model 737-100, -200, -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 737-100, -200, -300, -400, and -500

series airplanes, that requires an inspection of reworked aileron/

elevator power control units (PCU's) and rudder PCU's to determine if

reworked PCU manifold cylinder bores containing chrome plating are

installed, and replacement of the cylinder bores with bores that have

been reworked using the oversize method or the steel sleeve method, if

necessary. 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 a reduced rate of movement

of the elevator, aileron, or rudder due to contamination of hydraulic

fluid from chrome plating chips; such reduced rate of movement, if not

corrected, could result in reduced controllability of the airplane.

DATES: Effective June 6, 1997.

The incorporation by reference of certain publications listed in

the regulations is approved by the Director of the Federal Register as

of June 6, 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: Don Kurle, Senior 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) 227-2798; fax (206) 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 737-100, -200, -

300, -400, and -500 series airplanes was published in the Federal

Register on August 28, 1996 (61 FR 44241). That action proposed to

require an inspection of the aileron/elevator power control units (PCU)

and the rudder PCU to determine if reworked PCU manifold cylinder bores

containing chrome plating are installed, and replacement of the

cylinder bores with bores that have been reworked using the oversize

method or the steel sleeve method, if necessary.

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 proposed rule.

[[Page 24009]]

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.''

Requests To Withdraw the Proposal: No Supporting Data

One commenter contends that the proposal is not justified since it

cannot be supported by data. The commenter does not consider that the

proposal contributes to improving the safety aspects of Model 737

airplanes. The commenter states that the CDR team's report does not

indicate that there is any evidence to tie the referenced service

documents to any in-service problems or accidents. The commenter adds

that the FAA has not indicated it has reviewed any routine component

tear-down reports that would support the proposed actions. The

commenter concludes that the FAA does not understand the enormity of

the proposed action. A second commenter states that it has incorporated

the repair on several PCU's and has not witnessed a single failure of

the chrome plating of the cylinder bore. The FAA infers from these

remarks that the commenters request the proposed rule be withdrawn.

In support of its request to withdraw the proposal, the Air

Transport Association (ATA) of America, points out that any performance

degradation that might result from chrome plate separation would be

determined readily by flight crews prior to departure. The ATA also

indicates that if the plating repair were suspect, an incident

involving separation would have been identified early in the service

life of the units. The ATA contends that service experience and tests

conducted by the National Transportation Safety Board (NTSB) confirm

that there is no justification to consider this issue as an existing

airworthiness concern.

The FAA does not concur with the requests of these commenters to

withdraw the proposal. The FAA has received at least five reports from

operators of Model 737 series airplanes indicating that the chrome

plating separated from reworked cylinder bores of the aileron/elevator

PCU's. A number of aileron/elevator and rudder PCU's were repaired

using chrome plating on the aluminum cylinder bores. Separation of the

chrome plating could result in contamination of hydraulic fluid from

chrome plating chips. Such

[[Page 24010]]

contamination can result in a reduced rate of movement of the elevator,

aileron, or rudder, and consequent reduced controllability of the

airplane. The FAA's position is that this condition is a potential

unsafe condition that must be corrected in order to ensure the safety

of the affected fleet.

The FAA acknowledges that in some cases (depending on when chrome

plate separation occurred), prior to departure, flight crews could

determine any performance degradation that might result from chrome

plate separation. However, if the separation occurred during flight,

the flight crew may be unaware of the occurrence and, when the flight

crew's workload is heavy, the crew's ability to control the airplane

may be reduced. The FAA considers that this presents a potential unsafe

condition that must be corrected.

No commenter presented evidence that would indicate chrome

separation occurs early in the life of the unit. Further, the FAA

assumes the NTSB testing discussed by one commenter refers to chip

shear testing accomplished by the NTSB on the rudder PCU. While it

appears that a chrome chip should be able to be sheared by the

hydraulic action of the PCU and not cause a PCU jam, chrome chips can

still contaminate the interior of the rudder, aileron, and elevator

PCU's, which could cause sluggish flight control operation.

