Airworthiness Directives; Boeing Model 737 Series Airplanes

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 98-NM-11-AD]

RIN 2120-AA64

Airworthiness Directives; Boeing Model 737 Series Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: This document proposes the adoption of a new airworthiness

directive (AD) that is applicable to certain Boeing Model 737 series

airplanes. This proposal would require inspections of certain bonded

skin panel assemblies to detect delamination of the skin doublers (tear

straps) from the skin panels; and follow-on corrective actions, if

necessary. This proposal is prompted by reports indicating that certain

skin doublers were delaminated from their skin panels due to improper

processing of certain skin panels. The actions specified by the

proposed AD are intended to detect and correct such delamination, which

could result in fatigue cracks in the skin doublers and skin panels,

and consequent rapid decompression of the airplane.

DATES: Comments must be received by February 25, 1999.

ADDRESSES: Submit comments in triplicate to the Federal Aviation

Administration (FAA), Transport Airplane Directorate, ANM-114,

Attention: Rules Docket No. 98-NM-11-AD, 1601 Lind Avenue, SW., Renton,

Washington 98055-4056. Comments may be inspected at this location

between 9:00 a.m. and 3:00 p.m., Monday through Friday, except Federal

holidays.

The service information referenced in the proposed rule may be

obtained from Boeing Commercial Airplane Group, P.O. Box 3707, Seattle,

Washington 98124-2207. This information may be examined at the FAA,

Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton,

Washington.

may be inspected at this location

between 9:00 a.m. and 3:00 p.m., Monday through Friday, except Federal

holidays.

The service information referenced in the proposed rule may be

obtained from Boeing Commercial Airplane Group, P.O. Box 3707, Seattle,

Washington 98124-2207. This information may be examined at the FAA,

Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton,

Washington.

FOR FURTHER INFORMATION CONTACT: Rick Kawaguchi, Aerospace Engineer,

Airframe Branch, ANM-120S, FAA, Transport Airplane Directorate, Seattle

Aircraft Certification Office, 1601 Lind Avenue, SW., Renton,

Washington 98055-4056; telephone (425) 227-1153; fax (425) 227-1181.

SUPPLEMENTARY INFORMATION:

Comments Invited

Interested persons are invited to participate in the making of the

proposed rule by submitting such written data, views, or arguments as

they may desire. Communications shall identify the Rules Docket number

and be submitted in triplicate to the address specified above. All

communications received on or before the closing date for comments,

specified above, will be considered before taking action on the

proposed rule. The proposals contained in this notice may be changed in

light of the comments received.

Comments are specifically invited on the overall regulatory,

economic, environmental, and energy aspects of the proposed rule. All

comments submitted will be available, both before and after the closing

date for comments, in the Rules Docket for examination by interested

persons. A report summarizing each FAA-public contact concerned with

the substance of this proposal will be filed in the Rules Docket.

Commenters wishing the FAA to acknowledge receipt of their comments

submitted in response to this notice must submit a self-addressed,

stamped postcard on which the following statement is made: ``Comments

to Docket Number 98-NM-11-AD.'' The postcard will be date stamped and

returned to the commenter.

Availability of NPRMs

ith

the substance of this proposal will be filed in the Rules Docket.

Commenters wishing the FAA to acknowledge receipt of their comments

submitted in response to this notice must submit a self-addressed,

stamped postcard on which the following statement is made: ``Comments

to Docket Number 98-NM-11-AD.'' The postcard will be date stamped and

returned to the commenter.

Availability of NPRMs

Any person may obtain a copy of this NPRM by submitting a request

to the FAA, Transport Airplane Directorate, ANM-114, Attention: Rules

Docket No. 98-NM-11-AD, 1601 Lind Avenue, SW., Renton, Washington

98055-4056.

