[Federal Register Volume 65, Number 70 (Tuesday, April 11, 2000)]
[Rules and Regulations]
[Pages 19302-19305]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 00-8515]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 99-NM-81-AD; Amendment 39-11660; AD 2000-07-06]
RIN 2120-AA64


Airworthiness Directives; Boeing Model 737-100, -200, -200C, -
300, -400, and -500 Series Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Final rule.

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SUMMARY: This amendment adopts a new airworthiness directive (AD), 
applicable to all Boeing Model 737-100, -200, -200C, -300, -400, and -
500 series airplanes. This AD requires repetitive inspections to detect 
cracking of the lower corners of the door frame and cross beam of the 
forward cargo door, and corrective actions, if necessary. This AD also 
requires eventual modification of the outboard radius of the lower 
corners of the door frame and reinforcement of the cross beam of the 
forward cargo door, which would constitute terminating action for the 
repetitive inspections. This amendment is prompted by reports 
indicating that fatigue cracks have been detected in the lower corners 
of the door frame and cross beam of the forward cargo door. The actions 
specified by this AD are intended to prevent fatigue cracking of the 
lower corners of the door frame and cross beam of the forward cargo 
door, which could result in rapid depressurization of the airplane.

DATES: Effective May 16, 2000.
    The incorporation by reference of certain publications listed in 
the regulations is approved by the Director of the Federal Register as 
of May 16, 2000.

ADDRESSES: The service information referenced in this AD may be 
obtained from Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, 
Washington 98134-2207. 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: Nenita Odesa, Aerospace Engineer, 
Airframe Branch, ANM-120S, FAA, Transport Airplane Directorate, Seattle 
Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, 
Washington 98055-4056; telephone (425) 227-2557; 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 all Boeing Model 737-100, -200, -
200C, -300, -400, and -500 series airplanes was published in the 
Federal Register on August 20, 1999 (64 FR 45477). That action proposed 
to require repetitive inspections to detect cracking of the lower 
corners of the door frame and cross beam of the forward cargo door, and 
corrective actions, if necessary. That action also proposed to require 
eventual modification of the outboard radius of the lower corners of 
the door frame and reinforcement of the cross beam of the forward cargo 
door, which would constitute terminating action for the repetitive 
inspections.

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.

Request To Allow Repair In Lieu of Replacement

    Regarding the proposed requirement to replace any cracked door 
frame with a new door frame, one commenter questions whether there is 
no level of damage that can be repaired. The commenter states that it 
would be preferable for operators to repair a cracked door frame when 
possible, and only replace the door frame with a new door frame if 
damage is beyond repair limits.
    The FAA infers that the commenter is requesting that paragraph 
(a)(2)(i) of the proposal be revised to allow repair of the door frame, 
in lieu of replacement of the door frame with a new door frame, when 
cracking is within repair limits. The FAA concurs with this request. 
The FAA finds that it may be possible for damage within certain limits 
to be repaired. However, no service information that defines allowable 
limits for repairable damage is available. Without established limits 
and defined repair procedures, all proposed repairs on the door frame 
must be approved by the FAA or an authorized Boeing Company Designated 
Engineering Representative (DER). The FAA has revised paragraph 
(a)(2)(i) and added paragraphs (a)(2)(i)(A) and (a)(2)(i)(B) to this 
final rule, to provide repair of a cracked door frame and replacement 
of a cracked door frame with a new door frame as two alternatives for 
compliance with paragraph (a)(2)(i) of this AD. (Operators should note 
that regardless of which alternative for compliance is accomplished, 
this AD requires installation of a cross beam repair and reinforcement 
modification of the cross beam, as specified in paragraph (a)(2)(i) of 
this AD, and modification of the repaired or replaced door frame, as 
specified in paragraph (a)(2)(ii) of this AD.)

Request To Increase Threshold for Terminating Action

    One commenter requests that the compliance time for the terminating 
action be increased from four years, as proposed, to 75,000 total 
flight cycles, as required by AD 90-06-02, amendment 39-6489 (55 FR 
8372, March 7, 1990). The commenter states that a compliance threshold 
based on calendar time, rather than on the total number of flight 
cycles, is inconsistent, because fatigue cracking is related to cabin 
pressurization cycles. Further, the commenter states that the proposed 
threshold of four years will cause unnecessary cost to operators that 
have relatively new or low-flight-cycle airplanes.
    The FAA partially concurs with the commenter's request. The FAA 
does not concur that a threshold of 75,000 total flight cycles for 
accomplishment of the terminating action, as currently required by AD 
90-06-02, provides an adequate level of safety. However, the FAA does 
concur that fatigue cracking is a function of pressurization cycles 
and, thus, a threshold based on flight cycles should be included for 
the terminating action. Therefore, paragraphs (c) and (d) of this final 
rule have been revised to specify accomplishment of the actions 
required by that paragraph within 4 years or 12,000 flight cycles after 
the effective date of this AD, whichever occurs later.

