[Federal Register Volume 64, Number 105 (Wednesday, June 2, 1999)]
[Proposed Rules]
[Pages 29602-29606]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 99-13877]


=======================================================================
-----------------------------------------------------------------------

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 98-NM-150-AD]
RIN 2120-AA64


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

AGENCY: Federal Aviation Administration, DOT.

ACTION: Supplemental notice of proposed rulemaking; reopening of 
comment period.

-----------------------------------------------------------------------

SUMMARY: This document revises an earlier proposed airworthiness 
directive (AD), applicable to certain Boeing Model 737-100, -200, -300, 
-400, and -500 series airplanes, that would have required repetitive 
testing of certain main tank fuel boost pumps to identify those with 
degraded performance, and replacement of degraded pumps with new or 
serviceable pumps. That originally proposed AD also would have required 
eventual replacement of the existing low pressure switches for boost 
pumps located in the main fuel tanks with higher threshold low pressure 
switches, which, when accomplished, would terminate the repetitive 
testing. That proposal was prompted by reports of engine power loss 
caused by unsatisfactory performance of the fuel boost pumps. This new 
action revises the proposed rule by reducing the compliance time for 
certain airplanes. The actions specified by this new proposed AD are 
intended to prevent fuel suction feed operation on both engines without 
flight crew indication, and possible consequent multiple engine power 
loss.

DATES: Comments must be received by June 28, 1999.

ADDRESSES: Submit comments in triplicate to the Federal Aviation 
Administration (FAA), Transport Airplane Directorate, ANM-114, 
Attention: Rules Docket No. 98-NM-150-AD, 1601 Lind Avenue, SW., 
Renton, Washington 98055-4056. Comments may be inspected at this 
location between 9:00 a.m. and 3:00 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: 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:

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 98-NM-150-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. 98-NM-150-AD, 1601 Lind Avenue, SW., Renton, Washington 
98055-4056.

[[Page 29603]]

Discussion

    A proposal to amend part 39 of the Federal Aviation Regulations (14 
CFR part 39) to add an airworthiness directive (AD), applicable to 
certain Boeing Model 737-100, -200, -300, -400, and -500 series 
airplanes, was published as a notice of proposed rulemaking (NPRM) in 
the Federal Register on August 10, 1998 (63 FR 42596). That NPRM would 
have required repetitive testing of certain main tank fuel boost pumps 
to identify those with degraded performance, and replacement of 
degraded pumps with new or serviceable pumps. That NPRM also would have 
required eventual replacement of the existing low pressure switches for 
boost pumps located in the main fuel tanks with higher threshold low 
pressure switches, which, when accomplished, would terminate the 
repetitive testing. That NPRM was prompted by reports of engine power 
loss caused by unsatisfactory performance of the fuel boost pumps. That 
condition, if not corrected, could result in fuel suction feed 
operation on both engines without flight crew indication, and possible 
consequent multiple engine power loss.

Clarification of this Supplemental NPRM

    The FAA clarifies in this supplemental NPRM that any description of 
the relationship between the low pressure switches and the fuel pump 
assembly does not imply that those switches are part of the fuel pump 
assembly.

Comments

    Due consideration has been given to the comments received in 
response to the NPRM.

Request to Address All Fuel Pumps

    One commenter questions whether the proposed AD applies to fuel 
boost pumps other than those of the three manufacturers [i.e., Thompson 
Ramo Wooldridge (TRW), Argo-Tech, and General Electric Company (GEC)] 
identified in the proposed AD. The FAA infers that the commenter 
requests that the final rule be revised to include additional boost 
pumps to ensure that all possible pump configurations are addressed.
    The FAA concurs. The FAA agrees that all pump configurations on 
affected Boeing Model 737 series airplanes may be subject to the 
identified unsafe condition. In the originally proposed rule, the FAA 
addressed only currently certified pumps [GEC (formerly Plessey), TRW, 
and Argo-Tech]. However, in order to also consider additional pump 
types that may become certified in the future, the FAA has revised the 
groups affected by this AD to distinguish only ``GEC fuel pumps'' 
[paragraph (a)] and ``non-GEC fuel pumps'' [paragraph (b)].