Discussion

The FAA has received reports indicating that skin doublers (tear

straps) were found delaminated from their skin panels on certain Boeing

Model 737 series airplanes. These airplanes had accumulated as few as

10,200 total flight cycles. The subject skin doublers and skin panels

are installed above stringer S-26 from body station (BS) 259 to BS 1016

on both sides of the airplane. The cause of such delamination in all

incidents has been attributed to improper processing during the

phosphoric anodize application of the skin panels. This condition, if

not detected and corrected, could result in fatigue cracks in the skin

doublers and skin panels, and consequent rapid decompression of the

airplane.

Explanation of Relevant Service Information

The FAA has reviewed and approved Boeing Service Bulletin 737-53-

1179, dated June 22, 1995, as revised by Notice of Status Change (NSC)

737-53-1179 NSC 1, dated August 17, 1995, which describes procedures

for performing a one-time internal inspection (terminating inspection)

of the bonded skin panel assemblies to detect delamination of the skin

doublers from the skin panels; and follow-on corrective actions, if

necessary

ved Boeing Service Bulletin 737-53-

1179, dated June 22, 1995, as revised by Notice of Status Change (NSC)

737-53-1179 NSC 1, dated August 17, 1995, which describes procedures

for performing a one-time internal inspection (terminating inspection)

of the bonded skin panel assemblies to detect delamination of the skin

doublers from the skin panels; and follow-on corrective actions, if

necessary.

The above inspection includes an internal close visual inspection

(Figure 3 of the service bulletin), an internal close visual inspection

while trying to separate the skin doublers from the skin panels (Figure

3 of the service bulletin), and an ultrasonic inspection (Figure 4 of

the service bulletin). The service bulletin recommends that operators

perform these inspections on bonded skin panel assemblies, which are

composed of skin doublers (tear straps) that are bonded to skin panels

located above stringer S-26 from BS 259 to BS 1016 on both sides of the

airplane. In lieu of accomplishing the internal close visual

inspections of bonded skin panel assemblies (Figure 3 of the service

bulletin), the service bulletin describes procedures for performing an

internal or external ultrasonic inspection to detect delamination.

The follow-on corrective actions include internal close visual, low

frequency eddy current, and high frequency eddy current inspections;

and repair, if necessary. The service bulletin recommends that

operators perform such inspections to detect corrosion and cracks that

may have resulted from any skin doubler delaminating from its skin

panel.

The service bulletin also describes procedures for performing

repetitive external visual inspections (interim inspection) to detect

cracks in skin panels; and repair, if necessary. This service bulletin

recommends that operators perform the external visual inspections until

accomplishment of the one-time internal inspection described

previously.

Boeing has also issued NSC 737-53-1179 NSC 1, dated August 17,

1995

lso describes procedures for performing

repetitive external visual inspections (interim inspection) to detect

cracks in skin panels; and repair, if necessary. This service bulletin

recommends that operators perform the external visual inspections until

accomplishment of the one-time internal inspection described

previously.

Boeing has also issued NSC 737-53-1179 NSC 1, dated August 17,

1995. This NSC contains no new technical information but corrects two

typographical errors and adds a general note.

Accomplishment of the actions specified in the service bulletin and

the NSC are intended to adequately address the identified unsafe

condition.

Explanation of Requirements of Proposed Rule

Since an unsafe condition has been identified that is likely to

exist or develop on other products of this same type design, the

proposed AD would require accomplishment of the actions specified in

the service bulletin and the NSC described previously, except as

discussed below.

