Airworthiness Directives; Boeing Model 747-400 Series Airplanes

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 94-NM-07-AD; Amendment 39-8976; AD 94-15-05]

Airworthiness Directives; Boeing Model 747-400 Series Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Final rule.

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

applicable to all Boeing Model 747-400 series airplanes, that requires

various inspections and functional tests of the thrust reverser control

and indication system, and correction of any discrepancy found. This

amendment is prompted by an investigation to determine the

controllability of Model 747 series airplanes following an in-flight

thrust reverser deployment, which has revealed that, in the event of

thrust reverser deployment during high-speed climb or during cruise,

these airplanes could experience control problems. The actions

specified by this AD are intended to ensure the integrity of the fail

safe features of the thrust reverser system by preventing possible

failure modes in the thrust reverser control system that can result in

inadvertent deployment of a thrust reverser during flight.

DATES: Effective August 24, 1994.

The incorporation by reference of certain publications listed in

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

of August 24, 1994.

ADDRESSES: 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 Federal

Aviation Administration (FAA), Transport Airplane Directorate, Rules

Docket, 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: Jon Regimbal, Aerospace Engineer,

Propulsion Branch, ANM-140S, FAA, Transport Airplane Directorate,

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

Washington 98055-4056; telephone (206) 227-2687; fax (206) 227-1181.

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

Aviation Regulations (14 CFR part 39) to include an airworthiness

directive (AD) that is applicable to all Boeing Model 747-400 series

airplanes was published in the Federal Register on March 4, 1994 (59 FR

10336). That action proposed to require various inspections and

functional tests of the thrust reverser control and indication system,

and correction of any discrepancy found. -

Interested persons have been afforded an opportunity to participate

in the making of this amendment. Due consideration has been given to

the comments received. -

One commenter supports the proposed rule. -

The Air Transport Association (ATA) of America, on behalf of one of

its members, requests that the proposed repetitive inspections and

tests be withdrawn since those actions will be added to the revised

Maintenance Planning Document. The ATA acknowledges that the proposed

repetitive actions may not be incorporated uniformly into every

operator's maintenance program unless an AD is issued. Therefore, the

ATA asks that another provision be added to the proposal as follows:

Within 3 months after the effective date of the AD, revise the FAA-

approved maintenance inspection program to include a functional test of

the thrust reverser control and indication system at an initial 15-

month interval. Inspections for damage to the bullnose seal would be

conducted at an initial 1,500 flight hour interval. The AD would no

longer be applicable for operators that have acceptably revised the

maintenance program. Operators complying with this paragraph could use

an alternative recordkeeping method in lieu of that required by section

91.417 or 121.380 of the Federal Aviation Regulations (14 CFR 91.417 or

121.380). The FAA would be defined as the cognizant Principal

Maintenance Inspector (PMI) for operators electing this alternative.

The ATA believes that its suggestion should be adopted because the

proposed repetitive actions will likely continue for as long as Model

747-400 series airplanes are operated. The ATA acknowledges that, while

numerous AD's that require repetitive inspections continue for the life

of the aircraft, it has either been shown that a satisfactory

terminating action has not been developed or that service experience

has shown that control of the inspections cannot be administered safely

through an operator's maintenance program. The ATA states that its

proposal is intended to minimize the impact of the AD process on an

operator's maintenance program and cites other AD's that contain

provisions similar to its proposal.

The FAA recognizes the ATA's concerns regarding the requirement for

repetitive inspections and tests of the thrust reverser control and

indication systems. However, the FAA finds that this requirement is

necessary in order to provide an adequate level of safety by addressing

the specified unsafe condition. Further, the FAA determined the

required repetitive intervals based on the service history of similar

components and on an analysis of the system design to predict the

reliability of the system during the service life of the aircraft.

Lengthening these intervals would only be appropriate when a sufficient

sample of systems is allowed to operate through an entire system

overhaul cycle; adjustments made prior to that time may not account for

the effects of age and wear.

The FAA finds that addressing inspections and tests of the thrust

reverser control and indication systems in a document that is not FAA-

approved, such as a Maintenance Planning Document, will not ensure an

acceptable level of safety with regard to the thrust reverser system.

