[Federal Register Volume 59, Number 56 (Wednesday, March 23, 1994)]
[Unknown Section]
[Page 0]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 94-4835]
[[Page Unknown]]
[Federal Register: March 23, 1994]
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DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 39
[Docket No. 93-NM-144-AD; Amendment 39-8846; AD 94-05-08]
Airworthiness Directives; British Aerospace Model BAe 146-100A, -
200A, and -300A 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 British Aerospace Model BAe 146-100A, -200A, and
-300A series airplanes, that requires modification of the electrical
power supply system. This amendment is prompted by a report that a
single phase fault current can cause sequential failure of all onboard
main electrical generators. The actions specified by this AD are
intended to prevent such failures and subsequent loss of electrical
power sources onboard the airplane.
DATES: Effective April 22, 1994.
The incorporation by reference of certain publications listed in
the regulations is approved by the Director of the Federal Register as
of April 22, 1994.
ADDRESSES: The service information referenced in this AD may be
obtained from British Aerospace, PLC, Librarian for Service Bulletins,
P.O. Box 17414, Dulles International Airport, Washington, DC. 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: William Schroeder, Aerospace Engineer,
ANM-113, FAA, Transport Airplane Directorate, 1601 Lind Avenue, SW.,
Renton, Washington 98055-4056; telephone (206) 227-2148; fax (206) 227-
1320.
SUPPLEMENTARY INFORMATION: A proposal to amend part 39 of the Federal
Aviation Regulations to include an airworthiness directive (AD) that is
applicable to certain British Aerospace Model BAe 146-100A, -200A, and
-300A series airplanes was published in the Federal Register on October
13, 1993 (58 FR 52929). That action proposed to require modification of
the electrical power supply system.
Interested persons have been afforded an opportunity to participate
in the making of this amendment. Due consideration has been given to
the comments received.
One commenter supports the proposal.
Another commenter notes that a statement in the preamble to the
notice, which indicated that the cause of the subject single phase
fault currents ``had not been determined,'' was inaccurate. This
commenter advises that, following the original incident, an
investigation by the airplane manufacturer revealed that the cause was
due to the loosening of an adjustment locking nut in a remote control
circuit breaker (RCCB) that caused one phase of the 3-phase power
supply to remain energized. Replacement of the RCCB's was recommended
by British Aerospace Service Bulletin SB.24-69-70484A, Revision 1,
which was the subject of AD 91-04-07, Amendment 39-6899 (56 FR 5751,
February 13, 1991). Therefore, the cause of the original failure has
been determined and rectified. However, there may be other fault causes
that have not been identified; it is for this reason that the proposed
modification of the generator control unit (GCU) is necessary so that
the GCU can better handle failures of this type without causing the
loss of all primary electric power sources. The FAA acknowledges this
information.
This same commenter also points out that certain wording in the
preamble to the notice that described the addressed unsafe condition
could be misinterpreted. The statement indicates that a single fault in
one phase of a 3-phase power supply can cause ``sequential failure of
all onboard main electrical generators and subsequent loss of
electrical power sources onboard the airplane.'' The commenter states
that it is unlikely that all generated power will be lost, however,
since these airplanes have a hydraulically-driven standby generator
that could provide essential AC and DC current if all main generators
fail. The FAA concurs with this observation. However, since loss of all
main generators has been determined to be an unsafe condition, the
requirements of this rule are intended to address that condition.
This commenter also states that the description of the referenced
British Aerospace service bulletin in the preamble to the notice was
incomplete. This commenter states that, while British Aerospace Service
Bulletin SB.24-91-70488B&C does describe installation Modification
HCM70488B, which is the only modification referenced in the proposed AD
for mandatory installation, it also describes two other modifications:
Modification HCM70488C (which must be installed concurrently with
Modification HCM70488B) deletes the neutral connection from the Vickers
electrically-driven hydraulic pump; and Modification HCM01321A,
although not classified as mandatory, introduces into the GCU's
improved standard components that have a higher reliability. The
commenter also notes that Modification HCM70488B adds an unbalanced
current detector circuit into the GCU's, in addition to replacing the
lowest phase detector type undervoltage protection circuit with an
average voltage sensing detector circuit. The FAA acknowledges this
information.
