Airworthiness Directives; Boeing Model 737-100 and -200 Series Airplanes

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 94-NM-159-AD]

Airworthiness Directives; Boeing Model 737-100 and -200 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 737-100 and -

200 series airplanes. This proposal would require various inspections

for cracks in the outboard chord of the frame at Body Station (BS) 727

and in the outboard chord of Stringer 18A; and repair or replacement of

cracked parts. This proposal is prompted by reports of fatigue cracks

in those outboard chords. The actions specified by the proposed AD are

intended to prevent such fatigue cracking, which could result in

reduced structural integrity of the outboard chords, and subsequent

rapid decompression of the airplane.

DATES: Comments must be received by February 3, 1995.

ADDRESSES: Submit comments in triplicate to the Federal Aviation

Administration (FAA), Transport Airplane Directorate, ANM-103,

Attention: Rules Docket No. 94-ANM-159-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.

FOR FURTHER INFORMATION CONTACT: Thomas Rodriguez, Aerospace Engineer,

Airframe Branch, ANM-120S, Seattle Aircraft Certification Office, FAA,

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

Washington 98055-4056; telephone (206) 227-2779; fax (206) 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 94-NM-159-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-103, Attention: Rules

Docket No. 94-NM-159-AD, 1601 Lind Avenue, SW., Renton, Washington

98055-4056.

Discussion

The FAA has received several reports of cracking on Boeing Model

737-100 and -200 series airplanes in the outboard chord of the frame at

Body Station (BS) 727 where Stringer 18A is attached. There also have

been reports of cracking in the outboard chord of Stringer 18A. These

cracks were found on eight airplanes that had accumulated between

39,000 and 54,100 flight hours, and between 56,200 and 73,200 flight

cycles. The cracks have been determined to be caused by fatigue that

was initiated by fretting of adjacent parts. Fatigue cracks in the

chords, if not detected and corrected in a timely manner, could result

in reduced structural integrity of the structure, and subsequent rapid

decompression of the airplane.

The FAA has reviewed and approved Boeing Alert Service Bulletin

737-53A1166, dated June 30, 1994, which describes procedures for the

following repetitive inspections:

1. Close visual inspections to detect cracking of the edge of the

forward flange of the outboard chord of the frame at BS 727;

2. High frequency eddy current (HFEC) inspections to detect

cracking of the fastener holes in the outboard chord of the frame at BS

727;

3. Pulse echo shear wave (PESW) inspections to detect cracking in

the area of the two forward lower fastener holes in the outboard chord

where Stringer 18A is attached; and

4. HFEC inspections to detect cracking of the outboard surface of

the outboard chord of Stringer 18A at Station 727 and of the surface

around the heads of two fasteners.

The alert service bulletin also describes procedures for either the

installation of a time-limited repair or the replacement of the chords,

if any crack is found in the outboard chord of the frame at BS 727.

(The alert service bulletin references Boeing Service Bulletin 737-53-

1088 as an additional source of service information for replacement of

the outboard chords.) In addition, the alert service bulletin describes

procedures for installation of a preventative modification, which, when

accomplished, eliminates the need for repetitive inspections.

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 various inspections for cracks in the

outboard chord of the frame at BS 727 and in the outboard chord of

Stringer 18A; and repair or replacement of cracked parts. The proposed

AD would also provide for an optional terminating action for the

required inspections. The actions would be required to be accomplished

in accordance with the service bulletin described previously.

As a result of recent communications with the Air Transport

Association (ATA) of America, the FAA has learned that, in general,

some operators may misunderstand the legal effect of AD's on airplanes

that are identified in the applicability provision of the AD, but that

have been altered or repaired in the area addressed by the AD. Under

these circumstances, at least one operator appears to have incorrectly

assumed that its airplane was not subject to an AD. On the contrary,

all airplanes identified in the applicability provision of an AD are

legally subject to the AD. If an airplane has been altered or repaired

in the affected area in such a way as to affect compliance with the AD,

the owner or operator is required to obtain FAA approval for an

alternative method of compliance with the AD, in accordance with the

paragraph of each AD that provides for such approvals. A note has been

included in this notice to clarify this requirement.

There are approximately 999 Boeing Model 737-100 and -200 series

airplanes of the affected design in the worldwide fleet. The FAA

estimates that 296 airplanes of U.S. registry would be affected by this

proposed AD, that it would take approximately 4 work hours per airplane

to accomplish each of the proposed inspections, and that the average

labor rate is $60 per work hour. Based on these figures, the total cost

impact of the inspection requirements of this proposed AD on U.S.

operators is estimated to be $71,040, or $240 per airplane, per

inspection cycle.

