[Federal Register Volume 64, Number 223 (Friday, November 19, 1999)]
[Rules and Regulations]
[Pages 63178-63180]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 99-29737]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 99-NM-47-AD; Amendment 39-11416; AD 99-23-20]
RIN 2120-AA64


Airworthiness Directives; Boeing Model 737-100, -200, -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 certain Boeing Model 737-100, -200, -300, -400, and -500 
series airplanes. For certain airplanes, this AD requires installation 
of a transient suppression diode in the wiring circuit of the refueling 
valve-to-float switch of each fuel tank. For certain other airplanes, 
this AD requires replacement of the existing transient suppression 
diode with an improved diode. This AD also requires a functional test 
to verify proper installation of each diode, and corrective action, if 
necessary. This amendment is prompted by incidents of electrical fire 
during fueling of the airplane, due to a short circuit and overheating 
of a transient suppression diode. The actions specified by this AD are 
intended to prevent such conditions, which could result in electrical 
arcing and ignition of fuel vapors at the refueling receptacle for the 
fuel tanks, and consequent fire during airplane fueling.

DATES: Effective December 27, 1999.
    The incorporation by reference of certain publications listed in 
the regulations is approved by the Director of the Federal Register as 
of December 27, 1999.

ADDRESSES: The service information referenced in this AD may be 
obtained from Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, 
Washington 98124-2207. This information may be examined at the Federal 
Aviation Administration (FAA), Transport Airplane Directorate, Rules 
Docket, 1601 Lind Avenue, SW., Renton, Washington; or at the Office of 
the Federal Register, 800 North Capitol Street, NW., suite 700, 
Washington, DC.

FOR FURTHER INFORMATION CONTACT: Dorr Anderson, Aerospace Engineer, 
Propulsion Branch, ANM-140S, FAA, Transport Airplane Directorate, 
Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, 
Washington 98055-4056; telephone (425) 227-2684; fax (425) 227-1181.

SUPPLEMENTARY INFORMATION: A proposal to amend part 39 of the Federal 
Aviation Regulations (14 CFR part 39) to include an airworthiness 
directive (AD) that is applicable to certain Boeing Model 737-100, -
200, -300, -400, and -500 series airplanes was published in the Federal 
Register on June 14, 1999 (64 FR 31762). That action proposed to 
require, for certain airplanes, installation of a transient suppression 
diode in the wiring circuit of the refueling valve-to-float switch of 
each fuel tank. For certain other airplanes, the proposal would require 
replacement of the existing transient suppression diode with an 
improved diode. The proposal also would require a functional test to 
verify proper installation of each diode, and corrective action, if 
necessary.

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 Revise Cost Estimate

    Two commenters request that the FAA revise the cost estimate and 
the number of hours required to complete the installation or 
replacement. One commenter states that the estimated material cost 
alone, based on Boeing's quoted price for the wire kit, is $800. The 
other commenter states that the kit price is $1,106. In addition, one 
commenter estimates that 12 work hours are required to modify an 
airplane while another commenter estimates that 16 work hours are 
required to complete the modification. One of the commenters indicates 
that additional time is required to gain access to the transient 
suppression diodes, close up the area, and perform functional testing.
    The FAA partially concurs. The cost estimate for required parts has 
been increased to $800 per airplane from $50 per airplane, using the 
kit price that the commenter states is based upon Boeing's quoted 
price. The FAA work hour estimate has been increased to 12 work hours 
from 7 hours based upon information supplied by the commenters. 
However, the FAA is not

[[Page 63179]]

increasing the work hour estimate to account for functional testing 
since this has already been accounted for in the work hour estimate in 
the manufacturer's service bulletin. The final rule has been revised to 
incorporate the above changes in the cost estimate.

Request to Extend Compliance Time

    Three commenters request that the compliance period be extended to 
18 months from 12 months. Two commenters state that the circuit that 
includes the transient suppression diode is only powered on the ground 
during fueling and has no function in the air. One of the commenters 
also notes that the same circuit is affected by AD 99-05-12, which 
requires either deactivation of the circuit or installation of double 
teflon sleeving over the float switch wiring for the center fuel tank 
to prevent a possible short in the system. A third commenter notes that 
extending the compliance time to 18 months will allow for diode 
replacement at the same time as the replacement of the float switch 
wiring for the center fuel tank (per AD 99-05-12).
    Another commenter indicates that extending the compliance period to 
18 months will allow for installation or replacement (as applicable) 
during the next ``C'' check. In addition, this commenter states that 
the compliance time should be extended to account for the airplane 
manufacturer's estimate of a 300-day lead time for kits listed in the 
service bulletin.
    The FAA does not concur with the commenters' request to extend the 
compliance time. The FAA agrees that the circuit which includes the 
transient suppression diode is powered only on the ground during 
fueling and has no function in the air. However, this fact does not 
nullify the safety hazard posed by overheating of the transient 
suppression diode. During the comment period for the proposed AD, an 
overheated transient suppression diode caused another fire during 
fueling. Although the fire was extinguished before extensive damage 
occurred, the FAA finds that this condition is a significant safety 
hazard.
    With regard to the comment that installation of an improved 
transient suppression diode should be performed at the same time as 
modification of wiring for the center tank float switch in accordance 
with AD 99-05-12, the actions required by the two AD's are performed in 
different locations on the airplane and do not have a direct bearing on 
each other. Additionally, the compliance threshold for AD 99-05-12 is 
30,000 flight hours. The FAA estimates that there are more than 2,000 
airplanes that currently have fewer than 30,000 flight hours, and 
operators of those airplanes are not required to modify the wiring of 
the center tank float switch in accordance with AD 99-05-12 until the 
airplanes have accumulated 30,000 flight hours. The FAA finds that 
extending the compliance threshold for this AD to 30,000 flight hours, 
to allow for installation of an improved transient suppression diode at 
the same time as modification of wiring for the center tank float 
switch, is inappropriate because it would not address the identified 
unsafe condition in a timely manner.
    The FAA has determined that a 12-month compliance period, as 
proposed, is warranted. The manufacturer has advised that an ample 
number of required parts will be available for installation in the U.S. 
fleet within the compliance period. The manufacturer indicated that the 
300-day-lead-time quote was a standard quote for this type of part. 
However, production schedules have been modified to support this AD. 
The improved transient suppression diodes are being produced at a rate 
of 1,500 per month to ensure availability within the 12-month 
compliance period. In developing an appropriate compliance time for 
this action, the FAA considered not only the degree of urgency 
associated the addressing the subject unsafe condition, but the 
availability of required parts and the practical aspect of installing 
the required modification within an interval of time that parallels 
normal scheduled maintenance for the majority of affected operators. No 
change to the final rule is necessary in this regard.