The ATA's suggested provision for accomplishment of the inspections and

tests would permit each operator to determine whether and how often

these actions should be conducted. In light of the severity of the

unsafe condition, however, the FAA has determined that allowing this

degree of operator discretion is not appropriate at this time.

Therefore, this AD is necessary to ensure that operators accomplish the

repetitive actions in a common manner and at common intervals.

One commenter requests that the proposed compliance time for the

initial inspections and functional tests of the thrust reverser control

and indication systems be extended from 6 to 12 months. This commenter

offers no justification for the request. A second commenter indicates a

false impression that a 12-month compliance time was proposed for these

inspections and functional tests, and requests that the compliance time

be expressed in terms of maintenance checks (specifically, ``C''

checks) or 15 months to coincide with regularly scheduled maintenance.

(The FAA notes that no 12-month compliance time is specified for any

requirement contained in the proposal.) Another commenter requests that

the compliance times be specified in terms of maintenance check

intervals (``A'' checks, ``C'' checks, etc.). The commenter provides no

justification for this request.

The FAA concurs partially. Since only two comments were received in

response to the proposed 6-month compliance time, the FAA assumes that

most operators are able to accommodate that proposed compliance time.

In light of safety considerations, the FAA finds that a short initial

compliance time for the inspections and functional tests is warranted.

However, upon reconsideration, the FAA considers that extending the

proposed compliance time by 3 additional months will not adversely

affect safety, and will allow the required actions to be performed at a

base during regularly scheduled maintenance where special equipment and

trained maintenance personnel will be available, if necessary.

Paragraphs (a)(2), (b)(2), and (c) of the final rule have been revised

to specify a compliance time of 9 months for the initial inspections

and functional tests of the thrust reverser control and indication

systems.

The FAA does not agree that the compliance times specified in the

final rule should be expressed in terms of maintenance check intervals.

Since maintenance schedules vary from operator to operator, there would

be no assurance that the actions will be accomplished during those

maximum intervals. The FAA has determined that the compliance times, as

specified in the final rule, represent the maximum intervals of time

allowable for the affected airplanes to continue to operate prior to

accomplishing the required actions without compromising safety.

Several commenters request that the proposed compliance time for

repetitive inspections and functional tests of the thrust reverser

control and indication systems [specified in paragraphs (a)(2), (b)(2),

and (c) of the proposal] be extended from the proposed 15-month

intervals to accommodate current or future scheduled ``C'' check

maintenance intervals. Two commenters propose extension of the

compliance time to 18-month intervals. One commenter indicates that

Boeing Alert Service Bulletin 747-78A2115, Revision 1, dated March 10,

1994, recommends inspection intervals of 15 months or 5,000 flight

hours.

The FAA concurs partially. As discussed previously, the FAA does

not agree that these compliance times should be expressed in terms of

maintenance check intervals. However, the FAA does concur with the

commenters' requests to extend the proposed compliance time to 18

months. Extending the compliance time by 3 additional months will not

adversely affect safety, and will allow the inspections and tests to be

performed at a base during regularly scheduled maintenance where

special equipment and trained maintenance personnel will be available,

if necessary. Paragraphs (a)(2), (b)(2), and (c) of the final rule have

been revised to specify a compliance time of 18 months for repetitive

inspections and functional tests of the thrust reverser control and

indication systems.

Several commenters request that paragraph (d) of the proposed rule

be revised to allow dispatch with a thrust reverser inoperative in

accordance with the FAA-approved Master Minimum Equipment List (MMEL)

if any discrepancy is found during the required inspections and tests.

Several commenters point out that allowing dispatch with a thrust

reverser inoperative will provide operators time to obtain parts and

perform any necessary corrective action. One commenter explains that,

without this change, the dispatch capability of the airplane would be

downgraded for problems such as proximity sensor adjustments or auto

restow chafing, which are not related to the integrity of the stow lock

feature. One commenter requests 14-day dispatch relief.