Request To Increase Compliance Time

    For the initial inspections specified in paragraphs (a) and (b) of 
the proposal, one commenter requests, for certain airplanes, an 
increase in the proposed compliance time of one year or 4,500 flight 
cycles after the effective date of this AD, whichever occurs later, to 
prior to the accumulation of 12,000 total flight cycles on the cargo 
door. The commenter states that, ``if an operator

[[Page 19303]]

has accurate accounting of the history of the cargo door, then the 
number of flight cycles for this door can be determined.''
    Another commenter requests that the compliance time for the initial 
inspections specified in paragraphs (a) and (b) of the proposal be 
increased to between 15,000 and 20,000 total flight cycles. That 
commenter states that a compliance time of one year or 4,500 flight 
cycles is ``harsh for young aircraft.'' The commenter also claims that 
cracking in the door frames does not start until 20,000 to 30,000 total 
flight cycles.
    The FAA does not concur with the commenters' requests to increase 
the compliance time for the inspections. In the preamble of the 
proposal, the FAA explained the difference between the compliance time 
stated in the service bulletin and the proposed compliance time by 
stating that the number of total flight cycles for an airplane may not 
be a good indicator of the number of total flight cycles for the 
forward cargo door. For example, a door may have been removed from an 
airplane with many total flight cycles and installed on an airplane 
with fewer total flight cycles. Also, the FAA has received a report 
indicating that a cracked door frame was found on an airplane that had 
accumulated 15,700 total flight cycles. This report contradicts the 
second commenter's claim that cracking of the door frames does not 
start until 20,000 to 30,000 total flight cycles. In view of the nature 
of the cracking and the severity of the unsafe condition addressed by 
this AD (rapid depressurization of the airplane), the FAA finds that it 
would be inappropriate to extend the compliance time for the actions 
required by this AD. No change to the final rule is necessary in this 
regard.

Request for Clarification on Replacement Door Frame

    One commenter requests that paragraph (a)(2)(i) of the proposal be 
revised to specify a part number or modification status for the 
replacement door frame. The FAA infers that the commenter is stating 
that, by making the proposed paragraph (a)(2)(i) more specific, 
paragraph (a)(2)(ii) would be unnecessary and could be removed from the 
AD. The commenter states that it is not clear why a new door frame 
should have to be modified, and points out that no specific 
instructions are provided for modification of new door frames. The 
commenter also states that introduction of a new door frame that does 
not require additional modification [such as the modification described 
in paragraph (a)(2)(ii) of the proposal] is in order.
    The FAA does not concur with the commenter's request. To date, the 
manufacturer has not issued service information that provides specific 
instructions on how to modify new door frames. Without such 
instructions, the FAA cannot provide specific instructions for 
modification of replaced door frames and, therefore, cannot revise 
paragraphs (a)(2)(i) and (a)(2)(ii) of this AD. The FAA anticipates 
that the manufacturer will issue a new revision of the service bulletin 
that, among other things, will include instructions for modification of 
replaced door frames. However, based on the nature of the cracking and 
the unsafe condition addressed by this AD, the FAA finds that it would 
be inappropriate to delay this AD until the manufacturer issues a new 
revision of the service bulletin.
    With regard to the commenter's question of why it is necessary to 
modify new door frames, as stated in the preamble of the proposal, the 
FAA has received reports that cracks have been detected in redesigned 
door frames, though these frames were supposed to be less susceptible 
to fatigue cracking. No new design has been developed. Therefore, to 
prevent any more cracking, the FAA has determined that it is necessary 
to require a reinforcement modification on newly installed door frames. 
There is no door frame currently available that is acceptable for 
installation without such modification. No change to the final rule is 
necessary in this regard.

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 3,100 Model 737-100, -200, -200C, -300, -
400, and -500 series airplanes of the affected design in the worldwide 
fleet. The FAA estimates that 1,400 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 inspections, and that the average 
labor rate is $60 per work hour. Based on these figures, the cost 
impact of the inspections required by this AD on U.S. operators is 
estimated to be $84,000, or $60 per airplane, per inspection cycle.
    It will take approximately 38 work hours per airplane to accomplish 
the required terminating modifications at an average labor rate of $60 
per work hour. Required parts will cost $1,865 per airplane. Based on 
these figures, the cost impact of the terminating modifications 
required by this AD on U.S. operators is estimated to be $5,803,000, or 
$4,145 per airplane.
    The cost impact figures discussed above are 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.

