[Federal Register Volume 62, Number 103 (Thursday, May 29, 1997)]
[Proposed Rules]
[Pages 29081-29086]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 97-13962]


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 Proposed Rules
                                                 Federal Register
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 This section of the FEDERAL REGISTER contains notices to the public of 
 the proposed issuance of rules and regulations. The purpose of these 
 notices is to give interested persons an opportunity to participate in 
 the rule making prior to the adoption of the final rules.
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  Federal Register / Vol. 62, No. 103 / Thursday, May 29, 1997 / 
Proposed Rules  

[[Page 29081]]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 96-NM-263-AD]
RIN 2120-AA64


Airworthiness Directives; Boeing Model 727 Series Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: This document proposes the supersedure of an existing 
airworthiness directive (AD), applicable to certain Boeing Model 727 
series airplanes, that currently requires that the FAA-approved 
maintenance inspection program be revised to include inspections that 
will give no less than the required damage tolerance rating for each 
Structural Significant Item, and repair of cracked structure. That AD 
was prompted by a structural re-evaluation by the manufacturer which 
identified additional structural elements where, if damage were to 
occur, supplemental inspections may be required for timely detection. 
This action would require additional and expanded inspections, and 
repair of cracked structure. This action also would expand the 
applicability of the existing AD to include additional airplanes. The 
actions specified by the proposed AD are intended to ensure the 
continued structural integrity of the entire Boeing Model 727 fleet.

DATES: Comments must be received by July 7, 1997.

ADDRESSES: Submit comments in triplicate to the Federal Aviation 
Administration (FAA), Transport Airplane Directorate, ANM-103, 
Attention: Rules Docket No. 96-NM-263-AD, 1601 Lind Avenue, SW., 
Renton, Washington 98055-4056. Comments may be inspected at this 
location between 9:00 a.m. and 3:00 p.m., Monday through Friday, except 
Federal holidays.
    The service information referenced in the proposed rule may be 
obtained from Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, 
Washington 98124-2207. This information may be examined at the FAA, 
Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, 
Washington.

FOR FURTHER INFORMATION CONTACT: Walter Sippel, Aerospace Engineer, 
Airframe Branch, ANM-120S, FAA, Seattle Aircraft Certification Office, 
1601 Lind Avenue, SW., Washington; telephone (206) 227-2774; fax (206) 
227-1181.

SUPPLEMENTARY INFORMATION:

Comments Invited

    Interested persons are invited to participate in the making of the 
proposed rule by submitting such written data, views, or arguments as 
they may desire. Communications shall identify the Rules Docket number 
and be submitted in triplicate to the address specified above. All 
communications received on or before the closing date for comments, 
specified above, will be considered before taking action on the 
proposed rule. The proposals contained in this notice may be changed in 
light of the comments received.
    Comments are specifically invited on the overall regulatory, 
economic, environmental, and energy aspects of the proposed rule. All 
comments submitted will be available, both before and after the closing 
date for comments, in the Rules Docket for examination by interested 
persons. A report summarizing each FAA-public contact concerned with 
the substance of this proposal will be filed in the Rules Docket.
    Commenters wishing the FAA to acknowledge receipt of their comments 
submitted in response to this notice must submit a self-addressed, 
stamped postcard on which the following statement is made: ``Comments 
to Docket Number 96-NM-263-AD.'' The postcard will be date stamped and 
returned to the commenter.

Availability of NPRMs

    Any person may obtain a copy of this NPRM by submitting a request 
to the FAA, Transport Airplane Directorate, ANM-103, Attention: Rules 
Docket No. 96-NM-263-AD, 1601 Lind Avenue, SW., Renton, Washington 
98055-4056.

Determination to Develop the Supplemental Structural Inspection Program

    As part of its continuing work to maintain the structural integrity 
of older transport category airplanes, in the early 1980's, the FAA 
concluded that the incidence of fatigue cracking may increase as these 
airplanes reach or exceed their design service objective (DSO). A 
significant number of these airplanes were approaching or had exceeded 
the DSO on which the initial type certification approval was 
predicated. In light of this, and as a result of increased utilization, 
longer operational lives, and the high levels of safety expected of the 
currently operated transport category airplanes, the FAA determined 
that a supplemental structural inspection program (SSIP) was necessary 
to ensure a high level of structural integrity for all airplanes in the 
transport fleet.

Issuance of Advisory Circular

    As a follow-on from that determination, the FAA issued Advisory 
Circular (AC No. 91-56), ``Supplemental Structural Inspection Program 
for Large Transport Category Airplanes,'' dated May 6, 1981. The AC 
provides guidance material to manufacturers and operators for use in 
developing a continuing structural integrity program to ensure safe 
operation of older airplanes throughout their operational lives. This 
guidance material applies to large transport airplanes that were 
certified under the fail-safe requirements of Civil Air Regulations 4b 
or damage tolerance structural requirements of 14 CFR part 25, and that 
have a maximum gross weight greater than 75,000 pounds. The procedures 
set forth in this AC are applicable to the large transport category 
airplanes operated under subpart D of 14 CFR part 91 and parts 121, 
123, 125, and 135. The objective of the SSIP was to establish 
inspection programs to ensure timely detection of fatigue cracking.