Request to Develop a New Transient Suppression Diode

    One commenter requests that the FAA require the airplane 
manufacturer to develop a transient suppression diode with better 
mechanical protection from stresses to prevent possible overheating. 
The commenter states that the improved transient suppression diode is 
made of the same components as the existing diode, with essentially the 
same manufacturing process and the same mechanical protection (heat-
shrunk plastic sleeving); only the arrangement of the wiring is 
different. The commenter states that the lack of significant changes to 
the design may result in more failures of the improved diodes (due to 
damage during installation) than if the existing diodes had been left 
in place.
    The FAA does not concur. The manufacturer has made production 
changes to eliminate the stress conditions which occurred in the 
existing diode design. Based upon the production changes, the FAA does 
not anticipate that variation in installation will lead to failures of 
the improved diode as the commenter suggests. The improved diodes have 
been used on other Boeing model airplanes. A review of the service 
history on the improved diodes on other Boeing model airplanes confirms 
that they do not have a history of failure in service. 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 2,897 airplanes of the affected design in 
the worldwide fleet. The FAA estimates that 1,126 airplanes of U.S. 
registry will be affected by this AD.
    For all airplanes, it would take approximately 12 work hours per 
airplane to accomplish the replacement or installation (as applicable) 
and the functional test to verify proper installation, at an average 
labor rate of $60 per work hour. Required parts would cost 
approximately $800 per airplane. Based on these figures, the cost 
impact of the AD on U.S. operators is estimated to be $1,711,520 or 
$1,520 per airplane.
    The cost impact figure discussed above is based on assumptions that 
no operator has yet accomplished any of the 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 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.
    For the reasons discussed above, I certify that this action (1) is 
not a ``significant regulatory action'' under

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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:

    99-23-20 Boeing: Amendment 39-11416. Docket 99-NM-47-AD.

    Applicability: Model 737-100, -200, -300, -400, and -500 series 
airplanes; line numbers 1 through 3016 inclusive; 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 a short circuit and overheating of the transient 
suppression diode, which could result in electrical arcing and 
ignition of fuel vapors at the fueling receptacle for the fuel 
tanks, and consequent fire during airplane fueling, accomplish the 
following:

Corrective Action

    (a) For Group 1 airplanes, as identified in Boeing Service 
Bulletin 737-28-1115, dated March 4, 1999: Within 12 months after 
the effective date of this AD, install a transient suppression 
diode, part number (P/N) 69-58806-4, in the wire bundle (W264) of 
the refueling valve-to-float switch of each fuel tank, in accordance 
with the service bulletin.
    (b) For Groups 2, 3, and 4 airplanes, as identified in Boeing 
Service Bulletin 737-28-1115, dated March 4, 1999: Within 12 months 
after the effective date of this AD, replace the existing transient 
suppression diode, P/N 69-58806-1 or 69-58806-3, installed in the 
wire bundle (W264) of the refueling valve-to-float switch of each 
fuel tank, with an improved diode, P/N 69-58806-4, in accordance 
with the service bulletin.
    (c) Prior to further flight following accomplishment of the 
actions required by paragraph (a) or (b) of this AD, perform a 
functional test to verify proper installation of each diode in 
accordance with Boeing Service Bulletin 737-28-1115, dated March 4, 
1999. If any discrepancy is detected during any functional test, 
prior to further flight, replace the discrepant diode and repeat the 
functional test, in accordance with the service bulletin.

Spares Paragraph

    (d) As of the effective date of this AD, no person shall install 
a transient suppression diode having P/N 69-58806-1 or 69-58806-3 on 
any airplane.

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 
used if approved by the Manager, Seattle Aircraft Certification 
Office (ACO), FAA, Transport Airplane Directorate. 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 2: 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) The corrective actions shall be done in accordance with 
Boeing Service Bulletin 737-28-1115, dated March 4, 1999. This 
incorporation by reference was approved by the Director of the 
Federal Register in accordance with 5 U.S.C. 552(a) and 1 CFR part 
51. Copies may be obtained from Boeing Commercial Airplane Group, 
P.O. Box 3707, Seattle, Washington 98124-2207. Copies may be 
inspected at the FAA, Transport Airplane Directorate, 1601 Lind 
Avenue, SW., Renton, Washington; or at the Office of the Federal 
Register, 800 North Capitol Street, NW., suite 700, Washington, DC.
    (h) This amendment becomes effective on December 27, 1999.

    Issued in Renton, Washington, on November 4, 1999.
D.L. Riggin,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 99-29737 Filed 11-18-99; 8:45 am]
BILLING CODE 4910-13-P