[Federal Register Volume 65, Number 202 (Wednesday, October 18, 2000)]
[Rules and Regulations]
[Pages 62276-62279]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 00-26308]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 99-NM-248-AD; Amendment 39-11932; AD 2000-20-20]
RIN 2120-AA64


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 certain Boeing Model 747-400 series airplanes, that 
requires removal of existing inertial reference units (IRU) and 
installation of modified IRU's. This amendment is prompted by a report 
of the failure of the left and center IRU's on a single flight. The 
actions specified by this AD are intended to prevent loss of multiple 
IRU's in flight, which could result in the loss of navigation data 
during flight. This could compromise the ability of the flight crew to 
maintain the safe flight and landing of the airplane.

DATES: Effective November 22, 2000.
    The incorporation by reference of certain publications listed in 
the regulations is approved by the Director of the Federal Register as 
of November 22, 2000.

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: Jay G. Yi, Aerospace Engineer, Systems 
and Equipment Branch, ANM-130S, FAA, Seattle Aircraft Certification 
Office, 1601 Lind Avenue, SW., Renton, Washington 98055-4056; telephone 
(425) 227-1013; fax (425) 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 certain Boeing Model 747-400 
series airplanes was published in the Federal Register on October 6, 
1999 (64 FR 54229). That action proposed to require removal of existing 
inertial reference units (IRU) and installation of modified IRU's.

Comments

    Interested persons have been afforded an opportunity to participate 
in the making of this amendment. Due consideration has been given to 
the comments received.

Support for the Proposal

    One commenter supports the proposed rule.

Request To Extend Compliance Time

    Three commenters request that the FAA extend the proposed 
compliance time for the installation of modified IRU's.
    The first commenter states that sending all its units back to the 
parts manufacturer for modification will take at least two weeks per 
unit. Additionally, taking the unmodified units off all of its 
airplanes and shipping them will delay completion of the installation 
required by the proposed AD until receipt of the modified units. 
Therefore, the proposed installation would not be accomplished until 
February 2002. The commenter adds that the dual inertial reference 
system (IRS) failure that prompted this proposal, as stated in the 
preamble, was caused by a short circuit in the brake system control 
unit (BSCU). The airplane manufacturer later determined that the short 
circuit was due to moisture ingested into the BSCU, and released Boeing 
Service Bulletins 747-25-3080, Revision 2, dated February 29, 1996 
(improves the integrity of the drip shields), and 747-53-2402, dated 
December 21, 1995 (installs protective panels over the drip shields to 
protect them from damage) to address this condition. The commenter has 
completed these modifications, and notes that these modifications 
significantly reduce the likelihood of water damage to the BSCU. The 
commenter states that, considering these airplane modifications and the 
realities of the modification stated above, a two-year compliance time 
would be more realistic.
    The second commenter states that 12 months is an unrealistic and 
unnecessary compliance time, and submits the following factors for 
consideration:

[[Page 62277]]

    <bullet> First, the IRU part numbers addressed by the proposal are 
used on Boeing Model 737-300/400/500, 757, and 767 series airplanes, in 
addition to Model 747-400 series airplanes. Many of the 747-400 
operators also operate some of the other airplane types and have common 
spares. The operators will either have to maintain separate spares for 
the Model 747-400 series airplanes, or modify all of the spares. If the 
operators are forced into maintaining separate spares, this will 
increase the quantity of spare units required.
    <bullet> Second, while there is a potential for this condition to 
develop, the probability of occurrence is lower than implied in the 
proposal. The availability of standby heading and attitude systems, 
plus the ability of the IRU to recover heading and attitude capability, 
also reduce the urgency to complete all updates within 12 months. 
Considering the above factors, the commenter recommends the compliance 
time be extended from 12 months to at least 24 months, with the 
expectation that an extension will likely be needed for full 
compliance.
    The third commenter requests that the compliance time be changed 
from 12 months to 24 months, but does not give a reason for this 
request.
    The FAA concurs with the commenters' requests to extend the 
compliance time for installation of modified IRU's; however, the FAA 
does not concur with the length of time requested by the commenters. 
Following careful consideration of the comments, the FAA considers that 
an extension of the compliance time specified in paragraph (a) of this 
AD from 12 months to 18 months will not compromise safety. Paragraph 
(a) of this final rule has been revised accordingly.