Request to Revise Actions and Compliance Time for Certain Airplanes

    One commenter, a manufacturer of fuel boost pumps, requests that 
the actions and compliance times specified in the originally proposed 
rule apply to TRW and Argo-Tech pumps equally, based on the pumps' 
similarity and use of many common parts. The commenter reports that it 
builds TRW pumps with Argo-Tech nameplates.
    The FAA concurs with this request and rationale. As stated 
previously, new paragraph (b) of this supplemental NPRM would apply to 
all non-GEC fuel pumps, which includes both TRW and Argo-Tech fuel 
pumps. Fuel pumps manufactured by TRW or Argo-Tech are identified as 
``Argo-Tech/TRW'' pumps in this supplemental NPRM. This supplemental 
NPRM proposes a uniform compliance time of 2 years for all fuel pumps.

Conclusion

    Since these changes expand the scope of the originally proposed 
rule, the FAA has determined that it is necessary to reopen the comment 
period to provide additional opportunity for public comment.

Additional Comments Received

    The following are additional comments to the originally proposed 
rule, with the FAA's responses to those comments.

Support for the Proposal

    One commenter has no objection to the originally proposed rule. 
Another commenter states its intention to comply with the requirements 
of the originally proposed rule.

Request for Name Correction

    One commenter requests that the final rule identify ``Thompson Ramo 
Wooldridge,'' rather than ``Thompson Rand Wooldridge,'' as the correct 
name of the pump manufacturer. The FAA acknowledges this correction and 
has included the correct name in this supplemental NPRM.

Requests to Revise Compliance Time

    Several commenters discussed the compliance periods in the proposed 
rule.
    1. One commenter, a foreign civil airworthiness authority, 
indicates that a 2-year compliance period should be applied to all 
pumps regardless of the manufacturer, because the primary concern of 
the proposed AD is not the pump type but undetected low fuel delivery 
pressure.
    The FAA concurs with this request. As stated previously, this 
supplemental NPRM has been revised to apply the same compliance times 
for all pump types. In the originally proposed rule, the FAA proposed a 
compliance time of 3 years for airplanes equipped with TRW pumps to 
accommodate the fleetwide demand for parts (approximately 12,000 
pressure switches will be required), recognizing that the degraded mode 
of operation has not been observed to date on boost pumps other than 
those manufactured by GEC. However, in light of the amount of time that 
has elapsed since the originally proposed rule was issued, the FAA 
finds it likely that all parts will be available within the 2-year 
compliance time.
    2. Another commenter, an association of airline pilots, recommends 
a 1-year compliance time for airplanes equipped with boost pumps 
manufactured by GEC and a 2-year compliance time for all other affected 
airplanes. The commenter provides no justification for its request.
    As explained previously, the FAA has revised the compliance times 
for all airplanes to 2 years. The FAA does not concur with the request 
to reduce the compliance time to 1 year. Sufficient parts will not be 
available to support a 1-year incorporation period for the GEC pumps. 
In addition, the unsafe condition does not warrant the excessive amount 
of industry disruption that would result from a 1-year compliance time. 
In developing an appropriate compliance time, the FAA considered the 
safety implications, parts availability, and normal maintenance 
schedules for timely replacement of the low pressure switches. In 
consideration of all of these factors, the FAA determined that the 
compliance time, as proposed, represents an appropriate interval in 
which replacement of the switches can be accomplished in a timely 
manner within the fleet, while still maintaining an adequate level of 
safety. Operators are permitted to accomplish the requirements of an AD 
at a time earlier than that specified as the compliance time; 
therefore, if an operator elects to accomplish the switch replacement 
prior to the end of the compliance period (2 years after the effective 
date of this AD), it is that operator's prerogative to do so. If 
additional data are presented that would justify a shorter compliance 
time, the FAA may consider further rulemaking on this issue.

