[Federal Register Volume 62, Number 49 (Thursday, March 13, 1997)]
[Rules and Regulations]
[Pages 11760-11763]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 97-6086]
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DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 39
[Docket No. 97-NM-23-AD; Amendment 39-9961; AD 97-06-04]
RIN 2120-AA64
Airworthiness Directives; Boeing Model 757-200 Series Airplanes
AGENCY: Federal Aviation Administration, DOT.
ACTION: Final rule; request for comments.
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SUMMARY: This amendment adopts a new airworthiness directive (AD) that
is applicable to certain Boeing Model 757-200 series airplanes. This
action requires inspections to detect cracking on the free edge of the
tang, if necessary, and of the fastener holes in the lower spar chord;
and various follow-on actions. This action also provides for optional
terminating action for the requirements of this AD. This amendment is
prompted by a report of fatigue cracking in the lower spar chord of two
Model 757 series airplanes. The actions specified in this AD are
intended to detect and correct such fatigue cracking, which could
result in reduced structural integrity of the engine strut.
DATES: Effective March 28, 1997.
The incorporation by reference of certain publications listed in
the regulations is approved by the Director of the Federal Register as
of March 28, 1997.
Comments for inclusion in the Rules Docket must be received on or
before May 12, 1997.
ADDRESSES: Submit comments in triplicate to the Federal Aviation
Administration (FAA), Transport Airplane Directorate, ANM-103,
Attention: Rules Docket No. 97-NM-23-AD, 1601 Lind Avenue, SW., Renton,
Washington 98055-4056.
The service information referenced in this AD may be obtained from
Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, Washington
98124-2207. This information may be examined at the FAA, Transport
Airplane Directorate, 1601 Lind Avenue, SW., Renton, Washington; or at
the Office of the Federal Register, 800 North Capitol Street, NW.,
suite 700, Washington, DC.
FOR FURTHER INFORMATION CONTACT: Todd Martin, Aerospace Engineer,
Airframe Branch, ANM-120S, FAA, Seattle Aircraft Certification Office,
1601 Lind Avenue, SW., Renton, Washington; telephone (206) 227-2781;
fax (206) 227-1181.
SUPPLEMENTARY INFORMATION: The FAA received a report indicating that
fatigue cracking was found in the lower spar chord on two Boeing Model
757-200 series airplanes powered by Rolls Royce engines. On one of
these airplanes, the tang of the chord was cracked completely through.
The crack had propagated approximately five inches into the vertical
flange adjacent to the side skins. On the other airplane, a 0.3-inch
crack was found in the tang of the chord. Such fatigue cracking, if not
detected and corrected in a timely manner, could result in reduced
structural integrity of the engine strut.
An initial analysis conducted by Boeing revealed that the
stiffening straps, which were installed on the strut midchords of
twelve airplanes during production, were the primary cause of the
cracks. Consequently, to prevent cracks in the lower spar chords, the
stiffening straps were removed from the midchords in accordance with
Boeing Service Bulletin 757-54-0028. However, results of subsequent
analysis related to the structural reassessment of the strut structure
of the Model 757 revealed that cracks can continue to occur after
removal of the stiffening straps. The analysis also revealed that
cracks can occur in the same area on struts that are made without
stiffening straps.
Explanation of Relevant Service Information
The FAA has reviewed and approved Boeing Service Bulletin 757-54-
0031, Revision 2, dated December 19, 1996. The service bulletin
describes procedures for certain inspections and follow-on actions,
which include the following:
1. Tang Inspection: The service bulletin describes procedures for
an eddy current inspection to detect cracking on the free edge of the
tang. For airplanes on which cracking within certain limits is found,
the service bulletin describes procedures for removal of the midchord
channels, stop-drilling of the cracking, and installation of a repair.
The service bulletin recommends that if any cracking is found that is
outside specified limits, the lower spar chord must be replaced with a
new or serviceable chord; however, the service bulletin does not
provide procedures for such replacement.
2. Initial Bolt Hole Inspection: The service bulletin also
describes procedures for an eddy current inspection (bolt hole
inspection) to detect cracking of the two fastener holes in the lower
spar chord. For airplanes on which no cracking is found during
[[Page 11761]]
the bolt hole inspection, the service bulletin describes procedures for
increasing the diameter of the holes by specified dimensions and
installing new fasteners.