Differences Between Proposed Rule and Service Bulletin

Operators should note that, although the service bulletin

recommends accomplishing a one-time internal inspection (terminating

inspection), as described previously, prior to the accumulation of

40,000 total flight cycles or within 20,000 flight cycles after the

release of the service bulletin, whichever occurs later, the FAA has

determined that such a compliance time would not address the identified

unsafe condition in a timely manner. As described previously, operators

have found doublers delaminated from skin panels on certain Boeing

Model 737 series airplanes that had accumulated as few as 10,200 total

flight cycles. The FAA has determined that to have a high probability

of detecting cracking before it reaches a critical length, the

inspections described previously must be accomplished prior to the

accumulation of 20,000 total flight cycles

ly, operators

have found doublers delaminated from skin panels on certain Boeing

Model 737 series airplanes that had accumulated as few as 10,200 total

flight cycles. The FAA has determined that to have a high probability

of detecting cracking before it reaches a critical length, the

inspections described previously must be accomplished prior to the

accumulation of 20,000 total flight cycles. In developing an

appropriate compliance time for this proposed AD, the FAA considered

not only the manufacturer's recommendation, but the degree of urgency

associated with addressing the subject unsafe condition, the average

utilization of the affected fleet, and the time necessary to perform

the one-time inspection (136 work hours). In light of all of these

factors, the FAA finds that a proposed compliance time of 20,000 total

flight cycles, or 4,500 flight cycles or 18 months after the effective

date of this AD, whichever occurs later, for initiating the proposed

actions to be warranted. The FAA has determined that the proposed

compliance time represents an appropriate interval of time allowable

for affected airplanes to continue to operate without compromising

safety.

For those operators that elect to perform repetitive external

visual inspections (i.e., the interim inspection), the service bulletin

recommends accomplishing the one-time inspections within 20,000 flight

cycles (after the release of the service bulletin). For the same

reasons stated above, the FAA has determined that such a compliance

time would not address the identified unsafe condition in a timely

manner. Therefore, the FAA finds that a proposed compliance time of

15,000 flight cycles or 60 months after the effective date of this

proposed AD, whichever occurs first, for initiating the proposed

actions [i.e., the one-time (terminating) inspection] to be warranted

tated above, the FAA has determined that such a compliance

time would not address the identified unsafe condition in a timely

manner. Therefore, the FAA finds that a proposed compliance time of

15,000 flight cycles or 60 months after the effective date of this

proposed AD, whichever occurs first, for initiating the proposed

actions [i.e., the one-time (terminating) inspection] to be warranted.

The FAA has determined that the proposed compliance time represents an

appropriate interval of time allowable for affected airplanes to

continue to operate without compromising safety.

Operators also should note that the service bulletin does not

specify that the one-time inspection be accomplished after airplanes

accumulate 4,500 flight cycles on certain bonded skin panel assemblies.

Service history indicates that the bonded skin panel assemblies on the

affected airplanes need to be subjected to a minimal amount of loading

and environment before disbonding becomes detectable. For this reason,

the FAA finds a 4,500 flight cycle interval to be an appropriate

interval of time for ensuring that the operators are able to detect

delamination of the skin doublers from the skin panels. Therefore, the

proposed AD requires that the one-time inspection be performed after

the affected airplanes accumulate 4,500 total flight cycles or after

the affected airplanes accumulate 4,500 flight cycles after the date of

installation of any new or serviceable bonded skin panel assembly.

Although the effectivity listing of the service bulletin includes

airplanes having line numbers 611 through 2725 inclusive, the

applicability of this proposed AD includes airplanes having line

numbers 1 through 3072 inclusive. The service bulletin does not specify

that operators perform an inspection of any new or serviceable bonded

skin panel assembly that was installed prior to October 1, 1997, on any

airplane having line numbers 1 through 3072 inclusive

airplanes having line numbers 611 through 2725 inclusive, the

applicability of this proposed AD includes airplanes having line

numbers 1 through 3072 inclusive. The service bulletin does not specify

that operators perform an inspection of any new or serviceable bonded

skin panel assembly that was installed prior to October 1, 1997, on any

airplane having line numbers 1 through 3072 inclusive. The FAA has

determined that the identified unsafe condition could exist or develop

on those airplanes having such replacement bonded skin panel

assemblies. In light of this, the FAA finds that it is necessary that

the applicability of this proposed AD include Boeing Model 737 series

airplanes on which the bonded skin panel assemblies were replaced with

any new or serviceable bonded skin panel assemblies prior to October 1,

1997. Therefore, the applicability of this proposed AD includes line

numbers 1 through 3072 inclusive.

Operators should note that, although the service bulletin specifies

that the manufacturer may be contacted for disposition of certain

repair conditions, this proposal would require the repair of those

conditions to be accomplished in accordance with a method approved by

the FAA; or in accordance with data meeting the type certification

basis of the airplane approved by a Boeing Company Designated

Engineering Representative who has been authorized by the Manager,

Seattle Aircraft Certification Office, to make such findings.