[[Page 29604]]

    3. Another commenter, the airplane manufacturer, recommends that 
compliance times be based on airplane model (i.e., 2 years for Model 
737-300, -400, and -500 series airplanes; 3 years for Model 737-100 and 
-200 series airplanes), rather than boost pump type. The commenter 
provides no justification for its request.
    The FAA does not concur. No certification tests have been conducted 
confirming that Boeing Model 737-100 and -200 series airplanes are less 
susceptible to power loss on suction feed operation than Boeing Model 
737-300, -400, and -500 series airplanes. No change to the originally 
proposed rule in this regard is necessary.

Requests to Revise Applicability

    One commenter, the airplane manufacturer, requests that Boeing 
Model 737-100 and -200 series airplanes equipped with Argo-Tech/TRW 
pumps be excluded from the applicability statement of the originally 
proposed rule. In support of its request, the commenter states that 
there is no known history of problems with pressure degradation with 
Argo-Tech/TRW pumps, and no fleet experience of engine power loss 
events on Model 737-100 and -200 series airplanes due to the low 
threshold pressure switches. The manufacturer concludes that the data 
do not indicate that modification of airplanes equipped with Argo-Tech/
TRW pumps would improve safety.
    The FAA does not concur with the commenter's request to revise the 
applicability of this AD. The FAA recognizes that Argo-Tech/TRW fuel 
boost pumps have not exhibited pressure degradation to the extent that 
pump performance is affected. However, the unsafe condition addressed 
by this final rule is not limited to the causes of degraded pump output 
pressure. The FAA's determination of the unsafe condition is based on 
the fact that airplanes may transition to suction feed operation 
without an indication to the flight crew. With the currently installed 
low pressure switches, this transition may occur on any Boeing Model 
737-100, -200, -300, -400, or -500 series airplane. In addition, the 
FAA notes that no testing of in-service Boeing Model 737 series 
airplanes operating on suction feed fuel has been conducted to ensure 
proper operation during all phases of flight. In fact, the limited 
information available to the FAA and the airplane manufacturer 
regarding suction feed operation on Boeing Model 737 series airplanes 
indicates that the engines will experience power loss during particular 
phases of flight. This is true for both types of engines--on new as 
well as older airplanes. The FAA considers dual engine power loss to be 
an unsafe condition. No change to the applicability of this 
supplemental NPRM is necessary.

Request to Revise Repetitive Interval

    One commenter recommends that the boost pump pressure tests be 
repeated at intervals of 90 days rather than 6 months. This commenter 
provides no justification for its request.
    The FAA does not concur with the request to reduce the repetitive 
test interval. Based on the apparent gradual nature of pump 
degradation, the FAA has determined that the 6-month interval for the 
repetitive pressure tests is sufficient to verify acceptable pump 
performance and detect gradual pump degradation. Therefore, no change 
to the originally proposed rule in this regard is required.

Request to Remove Minimum Equipment List (MEL) Restriction

    One commenter, the airplane manufacturer, requests that the FAA 
remove the restriction on dispatch with the main tank boost pumps 
inoperative. The commenter indicates that the restriction would 
unnecessarily ground airplanes that are operating under the MEL. 
Alternatively, the commenter recommends a minimum amount of time (after 
the effective date of the AD) before the restriction becomes active. 
The commenter states that a 90-day compliance time for the initial test 
is sufficient to ensure that tests are completed in a timely manner. 
The commenter explains that such a grace period would ensure that no 
airplanes are grounded.
    The FAA does not concur with the commenter's request to remove the 
MEL restriction. The FAA cannot allow dispatch with inoperative boost 
pumps unless the assumed operative pump can be shown to be operating in 
a nondegraded mode. This restriction will prevent possible dispatch on 
suction feed operation. In addition, the FAA does not concur with the 
commenter's request for a grace period before restricting dispatch. In 
its efforts to prevent grounding airplanes, the FAA has considered 
several issues. The alert service bulletin informing operators of this 
potential condition (Boeing Alert Service Bulletin 737-28A1114) was 
issued October 30, 1997, and the FAA has determined that this initial 
testing has been completed on almost all U.S.-registered airplanes. In 
addition, any remaining airplanes on which initial testing has not been 
completed may be tested during overnight stops. Further, operators have 
had sufficient time to position spares to prevent grounding airplanes. 
Therefore, no change to the originally proposed NPRM in this regard is 
necessary.

