Airworthiness Directives; Boeing Model 747 Series Airplanes

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 99-NM-231-AD]

RIN 2120-AA64

Airworthiness Directives; Boeing Model 747 Series Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Notice of proposed rulemaking (NPRM).

-----------------------------------------------------------------------

SUMMARY: This document proposes the adoption of a new airworthiness

directive (AD) that is applicable to all Boeing Model 747 series

airplanes. This proposal would require repetitive inspections to detect

cracking of the forward and aft inner chords and the splice fitting of

the forward inner chord of the station 2598 bulkhead, and repair, if

necessary. This proposal is prompted by reports of fatigue cracking

found in those areas. The actions specified by the proposed AD are

intended to detect and correct such cracking, which could result in

reduced structural capability of the bulkhead and the inability of the

structure to carry horizontal stabilizer flight loads.

DATES: Comments must be received by December 20, 1999.

ADDRESSES: Submit comments in triplicate to the Federal Aviation

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

Attention: Rules Docket No. 99-NM-231-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: Bob Breneman, Aerospace Engineer,

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

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

Washington 98055-4056; telephone (425) 227-2776; 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 99-NM-231-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. 99-NM-231-AD, 1601 Lind Avenue, SW., Renton, Washington

98055-4056.

Discussion

The FAA has received reports indicating that fatigue cracking has

been detected in the forward and aft inner chords and the splice

fitting of the forward inner chord of the station 2598 bulkhead on

Boeing Model 747 series airplanes. The horizontal stabilizer hinge

fittings are attached to the station

[[Page 60387]]

2598 bulkhead. The bulkhead includes a large cutout that gives access

to the rear spar of the horizontal stabilizer. The reports indicate

that the cracking was detected around the upper corners of the cutout.

In addition, a recent report indicates that a fatigue crack was

detected in the station 2598 splice fitting where it attaches to the

upper and lower sections of the bulkhead forward inner chord. Such

cracking, if not detected and corrected, could result in reduced

structural capability of the bulkhead and the inability of the

structure to carry horizontal stabilizer flight loads.

Explanation of Relevant Service Information

The FAA has reviewed and approved Boeing Alert Service Bulletin

747-53A2427, dated December 17, 1998, which describes procedures for a

one-time high frequency eddy current (HFEC) inspection and repetitive

detailed visual inspections to detect cracking of the forward and aft

inner chords of the station 2598 bulkhead, and repair, if necessary.

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 a one-time HFEC inspection and repetitive

detailed visual inspections to detect cracking of the forward and aft

inner chords of the station 2598 bulkhead, and repair, if necessary.

These actions would be required to be accomplished in accordance with

the alert service bulletin described previously, except as discussed

below. The proposed AD also would require a one-time HFEC inspection

and repetitive detailed visual inspections to detect cracking of the

splice fitting of the forward inner chord of the station 2598 bulkhead.

Such inspections of the splice fitting of the forward inner chord would

be required to be accomplished in accordance with procedures included

in paragraphs (a)(2) and (b)(2) of this AD. If any cracking is found

during such inspections, repair would be required to be accomplished in

accordance with a method approved by the FAA, as specified in paragraph

(d) of this proposed AD.

Differences Between Proposed Rule and Alert Service Bulletin

Operators should note that, although the alert service bulletin

specifies that the manufacturer may be contacted for disposition of

certain repair conditions, this proposed AD 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

FAA to make such findings.

Operators also should note that, as described previously, this

proposed AD would require a one-time HFEC inspection and repetitive

detailed visual inspections to detect cracking of the splice fitting of

the forward inner chord of the station 2598 bulkhead. The alert service

bulletin does not specify such inspections of the splice fitting. Also,

though this inspection area is shown in Figure 2, Detail A, and Figure

3, Detail A, of the alert service bulletin, the inspection area is not

highlighted in those figures.

Interim Action

This is considered to be interim action. The manufacturer has

advised that it currently is developing a modification that will

positively address the unsafe condition addressed by this AD. Once this

modification is developed, approved, and available, the FAA may

consider additional rulemaking.

Cost Impact

There are approximately 1,301 airplanes of the affected design in

the worldwide fleet. The FAA estimates that 260 airplanes of U.S.

registry would be affected by this proposed AD.