Request To Withdraw the Proposal: Revise Component Maintenance/

Overhaul Manuals

One commenter recommends revising the proposal to require a

Component Maintenance Manual (CMM) revision to require inspection at

the next shop visit to identify any units with chrome bores and rework

those in accordance with the service letter in order to eliminate what

the commenter finds to be an enormous financial and operational impact

that would be imposed on operators if the proposed rule is issued.

One commenter, Boeing, indicates that separation of chrome plating

from aluminum cylinder bores has not been a significant in-service

problem; in fact, there have been no reports of chrome plating

separation since 1985. Boeing asserts that since no direct safety

hazard related to chrome plating has been established, the proposal

should be withdrawn and, instead, removal of chrome plating should be

required through a revision to the PCU overhaul manuals for the rudder

and aileron/elevator.

The FAA does not concur with the commenters' requests to withdraw

this AD and revise the component maintenance or overhaul manuals

instead. The FAA considers issuance of an AD necessary in this instance

since an unsafe condition has been identified, and AD's are the means

by which accomplishment of procedures and adherence to specific

compliance times are made mandatory to correct that unsafe condition.

While the FAA has no objection to Boeing revising the component

maintenance or overhaul manuals to provide a procedure for an

inspection to identify any units with chrome bores and rework of those

units in accordance with the service letter, or for removal of chrome

plating, such revision will not affect the requirements of this AD.

Requests To Limit Applicability to Certain PCU's

In lieu of withdrawing the proposal, several commenters suggest

limiting the applicability of the proposed AD to certain PCU's:

One commenter states that no PCU's containing chrome plated

manifold cylinder bores were produced or reworked after April 1, 1985

(the date of issuance of Boeing Service Letter 737-SL-27-30);

therefore, only those PCU's manufactured or reworked prior to that date

should be subject to the requirements of the proposal.

Two other commenters state that, as of June 5, 1985, the chrome

plating procedure was removed from the PCU overhaul manuals. One of

these commenters asserts that any PCU's manufactured after that date

would not have been reworked or manufactured with chrome plating in the

cylinder bores; therefore, those PCU's should be excluded from the

applicability of the proposal.

Another commenter states that the applicability of the proposal

should be limited only to those units manufactured prior to 1980. The

commenter does not provide justification for selecting 1980 as a cutoff

date. This commenter adds that a records search should be allowed to

confirm that no chrome plate repairs to the bore have been

accomplished.

One commenter states that inspection should be required only for

valve bodies made from 2024 aluminum, since the repair procedures were

changed in 1987 and there have been no problems since the original

issue of the service letter. The only reported problems have been with

the old-style valve bodies made from 2024 aluminum. (Production of the

7075 aluminum valve body started in the late 1970's.)

Boeing suggests that only those PCU's manufactured prior to June

1984 should be included in the applicability of the proposal. This date

is one year prior to the revisions of the overhaul manual, which

eliminated chrome plating as a repair procedure. (Since the average

overhaul interval is approximately 15,000 flight hours, it is

conservative to assume that no overhauls would occur within one year of

manufacture.) Boeing indicates that only serial numbers prior to 1252A

(for the rudder PCU) and those prior to 5360A (for the aileron/elevator

PCU) would need to be inspected. In addition, Boeing recommends that

any aileron/elevator actuators having a part number that includes an

``ss'' should be eliminated from the applicability of the proposal

since those PCU's have a steel sleeve (i.e., those PCU's could not have

chrome plating on aluminum).

One commenter states that the proposed rule should include an

exemption for PCU's that have been inspected previously and found to

have no chrome, or units on which the steel sleeve repair has been

incorporated.

The FAA concurs that the applicability of the final rule should be

revised. At the time the proposal was issued, the part and serial

numbers of PCU's that have been overhauled or repaired were not

available; therefore, the FAA was unable to include them in the

applicability of the proposal. However, Boeing has provided this

information in its comments to the proposed rule. The FAA has revised

the applicability of the final rule by specifying the part and serial

numbers of affected PCU's. In effect, such revision limits the

applicability of this AD to those PCU's manufactured prior to June

1984, and specifically excludes those aileron and elevator PCU's having

a part number that contains an ``ss'' (i.e., those that have been

reworked with a steel sleeve). In addition, paragraph (a) of the final

rule has been revised to specify the part and serial numbers of

affected PCU's.