Request to Apply Life Limits to Boost Pumps

    One commenter, an association of airline pilots, requests that the 
FAA impose appropriate life limiting measures to GEC-manufactured fuel 
boost pumps to minimize the possibility of significant degradation of 
pump performance. The commenter further requests that the FAA add a 
requirement to modify GEC pumps to eliminate the corrosion problem.
    The FAA does not concur with the requests. The FAA finds that this 
degraded mode condition is expected to affect less than 10% of GEC-
manufactured pumps. The FAA anticipates that the overwhelming majority 
of GEC boost pumps will not require replacement. Therefore, the FAA 
does not consider that imposing life limits on the pumps is an 
appropriate action at this time. In addition, the FAA finds that 
replacement of the low pressure switches with improved higher threshold 
pressure switches will ensure that low pump output pressure will be 
indicated properly and addressed to prevent engine operation on suction 
feed. Despite these findings, it should be noted that GEC has indicated 
its full intent to provide improved boost pumps to replace pumps that 
exhibit degraded mode operation, and in fact is implementing a retrofit 
plan to replace degraded pumps with improved pumps. The FAA's method to 
ensure that all pumps are performing to specification is to require 
periodic pressure tests and eventual replacement of the low pressure 
switches with higher threshold pressure switches. No change to this 
proposed AD in this regard is necessary.

Request for Revision of Parts Cost

    One commenter, the airplane manufacturer, requests that the cost 
impact information of the originally proposed rule be revised to 
clarify parts cost and responsibility. The commenter requests deletion 
of the incorrect claim that parts would be provided by the manufacturer 
at no cost to operators. The manufacturer also provides cost estimates 
for replacement switches.
    The FAA concurs with the commenter's request and acknowledges that 
the originally proposed rule implies that replacement parts will be 
provided at no cost by the manufacturer. The FAA's intent was that the 
originally proposed rule indicate that no parts cost would be 
associated with testing of the fuel boost pumps. The cost impact

[[Page 29605]]

information of this proposed AD has been revised to include the cost 
estimates for replacement switches provided by the manufacturer.

Request to Revise Compliance Time to Credit Work Accomplished

    One commenter, the airplane manufacturer, requests clarification of 
the compliance time specified as ``within 90 days after the effective 
date of the AD'' for the proposed requirement to perform initial 
testing of the boost pump. The commenter recommends that the compliance 
language be revised to ``Prior to 90 days after the effective date of 
this AD. * * *'' The commenter questions whether operators would be 
considered to be in compliance if they performed the initial tests 
prior to the effective date of the AD, or whether they would be 
required to repeat those tests.
    The FAA does not consider that a change to this supplemental NPRM 
is necessary in this regard. The FAA recognizes the commenter's concern 
regarding the 90-day compliance time for the initial test. Operators 
are given credit for work previously performed by means of the phrase 
in the Compliance section of the AD that states, ``Required as 
indicated, unless accomplished previously.'' Therefore, in the case of 
this supplemental NPRM, if the initial inspection has been accomplished 
previously (i.e., prior to the effective date of the AD), this 
supplemental NPRM would not require that the inspection be repeated. 
However, this supplemental NPRM does propose to require that repetitive 
tests be performed thereafter at intervals not to exceed 6 months, for 
airplanes equipped with GEC fuel pumps, and that the other follow-on 
actions be accomplished as necessary.