Development of the Supplemental Structural Inspection Program

    In order to evaluate the effect of increased fatigue cracking with 
respect to maintaining fail-safe design and damage tolerance of the 
structure of Boeing Model 727 series airplanes,

[[Page 29082]]

Boeing conducted a structural reassessment of those airplanes, using 
modern damage tolerance evaluation techniques. Boeing accomplished this 
reassessment using the criteria contained in AC No. 91-56, as well as 
14 CFR 25.571; Amdt. 25-45. During the reassessment, members of the 
airline industry participated with Boeing in working group sessions and 
developed the SSIP for Model 727 series airplanes. Engineers and 
maintenance specialists from the FAA also attended these sessions to 
observe these developments. Subsequently, based on the working group's 
recommendations, Boeing developed the Supplemental Structural 
Inspection Document (SSID).

Issuance of AD 84-21-05, Amendment 39-4920

    On September 7, 1984, the FAA issued AD 84-21-05, amendment 39-4920 
(49 FR 38931, October 2, 1984), which is applicable to certain Boeing 
Model 727 series airplanes. That AD currently requires that the FAA-
approved maintenance inspection program be revised to include 
inspections that will give no less than the required damage tolerance 
rating (DTR) for each Structural Significant Item (SSI), and repair of 
cracked structure. The AD references Boeing Document No. D6-48040-1, 
``Supplemental Structural Inspection Document'' (SSID), Revision E, 
dated June 21, 1983, as the appropriate source of service information. 
That action was prompted by a structural re-evaluation that identified 
additional structural components where fatigue cracking is likely to 
occur. The requirements of that AD are intended to ensure the continued 
structural integrity of the entire Boeing Model 727 fleet.

Actions Since Issuance of Previous AD

    Since issuance of AD 84-21-05, the FAA has reconsidered the 
following four aspects of the existing SSID:

1. Classification of Fuselage Skin as ``Damage Obvious'' or 
``Malfunction Evident''

    AC No. 91-56, Change 2, dated April 15, 1983, recommends that the 
SSID should contain inspections of all critical parts or components for 
each airplane to ensure the continued safe operation of the existing 
fleet. The fuselage skin is an example of a critical component. 
Cracking in any critical part or component, if not detected and 
corrected in a timely manner, could result in reduced structural 
integrity of the airplane.
    Revision E of the SSID excluded the fuselage skin from directed 
inspections, since it was classified as ``damage obvious'' or 
``malfunction evident.'' At the time of this classification, Revision E 
of the SSID relied on venting or flapping to indicate cracks in the 
fuselage skin.
    Venting is a gradual loss of cabin pressure as a result of cracking 
in the pressurized area of the fuselage skin. Based on the design 
philosophy of flapping, these cracks in the fuselage skin would grow 
only to a specific length and then turn direction because of certain 
structural components. Because venting and flapping were considered to 
be readily apparent, Boeing considered that it was unnecessary to 
provide for additional inspections of the fuselage skin. Reliance also 
was placed on venting or flapping to allow for the safe operation of an 
airplane with such cracks. This technique worked well in ground tests 
and in some in-service incidents, but proved to be unreliable in other 
cases.
    In one such case, a large portion of Section 43 of the fuselage 
structure separated from a Boeing Model 737 series airplane. Results of 
a National Transportation Safety Board (NTSB) investigation revealed 
that this incident occurred as a result of the catastrophic failure of 
the fuselage skin at a lap joint. The results also revealed that, 
contrary to the design philosophy, controlled decompression of the 
structure (i.e., flapping or venting) did not occur due to the presence 
of widespread fatigue damage. As a result of this failure, the NTSB 
recommended that the SSID be revised to discontinue classification of 
the fuselage skin as ``damage obvious'' or ``malfunction evident.''
    The FAA concurs with the NTSB's recommendation. Therefore, the FAA 
has determined that additional inspections are necessary to ensure 
timely detection of cracks in the fuselage skin structure.