Request To Revise Applicability

    Three commenters request that the applicability of the proposed 
rule be revised.
    The first commenter requests that the proposed applicability be 
revised to apply to all Model 747-400 series airplanes, not just 
specific line numbers as written in the applicability section. The 
commenter states that some of its recent deliveries of Model 747-400 
series airplanes had the upgraded IRU's installed at delivery, and 
those line numbers are not included in the current applicability of the 
proposed rule. The commenter also notes that it is possible that one or 
more of the upgraded IRU units were replaced with an older IRU after 
the airplane went into service; therefore, it is the commenter's intent 
to accomplish the proposed requirements on all of its Model 747-400 
series airplanes.
    The second commenter requests that the statement ``certain Boeing 
Model 747-400 series airplanes,'' in the preamble of the proposed rule 
be revised to read, ``all Boeing Model 747-400 series airplanes 
equipped with Honeywell inertial reference systems.'' The commenter 
notes that explicitly stating this up front in the proposed AD provides 
clarification of the airplanes affected by the proposal. The commenter 
also recommends identifying a second grouping in the applicability 
section to make the spares requirement [paragraph (b)] applicable to 
all Model 747-400 series airplanes.
    The third commenter states that some Model 747-400 series airplanes 
not specified in the proposal may have had replacement IRU's installed 
that should be modified.
    The FAA does not concur with the commenters' request. In response 
to the first and second commenters, all new 747-400 series airplanes 
after line number 1187 were delivered with newly designed IRU's 
installed, and the FAA previously disseminated instructions to 
operators about replacement or exchange of the new IRU's with older-
type IRU's. In response to the third commenter, the FAA has addressed 
the intent of the commenter's request in paragraph (b) of this AD.

Request To Revise Spares Paragraph

    One commenter suggests that since the problem referenced in the 
proposed rule is unique to Model 747-400 series airplanes, and other 
IRS-equipped fleets can continue using older part numbers, the text in 
the spares paragraph should be revised from ``any airplane'' to ``any 
747 airplane.''
    Two commenters recommend the wording in the spares paragraph be 
revised to read, ``As of the required compliance date for this AD, no 
person shall install an IRU with a Boeing part number which precedes 
S242T101-113 on a Boeing 747-400 series airplane,'' or ``Subsequent to 
the required compliance date of this AD, no person shall install a 
Honeywell IRU having a Boeing part number that precedes S242T101-113 on 
a Boeing Model 747-400 series airplane.'' The commenter states that 
this is to require the use of modified IRU's after the compliance date, 
thereby permitting the use of existing inventory during the interim 
period and to preclude the use of any IRU preceding part number 
S242T101-113 after the compliance date.
    The FAA does not concur with the commenters' requests to change the 
words in the spares paragraph from ``on any airplane'' to ``on any 
Boeing Model 747-400 airplane,'' or ``with a Boeing part number that 
precedes S242T202-113 on a Boeing Model 747-400 series airplane.'' The 
applicability statement of all AD actions lists all models affected by 
that AD. All of the requirements stated in an AD are applicable only to 
the airplane models listed in the applicability, and based on 
information received from the parts manufacturer, only the IRU's having 
the part numbers listed in the spares paragraph are affected by the AD.
    Additionally, the FAA does not concur with changing ``As of the 
effective date * * * '' to ``As of the compliance date * * * '' 
Removing an unsafe condition that already exists on an airplane 
necessarily involves performing maintenance on the airplane, and the 
FAA always provides some kind of ``grace period'' in order to minimize 
disruption of operations. On the other hand, prohibiting installation 
of spares that have been determined to create an unsafe condition does 
not require any additional maintenance activity; it simply requires use 
of one part rather than another. In general, once an unsafe condition 
has been determined to exist, it is the FAA's normal policy not to 
allow that condition to be introduced into the fleet. In developing the 
technical information on which every AD is based, one of the important 
considerations is the availability of parts that the AD will require to 
be installed. When it is determined that those (safe) parts are 
immediately available to operators, it is the FAA's policy to prohibit 
installation of the unsafe parts as of the effective date of the AD.
    Therefore, the FAA finds that there is no justification for making 
the changes requested by the commenters. No change to the final rule is 
necessary in this regard.

Request To Revise Statement of Unsafe Condition

    One commenter requests that the unsafe condition as stated in the 
proposed rule be revised from `` * * * compromise the ability of the 
flight crew to maintain the safe flight and landing of the airplane'' 
to `` * * * compromise the ability of the flight crew to subsequently 
cope with adverse operating conditions.'' The commenter states that the 
loss of primary data to both pilots, in addition to loss of other 
navigational information is improbable. The commenter adds that while 
loss of primary data could impact operations during adverse conditions, 
with standby data available, loss of primary data does not impact safe 
flight of the airplane.

