[Federal Register Volume 64, Number 155 (Thursday, August 12, 1999)]
[Proposed Rules]
[Pages 43950-43953]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 99-20881]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 99-NM-84-AD]
RIN 2120-AA64


Airworthiness Directives; Boeing Model 737-200, -200C, -300, and 
-400 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 737-
200, -200C, -300, and -400 series airplanes, that currently requires 
repetitive visual inspections to detect cracking of the corners of the 
door frame and the cross beams of the aft cargo door, and corrective 
actions, if necessary. That AD also provides an optional terminating 
action for certain repetitive inspections. This action would add 
requirements for repetitive high frequency eddy current (HFEC) 
inspections, and corrective actions, if necessary. This action also 
would mandate accomplishment of the previously optional terminating 
action. The actions specified by the proposed AD are intended to 
prevent fatigue cracking of the corners of the door frame and the cross 
beams of the aft cargo door, which could result in rapid 
depressurization of the airplane.

DATES: Comments must be received by September 27, 1999.

ADDRESSES: Submit comments in triplicate to the Federal Aviation 
Administration (FAA), Transport Airplane Directorate, ANM-114, 
Attention: Rules Docket No. 99-NM-84-AD, 1601 Lind Avenue, SW., Renton, 
Washington 98055-4056. Comments may be inspected at this location 
between 9 a.m. and 3 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: Rick Kawaguchi, Aerospace Engineer, 
Airframe Branch, ANM-120S, FAA, Transport Airplane Directorate, Seattle 
Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, 
Washington 98055-4056; telephone (425) 227-1153; fax (425) 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 99-NM-84-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-114, Attention: Rules 
Docket No. 99-NM-84-AD, 1601 Lind Avenue, SW., Renton, Washington 
98055-4056.

[[Page 43951]]

Discussion

    On November 30, 1998, the FAA issued AD 98-25-06, amendment 39-
10931 (63 FR 67769, December 9, 1998), applicable to certain Boeing 
Model 737-200, -200C, -300, and -400 airplanes, to require repetitive 
inspections to detect cracking of the corners of the door frame and the 
cross beams of the aft cargo door, and corrective actions, if 
necessary. That action also provides an optional terminating action for 
the repetitive inspection requirement of that AD. That action was 
prompted by reports indicating that fatigue cracks have been detected 
in the corners of the door frame and the cross beams of the aft cargo 
door on several in-service airplanes, and by another report indicating 
that rapid depressurization occurred during flight on one of those 
airplanes. The requirements of that AD are intended to prevent fatigue 
cracking of the corners of the door frame and the cross beams of the 
aft cargo door, which could result in rapid depressurization of the 
airplane.

Actions Since Issuance of Previous Rule

    Since the issuance of AD 98-25-06, the FAA has received a report 
indicating that during a high frequency eddy current inspection a one-
inch crack was detected in the forward corner frame of the aft cargo 
door. Further investigation revealed a crack in the aft corner frame 
and cracks in the lower cross beam. No cracking was detected during a 
detailed visual inspection of these areas that was accomplished 
approximately 925 flight cycles prior to an incident of rapid 
depressurization of the airplane. In light of this information, the FAA 
has determined that the detailed visual inspections of the door frame 
and the cross beams of the aft cargo door required by the existing AD 
are not providing the degree of safety assurance necessary for the 
affected airplanes.

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 98-25-06 to continue to require 
repetitive visual inspections to detect cracking of the corners of the 
door frame and the cross beams of the aft cargo door, and corrective 
actions, if necessary. This proposed AD would add requirements for 
repetitive high frequency eddy current (HFEC) inspections of the 
corners of the aft cargo door frame, and corrective actions, if 
necessary. This proposal also would mandate accomplishment of the 
previously optional terminating action.
    The HFEC inspections would be required to be accomplished in 
accordance with the procedures specified in Boeing 737 Nondestructive 
Test Manual, Part 6, Chapter 51-00-00 (Figure 4 or Figure 23). 
Modification of the door frame would be required to be accomplished in 
accordance with Boeing Service Bulletin 737-52-1079, Revision 5, dated 
May 16, 1996. Repairs of the outer chord of the upper and lower cross 
beams would be required to be accomplished 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 Designated Engineering Representative.

