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

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

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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]

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