As for allowing a records search to confirm that no chrome plate

repairs to the bore have been accomplished, the FAA finds that no

change to the final rule is necessary. The applicability of this final

rule specifies that the AD applies only to certain Model 737 series

airplanes that are equipped with an aileron, elevator, or rudder PCU

having a particular part and serial number. This AD does not preclude

an operator from performing a records search to determine if an

airplane in its fleet is subject to the requirements of this AD.

Request To Limit Applicability of Proposal to Rudder PCU's

One commenter requests that the requirements of the proposal be

limited to rudder PCU's only, rather than

[[Page 24011]]

aileron, elevator, and rudder PCU's. The commenter states that the

adoption of the proposed rule would overburden existing competent

repair facilities and would expose the airlines and the public to a

hazardous condition far greater than any condition that exists

presently from the identified unsafe condition. This commenter believes

the proposal implies that a simple inspection can determine the status

of chrome plated bores on the affected units; however, the commenter

indicates that, due to the fact that the chrome sleeving process was

used in both manufacturing and repair of the units, that implication is

incorrect. The commenter states that limiting the inspection to rudder

PCU's--especially those manufactured before chrome sleeving was

discontinued--would reduce the risk of unintended consequences

resulting from the overburdening of competent repair facilities.

The FAA does not agree that the applicability of the AD should be

revised to include only rudder PCU's. The FAA has determined that

sluggish ailerons and elevators pose a potential unsafe condition

similar to that of the rudder. Therefore, the FAA finds that it is

appropriate to address this potential unsafe condition as it applies to

aileron and elevator PCU's, as well as rudder PCU's.

Requests To Extend Compliance Time

The ATA, on behalf of several of its members, requests that the

proposed compliance time be extended from 18 months to at least five

years.

One ATA member states that it would be physically impossible and

unnecessary for operators to accomplish the required actions within the

proposed compliance time of 18 months. This commenter indicates that a

review of its maintenance records for the past 15 years showed that it

has never repaired either an aileron or rudder cylinder due to a worn

bore.

One ATA member states that it is important that ample time be

provided to accomplish the intent of the proposal because such

accomplishment requires the removal of PCU's from airplanes and partial

disassembly of PCU's in order to determine the type of rework of the

cylinder bore, which requires scheduling, airplane downtime, unit

turnaround time, and availability of spare PCU's. Another ATA member

states that removal of all PCU's would require industry to process

almost 750 PCU's per month for the next 18 months.

One commenter asks that the compliance time be extended to the next

shop overhaul in light of the fact that there is no documented unsafe

condition or in-service concern.

Boeing suggests an extension of the compliance time to five years

or 15,000 flight hours so that the majority of PCU's can be inspected

as a part of normal maintenance actions. Boeing adds that the

possibility of maintenance errors during PCU replacement will result in

a net degradation in airplane safety as a result of the inspection

schedule established by the proposed rule.

The FAA concurs with the commenters' requests to extend the

compliance time. In light of the information presented by the

commenters, the FAA finds that extending the compliance time to within

five years or 15,000 flight hours after the effective date of the AD,

or at the next time the PCU is sent to a repair facility (whichever of

these times occurs first), will not adversely affect safety. In

addition, this revised compliance time will allow the inspection to be

performed at a base during regularly scheduled maintenance where

special equipment and trained maintenance personnel will be available

if necessary. Paragraph (a) of the final rule has been revised to

specify this revised compliance time.

Request To Revise Cost Impact Information

Two commenters believe that the cost impact information presented

in the proposal has been underestimated greatly, and that the proposal

places an unreasonable financial burden on operators.

One of these commenters indicates that the inspection of the PCU

cylinder bores requires removal of PCU's from the airplane and

disassembly of those units. The commenter presents the following cost

estimates:

28 work hours for removal and reinstallation of five PCU's

per airplane;

20 work hours (per PCU) for disassembly, inspection,

assembly, and testing; and

$1,100 (per PCU) for parts required for reassembly of the

units after inspection. Using these figures, the commenter estimates

the cost impact on U.S. operators to be approximately $14.3 million, or

$13,180 per airplane.