For airplanes on which cracking is found during this bolt hole
inspection, and that cracking can be removed by increasing the diameter
of the hole, the service bulletin describes procedures for increasing
the diameter of the hole by specified dimensions, and installing new
fasteners. For airplanes on which cracking that is within certain
limits is found, but which cannot be removed by increasing the diameter
of the hole, the service bulletin describes procedures for installation
of a repair. Additionally, for airplanes on which cracking that is
outside certain limits is found, the service bulletin recommends that
the lower spar chord be replaced with a new or serviceable chord. The
service bulletin does not specify procedures for such replacement.
3. Repetitive Bolt Hole Inspections: The service bulletin
recommends that a repetitive bolt hole inspection be accomplished. (The
procedures for these inspections are the same as those provided for the
first bolt hole inspection.)
Installation of a repair eliminates the need for the inspections
described previously.
Explanation of the Requirements of the Rule
Since an unsafe condition has been identified that is likely to
exist or develop on other Boeing Model 757-200 series airplanes of the
same type design, this AD is being issued to detect and correct fatigue
cracking of the lower spar chord, and consequent reduced structural
integrity of the engine strut.
This AD requires repetitive eddy current inspections to detect
cracking on the free edge of the tang; and removal of the midchord
channels, stop-drilling of cracking, and installation of a repair; if
necessary. For airplanes on which cracking is found that is outside
specified limits, this AD requires replacement of the lower spar chord
with a new or serviceable chord.
This AD also requires repetitive eddy current inspections (bolt
hole inspections) to detect cracking of the two fastener holes in the
lower spar chord. For airplanes on which no cracking is found, this AD
requires increasing the diameter of the holes by specified dimensions,
and installing new fasteners. For airplanes on which cracking is found
that can be removed by increasing the diameter of the hole, this AD
requires increasing the diameter of the hole by specified dimensions,
and installing new fasteners. For airplanes on which cracking is found
that is within certain limits, but which cannot be removed by
increasing the diameter of the hole, this AD requires installation of a
repair. Additionally, for airplanes on which cracking that is outside
certain limits is found, this AD requires replacement of the lower spar
chord with a new or serviceable chord.
Accomplishment of the bolt hole inspections terminates the eddy
current inspections of the free edge of the tang.
This AD also provides for optional terminating action, which, if
accomplished, terminates the requirements of the AD.
Replacement of the lower spar chord, if necessary, is required to
be accomplished in accordance with a method approved by the FAA. Other
actions are required to be accomplished in accordance with the service
bulletin described previously.
Interim Action
This AD is considered to be interim action. Boeing currently is
developing a Strut Improvement Program for Model 757 series airplanes,
which will include installation of a new midchord configuration. The
FAA may consider further rulemaking to require accomplishment of that
installation.
Differences Between Service Bulletin and This AD
Operators should note that, although the service bulletin
referenced in this AD recommends a ``grace period'' of 120 days for
accomplishment of the inspections on airplanes that have exceeded
certain thresholds, this AD specifies a ``grace period'' of 60 days.
The FAA has been advised that a significant number of the affected
Model 757 series airplanes have already reached the specified
thresholds. In developing an appropriate compliance time for this
action, the FAA considered not only the degree of urgency associated
with addressing the subject unsafe condition, but the manufacturer's
recommendation as to an appropriate compliance time, parts
availability, and the practical aspect of accomplishing the required
inspections within an interval of time that parallels the normal
scheduled maintenance for the majority of affected operators.
In light of this, the FAA has determined that, for airplanes that
have already reached certain thresholds, a ``grace period'' of 60 days
is necessary to ensure that the affected airplanes are inspected in a
timely manner and that an acceptable level of safety is maintained.
This ``grace period'' is roughly equivalent to 300 flight cycles, which
the service bulletin specifies as the number of flight cycles that
should not be exceeded before inspection of the free edge of the tang
is accomplished on airplanes that have exceeded certain thresholds.
In addition, the FAA has determined that the eddy current
inspections of the free edge of the tang must be accomplished on a
repetitive basis until the bolt hole inspection is accomplished. (The
service bulletin recommends only a one-time inspection of the free edge
of the tang.) The FAA finds that these repetitive inspections of the
tang must be accomplished in the event an initial inspection of the
tang is performed well before the 15,000 flight cycle threshold.