Request for Clarification of Power Loss Events

    One commenter, the airplane manufacturer, requests that the FAA 
clarify the description of the engine power loss events to indicate 
that they occurred only on airplanes equipped with GEC pumps and that 
total power loss occurred on only one engine of an affected airplane.
    The FAA agrees that the Discussion section of the proposed rule may 
have been unclear regarding whether both engines on affected airplanes 
experienced power losses.
    The FAA acknowledges that power loss events have been reported on 
only one engine per airplane, that these events occurred only on 
airplanes equipped with GEC fuel boost pumps, and that no cases of dual 
engine power loss have been reported.

Request for Clarification of the Unsafe Condition

    One commenter requests that the proposed AD be revised to clarify 
whether ``products'' refers to airplanes or to fuel boost pumps in the 
statement ``. . . an unsafe condition is likely to exist or develop on 
other products of the same type design.''
    The FAA recognizes that the cited statement may have been unclear 
in the context of the originally proposed rule. By this statement, the 
FAA is addressing airplanes of the same type design as the Boeing Model 
737 series airplanes on which the engine power loss events occurred.

Request to Require Improved Pumps

    One commenter recommends that airplanes ``equipped with one or more 
of the subject GEC fuel pumps should be required to be equipped with at 
least one Argo-Tech, TRW, or new-design (if/when available) GEC fuel 
pump at the most critical position (if applicable) in each main tank 
within 2 years.'' The FAA infers that the commenter requests that GEC 
pumps be replaced with improved pumps within 2 years. The commenter 
provides no justification for its recommendation.
    The FAA does not concur with the commenter's request. The FAA has 
determined that the vast majority of GEC boost pumps will not 
experience such pump degradation. Therefore, a requirement to replace 
those boost pumps is considered an unjustifiable burden to operators. 
No change to this supplemental NPRM in this regard is necessary.

Request for Clarification of Requirements

    One commenter requests that the originally proposed rule be revised 
to clarify certain requirements. The commenter suggests that additional 
text be included under the heading ``Differences Between Proposed Rule 
and Service Bulletin'' to further specify those Argo-Tech/TRW fuel 
pumps that are affected by paragraphs (b) and (c) of the originally 
proposed rule.
    The FAA concurs partially. The FAA agrees that further 
specification of the parts numbers of the affected fuel pumps might 
have clarified certain proposed requirements; however, as stated 
previously, paragraphs (b) and (c) of the originally proposed rule have 
been revised to remove any distinction between Argo-Tech and TRW fuel 
pumps and to group them with ``non-GEC fuel pumps.''

Request for Clarification of Design Responsibility

    One commenter, the pump manufacturer, requests that the FAA clarify 
in the Discussion section that the low pressure switches are not part 
of the fuel pump assembly or within the pump manufacturer's control.
    The FAA concurs with the commenter's request. Although there was no 
intent in the originally proposed rule to imply such a relationship, 
the FAA acknowledges that low pressure switches are not part of the 
fuel pump assembly and has revised the Discussion section of this 
supplemental NPRM accordingly.

Request for a Review of Other Airplane Models

    One commenter, an association of airline pilots, recommends that 
the FAA conduct a review to determine whether similar incompatibilities 
between fuel system low pressure switches and check valves exist 
elsewhere in the transport airplane fleet. The commenter expressed 
concern that additional airplane models may be susceptible to the 
unsafe condition identified in the proposed rule.
    The FAA concurs with the commenter's request. The FAA has completed 
a review of large transport airplanes manufactured by Airbus, Boeing, 
and Lockheed. A deficiency in the low fuel pressure indication has not 
been identified on any of those other airplane models.

Additional Change to this Supplemental NPRM

    The FAA notes that it may be necessary to clarify the proposed 
criteria for allowing dispatch with a main tank fuel boost pump 
inoperative. As a result, paragraph (a)(1) of this supplemental NPRM 
has been revised to specify that, prior to dispatch, the operative pump 
must be tested and any necessary follow-on corrective actions 
performed.