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:


[[Page 19304]]


2000-07-06 Boeing: Amendment 39-11660. Docket 99-NM-81-AD.

    Applicability: All Model 737-100, -200, -200C, -300, -400, and -
500 series airplanes; 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 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 (e) 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 fatigue cracking of the lower corners of the door 
frame and cross beam of the forward cargo door, which could result 
in rapid depressurization of the airplane, accomplish the following:

High Frequency Eddy Current Initial/Repetitive Inspections

    (a) Within 1 year or 4,500 flight cycles after the effective 
date of this AD, whichever occurs later, perform a high frequency 
eddy current (HFEC) inspection to detect cracking of the lower 
corners (forward and aft) of the door frame of the forward cargo 
door in accordance with Boeing 737 Nondestructive Test Manual, Part 
6, Section 51-00-00, Figure 4 or Figure 23.
    (1) If no cracking is detected, repeat the HFEC inspection 
thereafter at intervals not to exceed 4,500 flight cycles, until the 
requirements of paragraph (c) of this AD have been accomplished.
    (2) If any cracking is detected during any inspection required 
by paragraph (a) of this AD, prior to further flight, accomplish the 
requirements of paragraphs (a)(2)(i) AND (a)(2)(ii) of this AD, 
which constitute terminating action for the repetitive inspections 
required by paragraph (a)(1) of this AD.
    (i) Accomplish the requirements of paragraph (a)(2)(i)(A) OR 
(a)(2)(i)(B) of this AD, and install a cross beam repair and 
reinforcement modification of the cross beam in accordance with 
Boeing Service Bulletin 737-52-1100, Revision 2, dated March 31, 
1994.
    (A) Repair the door frame of the forward cargo door in 
accordance with a method approved by the Manager, Seattle Aircraft 
Certification Office (ACO), FAA, Transport Airplane Directorate; or 
in accordance with data meeting the type certification basis of the 
airplane approved by a Boeing Company Designated Engineering 
Representative (DER) who has been authorized by the Manager, Seattle 
ACO, to make such findings. For a repair or modification method to 
be approved by the Manager, Seattle ACO, as required by this 
paragraph; and paragraphs (a)(2)(ii), (b)(2), (b)(3)(ii), and (c)(2) 
of this AD; the Manager's approval letter must specifically 
reference this AD.
    (B) Replace the door frame of the forward cargo door with a new 
door frame in accordance with Boeing Service Bulletin 737-52-1100, 
Revision 2, dated March 31, 1994.
    (ii) Modify the repaired or replaced door frame of the forward 
cargo door in accordance with a method approved by the Manager, 
Seattle ACO, or in accordance with data meeting the type 
certification basis of the airplane approved by a Boeing Company DER 
who has been authorized by the Manager, Seattle ACO, to make such 
findings.

Detailed Visual Initial/Repetitive Inspections

    (b) Within 1 year or 4,500 flight cycles after the effective 
date of this AD, whichever occurs later, perform a detailed visual 
inspection to detect cracking of the cross beam (i.e., upper and 
lower chord and web sections) of the forward cargo door in 
accordance with Boeing Service Bulletin 737-52-1100, Revision 2, 
dated March 31, 1994.

    Note 2: For the purposes of this AD, a detailed inspection is 
defined as: ``An intensive visual examination of a specific 
structural area, system, installation or assembly to detect damage, 
failure or irregularity. Available lighting is normally supplemented 
with a direct source of good lighting at intensity deemed 
appropriate by the inspector. Inspection aids such as mirror, 
magnifying lenses, etc. may be used. Surface cleaning and elaborate 
access procedures may be required.''


    (1) If no cracking is detected, repeat the inspection thereafter 
at intervals not to exceed 4,500 flight cycles until the 
requirements of paragraph (c) of this AD have been accomplished.
    (2) If any cracking is detected on the lower chord section of 
the cross beam during any inspection required by paragraph (b) of 
this AD, prior to further flight, repair in accordance with a method 
approved by the Manager, Seattle ACO, or in accordance with data 
meeting the type certification basis of the airplane approved by a 
Boeing Company DER who has been authorized by the Manager, Seattle 
ACO, to make such findings.
    (3) If any cracking is detected on any area excluding the lower 
chord section of the cross beam (i.e., upper chord and web section) 
during any inspection required by paragraph (b) of this AD, prior to 
further flight, accomplish the requirements of paragraph (b)(3)(i) 
or (b)(3)(ii), as applicable, of this AD, which constitute 
terminating action for the repetitive inspections required by 
paragraph (b)(1) of this AD.
    (i) For airplanes with line numbers 1 through 1231: Install a 
cross beam repair and preventative modification of the outboard 
radius of the lower corners (forward and aft) of the door frame in 
accordance with Boeing Service Bulletin 737-52-1100, Revision 2, 
dated March 31, 1994.