Determination of Rule's Effective Date
Since a situation exists that requires the immediate adoption of
this regulation, it is found that notice and opportunity for prior
public comment hereon are impracticable, and that good cause exists for
making this amendment effective in less than 30 days.
Comments Invited
Although this action is in the form of a final rule that involves
requirements affecting flight safety and, thus, was not preceded by
notice and an opportunity for public comment, comments are invited on
this rule. Interested persons are invited to comment on this rule by
submitting such written data, views, or arguments as they may desire.
Communications shall identify the Rules Docket number and be submitted
in triplicate to the address specified under the caption ADDRESSES. All
communications received on or before the closing date for comments will
be considered, and this rule may be amended in light of the comments
received. Factual information that supports the commenter's ideas and
suggestions is extremely helpful in evaluating the effectiveness of the
AD action and determining whether additional rulemaking action would be
needed.
Comments are specifically invited on the overall regulatory,
economic, environmental, and energy aspects of the rule that might
suggest a need to modify the rule. All comments submitted will be
available, both before and after the closing date for comments, in the
Rules Docket for examination by interested persons. A report that
summarizes each FAA-public contact concerned with the substance of this
AD will be filed in the Rules Docket.
Commenters wishing the FAA to acknowledge receipt of their comments
submitted in response to this rule must
[[Page 11762]]
submit a self-addressed, stamped postcard on which the following
statement is made: ``Comments to Docket Number 97-NM-23-AD.'' The
postcard will be date stamped and returned to the commenter.
Regulatory Impact
The regulations adopted herein will not have substantial direct
effects on the States, on the relationship between the national
government and the States, or on the distribution of power and
responsibilities among the various levels of government. Therefore, in
accordance with Executive Order 12612, it is determined that this final
rule does not have sufficient federalism implications to warrant the
preparation of a Federalism Assessment.
The FAA has determined that this regulation is an emergency
regulation that must be issued immediately to correct an unsafe
condition in aircraft, and that it is not a ``significant regulatory
action'' under Executive Order 12866. It has been determined further
that this action involves an emergency regulation under DOT Regulatory
Policies and Procedures (44 FR 11034, February 26, 1979). If it is
determined that this emergency regulation otherwise would be
significant under DOT Regulatory Policies and Procedures, a final
regulatory evaluation will be prepared and placed in the Rules Docket.
A copy of it, if filed, 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:
97-06-04 Boeing: Amendment 39-9961. Docket 97-NM-23-AD.
Applicability: Model 757-200 series airplanes having line
numbers 1 through 736 inclusive, powered by Rolls Royce engines,
certificated in any category.
Note 1: This AD applies to each airplane identified in the
preceding applicability provision, regardless of whether it has been
modified, altered, or repaired in the area subject to the
requirements of this AD. For airplanes that have been otherwise
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 (i) 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 detect and correct fatigue cracking of the lower spar chord,
and consequent reduced structural integrity of the engine strut,
accomplish the following:
(a) Prior to the accumulation of 15,000 total flight cycles, or
within 60 days after the effective date of this AD, whichever occurs
later: Perform an eddy current inspection to detect cracking on the
free edge of the tang, in accordance with the Accomplishment
Instructions of Boeing Service Bulletin 757-54-0031, Revision 2,
dated December 19, 1996. Repeat this inspection thereafter at
intervals not to exceed 3,000 flight cycles until the inspection
required by paragraph (d) of this AD is accomplished.
Note 2: The inspection required by paragraph (a) of this AD need
not be performed on airplanes on which the inspection required by
paragraph (d) of this AD is performed prior to the compliance time
specified in paragraph (a) of this AD.
(b) If any cracking is found during the inspection required by
paragraph (a) of this AD, and the cracking is within the limits
specified in the service bulletin: Prior to further flight, remove
the midchord channels, stop-drill the cracking, and install a repair
in accordance with the service bulletin. No further action is
required by this AD.
(c) If any cracking is found, and the cracking is outside the
limits specified in the service bulletin: Prior to further flight,
replace the lower spar chord with a new or serviceable chord in
accordance with a method approved by the Manager, Seattle Aircraft
Certification Office (ACO), FAA, Transport Airplane Directorate.