2. Deletions of Modified, Altered, or Repaired Structure From the SSIP

    Paragraph 1.4 of Appendix 1, ``Guidelines for Development of 
Supplemental Inspection Document,'' of AC No. 91-56, Change 2, dated 
April 15, 1983, states, ``the effect of repairs and modifications 
approved by the manufacturer should also be taken into account. In 
addition, it may be necessary to consider the effect of repairs and 
operator-approved modifications on individual airplanes. The operator 
has the responsibility for ensuring notification and consideration of 
any such aspects.''
    In addition, the FAA's current policy is that operators of 
transport category airplanes that are subject to AD's that mandate SSID 
programs should follow the guidelines of AC No. 91-56 and should 
continue to inspect any SSI that is modified, altered, or repaired in 
any way. Any modification that affects the loading spectrum, stress 
levels, or damage tolerance characteristics of the structure must be 
reassessed to determine its impact on the inspection program. Such a 
reassessment may require the development of additional inspection 
requirements for that modification.
    The FAA's policy also states that, ``* * * the [SSID] programs are 
based on type design crack growth data generated from analysis or 
structural tests using a realistic and conservative loading spectrum, 
material properties, part geometry, etc. For this reason, structural 
modifications that may increase stress levels in load carrying 
structures, including maximum weight limit increases, cargo door 
installations, and repairs to load carrying structures, must be 
reassessed for its impact on the structural inspection program.'' 
(Reference: Transport Airplane Directorate's Policy Letter, 
Information: Policy Regarding Impact of Modifications and Repairs on 
the Damage Tolerance Characteristics of Transport Category Airplanes, 
dated October 27, 1989. This letter will be retained in Rules Docket 
No. 96-NM-263-AD.)
    Section 5.0 of Revision E of the SSID contains provisions that 
allow for the deletion of modified, altered, or repaired areas from the 
SSIP because Boeing considers these areas not to be ``representative of 
the fleet.'' The FAA is aware that there have been a significant number 
of such deletions. As a result, contrary to the FAA's policy discussed 
above, operators are not following the guidelines of AC No. 91-56 and 
not continuing to inspect any SSI that is modified, altered, or 
repaired in any way.
    In addition, for Boeing Model 727 series airplanes that have been 
converted from a passenger configuration to an all-cargo configuration 
by the Supplemental Type Certification (STC) process, the FAA finds 
that Revision E of the SSID does not include procedures for inspection 
of new SSI's created by this conversion, or unmodified SSI's affected 
by this conversion. (There are approximately 304 of these airplanes in 
the worldwide fleet of which several are listed in the effectivity 
listing of Revision E of the SSID.) These conversions have the effect 
of removing SSI's from the SSIP and creating a large number of new 
SSI's that have not been assessed. Consequently, airplanes that have 
been

[[Page 29083]]

converted to an all-cargo configuration do not have a SSID that 
specifies an inspection method and compliance time for each new SSI. 
Additionally, an unmodified SSI also could require a new inspection 
method and compliance time because the modification may increase the 
loads or change the load distributions in that SSI. These conditions 
would necessitate that the inspection interval for that affected, 
unmodified SSI be shorter than required in the Boeing SSID. Hence, the 
FAA finds that the objectives of the SSIP are not being met for these 
modified airplanes.
    Likewise, a design change (such as an increase in the maximum 
certified weight or in the center of gravity limits) also may cause an 
increase in the loads or change the load distributions in the affected, 
unmodified SSI's. The effect of this increase or change would be 
similar to the effect that a cargo conversion would have on an 
unmodified SSI. As a result, the inspection interval for an affected, 
unmodified SSI may need to be lower than required in the Boeing SSID. 
Thus, the DTR specified in the SSID for any SSI affected by a design 
change may no longer be applicable. Therefore, the FAA finds that the 
objectives of the SSIP are not being met for airplanes with such design 
changes.
    Furthermore, in consideration of AC No. 91-56 and current FAA 
policy, the FAA has determined that new inspection methods and 
compliance times are necessary for areas that have been modified, 
altered, or repaired to ensure timely detection of cracking in those 
areas. The FAA also has determined that new inspection methods and 
compliance times are necessary for those areas that were deleted from 
the SSIP by previously approved alternative methods of compliance, 
which includes those areas deleted in accordance with the requirements 
of Section 5.0 of the SSID. Furthermore, the new inspection methods and 
compliance times should meet the requirements of 14 CFR 25.1529, Amdt. 
25-45; 14 CFR 25.571, Amdt. 25-45; 14 CFR 25.571, Amdt. 25-54; 14 CFR 
25.571, Amdt. 25-72; or the guidelines of AC 91-56.