    Note 3: Due to implications and consequences associated with 
cracking, this AD does not allow the option of replacing the door 
frame as an alternative method of compliance to installing the 
preventative modification.

    (ii) For airplanes with line numbers 1232 and subsequent: 
Install a cross beam repair and preventative modification of the 
outboard radius of the lower corners (forward and aft) of the door 
frame in accordance with a method approved by the Manager, Seattle 
ACO or in accordance with data meeting the type certification basis 
of the airplane approved by a Boeing Company DER who has been 
authorized by the Manager, Seattle ACO, to make such findings.

Terminating Action

    (c) Within 4 years or 12,000 flight cycles after the effective 
date of this AD, whichever occurs later: Install the preventative 
modification of the outboard radius of the lower corners (forward 
and aft) of the door frame and the reinforcement modification of the 
cross beam of the forward cargo door in accordance with paragraph 
(c)(1) or (c)(2) of this AD, as applicable. Accomplishment of 
paragraph (c)(1) or (c)(2) of this AD, as applicable, constitutes 
terminating action for the repetitive inspections required by 
paragraphs (a)(1) and (b)(1) of this AD.
    (1) For airplanes with line numbers 1 through 1231: Accomplish 
the preventative modification and the reinforcement modification in 
accordance with Boeing Service Bulletin 737-52-1100, Revision 2, 
dated March 31, 1994.
    (2) For airplanes with line numbers 1232 and subsequent: 
Accomplish the preventative modification and the reinforcement 
modification in accordance with a method approved by the Manager, 
Seattle ACO or in accordance with data meeting the type 
certification basis of the airplane approved by a Boeing Company DER 
who has been authorized by the Manager, Seattle ACO, to make such 
findings.

Modifications Previously Accomplished

    (d) For all airplanes on which modifications of the forward 
lower corner of the door frame and the cross beam of the forward 
cargo door were accomplished in accordance with Boeing Service 
Bulletin 737-52-1100, dated August 25, 1988, or Revision 1, dated 
July 20, 1989, or in accordance with the requirements of AD 90-06-
02, amendment 39-6489: Within 4 years or 12,000 flight cycles after 
the effective date of this AD, whichever occurs later, install the 
reinforcement modification of the aft corner of the door frame of 
the forward cargo door in accordance with Boeing Service Bulletin 
737-52-1100, Revision 2, dated March 31, 1994. Accomplishment of 
such modification constitutes terminating action for the repetitive 
inspections required by this AD.

    Note 4: Accomplishment of Boeing Service Bulletin 737-52-1100, 
Revision 2, dated March 31, 1994, does not supersede the 
requirements of AD 90-06-02, amendment 39-6489.

Alternative Methods of Compliance

    (e) An alternative method of compliance or adjustment of the 
compliance time that provides an acceptable level of safety may be

[[Page 19305]]

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 5: 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

    (f) 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

    (g) Except as provided by paragraphs (a)(2)(i)(A), (a)(2)(ii), 
(b)(2), (b)(3)(ii), and (c)(2) of this AD; the actions shall be done 
in accordance with Boeing Service Bulletin 737-52-1100, Revision 2, 
dated March 31, 1994; and Boeing 737 Nondestructive Test (NDT) 
Manual, D6-37239, Part 6, Section 51-00-00, Figure 4 or Figure 23; 
dated August 5, 1997, as applicable. Boeing 737 NDT Manual contains 
the following list of effective pages:

------------------------------------------------------------------------
                                    Revision level
            Page No.                 shown on page    Date shown on page
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Title Page......................  Not Shown.........  Not Shown.
List of Effective Pages, Pages    Not Shown.........  Aug. 5, 1997.
 1, 2.
List of Effective Pages, Page 2A  Not Shown.........  Feb. 5, 1997.
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    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 98134-2207. 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.
    (h) This amendment becomes effective on May 16, 2000.

    Issued in Renton, Washington, on March 31, 2000.
Donald L. Riggin,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 00-8515 Filed 4-10-00; 8:45 am]
BILLING CODE 4910-13-U