RULES and REGULATIONS

DEPARTMENT OF TRANSPORTATION

14 CFR Part 39

[Docket No. 89-NM-68-AD; Arndt. 39-6490]

Airworthiness Directives; Boeing Model 747 Series Airplanes

Wednesday, March 7, 1990

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final rule.

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

Boeing Model 747 series airplanes, which requires incorporation of certain structural

modifications. This amendment is prompted by reports of recent incidents involving fatigue

cracking and corrosion in transport category airplanes that are approaching or have exceeded

their design life goal. These incidents jeopardized the airworthiness of the affected airplanes.

These conditions, if not corrected, could result in a degradation in the structural capabilities of

the affected airplanes. This action also reflects FAA's decision that long term continued

operational safety should be assured by actual modification of the airframe rather than

repetitive inspection.

DATES: Effective April 17, 1990. The incorporation by reference of certain publications

listed in the regulations is approved by the Director of the Federal Register as of April 17, 1990.

ADDRESSES: The applicable service information may be obtained from Boeing Commercial

Airplanes, P.O. Box 3707, Seattle, Washington 98124. This information may be examined at the

FAA, Northwest Mountain Region, Transport Airplane Directorate, 17900 Pacific Highway South,

Seattle, Washington; at the Seattle Aircraft Certification Office, FAA, Northwest Mountain Region,

9010 East Marginal Way South, Seattle, Washington; or at the Office of the Federal Register, 1100 L

Street NW., Room 8301, Washington, DC.

FOR FURTHER INFORMATION CONTACT ,Mr. Richard H. Yarges, Airframe Branch, ANM-120S,

Seattle Aircraft Certification Office; telephone (206) 431-1923. Mailing address:

FAA, Northwest Mountain Region, 17900 Pacific Highway South, C-68966, Seattle, Washington 98168.

SUPPLEMENTARY INFORMATION: A proposal to amend part 39 of the Federal Aviation

Regulations to include an airworthiness directive, applicable to Boeing Model 747

series airplanes, which requires incorporation of certain structural modifications,

was published in the Federal Register on May 23, 1989 (54 FR 22304).
Interested persons have been afforded an opportunity to participate in the making

of this amendment. Due consideration has been given to the comments received.

The Air Transport Association (ATA) of America commented on behalf of its

members. While the ATA supports this program, it raised two primary

concerns: First, that all service bulletins be in final form prior to the

effective date of the AD; second, that parts are available in order to accomplish

the required modifications. The FAA has addressed these two concerns. All

associated service bulletins have been released prior to the issuance of this final

rule and the manufacturer has confirmed that ample parts will be available to meet

the mandatory requirements.

Another commenter requested that FAA Designated Engineering Representatives (DER) at

the manufacturer's facility be allowed to approve certain alternate means of compliance to

this AD. The FAA does not concur. Airworthiness directives are a primary responsibility

of the FAA, and alternate means of compliance must be approved by the Manager of the

Seattle Aircraft Certification Office. This function cannot be delegated to a DER. While DER's

are authorized to determine whether an alternate design complies with a specific requirement,

they are not authorized to make discretionary determinations as to what the applicable

requirement is.

Another commenter requested that the rule be revised to allow operators to perform minor

deviations from the AD without obtaining FAA approval. The FAA does not concur, because

what is "minor" is open to interpretation. The FAA must continue to approve all deviations.

Two commenters requested that the threshold for modification of certain pressurization sensitive

structure (e.g., reference Boeing Service Bulletins 747-53-2277, 747-53-3375 and 747-53-2283) be 

increased for Model 747SR series airplanes. These commenters pointed out that the Model 747SR

is operated at typically lower cabin differential pressures and will thereby not be subject to cracking

as early as other Model 7471s. The airworthiness directives that currently apply to these structures

allow the adjustment of compliance times by a factor of 1.2 or 1.3. These commenters requested that

the same factors be allowed to adjust the modification thresholds for the pressure sensitive structures 

for Model 747SR airplanes. The FAA does not concur with the request. The FAA is aware that the

operators who initially receive the Model 747SR airplanes are probably operating them at less than 

the maximum cabin differential pressure. Such operating procedures would allow the modification 

thresholds for pressure sensitive structure to be increased by some appropriate factor. However, since

the Model 747SR can be pressurized to the maximum differential pressure by the present operators, 

or by anyone who flies these airplanes, the FAA does not consider it appropriate to include in this

final rule higher values for these particular thresholds when, in fact, the airplanes might not be operated

at some lesser specified values. It is far more appropriate that those operators which can justify a

threshold increase present data to the FAA in accordance with the alternate means provision of this rule

(paragraph C.) to substantiate any threshold increase. Further, for the reasons explained above, the FAA

is considering deleting increased thresholds from existing AD’s which include such specific threshold

increases.
One commenter requested that the compliance time for replacement of a cracked 1241 bulkhead splice

strap, in accordance with Service Bulletin 747-53-2283, be revised to allow a reasonable time period

to accomplish the action if the crack discovery is made after the effective date of the AD and the airplane

has nearly, or more than, 20,000 flight cycles. The FAA agrees with this comment. The final rule has

been revised to allow at least two years to accomplish the replacement of the strap if it is found cracked. 