3. Candidate Fleet vs. Inspection Threshold Approach

    Paragraph 4.4 of AC No. 91-56, Change 2, dated April 15, 1983, 
states, ``Inspection thresholds for supplemental inspections should be 
established. These inspections would be supplemental to the normal 
inspection including the detailed internal inspections.'' Moreover, 
paragraph 4.4.2 of AC No. 91-56 states, ``* * * this threshold should 
be such as to include sufficient [high-cycle] airplanes in the 
inspection to develop added confidence in the integrity of the 
structure.* * *''
    A properly established inspection threshold ensures that: (1) The 
SSI inspections are accomplished; (2) fatigue cracks in SSI's are 
detected in a timely manner; (3) airplanes are automatically added to 
the SSIP; and (4) the SSIP includes a statistically valid number of 
airplanes.
    Among other things, Revision E of the SSID defines a candidate 
fleet approach to ensure that fatigue cracks in SSI's are detected in a 
timely manner in the entire fleet. The initial Boeing Model 727 
candidate fleet consisted of a number of airplanes that had exceeded 
30,000 flight cycles by January 31, 1983. In other words, Boeing 
considered 30,000 flight cycles to be the threshold for the airplanes 
in the candidate fleet. These airplanes were the most likely in the 
fleet to experience initial fatigue damage since they had the highest 
number of flight cycles. Boeing produced this SSID with the assumption 
that the airplanes in the candidate fleet would continue to represent 
the entire fleet and would have the highest number of flight cycles in 
the fleet.
    Under the existing SSIP, Boeing intended to periodically review the 
airplanes in the candidate fleet for significant changes in fleet 
distribution, composition, or utilization, and update the candidate 
fleet, if any significant change was detected. It was intended that the 
FAA would then mandate any change to the SSID through the rulemaking 
process.
    The FAA finds that the candidate fleet approach is deviating from 
Boeing's original philosophy in that the candidate fleet has not been 
updated to reflect changes (such as cargo conversions) in the fleet. 
This situation could result in a statistically invalid number of 
airplanes in the SSIP and undetected fatigue cracks in SSI's. The 
candidate fleet approach also does not automatically account for non-
candidate airplanes that eventually accumulate more flight cycles than 
that of certain candidate airplanes. High-cycle airplanes are more 
likely to experience initial fatigue damage in the fleet. The 
confidence in the structural integrity of the fleet of airplanes could 
be reduced if high-cycle airplanes are excluded from the SSIP.
    The FAA has reconsidered the candidate fleet approach described in 
Revision E of the SSID, since it does not meet the guidelines of AC No. 
91-56. The FAA has determined that the Boeing Model 727 SSIP must 
contain inspection thresholds for all Boeing Model 727 series airplanes 
to ensure the timely detection of fatigue cracks in the SSI's.
    The FAA has reviewed the thresholds derived from Boeing's 
reliability analysis. The analysis is based on a certain probability 
that cracks will be detected in the inspected fleet before they 
initiate on other airplanes that have not been inspected. The FAA has 
determined that the thresholds recommended in the analysis of past 
service experience of the Boeing Model 727 fleet are acceptable. 
Therefore, for Model 727-100C and 727-200F series airplanes, the FAA 
has determined that a threshold of 46,000 total flight cycles is 
necessary in order to produce a statistically valid assessment of the 
service history for these airplanes. For other Model 727 series 
airplanes, the FAA has determined that a threshold of 55,000 total 
flight cycles is necessary to produce a valid assessment. The threshold 
for Model 727-100C and 727-200F series airplanes is lower than that of 
other Model 727 series airplanes since Model 727-100C and 727-200F 
series airplanes have a lower utilization rate and fewer airplanes in 
the fleet. Since the utilization rate is lower for Model 727-100C and 
727-200F series airplanes, these airplanes have accumulated fewer 
flight cycles and have fewer airplanes with higher flight cycles than 
that of the remaining fleet.
    It should be noted that, although the proposed AD requires a 
threshold, the FAA may approve requests for adjustments to the 
compliance time [i.e., under paragraph (h)(1) of this proposed AD] 
provided that no cracking is detected in the airplane structure. The 
request should include a new inspection threshold and must include data 
to substantiate that such an adjustment would provide an acceptable 
level of safety.
    Operators should note that the alternative inspection threshold may 
be based solely on the analysis of the data of the existing fleet. 
However, the FAA has determined that the analysis that derives the new 
inspection threshold must include: (1) Data relevant to a sufficient 
number of high-cycle airplanes, and (2) data that shows accomplishment 
of the inspections of the SSI's. An adequate statistical sampling size 
will provide confidence in the structural integrity of the fleet of 
airplanes. Therefore, additional airplanes may need to be added to the 
inspected fleet until a sufficient number of airplanes have been 
inspected with no crack findings.