The FAA concurs partially. The FAA agrees that an option for

dispatch relief may be allowed in accordance with an operator's FAA-

approved Minimum Equipment List (MEL). However, the FAA does not concur

with the commenter's request for 14-day dispatch relief, since the MMEL

specifies 10-day dispatch relief. The FAA has revised paragraph (d) of

the final rule to provide an alternative for an airplane to be operated

in accordance with existing provisions and limitations specified in the

MEL, provided that no more than one thrust reverser on the airplane is

inoperative. -Three commenters request that the proposed interval of

1,000 hours time-in-service for repetitive inspections of the bullnose

seal and tests of the lock mechanism and of the position switch module

and cone brake be extended to coincide with operators' scheduled

maintenance intervals and to reduce the economic impact of the proposed

actions. One commenter suggests a repetitive interval of 1,300 hours

time-in-service. The second commenter proposes that the interval be

extended to 1,500 hours time-in-service. The third commenter recommends

that these actions be required every 15 months or during ``C'' checks.

The FAA does not concur. The FAA based the repetitive inspection

interval on data obtained from a reliability analysis submitted by

Boeing prior to the issuance of the proposed rule. The FAA based the

proposed interval of 1,000 hours time-in-service on that analysis and

on the fact that affected operators conduct ``A'' checks at intervals

of approximately 450 hours time-in-service. The FAA's intent was that

the proposed inspections and tests be conducted during every other

regularly scheduled ``A'' check, when the airplanes would be located at

a base where special equipment and trained personnel would be readily

available, if necessary. Further, the FAA has received no supporting

technical analysis to supplement or refute the manufacturer's original

reliability analysis. The FAA has determined that the compliance time,

as proposed, represents the maximum interval of time allowable for the

affected airplanes to accomplish the required repetitive actions

without compromising safety.

One commenter requests that a statement be added to the proposed

rule to indicate that the AD is considered to be interim action. The

FAA acknowledges that this AD is interim action, as specified in the

preamble to the proposed rule. The manufacturer has advised that it

currently is developing a modification that will positively address the

unsafe condition addressed by this AD, and that the modification should

be available within approximately 24 months. Once this modification is

developed, approved, and available, the FAA may consider additional

rulemaking.

One commenter requests that the proposal be revised to require that

operators report results from all inspections and tests, rather than

only initial inspections and tests, and that these results be used to

justify adjustments of inspection intervals or cancellation of

inspections. The commenter offers no justification for this request.

The FAA does not concur. The FAA is interested in the initial

inspection results for the purpose of determining the present state of

thrust reverser systems throughout the fleet. Since the actions

required by this AD are considered to be interim action and terminating

action is imminent, the FAA finds that gathering information for the

purpose of adjusting inspection intervals and cancelling inspections is

not needed and would pose an unnecessary burden on operators.

One commenter requests that the FAA review the probability

calculations made by Boeing in determining that an unsafe condition

exists. The commenter states that if the probability of inadvertent

thrust reverser deployment is lower than 1 in 109 flight hours, an

AD would not be required. The commenter points out two factors that

would reduce controllability: deployment of an outboard thrust

reverser, and deployment of that reverser during climb. Neither of

these factors was accounted for in the probability study that Boeing

presented to the operators. In addition, for Model 747-400 series

airplanes equipped with General Electric CF6-80C2 engines, deployment

of a single thrust reverser sleeve half is possible, and deployment of

a single sleeve half was assumed to have the same effect on airplane

controllability as full (both halves) deployment of a thrust reverser.

The FAA does not concur. The analysis presented by Boeing to the

FAA states clearly that the effect of deployment of an inboard thrust

reverser, or the effect of deployment of a single outboard thrust

reverser sleeve, had not yet been quantified. At that time, Boeing and

the FAA recognized the need for further study. However, in light of the

experience gained during investigation of the accident discussed in the

preamble to the proposed rule, Boeing had identified design

deficiencies that needed to be addressed as soon as practicable to

ensure the safety of the Model 747 fleet. The FAA did not determine

that an AD was warranted solely on the basis that a particular

probability threshold of 1 in 109 flight hours had been exceeded.

Rather, the FAA based its determination on the fact that design

deficiencies exist that could lead to an unsafe condition (reduction in

or loss of controllability of the airplane), which can be compensated

for by periodic inspections and tests until a design change becomes

available.

Since the issuance of the proposal, Boeing has issued Revision 1 of

Boeing Alert Service Bulletins 747-78A2112, dated March 7, 1994; 747-

78A2113, dated March 10, 1994; and 747-78A2115, dated March 4, 1994.