[[Page 62278]]

    The FAA does not concur with the commenter's request. The FAA has 
determined that, should an airplane lose all three IRU's, which would 
result in operating with only one standby instrument, it would indeed 
impact safe flight of the airplane due to reduced controllability 
resulting from loss of the IRU's. No change to the final rule is 
necessary in this regard.

Request To Revise Certain Sections in the Preamble

    One commenter describes revisions to various sections of the 
preamble of the proposed rule. In the ``Summary'' section, the 
commenter revises the wording to state that the proposed AD is 
applicable to 747-400 series airplanes equipped with the Honeywell IRS, 
and to present a logical sequence for the event and the consequences. 
The commenter also changes the statement of unsafe condition from `` * 
* * maintain the safe flight and landing of the airplane'' to `` * * * 
subsequently cope with adverse operating conditions.'' In the 
``Discussion'' and ``Explanation of Relevant Service Information'' 
sections, the commenter suggests revising the wording to ascribe the 
reported event specifically to a Model 747-400 series airplane equipped 
with the Honeywell IRS, to indicate the data loss, and to discuss 
attributed causes of the event. In the ``Explanation of Requirements of 
Proposed Rule'' section, the commenter revises the wording to clarify 
the intent of Boeing Alert Service Bulletin 747-34A2638, Revision 1, 
dated April 8, 1999, as applicable to multiple part numbers of 
Honeywell IRU's. In the ``Differences Between Proposed Rule and Alert 
Service Bulletin'' section, the commenter revises the wording to 
identify the time necessary to perform the required replacement as 
being consistent with the alert service bulletin estimate, and to 
identify compliance time based on initial estimates from Honeywell and 
operators' recommendations.
    Another commenter states that actions specified in the proposal are 
intended to prevent loss of navigation during flight. The commenter 
discusses the various navigation systems and notes that it is rare that 
navigation data from the IRU's are used during the approach and landing 
phase of flight. The commenter further states that the event that 
prompted the NPRM included loss of primary heading and attitude data 
from the left and center IRU's, as well as loss of navigation data. The 
right IRU was still providing valid heading and attitude reference, and 
the standby systems were available. The commenter adds that when the 
voltage was removed, the faulted IRU's could have been reset to the 
``ATTITUDE'' mode, which returns the primary heading and attitude 
functions.
    The same commenter states that the proposal states that this 
condition is likely to exist on other products of the same type design. 
However, the commenter notes that to its knowledge, this is the only 
occurrence of this condition throughout the entire service life of the 
Model 747-400 series airplane. In addition, the commenter states that 
service information has been issued to address the broken or damaged 
drip shields, which allowed liquid to enter the BSCU and cause the 
electrical fault. The commenter recommends the wording in the 
``Explanation of Requirements of Proposed Rule'' be changed to ``may 
develop'' or similar wording which better describes the low probability 
of occurrence for this condition.
    The FAA concurs with the commenter's description of the intent of 
these sections; however, because only the ``Summary'' section is 
restated in the final rule, no change to the other sections, as stated 
above, is necessary. Additionally, the ``Summary'' section of this 
final rule only represents a brief synopsis of the AD, it is accurate 
as proposed, therefore, no change to the final rule is necessary.