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4. Transferability of Airplanes

    Since issuance of the SSID and AD 84-21-05, the FAA has issued 
several AD's that implement Corrosion Prevention and Control Programs 
(CPCP) for aging airplanes. While developing the AD's that mandated the 
CPCP, the FAA recognized that an operator of an airplane that has been 
transferred from another operator could revise its maintenance program 
to restart the compliance times for the required corrosion tasks. This 
situation could lead to corrosion not being detected and corrected in a 
timely manner, which could reduce the structural integrity of the 
airplane.
    As a result, the CPCP AD's require that operators establish a 
program for accomplishment of the subject corrosion tasks before any 
airplane can be added to an air carrier's operations specification. 
Establishment of this program will ensure that airplanes transferred 
from operator to operator are inspected and that corrosion is detected 
in a timely manner.
    The FAA's intent in AD 84-21-05 was that operators of candidate 
fleet airplanes that have been previously operated under an FAA-
approved maintenance program accomplish the SSID inspections within the 
compliance time established by the previous operator. The FAA assumed 
that, under the existing SSID, these airplanes would be inspected in a 
manner similar to CPCP requirements. However, the SSID and AD 84-21-05 
do not address the transfer of airplanes in the candidate fleet from 
one operator to another.
    AD 84-21-05 currently requires that the revision to the maintenance 
program be included and be implemented in accordance with the 
procedures specified in Sections 5.0 and 6.0 of the SSID. However, the 
FAA finds that these sections do not provide explicit instructions to 
repetitively inspect airplanes that have been transferred from one 
operator to another. It also does not specify that new operators must 
continue the SSID inspections at the same frequency established by the 
previous operator.
    In addition, as AD 84-21-05 is currently worded, the FAA finds that 
operators that acquire candidate fleet airplanes that have been 
previously operated under a maintenance inspection program could revise 
their programs to restart the compliance times. This situation is 
contrary to standard AD requirements. An AD typically mandates an 
initial compliance time and a repetitive interval that remains 
unchanged for all operators of the affected airplanes.
    As a result of these omissions, the SSID inspections of a candidate 
fleet airplane could be deferred until it is required by the 
maintenance inspection program of the new operator. For airplanes that 
are transferred frequently, this situation could continue for the life 
of the airplane. As a result, fewer Boeing Model 727 candidate fleet 
airplanes are being inspected; thus, the size of the candidate fleet is 
in effect reduced. Even if airplanes are ultimately inspected under 
these circumstances, inspections would not be performed frequently 
enough to maintain the applicable DTR. The FAA has determined that such 
a reduction does not ensure the continued structural integrity of the 
entire Boeing Model 727 fleet.
    Implementation of procedures in the SSID that are similar to the 
CPCP will ensure that: (1) Airplanes transferred from operator to 
operator are inspected; (2) the SSIP includes a statistically valid 
number of airplanes; and (3) fatigue cracks are detected in a timely 
manner.
    Therefore, the FAA finds that, to ensure the continued structural 
integrity of the entire Model 727 fleet, the AD 84-21-05 must be 
revised to include provisions that address the transfer of airplanes. 
The FAA also finds that a program must be established to accomplish the 
inspections before any airplane that is subject to this proposal can be 
added to an air carrier's operations specifications.

FAA's Conclusions

    In light of all the factors discussed above, the FAA has determined 
that AD 84-21-05 does not adequately ensure timely detection of fatigue 
cracking in SSI's. Fatigue cracking in those items, if not detected and 
corrected in a timely manner, could result in reduced structural 
integrity of the airplane.

Explanation of New Relevant Service Information

    The FAA has reviewed and approved Boeing Document No. D6-48040-1, 
``Supplemental Structural Inspection Document'' (SSID), Revision H, 
dated June 29, 1994, which describes procedures for revising the FAA-
approved maintenance inspection program for all Boeing Model 727 series 
airplanes. This revision of the Model 727 SSID incorporates additional 
and expanded inspections from those that were contained in the previous 
version and mandated by AD 84-21-05. The fuselage skin structure that 
was the subject of an NTSB recommendation is included in these 
inspections. The FAA finds that accomplishment of these inspections 
will ensure the continuing structural integrity of the total Boeing 
Model 727 fleet.

Explanation of Requirements of Proposed Rule

    Since an unsafe condition has been identified that is likely to 
exist or develop on other products of this same type design, the 
proposed AD would supersede AD 84-21-05.
    Paragraph (a) of the proposed AD restates the requirements of AD 
84-21-05.
    Paragraph (b) of the proposed AD would require incorporation of a 
revision into the FAA-approved maintenance inspection program that 
provides no less than the required DTR for each SSI listed in Revision 
H of the SSID.
    Paragraph (c) of the proposed AD would establish specific 
compliance times for performing the initial inspection of the structure 
identified in Revision H of the SSID. Once the initial inspection has 
been performed, operators would be required to perform repetitive 
inspections at the intervals specified in the Document in order to 
remain in compliance with their maintenance inspection programs, which 
would have been revised in accordance with paragraph (b) of this 
proposed AD.
    Paragraph (d) of the proposed AD would require, for airplanes on 
which any design change or repair has been accomplished prior to the 
effective date of this proposed AD, a revision to the FAA-approved 
maintenance inspection program to include an inspection method for any 
new or affected SSI, and to include the compliance times for this 
inspection. This paragraph also would require that any new inspection 
method and the compliance times be approved by the FAA.
    Paragraph (e) of the proposed AD would require that the repair of 
any cracked structure is to be accomplished in accordance with an FAA-
approved method.
    Paragraph (f) of the proposed AD would require, for airplanes on 
which any design change or repair has been accomplished after the 
effective date of this proposed AD, a revision to the FAA-approved 
maintenance inspection program to include a new inspection method for 
any new or affected SSI, and to include the compliance times for this 
inspection. This paragraph also would require that any new inspection 
method and the compliance times be approved by the FAA.
    Before any airplane that is subject to this proposed AD can be 
added to an air carrier's operations specifications, a program for the 
accomplishment of the