(The original issues of these service bulletins were cited in the

proposal as the appropriate sources of service information.) These

alert service bulletin revisions reclassify the service bulletin type

from standard to alert, recommend certain revised compliance times to

coincide with operators' maintenance schedules, and revise certain test

procedures. The FAA has reviewed and approved these alert service

bulletins and has revised the final rule to reflect these latest

revisions as additional sources of service information. In addition,

the FAA has revised the final rule to specify the appropriate

paragraphs of the Accomplishment Instructions of these alert service

bulletins for performing the actions required by this AD.

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.

This is considered to be interim action until final action is

identified for these airplanes, at which time the FAA may consider

further rulemaking.

There are approximately 286 Model 747-400 series airplanes of the

affected design in the worldwide fleet. The FAA estimates that 39 Model

747-400 series airplanes powered by Pratt & Whitney PW4000 series

engines of U.S. registry will be affected by this AD, that it will take

approximately 48 work hours per airplane to accomplish the required

actions, and that the average labor rate is $55 per work hour. Based on

these figures, the total cost impact of the AD on U.S. operators of

Model 747-400 series airplanes powered by Pratt & Whitney PW4000 series

engines is estimated to be $102,960, or $2,640 per airplane.

The total cost impact figure discussed above is based on

assumptions that no operator has yet accomplished any of the

requirements of this AD action, and that no operator would accomplish

those actions in the future if this AD were not adopted.

Currently, there are no Model 747-400 series airplanes powered by

General Electric CF6-80C2 series engines on the U.S. Register. However,

should one of these airplanes be imported and placed on the U.S.

Register in the future, it will require approximately 60 work hours to

accomplish the required actions, at an average labor charge of $55 per

work hour. Based on these figures, the total cost impact of this AD is

estimated to be $3,300 per airplane.

Additionally, there are no Model 747-400 series airplanes powered

by Rolls-Royce RB211-524G/H series engines on the U.S. Register at this

time. However, should one of these airplanes be imported and placed on

the U.S. Register in the future, it will require approximately 30 hours

to accomplish the required actions, at an average labor charge of $55

per work hour. Based on these figures, the total cost impact of this AD

is estimated to be $1,650 per airplane.

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. 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:

94-15-05 Boeing: Amendment 39-8976. Docket 94-NM-07-AD.

Applicability: All Model 747-400 series airplanes, certificated

in any category.

Compliance: Required as indicated, unless accomplished

previously.

To ensure the integrity of the fail safe features of the thrust

reverser system, accomplish the following:

(a) For Model 747-400 series airplanes powered by Pratt &

Whitney PW4000 series engines: Accomplish paragraphs (a)(1) and

(a)(2) of this AD.

(1) Within 90 days after the effective date of this AD, perform

an inspection to detect damage to the bullnose seal on the

translating sleeve of the thrust reverser, and perform a test of the

lock mechanism of the center locking actuator, in accordance with

paragraphs III.C. and III.E. of the Accomplishment Instructions of

Boeing Service Bulletin 747-78-2112, dated November 11, 1993; or

paragraphs III.E. and III.H. of the Accomplishment Instructions of

Boeing Alert Service Bulletin 747-78A2112, Revision 1, dated March

7, 1994. Repeat this inspection and test thereafter at intervals not

to exceed 1,000 hours time-in-service.

(2) Within 9 months after the effective date of this AD, perform

inspections and functional tests of the thrust reverser control and

indication systems in accordance with paragraphs III.A., III.B.,

III.D., and III.F. through III.M. of the Accomplishment Instructions

of Boeing Service Bulletin 747-78-2112, dated November 11, 1993; or

paragraphs III.C., III.D., III.F., III.G., and III.I. through III.P.

of the Accomplishment Instructions of Boeing Alert Service Bulletin

747-78A2112, Revision 1, dated March 7, 1994. Repeat these

inspections and functional tests thereafter at intervals not to

exceed 18 months.

(b) For Model 747-400 series airplanes powered by General

Electric CF6-80C2 series engines: Accomplish paragraphs (b)(1) and

(b)(2) of this AD.

(1) Within 90 days after the effective date of this AD, perform

an inspection to detect damage to the bullnose seal on the

translating sleeve of the thrust reverser, and a continuity test of

the position switch module of the center drive unit (CDU) and a cone

brake test of the CDU, in accordance with paragraphs III.B. and

III.C. of the Accomplishment Instructions of Boeing Service Bulletin

747-78-2113, dated November 11, 1993; or paragraphs III.E. through

III.G. of Boeing Alert Service Bulletin 747-78A2113, Revision 1,

dated March 10, 1994. Repeat the inspection and tests thereafter at

intervals not to exceed 1,000 hours time-in-service.