Other Relevant Rulemaking

    The FAA previously has issued AD 90-06-02, amendment 39-6489 (55 FR 
8372, March 7, 1990), applicable to certain Boeing Model 737 series 
airplanes. AD 90-06-02 requires accomplishment of certain structural 
modifications, which constitutes terminating action for the repetitive 
inspection requirements of this proposed AD.

Differences Between Service Bulletin and This Proposed AD

     As stated in AD 98-25-06, operators should note that, 
unlike the procedures described in the service bulletin, this proposed 
AD would not permit further flight with stop-drilled cracks in the 
frame of the aft cargo door. The FAA has determined that, because of 
the safety implications and consequences associated with such cracking, 
any subject aft cargo door frame that is found to be cracked must be 
permanently repaired and modified prior to further flight.
     As stated in AD 98-25-06, operators should note that the 
effectivity listing of the service bulletin includes Boeing Model 737-
200 and -200C series airplanes having line numbers 6 through 873 
inclusive. The applicability of this proposed AD includes not only 
those airplanes listed in the effectivity listing of the service 
bulletin, but also Boeing Model 737-200, -200C, -300, and -400 series 
airplanes; having line numbers 874 through 1642 inclusive; that have 
certain replacement doors installed and that have not been modified in 
accordance with Boeing Service Bulletin 737-52-1079.
     Operators also should note that, although the service 
bulletin specifies that the manufacturer may be contacted for 
disposition of certain repair conditions, this proposed AD would 
require the repair of those conditions to be accomplished in accordance 
with a method approved by the FAA, or in accordance with data meeting 
the type certification basis of the airplane approved by a Boeing 
Company Designated Engineering Representative who has been authorized 
by the FAA to make such findings.
     Operators should note that, although the service bulletin 
describes accomplishment of a visual inspection of the corners of the 
door frame and the cross beams of the aft cargo door, for the reasons 
discussed previously, the FAA has determined that accomplishment of a 
visual inspection only is inadequate to detect cracking in certain 
areas. Therefore, this proposed AD would add repetitive high frequency 
eddy current inspections to detect cracking of the four corners of the 
aft cargo door frame.
     Operators should note that this AD proposes to mandate, 
within 4 years after the effective date of this AD, the modification of 
the door frame of the aft cargo door described in Boeing Service 
Bulletin 737-52-1079, Revision 5, dated May 16, 1996, as terminating 
action for the repetitive inspections of the door frame. The FAA has 
determined that long-term continued operational safety will be better 
assured by design changes to remove the source of the problem, rather 
than by repetitive inspections. Long-term inspections may not be 
providing the degree of safety assurance necessary for the transport 
airplane fleet. This, coupled with a better understanding of the human 
factors associated with numerous continual inspections, has led the FAA 
to consider placing less emphasis on inspections and more emphasis on 
design improvements. The proposed modification is in consonance with 
these conditions.

Cost Impact

    There are approximately 1,636 Model 737 series airplanes of the 
affected design in the worldwide fleet. The FAA estimates that 707 
airplanes of U.S. registry would be affected by this proposed AD.
    The detailed visual inspections that currently are required by AD 
98-25-06, and retained in this proposed AD, take approximately 2 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 currently 
required inspections on U.S. operators is estimated to be $84,840, or 
$120 per airplane, per inspection cycle.
    The new high frequency eddy current inspections that are proposed 
in this AD action would take approximately 4 work

[[Page 43952]]

hours per airplane to accomplish, at an average labor rate of $60 per 
work hour. Based on these figures, the cost impact of the new 
inspections proposed by this AD on U.S. operators is estimated to be 
$169,680, or $240 per airplane, per inspection cycle.
    The modification that is proposed in this AD action would take 
approximately 144 work hours per airplane to accomplish, at an average 
labor rate of $60 per work hour. Required parts would cost 
approximately $4,530 per airplane. Based on these figures, the cost 
impact of the modification proposed by this AD on U.S. operators is 
estimated to be $9,311,190, or $13,170 per airplane.
    The cost impact figures discussed above are 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.