Should an operator elect to accomplish the optional terminating

action that would be provided by this AD action, it would take

approximately 50 work hours to accomplish it, at an average labor rate

of $60 per work hour. Required parts would cost approximately $3,680

per airplane. Based on these figures, the total cost impact of this

optional terminating action is estimated to be $6,680 per airplane.

The total cost impact figure discussed above is 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.

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. App. 1354(a), 1421 and 1423; 49 U.S.C.

106(g); and 14 CFR 11.89.

Sec. 39.13 [Amended]

2. Section 39.13 is amended by adding the following new

airworthiness directive:

Boeing: Docket 94-NM-159-AD.

Applicability: Model 737-100 and -200 series airplanes; line

numbers 1 through 999, inclusive; 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 use the authority

provided in paragraph (h) to request approval from the FAA. This

approval may address either no action, if the current configuration

eliminates the unsafe condition; or different actions necessary to

address the unsafe condition described in this AD. Such a request

should include an assessment of the effect of the changed

configuration on the unsafe condition addressed by this AD. In no

case does the presence of any modification, alteration, or repair

remove any airplane from the applicability of this AD.

Compliance: Required as indicated, unless accomplished

previously.

To prevent reduced structural integrity of the outboard chords,

and subsequent rapid decompression of the airplane, accomplish the

following:

(a) For airplanes on which the upper outboard chord has been

replaced in accordance with Boeing Service Bulletin 737-53-1088:

Prior to the accumulation of 30,000 total flight cycles since

replacement of the upper outboard chord, or within 4,500 flight

cycles after the effective date of this AD, whichever occurs later,

perform close visual, pulse echo shear wave (PESW), and high

frequency eddy current (HFEC) inspections to detect cracks in the

outboard chord of the frame at Body Station (BS) 727 and in the

outboard chord of Stringer 18A , in accordance with Part I of the

Accomplishment Instructions of Boeing Alert Service Bulletin 737-

53A1166, dated June 30, 1994.

(b) Repeat the inspections required by paragraph (a) of this AD

as follows, until the optional terminating action described in

paragraph (g) of this AD is accomplished:

(1) If, at the time of the most recent inspection required by

paragraph (a) or (b) of this AD, the airplane has accumulated 27,000

or more flight cycles, but fewer than 50,000 flight cycles, since

the replacement of the outboard chord: Perform the next inspection

within 15,000 flight cycles. Repeat the inspection thereafter at

intervals not to exceed 15,000 flight cycles until the airplane has

accumulated 50,000 or more flight cycles since the replacement of

the outboard chord; then perform the inspections required by

paragraph (b)(2) of this AD.

(2) If, at the time of the most recent inspection required by

paragraph (a) or (b) of this AD, the airplane has accumulated 50,000

or more flight cycles, but fewer than 60,000 flight cycles, since

the replacement of the outboard chord: Perform the next inspection

within 7,500 flight cycles. Repeat the inspection thereafter at

intervals not to exceed 7,500 flight cycles until the airplane has

accumulated 60,000 or more flight cycles since the replacement of

the outboard chord; then perform the inspections required by

paragraph (b)(3) of this AD.

(3) If, at the time of the most recent inspection required by

paragraph (a) or (b) of this AD, the airplane has accumulated 60,000

or more flight cycles, but fewer than 70,000 flight cycles, since

the replacement of the outboard chord: Perform the next inspection

within 5,000 flight cycles. Repeat the inspection thereafter at

intervals not to exceed 5,000 flight cycles until the airplane has

accumulated 70,000 or more flight cycles since the replacement of

the outboard chord; then perform the inspections required by

paragraph (b)(4) of this AD.

(4) If, at the time of the most recent inspection required by

paragraph (a) or (b) of this AD, the airplane has accumulated 70,000

or more flight cycles since replacement of the outboard chord:

Perform the next inspection within 3,000 flight cycles. Repeat the

inspection thereafter at intervals not to exceed 3,000 flight

cycles.

(c) For airplanes on which the outboard chord has not been

replaced or on which only the lower outboard chord has been replaced

in accordance with Boeing Service Bulletin: 737-53-1088: Perform

close visual, pulse echo shear wave (PESW), and high frequency eddy

current (HFEC) inspections to detect cracks in the outboard chord of

the frame at BS 727 and in the outboard chord of Stringer 18A, in

accordance with Part I of the Accomplishment Instructions of Boeing

Alert Service Bulletin 737-53A1166, dated June 30, 1994. Perform

these inspections initially at the time specified in paragraph

(c)(1), (c)(2), (c)(3), or (c)(4), as applicable. Repeat these

inspections thereafter at the intervals specified in paragraph (d)

of this AD.

(1) For airplanes that have accumulated 27,000 or more total

flight cycles, but fewer than 50,000 total flight cycles, as of the

effective date of this AD: Inspect prior to the accumulation of

4,500 flight cycles after the effective date of this AD.