(2) Within 9 months after the effective date of this AD, perform

inspections and functional tests of the thrust reverser control and

indication systems in accordance with paragraphs III.A., III.D.,

III.F., III.G., III.H., and III.J. through III.M. of the

Accomplishment Instructions of Boeing Service Bulletin 747-78-2113,

dated November 11, 1993; or paragraphs III.D. and III.H. through

III.N. of Boeing Alert Service Bulletin 747-78A2113, Revision 1,

dated March 10, 1994. Repeat these inspections and functional tests

thereafter at intervals not to exceed 18 months.

(c) For Model 747-400 series airplanes powered by Rolls-Royce

RB211-524G/H series engines: Within 9 months after the effective

date of this AD, and thereafter at intervals not to exceed 18

months, perform inspections and functional tests of the thrust

reverser control and indication systems in accordance with

paragraphs III.D. through III.K. of the Accomplishment Instructions

of Boeing Service Bulletin 747-78-2115, dated October 28, 1993; or

paragraphs III.D. through III.L. of the Accomplishment Instructions

of Boeing Alert Service Bulletin 747-78A2115, Revision 1, dated

March 4, 1994.

(d) If any of the inspections and/or functional tests required

by this AD cannot be successfully performed, or if any discrepancy

is found during those inspections and/or functional tests,

accomplish either paragraph (d)(1) or (d)(2) of this AD.

(1) Prior to further flight, correct the discrepancy found, in

accordance with Boeing Service Bulletin 747-78-2112, dated November

11, 1993, or Boeing Alert Service Bulletin 747-78A2112, Revision 1,

dated March 7, 1994 (for Model 747-400 series airplanes powered by

Pratt & Whitney PW4000 series engines); Boeing Service Bulletin 747-

78-2113, dated November 11, 1993, or Boeing Alert Service Bulletin

747-78A2113, Revision 1, dated March 10, 1994 (for Model 747-400

series airplanes powered by General Electric CF6-80C2 series

engines); or Boeing Service Bulletin 747-78-2115, dated October 28,

1993, or Boeing Alert Service Bulletin 747-78A2115, Revision 1,

dated March 4, 1994 (for Model 747-400 series airplanes powered by

Rolls-Royce RB211-524G/H series engines); as applicable. Or

(2) The airplane may be operated in accordance with the

provisions and limitations specified in an operator's FAA-approved

Minimum Equipment List (MEL), provided that no more than one thrust

reverser on the airplane is inoperative.

(e) Within 10 days after performing each initial inspection and

test required by this AD, submit a report of the inspection and/or

test results, both positive and negative, to the FAA, Seattle

Aircraft Certification Office (ACO), ANM-100S, 1601 Lind Avenue,

SW., Renton, Washington 98055-4056; fax (206) 227-1181. Information

collection requirements contained in this regulation have been

approved by the Office of Management and Budget (OMB) under the

provisions of the Paperwork Reduction Act of 1980 (44 U.S.C. 3501 et

seq.) and have been assigned OMB Control Number 2120-0056.

(f) 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, 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: Information concerning the existence of approved

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

obtained from the Seattle ACO.

(g) 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.

(h) The actions shall be done in accordance with Boeing Service

Bulletin 747-78-2112, dated November 11, 1993; Boeing Alert Service

Bulletin 747-78A2112, Revision 1, dated March 7, 1994; Boeing

Service Bulletin 747-78-2113, dated November 11, 1993; Boeing Alert

Service Bulletin 747-78A2113, Revision 1, dated March 10, 1994;

Boeing Service Bulletin 747-78-2115, dated October 28, 1993; or

Boeing Alert Service Bulletin 747-78A2115, Revision 1, dated March

4, 1994; as applicable. 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.

(i) This amendment becomes effective on August 24, 1994.

Issued in Renton, Washington, on July 13, 1994.

S.R. Miller,

Acting Manager, Transport Airplane Directorate, Aircraft Certification

Service.

[FR Doc. 94-17593 Filed 7-22-94; 8:45 am]

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