[[Page 29085]]

inspections required by this proposed AD must be established. Paragraph 
(g) of the proposed AD would require accomplishment of the following:
    1. For airplanes that have been inspected in accordance with this 
proposed AD, the inspection of each SSI must be accomplished by the new 
operator in accordance with the previous operator's schedule and 
inspection method, or the new operator's schedule and inspection 
method, whichever would result in the earlier accomplishment date for 
that SSI inspection. The compliance time for accomplishment of this 
inspection must be measured from the last inspection accomplished by 
the previous operator. After each inspection has been performed once, 
each subsequent inspection must be performed in accordance with the new 
operator's schedule and inspection method.
    2. For airplanes that have not been inspected in accordance with 
this proposed AD, the inspection of each SSI must be accomplished 
either prior to adding the airplane to the air carrier's operations 
specification, or in accordance with a schedule and an inspection 
method approved by the FAA. After each inspection has been performed 
once, each subsequent inspection must be performed in accordance with 
the new operator's schedule.
    Accomplishment of these inspections will ensure that: (1) 
Operators' newly acquired airplanes comply with its SSIP before being 
operated; and (2) frequently transferred aircraft are not permitted to 
operate without accomplishment of the inspections defined in the SSID.

Differences Between SSID and Proposed AD

    Operators should note the following differences between the 
procedures specified in Revision H of the SSID and the proposed 
requirements of this AD:
    1. Paragraphs 5.1.17 and 5.1.18 of the General Instructions of 
Revision H of the SSID permit deletions of modified, altered, or 
repaired structure from the SIP. As described previously in Item 2 of 
the ``Actions Since Issuance of Previous AD'' section of this preamble, 
the FAA has determined that such deletions are unacceptable. Therefore, 
for airplanes on which the areas specified in the SSID have been 
modified, altered, or repaired, the proposed AD would require a 
revision to the operator's existing SSIP to include procedures for 
accomplishing a new FAA-approved inspection method that provides a new 
DTR for that SSI.
    2. Revision H of the SSID bases the supplemental inspections on 
specific high-cycle airplanes (i.e., candidate fleet airplanes) and 
does not include an inspection threshold for those airplanes. It also 
does not automatically add airplanes to the candidate fleet. Based on 
the discussion described previously in Item 3 of the ``Actions Since 
Issuance of Previous AD'' section of this preamble, the FAA has 
determined that the proposed AD would expand the applicability of this 
AD action to include all Model 727 series airplanes. In addition, for 
Model 727-100C and 727-200F series airplanes, the proposed inspection 
of all SSI's would be required to be accomplished prior to the 
accumulation of 46,000 total flight cycles, or within 18 months, 
whichever occurs later. For other Model 727 series airplanes, the 
proposed inspection of all SSI's would be required to be accomplished 
prior to the accumulation of 55,000 total flight cycles, or within 18 
months, whichever occurs later.

Cost Impact

    There are approximately 1,542 Boeing Model 727 series airplanes of 
the affected design in the worldwide fleet. The FAA estimates that 74 
airplanes of U.S. registry would be affected by this proposed AD.
    The actions that are proposed in this AD action would take 
approximately 1,200 work hours per airplane to accomplish, at an 
average labor rate of $60 per work hour. Based on these figures, the 
cost impact of the proposed requirements of this AD on U.S. operators 
is estimated to be $5,328,000, or $72,000 per airplane, per inspection 
cycle.
    The cost impact figure discussed above is based on assumptions that 
no operator has yet accomplished any of the current or proposed 
requirements of this AD action, and that no operator would accomplish 
those actions in the future if this AD were not adopted.
    The number of required work hours, as indicated above, is presented 
as if the accomplishment of the actions proposed in this AD were to be 
conducted as ``stand alone'' actions. However, in actual practice, 
these actions for the most part would be accomplished coincidentally or 
in combination with normally scheduled airplane inspections and other 
maintenance program tasks. Therefore, the actual number of necessary 
additional work hours would be minimal in many instances. Additionally, 
any costs associated with special airplane scheduling would be minimal.