Safety will be maintained by the existing inspection requirements of AD 84-18-01, Amendment 39-4905,

until the cracked strap is replaced.

One commenter requested that the compliance time for replacement of the trailing edge flaps specified

in paragraph B.1., be revised from "within 5 years after the effective date of the AD” to ”within 5 years

after the effective date of the AD or within 5 years after rework in accordance with Boeing Service

Bulletin 747-57A2229, whichever is later.” The FAA does not consider this change to be warranted.

Because of the timing of this final rule and AD 89-05-04, Amendment 39-6148 (54 FR7759,

February 23, 1989), which addresses Boeing Service Bulletin 747-57A2229, there will be little or no

difference between the effective date of this AD and the date by which rework in accordance with

Service Bulletin 747-57A2229 is required.

One commenter requested that the compliance time specified in paragraph B.2. be revised to read

“. . . • shall be accomplished within 6 years after the effective date of this AD, or prior to the

accumulation of 20,000 flights on the landing gear, whichever occurs later." This comment was

directed at FAA's concern that a "hard time" be established for accomplishment of the landing gear

related bulletins, but also allow additional time if the landing gear has not yet accumulated 20,000

flight cycles. This is consistent with the threshold for modification of airframe related items, except

that is it referenced to landing gear time. The FAA concurs. Landing gear time is tracked separately

from airframe time because landing gear units may be transferred between airplanes. The final rule

has been revised accordingly. With this change, there is no need to callout “. . . at next overhaul after

10,000 flight cycles” for replacement of the wing landing gear jury strut spindle, and that phrase

has been deleted from the final rule.

One commenter requested that the AD be clarified to state that replacement of flap tracks in accordance

with Boeing Service Bulletins 747-57A2229, Revision 7, or 747-57-2146, Revision 3, is equivalent to 

replacement in accordance with Boeing Service Bulletin 747-57A2229, Revision 8, as specified in the

NPRM. The FAA concurs and has added a clarifying note to this effect in the final rule.

Various foreign airworthiness authorities stated that (1) the compliance times were arbitrarily 

chosen, independent of any fatigue history; (2) no mandatory inspections were required for all 

areas not affected by an existing AD; and (3) no post-modification inspections were proposed.

As for item (1), the FAA does not concur with the suggestion that the compliance times

for the modifications were arbitrarily chosen. On the contrary, in developing the

appropriate compliance times for this AD action, the FAA, with input from the aviation

industry/community, considered not only the degree of urgency associated with addressing

the identified unsafe condition, but the practical aspects of the availability of required

parts, the time necessary to install the required modifications, and the availability of

overhaul facilities to perform the necessary work. Further, fatigue history is always

considered when assessing inspection thresholds for problems caused by fatigue. Likewise,

repetitive inspection intervals are based on damage tolerance assessments when appropriate.
As for item (2), the FAA does not fully agree. While several of the service bulletins included

in Boeing Document 00-38505 are the subject of current existing AD's (which require

inspections and optional modifications), other service bulletins and their related inspections

are currently under consideration for mandatory action, and will be handled on a

case-by-case basis. As was explained in detail in the preamble to the Notice, safety will

continue to be maintained by various means currently in place that are considered

satisfactory to detect damage prior to the occurrence of an unsafe condition. These include

on-going basic maintenance programs, inspections/modifications required by existing AD’s,

Supplemental Structural Inspection Document programs, and the like.

As for item (3), the FAA has determined that there is no need to stipulate special

"post-modification inspections” since the operators' existing on-going inspection

programs include such inspections and are acceptable to monitor the affected area.

Accordingly, the FAA has determined that no change to the final rule is warranted

based on these comments made by the foreign airworthiness authorities.

One commenter asked that, for the longitudinal floor beam modifications, the equivalence

of the terminating action between Service Bulletin 747-53-2224 and Service Bulletins

747-53-2176 and 747-53-2183 be explicitly stated in the AD. The FAA concurs and the AD

has been revised accordingly.

After careful review of the available data, including the comments noted above, the FAA

has determined that air safety and the public interest require the adoption of the rule with

the changes previously described. The FAA has determined that these changes will

neither increase the economic burden on any operator nor increase the scope of the AD.

There are approximately 680 Model 747 series airplanes of the affected design in the worldwide

fleet. It is estimated that 20 airplanes of U.S. registry will be affected by this AD within the

initial threshold of 4 years. The cost to modify each airplane is estimated to be $2,300,000.

This cost includes the price of modifications kits, which is $900,000 per airplane, and the

estimated number of manhours to accomplish the modifications, which is approximately

35,000 manhours at $40 per manhour. It does not include downtime, planning, set up,

familiarization, or tool acquisition costs. Based on these figures, the total cost impact of the AD

on U.S. operators is estimated to be $46,000,000 over the initial threshold of 4 years.