Additionally, the service bulletin specifies that certain actions

may be accomplished in accordance with ``an equivalent'' procedure.

However, this proposed AD requires that those actions be accomplished

in accordance with the procedures specified in Part 6, Subject 51-00-

00, Figure 4, of the 737 Nondestructive Test Manual. An ``equivalent''

procedure may be used only if approved as an alternative method of

compliance in accordance with the provisions of paragraph (j) of the

proposed AD.

Cost Impact

quivalent'' procedure.

However, this proposed AD requires that those actions be accomplished

in accordance with the procedures specified in Part 6, Subject 51-00-

00, Figure 4, of the 737 Nondestructive Test Manual. An ``equivalent''

procedure may be used only if approved as an alternative method of

compliance in accordance with the provisions of paragraph (j) of the

proposed AD.

Cost Impact

There are approximately 2,083 airplanes of the affected design in

the worldwide fleet. The FAA estimates that 863 airplanes of U.S.

registry would be affected by this proposed AD.

It would take approximately 136 work hours per airplane to

accomplish the proposed terminating inspection, at an average labor

rate of $60 per work hour. Based on these figures, the cost impact of

the terminating inspection proposed by this AD on U.S. operators is

estimated to be $7,042,080, or $8,160 per airplane.

It would take approximately 32 work hours per airplane to

accomplish the proposed interim inspection, at an average labor rate of

$60 per work hour. Based on these figures, the cost impact of the

interim inspection proposed by this AD on U.S. operators is estimated

to be $1,656,960, or $1,920 per airplane, per inspection cycle.

The cost impact figures discussed above are based on assumptions

that no operator has yet accomplished any of the proposed requirements

of this AD action, and that no operator would accomplish those actions

in the future if this AD were not adopted.

Regulatory Impact

The regulations proposed herein would not have substantial direct

effects on the States, on the relationship between the national

government and the States, or on the distribution of power and

responsibilities among the

plished any of the proposed requirements

of this AD action, and that no operator would accomplish those actions

in the future if this AD were not adopted.

Regulatory Impact

The regulations proposed herein would not have substantial direct

effects on the States, on the relationship between the national

government and the States, or on the distribution of power and

responsibilities among the

various levels of government. Therefore, in accordance with Executive

Order 12612, it is determined that this proposal would not have

sufficient federalism implications to warrant the preparation of a

Federalism Assessment.

For the reasons discussed above, I certify that this proposed

regulation (1) is not a ``significant regulatory action'' under

Executive Order 12866; (2) is not a ``significant rule'' under the DOT

Regulatory Policies and Procedures (44 FR 11034, February 26, 1979);

and (3) if promulgated, will not have a significant economic impact,

positive or negative, on a substantial number of small entities under

the criteria of the Regulatory Flexibility Act. A copy of the draft

regulatory evaluation prepared for this action is contained in the

Rules Docket. A copy of it may be obtained by contacting the Rules

Docket at the location provided under the caption ``ADDRESSES.''

List of Subjects in 14 CFR Part 39

Air transportation, Aircraft, Aviation safety, Safety.

The Proposed Amendment

Accordingly, pursuant to the authority delegated to me by the

Administrator, the Federal Aviation Administration proposes to amend

part 39 of the Federal Aviation Regulations (14 CFR part 39) as

follows:

PART 39--AIRWORTHINESS DIRECTIVES

1. The authority citation for part 39 continues to read as follows:

Authority: 49 U.S.C. 106(g), 40113, 44701.

Sec. 39.13 [Amended]

2. Section 39.13 is amended by adding the following new

airworthiness directive:

Boeing: Docket 98-NM-11-AD.

viation Administration proposes to amend

part 39 of the Federal Aviation Regulations (14 CFR part 39) as

follows:

PART 39--AIRWORTHINESS DIRECTIVES

1. The authority citation for part 39 continues to read as follows:

Authority: 49 U.S.C. 106(g), 40113, 44701.