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 39-10931 (63 FR 
67769, December 9, 1998), and by adding a new airworthiness directive 
(AD), to read as follows:

Boeing: Docket 99-NM-84-AD. Supersedes AD 98-25-06, Amendment 39-
10931.

    Applicability: The following airplane models, certificated in 
any category:
     Model 737-200 and -200C series airplanes, line numbers 
6 through 873 inclusive;
     Model 737-200, -200C, -300, and -400 series airplanes; 
line numbers 874 through 1642 inclusive; equipped with an aft cargo 
door having Boeing part number (P/N) 65-47952-1 or P/N 65-47952-524; 
excluding:
    1. Those airplanes on which that door has been modified in 
accordance with Boeing Service Bulletin 737-52-1079; or
    2. Those airplanes on which the door assembly having P/N 65-
47952-524 includes four straps (P/N's 65-47952-139, 65-47952-140, 
65-47952-141, and 65-47952-142) and a thicker lower cross beam web 
(P/N 65-47952-157).

    Note 1: This AD applies to each airplane identified in the 
preceding applicability provision, regardless of whether it has been 
otherwise 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 (f)(1) 
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 corners of the door frame and 
the cross beams of the aft cargo door, which could result in rapid 
depressurization of the airplane, accomplish the following:

Restatement of the Requirements of AD 98-25-06:

Inspections and Corrective Actions

    (a) Within 90 days or 700 flight cycles after December 24, 1998 
(the effective date of AD 98-25-06, amendment 39-10931), whichever 
occurs later, perform an internal detailed visual inspection to 
detect cracking of the corners of the door frame and the cross beams 
of the aft cargo door, in accordance with Boeing Service Bulletin 
737-52-1079, Revision 5, dated May 16, 1996.
    (1) If no cracking is detected, accomplish the requirements of 
either paragraph (a)(1)(i) or (a)(1)(ii) of this AD.
    (i) Repeat the internal visual inspection thereafter at 
intervals not to exceed 4,500 flight cycles. Or
    (ii) Prior to further flight, modify the corners of the door 
frame and the cross beams of the aft cargo door in accordance with 
the service bulletin. Accomplishment of such modification 
constitutes terminating action for the repetitive inspection 
requirements of paragraph (a)(1)(i) of this AD.
    (2) If any cracking is detected in the upper or lower cross 
beams, prior to further flight, modify the cracked beam in 
accordance with paragraph III.C. of Part I of the Accomplishment 
Instructions of the service bulletin. Accomplishment of such 
modification constitutes terminating action for the repetitive 
inspection requirements of paragraph (a)(1)(i) of this AD for the 
repaired beam.
    (3) If any cracking is detected in the forward or aft upper door 
frame, prior to further flight, repair the frame and modify the 
corners of the door frame of the aft cargo door, in accordance with 
paragraph III.E. of Part I of the Accomplishment Instructions of the 
service bulletin, except as provided by paragraph (b) of this AD. 
Accomplishment of such modification constitutes terminating action 
for the repetitive inspection requirements of paragraph (a)(1)(i) of 
this AD for the upper door frame.

    Note 2: Cracks of the forward or aft upper door frame, 
regardless of length, must be repaired prior to further flight in 
accordance with paragraph III.E. of Part I of the Accomplishment 
Instructions of the service bulletin.