Cost Impact

    There are approximately 2,772 airplanes of the affected design in 
the worldwide fleet. The FAA estimates that 1,140 airplanes of U.S. 
registry would be affected by this proposed AD.
    It would take approximately 2-8 work hours per airplane to 
accomplish the proposed testing for airplanes equipped with GEC pumps, 
at an average labor rate of $60 per work hour. Based on these figures, 
the cost impact of the testing proposed by this AD on U.S. operators is 
estimated to be $120-$480 per airplane, per testing cycle.

[[Page 29606]]

    It would take approximately 4-6 work hours per airplane to 
accomplish the proposed modification, at an average labor rate of $60 
per work hour. Required parts would cost $1,900 [for airplanes equipped 
with part number (P/N) 60B92400-3 low pressure switches] or $2,700 (for 
airplanes equipped with P/N 10-3067-3 low pressure switches). Based on 
these figures, the cost impact of the modification proposed by this AD 
on U.S. operators is estimated to be $273,600-$410,400, or $2,140-
$3,060 per airplane.
    The cost impact figures discussed above are 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 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 adding the following new 
airworthiness directive:

Boeing: Docket 98-NM-150-AD.

    Applicability: Model 737-100, -200, -300, -400, and -500 series 
airplanes; line numbers 1 through 3002 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 (c) 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 fuel suction feed operation on both engines without 
flight crew indication, and possible consequent multiple engine 
power loss, accomplish the following:

Requirements for Airplanes Equipped with GEC Boost Pumps:

    (a) For airplanes equipped with one or more main tank fuel boost 
pumps manufactured by the General Electric Company (GEC), of the 
United Kingdom: Accomplish paragraphs (a)(1), (a)(2), (a)(3), and 
(a)(4) of this AD.
    (1) As of the effective date of this AD, no airplane shall be 
dispatched with any main tank fuel boost pump inoperative unless the 
initial testing and any follow-on corrective actions required by 
paragraph (a)(2) of this AD have been accomplished on the operative 
pump in that main tank.
    (2) Test each GEC-manufactured main tank fuel boost pump to 
determine the output pressure, in accordance with Boeing Alert 
Service Bulletin 737-28A1114, Revision 1, dated April 2, 1998; at 
the later of the times specified in paragraphs (a)(2)(i) and 
(a)(2)(ii) of this AD. If the fuel boost pump output pressure 
measured during the testing required by this paragraph is less than 
23 pounds per square inch gauge (psig), as measured at the input to 
the engine fuel pump; or less than 36 psig, as measured at the fuel 
boost pump low pressure switch; prior to further flight, replace the 
fuel boost pump with a new or serviceable fuel pump, in accordance 
with the alert service bulletin.
    (i) Prior to the accumulation of 3,000 total flight hours, or 
within 1 year since date of manufacture of the airplane, whichever 
occurs first; or
    (ii) Within 90 days after the effective date of this AD.
    (3) Repeat the testing required by paragraph (a)(2) of this AD 
thereafter at intervals not to exceed 6 months, until accomplishment 
of the requirements of paragraph (a)(4) of this AD.
    (4) Within 2 years after the effective date of this AD, replace 
all four low pressure switches installed downstream of the main tank 
fuel boost pumps with higher threshold low pressure switches, in 
accordance with Boeing Alert Service Bulletin 737-28A1114, Revision 
1, dated April 2, 1998. Accomplishment of this replacement 
constitutes terminating action for the requirements of paragraph (a) 
of this AD.

Requirements for Airplanes Equipped with non-GEC boost pumps:

    (b) For airplanes other than those identified in paragraph (a) 
of this AD: Within 2 years after the effective date of this AD, 
replace all four low pressure switches installed downstream of the 
main tank fuel boost pumps with higher threshold low pressure 
switches, in accordance with Boeing Alert Service Bulletin 737-
28A1114, Revision 1, dated April 2, 1998.

Alternative Methods of Compliance

    (c) 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

    (d) 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 May 21, 1999.
D.L. Riggin,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 99-13877 Filed 6-1-99; 8:45 am]
BILLING CODE 4910-13-P