Sec. 39.13 [Amended]

2. Section 39.13 is amended by adding the following new

airworthiness directive:

Boeing: Docket 98-NM-11-AD.

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

series airplanes, line numbers 1 through 3072 inclusive, certified

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 (j) 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.

Note 2: Where there are differences between this AD and the

referenced service bulletin, the AD prevails.

Compliance: Required as indicated, unless accomplished

previously.

To detect and correct delamination of the skin doublers (tear

straps) from the skin panels, which could result in fatigue cracks

in the skin doublers and the skin panels, and consequent rapid

decompression of the airplane, accomplish the following:

rences between this AD and the

referenced service bulletin, the AD prevails.

Compliance: Required as indicated, unless accomplished

previously.

To detect and correct delamination of the skin doublers (tear

straps) from the skin panels, which could result in fatigue cracks

in the skin doublers and the skin panels, and consequent rapid

decompression of the airplane, accomplish the following:

(a) For airplanes having line numbers 611 through 2725

inclusive, on which any bonded skin panel assembly has not been

replaced with any new or serviceable bonded skin panel assembly:

Accomplish the actions required either by paragraph (a)(1) of this

AD, or by both paragraphs (a)(2) and (a)(3) of this AD, in

accordance with Boeing Service Bulletin 737-53-1179, dated June 22,

1995, as revised by Notice of Status Change 737-53-1179 NSC 1, dated

August 17, 1995.

Note 3: For the purposes of this AD, bonded skin panel

assemblies consist of skin doublers (tear straps) that are bonded to

skin panels located above stringer S-26 from body station (BS) 259

to BS 1016 on both sides of the airplane.

Note 4: If the skin panel is solid with no doublers (tear

straps) bonded to it, the inspections required by this AD are not

necessary for that skin panel.

(1) Prior to the accumulation of 20,000 total flight cycles, but

after the accumulation of 4,500 total flight cycles; or within 18

months or 4,500 flight cycles after the effective date of this AD;

whichever occurs latest; perform a one-time internal inspection

(terminating inspection) of the bonded skin panel assemblies to

detect delamination of the skin doublers from the skin panels, in

accordance with Figures 3 and 4 of the service bulletin. In lieu of

accomplishing the inspections specified in Figure 3 of the service

bulletin, operators can perform an internal or external ultrasonic

inspection in accordance with Note 1. of paragraph A. of the

``Terminating Inspection'' Section of the Accomplishment

Instructions of the service bulletin.

in doublers from the skin panels, in

accordance with Figures 3 and 4 of the service bulletin. In lieu of

accomplishing the inspections specified in Figure 3 of the service

bulletin, operators can perform an internal or external ultrasonic

inspection in accordance with Note 1. of paragraph A. of the

``Terminating Inspection'' Section of the Accomplishment

Instructions of the service bulletin.

Note 5: For the purposes of this AD, the one-time internal

inspection includes an internal close visual inspection (Figure 3),

an internal close visual inspection while trying to separate the

skin doublers from the skin panels (Figure 3), and an ultrasonic

inspection (Figure 4).

(2) Within 4,500 flight cycles or 18 months after the effective

date of this AD, whichever occurs later, perform an external visual

inspection of the bonded skin panel assemblies to detect cracks in

the skin panels, in accordance with paragraph A. of the ``Interim

Inspection'' Section of the Accomplishment Instructions of the

service bulletin. Repeat the external visual inspection thereafter

at intervals not to exceed 4,500 flight cycles, until accomplishment

of the requirements specified in paragraph (a)(3) of this AD.

(3) Within 15,000 flight cycles or 60 months after the effective

date of this AD, whichever occurs first, accomplish the one-time

internal inspection required by paragraph (a)(1) of this AD.

Accomplishment of this action constitutes terminating action for the

repetitive inspections required by paragraph (a)(2) of this AD.

lishment

of the requirements specified in paragraph (a)(3) of this AD.

(3) Within 15,000 flight cycles or 60 months after the effective

date of this AD, whichever occurs first, accomplish the one-time

internal inspection required by paragraph (a)(1) of this AD.