    (4) If any cracking is detected in the forward or aft lower door 
frame, prior to further flight, replace the damaged frame with a new 
frame, and modify the corners of the door frame of the aft cargo 
door, in accordance with paragraph III.F. of Part I of the 
Accomplishment Instructions of the service bulletin. Accomplishment 
of such modification constitutes terminating action for the 
repetitive inspection requirements of paragraph (a)(1)(i) of this AD 
for the lower door frame.
    (b) Where Boeing Service Bulletin 737-52-1079, Revision 5, dated 
May 16, 1996, specifies that certain repairs are to be accomplished 
in accordance with instructions received from Boeing, this AD 
requires that, prior to further flight, such repairs be accomplished 
in accordance with a method approved by the Manager, Seattle 
Aircraft Certification Office (ACO), FAA, Transport Airplane 
Directorate.

New Requirements of This AD:

Inspections and Corrective Actions

    (c) If any cracking of the outer chord of the upper or lower 
cross beams of the aft cargo door is detected as a result of any 
inspection required by paragraph (a) 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 
Designated Engineering Representative who has been authorized by the 
FAA to make such findings.

[[Page 43953]]

    (d) Within 4,500 flight cycles or one year after the effective 
date of this AD, whichever occurs later: Perform a high frequency 
eddy current inspection (HFEC) to detect cracking of the four 
corners of the door frame of the aft cargo door, in accordance with 
the procedures specified in Boeing 737 Nondestructive Test Manual, 
Part 6, Chapter 51-00-00 (Figure 4 or Figure 23) .
    (1) If no cracking of the corners of the door frame of the aft 
cargo door is detected, repeat the HFEC inspections thereafter at 
intervals not to exceed 4,500 flight cycles until accomplishment of 
the modification specified in paragraph (e) of this AD.
    (2) If any cracking of the corners of the door frame of the aft 
cargo door is detected, prior to further flight, replace the damaged 
frame with a new frame, and modify the four corners of the door 
frame, in accordance with Parts II and III of the Accomplishment 
Instructions of Boeing Service Bulletin 737-52-1079, Revision 5, 
dated May 16, 1996. Accomplishment of such modification constitutes 
terminating action for the repetitive inspection requirements of 
paragraph (d)(1) of this AD for that door frame.

Terminating Action

    (e) Within 4 years after the effective date of this AD: Modify 
the four corners of the door frame and the cross beams of the aft 
cargo door, in accordance with Part II of the Accomplishment 
Instructions of Boeing Service Bulletin 737-52-1079, Revision 5, 
dated May 16, 1996. Accomplishment of such modification constitutes 
terminating action for the repetitive inspection requirements of 
this AD.

    Note 3: Accomplishment of the modification required by paragraph 
(a) of AD 90-06-02, amendment 39-6489, is considered acceptable for 
compliance with paragraph (e) of this AD.

    Note 4: Modification of the corners of the door frame and the 
cross beams of the aft cargo door accomplished prior to the 
effective date of this AD in accordance with Boeing Service Bulletin 
737-52-1079, dated December 16, 1983; Revision 1, dated December 15, 
1988; Revision 2, dated July 20, 1989; Revision 3, dated May 17, 
1990; or Revision 4, dated February 21, 1991; is considered 
acceptable for compliance with paragraph (e) of this AD.

Alternative Methods of Compliance

    (f)(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.
    (f)(2) Alternative methods of compliance, approved previously in 
accordance with AD 98-25-06, amendment 39-10931, are approved as 
alternative methods of compliance with this AD.

    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

    (g) Special flight permits may be issued in accordance with 
sections 21.197 and 21.199 of the Federal Aviation Regulations (14 
CFR 21.197 and 21.199) to operate the airplane to a location where 
the requirements of this AD can be accomplished.

    Issued in Renton, Washington, on August 6, 1999.
D.L. Riggin,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 99-20881 Filed 8-11-99; 8:45 am]
BILLING CODE 4910-13-P