Airworthiness Directives; Boeing Model 737-600 Series Airplanes

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 99-NM-155-AD; Amendment 39-11229; AD 99-15-09]

RIN 2120-AA64

Airworthiness Directives; Boeing Model 737-600 Series Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Final rule; request for comments.

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SUMMARY: This amendment adopts a new airworthiness directive (AD),

applicable to certain Boeing Model 737-600 series airplanes. This

action requires revising the Airplane Flight Manual (AFM) to prohibit

operation of the airplane under certain conditions; repetitive

inspections of the tab mast fittings of the elevator tab assemblies to

detect cracking; an elevator tab freeplay check; and corrective

actions, if necessary. This AD also requires installing an additional

fastener on the elevator tab mast fitting, which terminates the AFM

revision and extends certain repetitive inspections. This AD also

requires replacement of the elevator tab mast fitting with a new,

improved fitting, which constitutes terminating action for the

requirements of this AD. This amendment is prompted by a report of a

severe vibration incident on a Boeing Model 737-800 series airplane;

inspection revealed fracturing of the elevator tab mast fitting and

excessive freeplay in the elevator tab. The actions specified in this

AD are intended to prevent loss of controllability of the airplane due

to excessive freeplay in the elevator tab or a free tab.

DATES: Effective August 11, 1999.

The incorporation by reference of certain publications listed in

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

of August 11, 1999.

Comments for inclusion in the Rules Docket must be received on or

before September 27, 1999.

ADDRESSES: Submit comments in triplicate to the Federal Aviation

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

Attention: Rules Docket No. 99-NM-155-AD, 1601 Lind Avenue, SW.,

Renton, Washington 98055-4056.

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 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.

FOR FURTHER INFORMATION CONTACT: Gregory L. Schneider, Aerospace

Engineer, Airframe Branch, ANM-120S, FAA, Transport Airplane

Directorate, Seattle Aircraft Certification Office, 1601 Lind Avenue,

SW., Renton, Washington 98055-4056; telephone (425) 227-2028; fax (425)

227-1181.

SUPPLEMENTARY INFORMATION: On June 2, 1999, the FAA received a report

of a severe vibration incident on a Boeing Model 737-800 series

airplane, which had accumulated 3,517 total flight hours and 1,284

total flight cycles. The airplane was involved in a high-speed descent

with speed brakes extended while operating at an airspeed of 320 knots.

During the descent, severe vibration occurred at 250 knots. At 230

knots, the speed brakes were retracted and the vibration stopped. The

landing was uneventful.

Inspection of the airplane revealed that the upper flange of the

right elevator tab mast fitting, to which the elevator tab push rods

are attached, was found fractured. The lower flange of the fitting was

not damaged. In addition, excessive freeplay in the elevator tab also

was observed and measured during the inspection.

Further analysis confirmed that the damage to the fitting was

aggravated by speed-brake-induced airframe vibration. Such vibration

could lead to damage of the elevator tab mast fitting, excessive

freeplay in the tab, and consequent separation of the tab mast fitting

from the tab. Excessive freeplay in the tab could result in severe

airframe vibration and consequent damage to the tab, elevator, and

horizontal stabilizer. Separation of the elevator tab mast fitting will

result in a free tab. These conditions, if not corrected, could result

in loss of controllability of the airplane.

In light of this information, on June 10, 1999, the FAA issued

telegraphic AD T99-13-51, which is applicable to certain Boeing Model

737-700 and -800 series airplanes. In addition, the FAA has received

information indicating that Boeing Model 737-600 series airplanes also

are subject to the unsafe condition identified in telegraphic AD T99-

13-51. Therefore, the FAA has determined that rulemaking action is

necessary to address that unsafe condition on Model 737-600 series

airplanes.

Explanation of Relevant Service Information

The FAA has reviewed and approved Boeing Alert Service Bulletin

737-55A1068, Revision 1, dated June 11, 1999, which describes

procedures for repetitive high frequency eddy current (HFEC) and

detailed visual inspections of the tab mast fittings of the left and

right elevator tab assemblies to detect cracking, and a one-time

elevator tab freeplay check to detect excessive freeplay of the

elevator tabs; and corrective actions, if necessary. The alert service

bulletin also describes procedures for installing an additional high-

strength fastener on the elevator tab mast fitting (time-limited

modification).

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

55-1063, dated July 1, 1999, which describes procedures for replacing a

cracked elevator tab mast fitting with a new, improved fitting. Such

replacement eliminates the need for repetitive inspections of the

elevator tab mast fittings.