The other commenter states that the proposal does not account for

any return-to-service checks after the units have been changed,

overhaul costs once the units are in the shop, or costs of frequent

repetitive checks and short compliance periods for changing the units.

The FAA infers from these remarks that the commenters request the

cost impact information, below, be revised.

The FAA does not concur. The cost impact information, below,

describes only the ``direct'' costs of the specific actions required by

this AD. The number of work hours necessary to accomplish the required

action (i.e., the inspection), specified as 5 in the cost impact

information, was provided to the FAA by the manufacturer based on the

best data available to date. This number represents the time necessary

to perform only the action (inspection) that is actually required by

this AD. The FAA recognizes that, in accomplishing the requirements of

any AD, operators may incur ``incidental'' costs in addition to the

``direct'' costs. The cost analysis in AD rulemaking actions, however,

typically does not include incidental costs, such as the time required

to gain access and close up; planning time; or time necessitated by

other administrative actions. Because incidental costs may vary

significantly from operator to operator, they are almost impossible to

calculate.

Additionally, the revised compliance time presented in this AD

should coincide with normal overhaul schedules (within 5 years or

15,000 flight hours). The FAA estimates that the PCU inspections (and

any ``on condition'' replacements) will be accomplished during normal

overhauls, which will minimize the economic impact on operators and

accomplish the safety objectives addressed in this AD.

Request To Clarify Inspection of Reworked or Overhauled PCU's

One commenter requests that the FAA revise the proposal to clarify

that only reworked or overhauled PCU's must be inspected. The commenter

suggests the following wording for the Summary section of the preamble

to the proposal: ``* * * This proposal would require an inspection of

reworked aileron/elevator PCU's and rudder PCU's to determine * * *.''

The commenter asks that paragraph (a) of the proposal be revised to

state clearly that ``reworked'' or ``overhauled'' PCU's must be

inspected. The commenter considers that foreign operators and

airworthiness authorities may misinterpret the intent of this AD as

proposed.

The FAA concurs with the commenter's request. The intent of this

final rule is that operators inspect only reworked or overhauled PCU's

to determine if chrome plating is applied in the cylinder bores. The

Summary section of the preamble to the final rule has been revised to

clarify this intent. Additionally, paragraph (a) of the final

[[Page 24012]]

rule has been revised to specify that only reworked or overhauled PCU's

must be inspected.

Request To Address Cause of Chrome Plating Separation

One commenter contends that chrome plating on aluminum is

successful (the component will have the required integrity for

airworthiness) when the base metal has been subjected to the proper

pretreatment (cleaned), proper chrome plating, and properly executed

post plating operations such as finish grinding and nondestructive

testing. The commenter states that poor maintenance techniques,

environmental factors, or overlooked design parameters present a more

relevant and detrimental concern to flight safety than a properly

applied chrome on aluminum repair. The commenter believes that removal

of the chrome repair is treating the effect without fully understanding

the cause and addressing the underlying issues.

The FAA infers from these remarks that the commenter requests that

the FAA address the cause for chrome plating separation, rather than

remove the chrome plating repair as an option.

The FAA agrees that if the repair is done properly, it could

provide satisfactory service. In any event, the FAA is aware of

instances of failure of the repair. The FAA finds that issuance of this

AD is necessary to ensure that all chrome plating repairs are removed

from the affected Model 737 fleet so that an acceptable level of safety

for these airplanes is attained. However, the FAA would consider a

request for approval of an alternative method of compliance, provided

that a satisfactory repeatable repair procedure using chrome plating

can be developed.

Request To Revise Preamble of Proposal

Boeing requests that the wording of the ``Reports Received by FAA''

section of the preamble to the proposed rule be revised. The commenter

notes that this section of the preamble states that chrome plating

chips could block or jam the rudder PCU control valve and thereby cause

partial or full rudder deflection. Boeing indicates that this statement

is incorrect. Boeing remarks that testing conducted by the NTSB systems

group showed that a chrome chip in the control valve could be sheared

by a force of six pounds. This force would be provided by the rudder

feel and centering unit (in combination with system friction) before

any significant rudder deflected had occurred.