It would take approximately 2 work hours per airplane to accomplish

the proposed HFEC inspection, at an average labor rate of $60 per work

hour. Based on these figures, the cost impact of the proposed

inspection on U.S. operators is estimated to be $31,200, or $120 per

airplane.

It would take approximately 2 work hours per airplane to accomplish

the proposed detailed visual inspections, at an average labor rate of

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

proposed inspections on U.S. operators is estimated to be $31,200, or

$120 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 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 99-NM-231-AD.

Applicability: All Model 747 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 (e) 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

[[Page 60388]]

been eliminated, the request should include specific proposed

actions to address it.

Compliance: Required as indicated, unless accomplished

previously.

To detect and correct cracking of the forward and aft inner

chords and the splice fitting of the forward inner chord of the

station 2598 bulkhead, which could result in reduced structural

capability of the bulkhead and the inability of the structure to

carry horizontal stabilizer flight loads, accomplish the following:

Initial Inspection

(a) Prior to the accumulation of 13,000 total flight cycles, or

within 1,000 flight cycles after the effective date of this AD,

whichever occurs later: Accomplish the requirements specified in

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

(1) Perform a high frequency eddy current inspection (HFEC) to

detect cracking of the forward and aft inner chords of the station

2598 bulkhead, in accordance with Boeing Alert Service Bulletin 747-

53A2427, dated December 17, 1998.

(2) Perform an HFEC inspection to detect cracking of the splice

fitting along the upper and lower attachment to the forward inner

chord of the station 2598 bulkhead, as shown in Figure 2, Detail A,

of Boeing Alert Service Bulletin 747-53A2427, dated December 17,

1998.

Note 2: Operators should note that the inspection area specified

in paragraph (a)(2) of this AD is NOT highlighted in Figure 2,

Detail A, of Boeing Alert Service Bulletin 747-53A2427, dated

December 17, 1998.

Repetitive Inspections

(b) Within 3,000 flight cycles after accomplishment of the

inspections required by paragraph (a) of this AD: Accomplish the

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

Repeat the inspection thereafter at intervals not to exceed 3,000

flight cycles.

(1) Perform a detailed visual inspection to detect cracking of

the forward and aft inner chords of the station 2598 bulkhead, in

accordance with Boeing Alert Service Bulletin 747-53A2427, dated

December 17, 1998.

Note 3: For the purposes of this AD, a detailed visual

inspection is defined as: ``An intensive visual examination of a

specific structural area, system, installation, or assembly to

detect damage, failure, or irregularity. Available lighting is

normally supplemented with a direct source of good lighting at

intensity deemed appropriate by the inspector. Inspection aids such

as mirror, magnifying lenses, etc., may be used. Surface cleaning

and elaborate access procedures may be required.''

(2) Perform a detailed visual inspection to detect cracking of

the splice fitting along the upper and lower attachment to the

forward inner chord of the station 2598 bulkhead, as shown in Figure

3, Detail A, of Boeing Alert Service Bulletin 747-53A2427, dated

December 17, 1998.

Note 4: Operators should note that the inspection area specified

in paragraph (b)(2) of this AD is NOT highlighted in Figure 3,

Detail A, of Boeing Alert Service Bulletin 747-53A2427, dated

December 17, 1998.

Repair

(c) If any cracking is detected during the inspections required

by paragraph (a)(1) or (b)(1) of this AD, prior to further flight,

repair in accordance with Boeing Alert Service Bulletin 747-53A2427,

dated December 17, 1998, except as provided by paragraph (d) of this

AD.

(d) If any cracking is detected during the inspections required

by paragraph (a)(2) or (b)(2) of this AD, or where the alert service

bulletin specifies that the manufacturer may be contacted for

disposition of certain repair conditions, prior to further flight,

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 (DER) who has been authorized

by the Manager, Seattle ACO, to make such findings. For a repair

method to be approved by the Manager, Seattle ACO, or a Boeing DER,

as required by this paragraph, the approval letter must specifically

reference this AD.

Alternative Methods of Compliance

(e) 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 5: Information concerning the existence of approved

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

obtained from the Seattle ACO.

Special Flight Permits

(f) 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 November 1, 1999.

D. L. Riggin,

Acting Manager, Transport Airplane Directorate, Aircraft Certification

Service.

[FR Doc. 99-29056 Filed 11-4-99; 8:45 am]

BILLING CODE 4910-13-U