Additional airplanes will be affected as they accumulate time-in-service and reach the threshold

for modifications.

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 "major rule" under 

Executive Order 12291; (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 is contained in the

regulatory docket. A copy of it may be obtained from the Rules Docket.

List of Subjects in 14 CFR Part 39

Air transportation, Aircraft, Aviation safety, Safety, Incorporation by reference.

Adoption of the Amendment

Accordingly, pursuant to the authority delegated to me by the Administrator, the

Federal Aviation Administration amends 14 CPR Part 39 of the Federal Aviation

Regulations as follows:

PART 39--[AMENDED]

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

Authority: 49 U.S.C. 1354(a), 1421 and 1423; 49 U.S.C. 106(g) (Revised Pub. L.

97-449, January 12, 1983); and 14 CFR 11.89.

§ 39.13 [Amended]

2. Section 39.13 is amended by adding the following new airworthiness directive:

Boeing: Applies to Model 747 series airplanes, listed in Boeing Document No. D6-35999,

dated March 31, 1989, certificated in any category. Compliance required as indicated,

unless previously accomplished.

To prevent structural failure, accomplish the following:

A. Prior to reaching the incorporation thresholds listed in Boeing Document No. D6-35999,

dated March 31, 1989 (hereinafter called "the Document"), or within the next 4 years after the

effective date of this AD, whichever occurs later, except as noted in paragraph B., below,

accomplish the structural modifications listed in section 3 of the Document.

B. l. Accomplish replacement of the trailing edge flap tracks in accordance with 

Boeing Alert Service Bulletin 747-57A2229, Revision 8, dated January 31, 1989,

within the next 5 years after the effective date of this AD.

Note: For the purpose of complying with this AD, replacement of trailing edge flap

tracks in accordance with Boeing Alert Service Bulletin 747-53A2229, Revision 8,

dated January 31, 1989, is considered equivalent to replacement in accordance with

either Boeing Alert Service Bulletin 747-57A2229, Revision 7, dated October 13,

1988, or Revision 9, dated November 2, 1989, or Boeing Service Bulletin 747-57-

2146, Revision 3, dated May 9, 1986.
2. Incorporation thresholds expressed as "at next overhaul," shall be accomplished

within the next 6 years after the effective date of this AD, or prior to the

accumulation of 20,000 flights, whichever occurs later.

3. Accomplish the APU cutout reinforcement in accordance with Boeing Service

Bulletin 747-53-2275, Revision 3, dated January 25, 1990, prior to the accumulation

of 20,000 flights, or within the next 5,000 flights after the effective date of this AD,

whichever occurs later.

4. If the 1241 bulkhead splice strap is cracked, replace the strap in accordance with 

Boeing Service Bulletin 747-53-2283. Revision 3, dated November 1, 1989, within 

the next 4 years after effective date of the AD, or prior to the accumulation of 20,000

flight cycles, or within 2 years of crack discovery, whichever occurs latest.

Note: For the purpose of complying with this AD, the incorporation of the terminating

modification for the longitudinal floor beams contained in Boeing Service Bulletin 747-53-2224,

Revision 6, dated July 27, 1989, is considered equivalent to the incorporation of the terminating

actions contained in Service Bulletins 747-53-2176, Revision 3, dated December 15, 1978,

and 747-53-2183, Revision 1, dated March 14, 1980.

Note: The modifications required by paragraphs A. and B., above, do not terminate the

inspection requirements of any other AD unless that AD specifies that any such modification

constitutes terminating action of the inspection requirements.

C. An alternate means of compliance or adjustment of the compliance time, which provides

an acceptable level of safety, may be used when approved by the Manager, Seattle Aircraft

Certification Office, FAA, Northwest Mountain Region.

Note: The request should be forwarded through an FAA Principal Maintenance Inspector (PMI),

who will either concur or comment and then send it to the Manager, Seattle Aircraft Certification Office.

D. Special flight permits may be issued in accordance with FAR 21.197 and 21.199 to operate

airplanes to a base in order to comply with the requirements of this AD.

The modifications shall be done in accordance with Boeing Document No. D6- 35999, dated March 1989,

"Aging Airplane Service Bulletin Structural Modification Program--Model 747." 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 Airplanes, P.O. Box 3707,

Seattle, Washington 98124. Copies may be inspected at the FAA, Northwest Mountain Region, 17900

Pacific Highway South, Seattle, Washington; or at the Seattle Aircraft Certification Office, FAA,

Northwest Mountain Region, 9010 East Marginal Way South, Seattle, Washington; or at the Office

of the Federal Register, 1100 L Street NW., Room 8301, Washington, DC.

This amendment becomes effective April 17, 1990.

Issued in Seattle, Washington, on January 16, 1990.

Leroy A. Keith,

Manager, Transport Airplane Directorate, Aircraft Certification Service.

55 FR 8374