The commenter also states that this section of the preamble refers

only to the rudder PCU, but also should refer to the aileron and

elevator PCU's.

The FAA concurs with the remarks submitted by the commenter.

However, the section of the preamble to the proposed rule referenced by

the commenter does not reappear in this final rule. Therefore, no

change to the final rule is necessary.

Request To Correct PCU Part Number

One commenter requests that the part number referenced in the

proposal for the rudder PCU be corrected to 65-44861. The FAA concurs

with this request. The FAA has revised paragraphs (a) and (c) of this

final rule to correct this inadvertent typographical error.

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

increase the economic burden on any operator nor increase the scope of

the AD.

Cost Impact

There are approximately 2,675 Model 737 series airplanes of the

affected design in the worldwide fleet. The FAA estimates that 1,091

airplanes of U.S. registry will be affected by this AD, that it will

take approximately 5 work hours per airplane to accomplish the required

inspection, and that the average labor rate is $60 per work hour. Based

on these figures, the cost impact of the AD on U.S. operators is

estimated to be $327,300, or $300 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.

Should an operator be required to accomplish the necessary

replacement, it would take approximately 18 work hours per airplane to

accomplish, at an average labor rate of $60 per work hour. Required

parts will cost approximately $15,800 per airplane. Based on these

figures, the cost impact of any necessary replacement action is

estimated to be $16,880 per airplane.

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:

97-09-14 Boeing: Amendment 39-10010. Docket 96-NM-150-AD.

Applicability: Model 737-100, -200, -300, -400, and -500 series

airplanes equipped with a rudder power control unit (PCU) having

part number (P/N) 65-44861-( ) and a serial number less than 1252A;

or an aileron or elevator PCU having P/N 65-44761-( ) (except those

having P/N's that contain an ``ss'') and a serial number less than

5360A; certificated in any category.

Note 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

[[Page 24013]]

accordance with paragraph (d) 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 reduced rate of movement of the elevator, aileron,

or rudder, which, if not corrected, could result in reduced

controllability of the airplane, accomplish the following:

(a) Perform an inspection of reworked or overhauled aileron and

elevator PCU's having P/N 65-44761-( ) (except those having P/N's

that contain an ``ss'') and a serial number less than 5360A; and

rudder PCU's having part number (P/N) 65-44861-( ) and a serial

number less than 1252A; to determine if reworked PCU manifold

cylinder bores containing chrome plating are installed, in

accordance with Boeing Service Letter 737-SL-27-30, dated April 1,

1985. Accomplish the inspection at the earlier of the times

specified in paragraphs (a)(1) and (a)(2) of this AD.

(1) Within 5 years or 15,000 flight hours after the effective

date of this AD, whichever occurs first.

(2) At the next time the PCU is sent to a repair facility.

(b) If any reworked PCU manifold cylinder bores containing

chrome plating are installed: Prior to further flight, replace the

cylinder bores with bores that have been reworked using the oversize

method or the steel sleeve method specified in Boeing

Service Letter 737-SL-27-30, dated April 1, 1985. Accomplish the

replacement in accordance with the service letter.

(c) As of the effective date of this AD, no person shall install

a reworked PCU manifold cylinder bore containing chrome plating on

an aileron or elevator PCU having P/N 65-44761-( ), or on a rudder

PCU having P/N 65-44861-( ), of any airplane unless the cylinder

bore has been reworked using the oversize method or the steel sleeve

method specified in Boeing Service Letter 737-SL-27-30, dated April

1, 1985.

(d) 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 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.

(e) 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.

(f) The inspection and repair shall be done in accordance with

Boeing Service Letter 737-SL-27-30, dated April 1, 1985. 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.

(g) This amendment becomes effective on June 6, 1997.

Issued in Renton, Washington, on April 24, 1997.

Darrell M. Pederson,

Acting Manager, Transport Airplane Directorate, Aircraft Certification

Service.

[FR Doc. 97-11200 Filed 5-1-97; 8:45 am]

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