(2) For airplanes that have accumulated 50,000 or more total

flight cycles, but fewer than 60,000 total flight cycles, as of the

effective date of this AD: Inspect prior to the accumulation of

2,500 flight cycles after the effective date of this AD.

(3) For airplanes that have accumulated 60,000 or more total

flight cycles, but fewer than 70,000 total flight cycles as of the

effective date of this AD: Inspect prior to the accumulation of

1,500 flight cycles after the effective date of this AD.

(4) For airplanes that have accumulated 70,000 or more total

flight cycles as of the effective date of this AD: Inspect prior to

the accumulation of 500 flight cycles or within 90 days after the

effective date of this AD, whichever occurs first.

(d) Repeat the inspections required by paragraph (c) of this AD

as follows, until the optional terminating action described in

paragraph (g) of this AD is accomplished:

(1) If, at the time of the most recent inspection required by

paragraph (c) or (d) of this AD, the airplane has accumulated 27,000

or more total flight cycles, but fewer than 50,000 total flight

cycles: Perform the next inspection within 15,000 flight cycles.

Repeat the inspection thereafter at intervals not to exceed 15,000

flight cycles until the airplane has accumulated 50,000 or more

total flight cycles; then perform the inspections required by

paragraph (d)(2) of this AD.

(2) If, at the time of the most recent inspection required by

paragraph (c) or (d) of this AD, the airplane had accumulated 50,000

or more total flight cycles, but fewer than 60,000 total flight

cycles: Perform the next inspection within 7,500 flight cycles.

Repeat the inspection thereafter at intervals not to exceed 7,500

flight cycles until the airplane has accumulated 60,000 or more

total flight cycles; then perform the inspections required by

paragraph (d)(3) of this AD.

(3) If, at the time of the most recent inspection required by

paragraph (c) or (d) of this AD, the airplane had accumulated 60,000

or more total flight cycles, but fewer than 70,000 total flight

cycles: Perform the next inspection within 5,000 flight cycles.

Repeat the inspection thereafter at intervals not to exceed 5,000

flight cycles until the airplane has accumulated 70,000 or more

total flight cycles; then perform the inspections required by

paragraph (b)(4) of this AD.

(4) If, at the time of the most recent inspection required by

paragraph (c) or (d) of this AD, the airplane had accumulated 70,000

or more total flight cycles: Perform the next inspection within

3,000 flight cycles. Repeat the inspection thereafter at intervals

not to exceed 3,000 flight cycles.

(e) If any crack is found in the outboard chord of Stringer 18A

during any inspection required by this AD, prior to further flight,

repair in accordance with a method approved by the Manager, Seattle

Aircraft Certification Office, FAA, Transport Airplane Directorate.

(f) If any crack is found in the outboard chord of the frame at

BS 727 during any inspection required by this AD, accomplish

paragraph (f)(1) or (f)(2) of this AD, as applicable, in accordance

with Boeing Alert Service Bulletin 737-53A1166, dated June 30, 1994.

(1) For any crack that extends from the forward edge of the

chord or from the forward fastener hole, but that does not extend

past the second fastener hole, accomplish either paragraph (f)(1)(i)

or (f)(1)(ii) of this AD. Thereafter, perform initial and repetitive

inspections in accordance with paragraphs (a) and (b) of this AD.

(i) Prior to further flight, install the time limited repair.

Prior to the accumulation of 4,500 flight cycles or within 18

months, after accomplishing the time-limited repair, whichever

occurs first, replace the outboard chord. Or

(ii) Prior to further flight, replace the outboard chord.

Note 4: Boeing Alert Service Bulletin 737-53A1166 references

Boeing Service Bulletin 737-53-1088 as an additional source of

service information for procedures to replace the chord.

(2) For any crack that extends from the forward edge of the

chord, or from the forward fastener hole, and that extends past the

second fastener hole, prior to further flight, replace the outboard

chord in accordance with the alert service bulletin. Thereafter,

perform initial and repetitive inspections in accordance with

paragraphs (a) and (b) of this AD.

(g) Accomplishment of the following actions in accordance with

Boeing Alert Service Bulletin 737-53A1166, dated June 30, 1994,

constitutes terminating actions for the requirements of this AD:

(1) For airplanes on which no crack is found: Install the

preventative modification in accordance with the alert service

bulletin.

(2) For airplanes on which any crack is found: Prior to further

flight, replace the outboard chords and install the preventative

modification in accordance with the alert service bulletin.

(h) 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 5: Information concerning the existence of approved

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

obtained from the Seattle ACO.

(i) 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 1, 1994.

James V. Devany,

Acting Manager, Transport Airplane Directorate, Aircraft Certification

Service.

[FR Doc. 94-30086 Filed 12-6-94; 8:45 am]

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