Accomplishment of this action constitutes terminating action for the

repetitive inspections required by paragraph (a)(2) of this AD.

(b) For airplanes having line numbers 611 through 2725

inclusive, on which any bonded skin panel assembly was replaced with

any new or serviceable bonded skin panel assembly prior to October

1, 1997: Accomplish the actions required by both paragraphs (b)(1)

and (b)(2) of this AD, or by both paragraphs (b)(3) and (b)(4) of

this AD, in accordance with Boeing Service Bulletin 737-53-1179,

dated June 22, 1995, as revised by Notice of Status Change 737-53-

1179 NSC 1, dated August 17, 1995.

(1) Prior to the accumulation of 20,000 total flight cycles, but

after the accumulation of 4,500 total flight cycles; or within 4,500

flight cycles or 18 months after the effective date of this AD;

whichever occurs latest; perform a one-time internal inspection

(terminating inspection) of the bonded skin panel assemblies that

have not been replaced to detect delamination of the skin doublers

from the skin panels, in accordance with Figures 3 and 4 of the

service bulletin. In lieu of accomplishing the inspections specified

in Figure 3 of the service bulletin, operators can perform an

internal or external ultrasonic inspection in accordance with Note

1. of paragraph A. of the ``Terminating Inspection'' Section of the

Accomplishment Instructions of the service bulletin.

assemblies that have and have not been

replaced to detect cracks in the skin panels, in accordance with

paragraph A. of the ``Interim Inspection'' Section of the

Accomplishment Instructions of the service bulletin. Repeat the

external visual inspection thereafter at intervals not to exceed

4,500 flight cycles, until accomplishment of the requirements

specified in paragraph (b)(4) of this AD.

(4) Within 15,000 flight cycles or 60 months after the effective

date of this AD, whichever occurs first, accomplish the one-time

internal inspection required by both paragraphs (b)(1) and (b)(2) of

this AD. Accomplishment of this action constitutes terminating

action for the repetitive inspections required by paragraph (b)(3)

of this AD.

(c) For airplanes having line numbers 611 through 2725

inclusive, on which any

bonded skin panel assembly was replaced with any new or serviceable

bonded skin panel assembly after September 30, 1997: Accomplish the

actions required either by paragraph (c)(1) or by both paragraphs

(c)(2) and (c)(3) of this AD, in accordance with Boeing Service

Bulletin 737-53-1179, dated June 22, 1995, as revised by Notice of

Status Change 737-53-1179 NSC 1, dated August 17, 1995.

(1) Prior to the accumulation of 20,000 total flight cycles, but

not prior to the accumulation of 4,500 total flight cycles; or

within 4,500 flight cycles or 18 months after the effective date of

this AD; whichever occurs latest; perform a one-time internal

inspection (terminating inspection) of the bonded skin panel

assemblies that have not been replaced to detect delamination of the

skin doublers from the skin panels, in accordance with Figures 3 and

4 of the service bulletin. In lieu of accomplishing the inspections

identified in Figure 3 of the service bulletin, operators can

perform an internal or external ultrasonic inspection in accordance

with NOTE 1. of paragraph A. of the ``Terminating Inspection''

Section of the Accomplishment Instructions of the service bulletin.

in doublers from the skin panels, in accordance with Figures 3 and

4 of the service bulletin. In lieu of accomplishing the inspections

identified in Figure 3 of the service bulletin, operators can

perform an internal or external ultrasonic inspection in accordance

with NOTE 1. of paragraph A. of the ``Terminating Inspection''

Section of the Accomplishment Instructions of the service bulletin.

(2) Within 4,500 flight cycles or 18 months after the effective

date of this AD, whichever occurs later, perform an external visual

inspection of the bonded skin panel assemblies that have not been

replaced to detect cracks in the skin panels, in accordance with

paragraph A. of the ``Interim Inspection'' Section of the

Accomplishment Instructions of the service bulletin. Repeat the

external visual inspection thereafter at intervals not to exceed

4,500 flight cycles, until accomplishment of the requirements

specified in paragraph (c)(3) of this AD.