Explanation of Requirements of the Rule

Since an unsafe condition has been identified that is likely to

exist or develop on other airplanes of the same type design, this AD is

being issued to prevent loss of controllability of the airplane due to

excessive freeplay in the elevator tab or a free tab. This AD requires

revising the Limitations Section of the FAA-approved Airplane Flight

Manual (AFM) to prohibit operation of the airplane at certain airspeeds

with the speed brakes extended, and at certain altitudes.

This AD also requires repetitive HFEC and detailed visual

inspections of the tab mast fittings of the left and right elevator tab

assemblies to detect cracking, and a one-time elevator tab freeplay

check to detect excessive freeplay of the elevator tab; and corrective

actions, if necessary.

Additionally, this AD requires installing an additional high-

strength fastener on the elevator tab mast fitting (time-limited

modification). Such installation terminates the AFM revision and allows

extension of the repetitive interval for accomplishment of the HFEC and

detailed visual inspections.

This AD also requires replacement of the elevator tab mast fittings

with new, improved fittings, which constitutes

[[Page 40515]]

terminating action for the requirements of this AD.

Certain inspections and checks are required to be accomplished in

accordance with Boeing Alert Service Bulletin 737-55A1068, Revision 1.

Replacement actions are required to be accomplished in accordance with

Boeing Service Bulletin 737-55-1063, dated July 1, 1999.

It should be noted that, except as otherwise provided for in the

AFM emergency procedures, this AD prohibits the deployment of the

spoilers at speeds in excess of 310 knots indicated airspeed (IAS) with

speed brakes extended. This AD also prohibits operation of the airplane

above FL 390. The FAA recognizes that under emergency circumstances, as

specified in the AFM, it might become necessary to deploy spoilers in

excess of 310 knots IAS. In that event, this AD requires accomplishment

of the HFEC and detailed visual inspections of the elevator tab mast

fittings and of the check of the tabs for freeplay, prior to further

flight after landing.

Cost Impact

None of the Model 737-600 series airplanes affected by this action

are on the U.S. Register. All airplanes included in the applicability

of this rule currently are operated by non-U.S. operators under foreign

registry; therefore, they are not directly affected by this AD action.

However, the FAA considers that this rule is necessary to ensure that

the unsafe condition is addressed in the event that any of these

subject airplanes are imported and placed on the U.S. Register in the

future.

Should an affected airplane be imported and placed on the U.S.

Register in the future:

It would require approximately 2 work hours to accomplish the

inspection and check, at an average labor rate of $60 per work hour.

Based on this figure, the cost impact of the inspection and check

required by this AD would be $120 per airplane.

It would require approximately 3 work hours to accomplish the time-

limited modification, at an average labor rate of $60 per work hour.

Based on this figure, the cost impact of the time-limited modification

required by this AD would be $180 per airplane.

It would require approximately 8 work hours to accomplish the

replacement action, at an average labor rate of $60 per work hour.

Required parts would cost approximately $5,149 per airplane. Based on

these figures, the cost impact of the replacement required by this AD

would be $5,629 per airplane.

Determination of Rule's Effective Date

Since this AD action does not affect any airplane that is currently

on the U.S. register, it has no adverse economic impact and imposes no

additional burden on any person. Therefore, prior notice and public

procedures hereon are unnecessary and the amendment may be made

effective in less than 30 days after publication in the Federal

Register.

Comments Invited

Although this action is in the form of a final rule and was not

preceded by notice and opportunity for public comment, comments are

invited on this rule. Interested persons are invited to comment on this

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 under the caption

ADDRESSES. All communications received on or before the closing date

for comments will be considered, and this rule may be amended in light

of the comments received. Factual information that supports the

commenter's ideas and suggestions is extremely helpful in evaluating

the effectiveness of the AD action and determining whether additional

rulemaking action would be needed.

Comments are specifically invited on the overall regulatory,

economic, environmental, and energy aspects of the rule that might

suggest a need to modify the 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 that

summarizes each FAA-public contact concerned with the substance of this

AD will be filed in the Rules Docket.

Commenters wishing the FAA to acknowledge receipt of their comments

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

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

to Docket Number 99-NM-155-AD.'' The postcard will be date stamped and

returned to the commenter.

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:

99-15-09 Boeing: Amendment 39-11229. Docket 99-NM-155-AD.