Regulatory Impact

    The regulations proposed herein would not have substantial direct 
effects on the States, on the relationship between the national 
government and the States, or on the distribution of power and 
responsibilities among the various levels of government. Therefore, in 
accordance with Executive Order 12612, it is determined that this 
proposal would not have sufficient federalism implications to warrant 
the preparation of a Federalism Assessment.
    For the reasons discussed above, I certify that this proposed 
regulation (1) is not a ``significant regulatory action'' under 
Executive Order 12866; (2) is not a ``significant rule'' under the DOT 
Regulatory Policies and Procedures (44 FR 11034, February 26, 1979); 
and (3) if promulgated, will not have a significant economic impact, 
positive or negative, on a substantial number of small entities under 
the criteria of the Regulatory Flexibility Act. A copy of the draft 
regulatory evaluation prepared for this action is contained in the 
Rules Docket. A copy of it may be obtained by contacting the Rules 
Docket at the location provided under the caption ADDRESSES.

List of Subjects in 14 CFR Part 39

    Air transportation, Aircraft, Aviation safety, Safety.

The Proposed Amendment

    Accordingly, pursuant to the authority delegated to me by the 
Administrator, the Federal Aviation Administration proposes to amend 
part 39 of the Federal Aviation Regulations (14 CFR part 39) as 
follows:

PART 39--AIRWORTHINESS DIRECTIVES

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

    Authority: 49 U.S.C. 106(g), 40113, 44701.

Sec. 39.13  [Amended]

    2. Section 39.13 is amended by removing amendment 39-4920 (49 FR 
38931, October 2, 1984), and by adding a new airworthiness directive 
(AD), to read as follows:

Boeing: Docket 96-NM-263-AD. Supersedes AD 84-21-05, Amendment 39-
4920.

    Applicability: All Model 727 series airplanes, certificated in 
any category.
    Compliance: Required as indicated, unless accomplished 
previously.
    To ensure the continued structural integrity of the total Boeing 
Model 727 fleet, accomplish the following:

    Note 1. Where there are differences between the AD and the 
Supplemental Structural Inspection Document, the AD prevails.

    (a) For airplanes listed in Section 3.0 of Boeing Document No. 
D6-48040-1,

[[Page 29086]]

``Supplemental Structural Inspection Document'' (SSID), Revision E, 
dated June 21, 1983: Within 12 months after November 1, 1984 (the 
effective date of AD 84-21-05, amendment 39-4920), incorporate a 
revision into the FAA-approved maintenance inspection program which 
provides no less than the required damage tolerance rating (DTR) for 
each Structural Significant Item (SSI) listed in that document. (The 
required DTR value for each SSI is listed in the document.) The 
revision to the maintenance program shall include and shall be 
implemented in accordance with the procedures in Sections 5.0 and 
6.0 of the SSID. This revision shall be deleted following 
accomplishment of the requirements of paragraph (b) of this AD.

    Note 2. For the purposes of this AD, an SSI is defined as a 
principal structural element that could fail and consequently reduce 
the structural integrity of the airplane.

    (b) Within 12 months after the effective date of this AD, 
incorporate a revision into the FAA-approved maintenance inspection 
program that provides no less than the required DTR for each SSI 
listed in Boeing Document No. D6-48040-1, ``Supplemental Structural 
Inspection Document'' (SSID), Revision H, dated June 29, 1994 
(hereinafter referred to as ``Revision H''). (The required DTR value 
for each SSI is listed in the document.) The revision to the 
maintenance program shall include and shall be implemented in 
accordance with the procedures in Section 5.0, ``Damage Tolerance 
Rating (DTR) System Application'' and Section 6.0, ``SSI Discrepancy 
Reporting'' of Revision H. Upon incorporation of the revision 
required by this paragraph, the revision required by paragraph (a) 
of this AD may be deleted.
    (c) Except as provided in paragraph (d) or (f) of this AD, as 
applicable, perform an inspection to detect cracks in all structure 
identified in Revision H at the time specified in paragraph (c)(1) 
or (c)(2) of this AD, as applicable.
    (1) For Model 727-100C and 727-200F series airplanes: Inspect 
prior to the accumulation of 46,000 total flight cycles, or within 
18 months after the effective date of this AD, whichever occurs 
later.
    (2) For all airplanes, except for those airplanes identified in 
paragraph (c)(1) of this AD: Inspect prior to the accumulation of 
55,000 total flight cycles, or within 18 months after the effective 
date of this AD, whichever occurs later.