(3) Within 15,000 flight cycles or 60 months after the effective

date of this AD, whichever occurs first, accomplish the one-time

internal inspection required by paragraph (c)(1) of this AD.

Accomplishment of this action constitutes terminating action for the

repetitive inspections required by paragraph (c)(2) of this AD.

(d) For airplanes having line numbers 1 through 610 inclusive,

and 2726 through 3072 inclusive, on which any bonded skin panel

assembly was replaced with any new or serviceable bonded skin panel

assembly prior to October 1, 1997: Accomplish the actions required

either by paragraph (d)(1) or by both paragraphs (d)(2) and (d)(3)

of this AD, in accordance with Boeing Service Bulletin 737-53-1179,

dated June 22, 1995, as revised by Notice of Status Change 737-53-

1179 NSC 1, dated August 17, 1995.

h any bonded skin panel

assembly was replaced with any new or serviceable bonded skin panel

assembly prior to October 1, 1997: Accomplish the actions required

either by paragraph (d)(1) or by both paragraphs (d)(2) and (d)(3)

of this AD, in accordance with Boeing Service Bulletin 737-53-1179,

dated June 22, 1995, as revised by Notice of Status Change 737-53-

1179 NSC 1, dated August 17, 1995.

(1) Prior to the accumulation of 20,000 flight cycles after the

date of replacement of the skin panel assembly, but not prior to the

accumulation of 4,500 flight cycles after the date of such

replacement; or within 4,500 flight cycles or 18 months after the

effective date of this AD; whichever occurs latest; perform a one-

time internal inspection (terminating inspection) of the bonded skin

panel assemblies that have been replaced to detect delamination of

the skin doublers from the skin panels, in accordance with Figures 3

and 4 of the service bulletin. In lieu of accomplishing the

inspections specified in Figure 3 of the service bulletin, operators

can perform an internal or external ultrasonic inspection in

accordance with NOTE 1. of paragraph A. of the ``Terminating

Inspection'' Section of the Accomplishment Instructions of the

service bulletin.

(2) Within 4,500 flight cycles or 18 months after the effective

date of this AD, whichever occurs later, perform an external visual

inspection of the bonded skin panel assemblies that have been

replaced to detect cracks in the skin panels, in accordance with

paragraph A. of the Interim Inspection of the Accomplishment

Instructions of the service bulletin. Repeat the external visual

inspection thereafter at intervals not to exceed 4,500 flight

cycles, until accomplishment of the requirements specified in

paragraph (d)(3) of this AD.

of the bonded skin panel assemblies that have been

replaced to detect cracks in the skin panels, in accordance with

paragraph A. of the Interim Inspection of the Accomplishment

Instructions of the service bulletin. Repeat the external visual

inspection thereafter at intervals not to exceed 4,500 flight

cycles, until accomplishment of the requirements specified in

paragraph (d)(3) of this AD.

(3) Within 15,000 flight cycles or 60 months after the effective

date of this AD, whichever occurs first, accomplish the one-time

internal inspection required by paragraph (d)(1) of this AD.

Accomplishment of this action constitutes terminating action for the

repetitive inspections required by paragraph (d)(2) of this AD.

(e) If any crack is detected during any inspection required by

paragraph (a)(2), (b)(3), (c)(2), or (d)(2) of this AD, prior to

further flight, accomplish the actions required by paragraph (b)(1)

and (b)(2) of this AD, as applicable.

(1) If any crack is detected in any skin panel that is above

stringer S-10 or between stringers S-14 and S-26, repair in

accordance with Boeing Service Bulletin 737-53-1179, dated June 22,

1995, as revised by Notice of Status Change 737-53-1179 NSC 1, dated

August 17, 1995.

(2) If any crack is detected in any skin panel that is between

stringers S-10 and S-14 (window belt), repair in accordance with a

method approved by the Manager, Seattle Aircraft Certification

Office (ACO), FAA, Transport Airplane Directorate; or in accordance

with data meeting the type certification basis of the airplane

approved by a Boeing Company Designated Engineering Representative

who has been authorized by the Manager, Seattle ACO, to make such

findings.