(d) Perform an eddy current inspection (bolt hole inspection) to
detect cracking of the two fastener holes in the lower spar chord,
in accordance with the Accomplishment Instructions of Boeing Service
Bulletin 757-54-0031, Revision 2, dated December 19, 1996, at the
time specified in paragraph (d)(1) and (d)(2) of this AD, as
applicable. Accomplishment of this inspection terminates the
inspections required by paragraph (a) of this AD.
(1) For airplanes on which the stiffening straps have been
removed from the midchord in accordance with Boeing Service Bulletin
757-54-0028 prior to the effective date of this AD: Accomplish the
inspection at the time specified in paragraph I.D. of Boeing Service
Bulletin 757-54-0031, Revision 2, dated December 19, 1996.
(2) For airplanes other than those identified in paragraph
(d)(1) of this AD: Accomplish the inspection prior to the
accumulation of 18,000 total flight cycles, or within 60 days after
the effective date of this AD, whichever occurs later.
(e) If no cracking is found during the inspection required by
paragraph (d) of this AD, prior to further flight, increase the
diameter of the holes by the dimensions specified in the
Accomplishment Instructions of Boeing Service Bulletin 757-54-0031,
Revision 2, dated December 19, 1996, and install new fasteners in
accordance with the service bulletin.
(f) If any cracking is found during the inspection required by
paragraph (d) of this AD, prior to further flight, accomplish
paragraph (f)(1), (f)(2), or (f)(3) of this AD, as applicable, in
accordance with the Accomplishment Instructions of Boeing Service
Bulletin 757-54-0031, Revision 2, dated December 19, 1996.
(1) If the cracking can be removed by increasing the diameter of
the hole in accordance with the service bulletin: Increase the
diameter of the hole by the dimensions specified in the
Accomplishment Instructions of the service bulletin, and install new
fasteners in accordance with the service bulletin.
(2) If the cracking cannot be removed by increasing the diameter
of the hole in accordance with the Accomplishment Instructions of
the service bulletin, but the cracking is within the limits
specified in the service bulletin: Install the repair in accordance
with the service bulletin. No further action is required by this AD.
(3) If the cracking is outside the limits specified in the
service bulletin: Replace the lower spar chord with a new or
serviceable chord in accordance with a method approved by the
Manager, Seattle ACO.
(g) Accomplish either paragraph (g)(1) or (g)(2) of this AD, as
applicable, in accordance with Boeing Service Bulletin 757-54-0031,
Revision 2, dated December 19, 1996.
(1) If any fastener installed as a result of an inspection
required by paragraph (d) of this AD has a diameter of \5/8\-inch or
greater: Install the repair prior to the accumulation of the number
of flight cycles specified in the ``Subsequent Inspection Interval''
column of the Threshold Table included in paragraph I.D. of the
service bulletin.
(2) If any fastener installed as a result of an inspection
required by paragraph (d) of this AD has a diameter of less than \5/
8\-inch: Repeat the bolt hole inspection required by paragraph (d)
of this AD prior to the accumulation of the number of flight cycles
specified in the ``Subsequent Inspection Interval'' column of the
Threshold Table included in paragraph I.D. of the service bulletin
until the repair specified in paragraph (h) of this AD is installed.
(h) Installation of the repair in accordance with the
Accomplishment Instructions of Boeing Service Bulletin 757-54-0031,
Revision 2, dated December 19, 1996, constitutes terminating action
for the requirements of this AD.
[[Page 11763]]
(i) 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 3: Information concerning the existence of approved
alternative methods of compliance with this AD, if any, may be
obtained from the Seattle ACO.
(j) 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.
(k) The actions shall be done in accordance with Boeing Service
Bulletin 757-54-0031, Revision 2, dated December 19, 1996. This
incorporation by reference was approved by the Director of the
Federal Register in accordance with 5 U.S.C. 552(a) and 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.
(l) This amendment becomes effective on March 28, 1997.
Issued in Renton, Washington, on March 5, 1997.
Darrell M. Pederson,
Acting Manager, Transport Airplane Directorate, Aircraft Certification
Service.
[FR Doc. 97-6086 Filed 3-12-97; 8:45 am]
BILLING CODE 4910-13-U