    Note 3. Once the initial inspection has been performed, 
operators are required to perform repetitive inspections at the 
intervals specified in Revision H in order to remain in compliance 
with their maintenance inspection programs, as revised in accordance 
with paragraph (b) of this AD.
    (d) For airplanes on which the structure identified in Revision 
H is affected by any design change or repair that was accomplished 
prior to the effective date of this AD: Within 18 months after the 
effective date of this AD, revise the FAA-approved maintenance 
inspection program to include an inspection method for any new or 
affected SSI, and to include the compliance times for initial and 
repetitive accomplishment of this inspection. For purposes of this 
section, an SSI is ``affected'' if it has been altered or repaired, 
or if the loads acting on the SSI have been increased or 
redistributed. Following accomplishment of the revision and within 
the compliance times established, perform an inspection to detect 
cracks in the structure affected by any design change or repair, in 
accordance with the new inspection method. The new inspection method 
and the compliance times shall be approved by the Manager, Seattle 
Aircraft Certification Office (ACO), FAA, Transport Airplane 
Directorate, 1601 Lind Avenue, SW., Renton, Washington 98055-4056, 
fax (206) 227-1181.

    Note 4. Notwithstanding the provisions of paragraphs 5.1.17 and 
5.1.18 of the General Instructions of Revision H, which would permit 
deletions of modified, altered, or repaired structure from the SIP, 
the inspection of SSI's that are modified, altered, or repaired 
shall be done in accordance with a method approved by the Manager, 
Seattle ACO.
    Note 5. For the purposes of this AD, a design change is defined 
as any modification, alteration, or change to operating limitations.

    (e) Cracked structure found during any inspection required by 
this AD shall be repaired, prior to further flight, in accordance 
with an FAA-approved method.
    (f) For airplanes on which the structure identified in Revision 
H is affected by any design change or repair that is accomplished 
after the effective date of this AD: Within 12 months after that 
modification, alteration, or repair for any new or affected SSI, 
revise the FAA-approved maintenance inspection program to include an 
inspection method for any new or affected SSI, and to include the 
compliance times for initial and repetitive accomplishment of this 
inspection. For purposes of this section, an SSI is ``affected'' if 
it has been altered or repaired, or if the loads acting on the SSI 
have been increased or redistributed. Following accomplishment of 
the revision and within the compliance times established, perform an 
inspection to detect cracks in the structure affected by any design 
change or repair, in accordance with the new inspection method. The 
new inspection method and the compliance times shall be approved by 
the Manager, Seattle ACO.

    Note 6. Notwithstanding the provisions of paragraphs 5.1.17 and 
5.1.18 of the General Instructions of Revision H, which would permit 
deletions of modified, altered, or repaired structure from the SIP, 
the inspection of SSI's that are modified, altered, or repaired 
shall be done in accordance with a method approved by the Manager, 
Seattle ACO.

    (g) Before any airplane that is subject to this AD and that has 
exceeded the applicable compliance times specified in paragraph (c) 
of this AD can be added to an air carrier's operations 
specifications, a program for the accomplishment of the inspections 
required by this AD must be established in accordance with paragraph 
(g)(1) or (g)(2) of this AD, as applicable.
    (1) For airplanes that have been inspected in accordance with 
this AD, the inspection of each SSI must be accomplished by the new 
operator in accordance with the previous operator's schedule and 
inspection method, or the new operator's schedule and inspection 
method, whichever would result in the earlier accomplishment date 
for that SSI inspection. The compliance time for accomplishment of 
this inspection must be measured from the last inspection 
accomplished by the previous operator. After each inspection has 
been performed once, each subsequent inspection must be performed in 
accordance with the new operator's schedule and inspection method.
    (2) For airplanes that have not been inspected in accordance 
with this AD, the inspection of each SSI required by this AD must be 
accomplished either prior to adding the airplane to the air 
carrier's operations specification, or in accordance with a schedule 
and an inspection method approved by the Manager, Seattle ACO. After 
each inspection has been performed once, each subsequent inspection 
must be performed in accordance with the new operator's schedule.
    (h)(1) An alternative method of compliance or adjustment of the 
compliance time that provides an acceptable level of safety may be 
used if approved by the Manager, Seattle ACO. Operators shall submit 
their requests through an appropriate FAA Principal Maintenance 
Inspector, who may add comments and then send it to the Manager, 
Seattle ACO.

    Note 7. Information concerning the existence of approved 
alternative methods of compliance with this AD, if any, may be 
obtained from the Seattle ACO.

    (2) Alternative methods of compliance, approved previously in 
accordance with AD 84-21-05, amendment 39-4920, are not considered 
to be approved as alternative methods of compliance with this AD.
    (i) Special flight permits may be issued in accordance with 
sections 21.197 and 21.199 of the Federal Aviation Regulations (14 
CFR 21.197 and 21.199) to operate the airplane to a location where 
the requirements of this AD can be accomplished.

    Issued in Renton, Washington, on May 19, 1997.
S.R. Miller,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 97-13962 Filed 5-28-97; 8:45 am]
BILLING CODE 4910-13-U