(f) If no delamination is detected during any inspection

required by paragraph (a)(1), (a)(3), (b)(1), (b)(2), (b)(4),

(c)(1), (c)(3), (d)(1), or (d)(3) of this AD, no further action is

required by this AD.

he type certification basis of the airplane

approved by a Boeing Company Designated Engineering Representative

who has been authorized by the Manager, Seattle ACO, to make such

findings.

(f) If no delamination is detected during any inspection

required by paragraph (a)(1), (a)(3), (b)(1), (b)(2), (b)(4),

(c)(1), (c)(3), (d)(1), or (d)(3) of this AD, no further action is

required by this AD.

(g) If any delamination is detected during any inspection

required by paragraph (a)(1), (a)(3), (b)(1), (b)(2), (b)(4),

(c)(1), (c)(3), (d)(1), or (d)(3) of this AD, prior to further

flight, accomplish the actions required by either paragraph (g)(1)

or (g)(2) of this AD, as applicable.

(1) If the delaminated area is less than 3 square inches and is

not at the edge of a skin doubler or under a fastener head, no

further action is required by this AD for that delaminated area.

(2) If the delaminated area is equal to or greater than 3 square

inches or is located at the edge of a skin doubler or under a

fastener head, prior to further flight, accomplish the follow-on

corrective actions in accordance with the ``Terminating Inspection''

Section of the Accomplishment Instructions of Boeing Service

Bulletin 737-53-1179, dated June 22, 1995, as revised by Notice of

Status Change 737-53-1179 NSC 1, dated August 17, 1995, except as

provided by paragraphs (h) and (i) of this AD.

(h) Where Boeing Service Bulletin 737-53-1179, dated June 22,

1995, as revised by Notice of Status Change 737-53-1179 NSC 1, dated

August 17, 1995, specifies that the actions required by this AD may

be accomplished in accordance with an ``equivalent'' procedure, the

actions must be accomplished in accordance with the chapter of the

Boeing 737 Nondestructive Test Manual specified in the service

bulletin.

eing Service Bulletin 737-53-1179, dated June 22,

1995, as revised by Notice of Status Change 737-53-1179 NSC 1, dated

August 17, 1995, specifies that the actions required by this AD may

be accomplished in accordance with an ``equivalent'' procedure, the

actions must be accomplished in accordance with the chapter of the

Boeing 737 Nondestructive Test Manual specified in the service

bulletin.

(i) Where Boeing Service Bulletin 737-53-1179, dated June 22,

1995, as revised by Notice of Status Change 737-53-1179 NSC 1, dated

August 17, 1995, specifies that the repair of a delaminated lap

splice is to be accomplished in accordance with instructions

received from Boeing, this AD requires that the repair be

accomplished in accordance with a method approved by the Manager,

Seattle ACO; or in accordance with data meeting the type

certification basis of the airplane approved by a Boeing Company

Designated Engineering Representative who has been authorized by the

Manager, Seattle ACO, to make such findings.

(j) An alternative method of compliance or adjustment of the

compliance time that provides an acceptable level of safety may be

used if approved by the Manager, Seattle ACO. Operators shall submit

their requests through an appropriate FAA Principal Maintenance

Inspector, who may add comments and then send it to the Manager,

Seattle ACO.

Note 6: Information concerning the existence of approved

alternative methods of compliance with this AD, if any, may be

obtained from the Seattle ACO.

(k) Special flight permits may be issued in accordance with

sections 21.197 and 21.199 of the Federal Aviation Regulations (14

CFR 21.197 and 21.199) to operate the airplane to a location where

the requirements of this AD can be accomplished.

Issued in Renton, Washington, on December 31, 1998.

Darrell M. Pederson,

Acting Manager, Transport Airplane Directorate, Aircraft Certification

Service.

[FR Doc. 99-481 Filed 1-8-99; 8:45 am]

BILLING CODE 4910-13-U