[Federal Register Volume 66, Number 165 (Friday, August 24, 2001)]
[Proposed Rules]
[Pages 44561-44562]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 01-21496]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 98-NM-353-AD]
RIN 2120-AA64


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

AGENCY: Federal Aviation Administration, DOT.

ACTION: Proposed rule; withdrawal.

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SUMMARY: This action withdraws a notice of proposed rulemaking (NPRM) 
that proposed a new airworthiness directive (AD), applicable to certain 
Boeing Model 737-100, -200, -300, -400, and -500 series airplanes. That 
action would have required modification of certain filter module 
assemblies of the generator control units (GCU). Since the issuance of 
the NPRM, the Federal Aviation Administration (FAA) has received new 
data that indicate that the unsafe condition identified in the NPRM 
does not exist. Accordingly, the proposed rule is withdrawn.

FOR FURTHER INFORMATION CONTACT: Forrest Keller, Senior Aerospace 
Engineer, Systems and Equipment Branch, ANM-130S, FAA, Seattle Aircraft 
Certification Office, 1601 Lind Avenue, SW., Renton, Washington 98055-
4056; telephone (425) 227-2790; fax (425) 227-1181.

SUPPLEMENTARY INFORMATION: A proposal to amend part 39 of the Federal 
Aviation Regulations (14 CFR part 39) to add a new airworthiness 
directive (AD),

[[Page 44562]]

applicable to certain Boeing Model 737-100, -200, -300, -400, and -500 
series airplanes, was published in the Federal Register as a Notice of 
Proposed Rulemaking (NPRM) on March 5, 1999 (64 FR 10578). The proposed 
rule would have required modification of certain filter module 
assemblies of the generator control units (GCU). That action was 
prompted by reports of smoke and occasional fire in the flight 
compartment as a direct result of a GCU failure. The proposed actions 
were intended to prevent failure of the filter module assemblies of the 
GCUs due to overcurrent conditions, which could result in an increased 
risk of smoke, and/or fire in the flight compartment.

Actions Since Issuance of the NPRM

    The NPRM proposed to require modification of certain filter module 
assemblies of the GCUs to prevent smoke and/or fire in the flight 
compartment due to overcurrent conditions in the GCUs. Since the 
issuance of the NPRM, the manufacturer has advised the FAA that there 
have been no reports of fire as a result of GCU overcurrent conditions. 
The manufacturer has further advised that GCUs that were examined and/
or repaired by the supplier have shown no evidence of fire. In those 
cases where fires were reported, the manufacturer asserts that the 
erroneous identification of an actual fire had been inferred from the 
presence of smoke, which resulted from unrelated conditions and did not 
represent a hazard to the airplane.
    In addition, the modifications proposed by the NPRM may have 
contributed, in part, to an event that occurred on a Model 737-200 
series airplane during which all electrical power was lost in flight. 
As a result of that incident, the FAA issued AD 99-18-17, amendment 39-
11283 (64 FR 47656, September 1, 1999), which was later superseded by 
AD 99-24-08, amendment 39-11432 (64 FR 66368, November 26, 1999), to 
require, among other things, repetitive testing of GCU diodes and 
repetitive replacement of airplane batteries. In this case, the attempt 
to minimize the incidence of smoke resulted in an increased probability 
of a total loss of electrical power. Total loss of electrical power 
represents a greater hazard to the airplane, and the information 
provided by the manufacturer indicates that the existing GCUs are 
adequate to ensure the safety of the fleet.

FAA's Conclusions

    Upon further consideration of the above information, the FAA has 
determined that the hazard associated with GCU overcurrent conditions 
does not justify a requirement to modify the filter module. The FAA has 
further determined that incorporation of the proposed modifications 
could actually decrease the reliability of the electrical power system. 
Accordingly, the proposed rule is hereby withdrawn.
    Withdrawal of this NPRM constitutes only such action, and does not 
preclude the agency from issuing another action in the future, nor does 
it commit the agency to any course of action in the future.

Regulatory Impact

    Since this action only withdraws a notice of proposed rulemaking, 
it is neither a proposed nor a final rule and therefore is not covered 
under Executive Order 12866, the Regulatory Flexibility Act, or DOT 
Regulatory Policies and Procedures (44 FR 11034, February 26, 1979).

List of Subjects in 14 CFR Part 39

    Air transportation, Aircraft, Aviation safety, Safety.

The Withdrawal

    Accordingly, the notice of proposed rulemaking, Docket 98-NM-353-
AD, published in the Federal Register on March 5, 1999 (64 FR 10578), 
is withdrawn.

    Issued in Renton, Washington, on August 20, 2001.
Vi L. Lipski,
Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 01-21496 Filed 8-23-01; 8:45 am]
BILLING CODE 4910-13-P