Applicability: Model 737-600 series airplanes having line

numbers 1 through 190, 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 (g) 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 loss of controllability of the airplane due to

excessive freeplay in the elevator tab or a free tab, accomplish the

following:

[[Page 40516]]

Airplane Flight Manual (AFM) Revision

(a) Within 24 clock hours after the effective date of this AD,

revise the Limitations Section of the FAA-approved AFM to include

the following information.

This may be accomplished by inserting a copy of this AD into the

AFM.

Except as otherwise provided for in the AFM emergency

procedures, do not operate the airplane at speeds in excess of 310

knots indicated airspeed (IAS) with speed brakes extended. Do not

operate the airplane above FL 390.

(b) In the event of deployment of the speed brakes at speeds in

excess of 310 knots indicated airspeed (IAS), prior to further

flight after landing, accomplish the requirements of paragraph (c)

of this AD.

Inspections and Check

Note 2: Accomplishment of the inspections and check required by

this AD, prior to the effective date of this AD, in accordance with

Boeing Alert Service Bulletin 737-55A1068, dated June 9, 1999, is

considered acceptable for compliance with the repetitive inspections

and checks required by paragraphs (c) and (d) of this AD.

(c) Within 10 days after the effective date of this AD, perform

a high frequency eddy current (HFEC) inspection, and a detailed

visual inspection of the elevator tab mast fittings of the left and

right elevator tab assemblies to detect cracking, and a one-time

elevator tab freeplay check to detect freeplay of the elevator tabs,

in accordance with Boeing Alert Service Bulletin 737-55A1068,

Revision 1, dated June 11, 1999.

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

(1) If no cracking is found in any elevator tab mast fitting,

repeat the HFEC and detailed visual inspections thereafter at

intervals not to exceed 15 days, until accomplishment of the actions

required by paragraph (d) of this AD.

(2) If any cracking is found in any elevator tab mast fitting,

prior to further flight, accomplish the requirements of paragraph

(e) of this AD.

(3) If any freeplay is found in any elevator tab, which is

outside the limits specified in the alert service bulletin, prior to

further flight, perform corrective actions in accordance with the

alert service bulletin.

Note 4: Boeing Alert Service Bulletin 737-55A1068, Revision 1,

dated June 11, 1999, references Boeing Model 737-600/-700/-800

Maintenance Manual (AMM), Subjects 27-09-91, 27-31-00, and 51-21-99;

737 Nondestructive Test (NDT) Manual D6-37239, Part 6, Subject 55-

00-00; 737 Structural Repair Manual (SRM) Subject 51-20-81; and

Operations Manual Service Bulletin D6-27370-TBC (``Elevator Tab

Operational Limitations''), dated June 10, 1999; as additional

sources of service information to accomplish certain requirements of

this AD.

Time-Limited Modification

(d) Within 90 days after the effective date of this AD, install

an additional high-strength fastener on the elevator tab mast

fitting in accordance with Boeing Alert Service Bulletin 737-

55A1068, Revision 1, dated June 11, 1999. Accomplishment of this

modification constitutes terminating action for the requirements of

paragraph (b) of this AD. Following accomplishment of the

installation, the AFM revision required by paragraph (a) of this AD

may be removed from the AFM. Following accomplishment of the

installation, repeat the HFEC and detailed visual inspections

required by paragraph (c) of this AD thereafter at intervals not to

exceed 90 days until accomplishment of paragraph (e) of this AD.

Terminating Action

(e) Within 4,000 flight cycles or 18 months after the effective

date of this AD, whichever occurs earlier, replace the elevator tab

mast fittings with new, improved tab mast fittings, in accordance

with Boeing Service Bulletin 737-55-1063, dated July 1, 1999.

Accomplishment of this replacement action constitutes terminating

action for the requirements of this AD.

Spares

(f) As of the effective date of this AD, no elevator tab mast

fitting, part number (P/N) 183A8400-1 or 183A8400-2, shall be

installed on any airplane.

Alternative Methods of Compliance

(g) 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.

Special Flight Permits

(h) 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.

Incorporation by Reference

(i) Except as provided by paragraphs (a) and (b) of this AD, the

actions shall be done in accordance with Boeing Alert Service

Bulletin 737-55A1068, Revision 1, dated June 11, 1999, and Boeing

Service Bulletin 737-55-1063, dated July 1, 1999. 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.

(j) This amendment becomes effective on August 11, 1999.

Issued in Renton, Washington, on July 13, 1999.

D.L. Riggin,

Acting Manager, Transport Airplane Directorate, Aircraft Certification

Service.

[FR Doc. 99-18364 Filed 7-26-99; 8:45 am]

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