Request To Revise Cost Impact Information

    Three commenters request that the cost information in the proposed 
rule be revised.
    The first commenter states that the cost to U.S. operators 
estimated in the proposal is approximately $3,000, and reasons that the 
true costs involved are significantly higher for the following reasons:
    <bullet> First, the cost estimate in the proposal allowed for 1 
hour per airplane; however, the actual time to remove, install, and 
functionally check all three IRU's will be longer.
    <bullet> Second, the cost estimate did not include any of the 
operators' costs for internal processing, shipping, and handling.
    <bullet> Third, the operators may have to purchase additional spare 
units to support rotation of IRU's through the modification program.
    <bullet> Fourth, the estimate does not include the cost to modify 
or update the IRU's. In addition, the commenter notes that, although 
there is no cost specified in the proposal for the required parts, the 
parts manufacturer will charge for the modification of some parts. 
Therefore, the statement that the manufacturer will provide parts at no 
cost is inaccurate and should not be included in the proposal.
    The second commenter states that the estimated work hours in the 
cost information section should be revised from 1 work hour to 2.25 
work hours to identify cost impacts consistent with the estimated time 
to perform the proposed replacement.
    The third commenter makes no specific request for a change to the 
proposed rule, but states that, if the 12-month compliance time is 
retained, it could be faced with purchasing additional shipsets of IRS 
units (assuming they are available in time) in order to expedite 
accomplishment of the fleet campaign. The commenter notes that a 
shipset costs about $450,000, and two additional shipsets might be 
needed.
    The FAA agrees with the first commenter, in that the service 
bulletin does not specify that the required parts will be supplied by 
the parts manufacturer at no cost to the operators. The service 
bulletin merely states that the operator can supply the parts. 
Information received from the parts manufacturer states that it will 
supply the parts for the actions required by this AD; however, any 
other modifications will be paid for by the operators. No change to the 
final rule is necessary in this regard.
    The FAA does not concur with revising the work hours necessary for 
accomplishment of the required replacement. The cost impact information 
describes only the ``direct'' costs of the specific actions required by 
this AD. The number of work hours necessary to accomplish the required 
actions, specified as 1 work hour in the cost impact information below, 
was provided to the FAA by the manufacturer based on the best data 
available to date. This number represents the time necessary to perform 
only the actions actually required by this AD. The FAA recognizes that, 
in accomplishing the requirements of any AD, operators may incur 
``incidental'' costs in addition to the ``direct'' costs. The cost 
analysis in AD rulemaking actions, however, typically does not include 
incidental costs, such as the time required to gain access and close 
up, planning time, or time necessitated by other administrative 
actions. Because incidental costs may vary significantly from operator 
to operator, they are almost impossible to calculate. No change to the 
final rule is necessary in this regard.

[[Page 62279]]

Conclusion

    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.

Cost Impact

    There are approximately 429 Model 747-400 series airplanes of the 
affected design in the worldwide fleet. The FAA estimates that 50 
airplanes of U.S. registry will be affected by this AD, that it will 
take approximately 1 work hour per airplane to accomplish the required 
replacement, and that the average labor rate is $60 per work hour. 
Required parts will be supplied by the parts manufacturer at no cost to 
the operators. Based on these figures, the cost impact of the AD on 
U.S. operators is estimated to be $3,000, or $60 per airplane.
    The 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. The cost impact figures discussed 
in AD rulemaking actions represent only the time necessary to perform 
the specific actions actually required by the AD. These figures 
typically do not include incidental costs, such as the time required to 
gain access and close up, planning time, or time necessitated by other 
administrative actions.

Regulatory Impact

    The regulations adopted herein will not have a substantial direct 
effect 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, it 
is determined that this final rule does not have federalism 
implications under Executive Order 13132.
    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:

2000-20-20  Boeing: Amendment 39-11932. Docket 99-NM-248-AD.

    Applicability: Model 747-400 series airplanes, having line 
numbers 696 through 1187 inclusive, certificated in any category; 
equipped with Honeywell inertial reference units (IRU).

    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 (c) 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 multiple IRU's in flight, which could result 
in the loss of navigation data, and compromise the ability of the 
flight crew to maintain the safe flight and landing of the airplane, 
accomplish the following:

Replacement

    (a) Within 18 months after the effective date of this AD, remove 
the left, center, and right IRU's, and install modified IRU's, in 
accordance with Boeing Alert Service Bulletin 747-34A2638, Revision 
1, dated April 8, 1999.

    Note 2: Removal of existing left, center, and right IRU's and 
replacement with modified IRU's in accordance with Boeing Alert 
Service Bulletin 747-34A2638, dated January 29, 1999, is considered 
acceptable for compliance with paragraph (a) of this AD.

Spares

    (b) As of the effective date of this AD, no person shall install 
an IRU having Boeing part number S242T101-110, S242T101-111, or 
S242T101-112, on any airplane.

Alternative Methods of Compliance

    (c) 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. Operators shall submit their requests through an 
appropriate FAA Principal Avionics Inspector, who may add comments 
and then send it to the Manager, Seattle ACO.

    Note 3: 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

    (d) 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

    (e) The replacement shall be done in accordance with Boeing 
Alert Service Bulletin 747-34A2638, Revision 1, dated April 8, 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.
    (f) This amendment becomes effective on November 22, 2000.

    Issued in Renton, Washington, on October 6, 2000.
Donald L. Riggin,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 00-26308 Filed 10-17-00; 8:45 am]
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