This same commenter requests that the proposed compliance time of
3,100 hours time-in-service be revised to ``December 15, 1995,'' since
the referenced British Aerospace service bulletin recommends that
airplanes be modified by that date. The manufacturer of the required
modification parts has estimated that it will take until that date to
accomplish the modification of all of the affected GCU's worldwide. In
light of this, the commenter states that it is possible that operators
who accumulate 3,100 hours prior to December 15, 1995, may not be able
to obtain the required modified units. The FAA does not concur that a
change to the compliance time is necessary. It is the FAA's normal
policy to use a calendar date as a compliance time only when a direct
analytical relationship can be established between that date and
failure of subject component. In developing an appropriate compliance
times for AD actions, the FAA normally takes into account the safety
implications, the fleet's average utilization rate, logistical support
considerations (parts availability, repair facility availability),
normal maintenance schedules for timely accomplishment of the
modification, and parameters to which failure of subject component is
related. The FAA took into account all of these factors, as well as the
manufacturer's recommended time for modification installation, and has
determined that 3,100 flight hours is the appropriate compliance time
interval. Since the average operating time for most of the affected
U.S.-registered Model BAe 146 series airplanes is 148 hours per month,
most U.S. operators will have accumulated 3,100 flight hours by
approximately December 15, 1995.
This commenter also requests that the proposed rule be revised to
cite the latest revision of the referenced service bulletin. British
Aerospace has issued Service Bulletin SB.24-91-70488B&C, Revision 2,
dated July 19, 1993, which provides additional details concerning the
effectivity listing in the service bulletin. This revision also
specifies that the Model BAe 146RJ series of airplanes are not affected
by the service bulletin. The FAA concurs and has revised the final rule
to include this later revision of the referenced service bulletin as an
additional source of service information.
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 change previously
described. The FAA has determined that this change will neither
increase the economic burden on any operator nor increase the scope of
the AD.
The FAA estimates that 49 airplanes of U.S. registry will be
affected by this AD, that it will take approximately 4 work hours per
airplane to accomplish the required actions, and that the average labor
rate is $55 per work hour. Based on these figures, the total cost
impact of the AD on U.S. operators is estimated to be $10,780, or $220
per airplane.
The total cost impact figure discussed above is based on
assumptions that no operator has yet accomplished any of the
requirements of this AD action, and that no operator would accomplish
those actions in the future if this AD were not adopted.
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 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 14 CFR part
39 of the Federal Aviation Regulations as follows:
PART 39--AIRWORTHINESS DIRECTIVES
1. The authority citation for part 39 continues to read as follows:
Authority: 49 U.S.C. App. 1354(a), 1421 and 1423; 49 U.S.C.
106(g); and 14 CFR 11.89.
Sec. 39.13 [Amended]
2. Section 39.13 is amended by adding the following new
airworthiness directive:
94-05-08 British Aerospace: Amendment 39-8846. Docket 93-NM-144-AD.
Applicability: Model BAe 146-100A, -200A, and -300A series
airplanes, on which Modification HCM70488B has not been
accomplished, certificated in any category.
Compliance: Required as indicated, unless accomplished
previously.
To prevent sequential failure of all onboard main electrical
generators and subsequent loss of electrical power sources onboard
the airplane, accomplish the following:
(a) Within 3,100 hours time-in-service after the effective date
of this AD, modify the electrical power supply system by installing
Modification HCM70488B in accordance with British Aerospace Service
Bulletin SB.24-91-70488B&C, Revision 1, dated March 29, 1993, or
Revision 2, dated July 19, 1993.
(b) 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, Standardization Branch, ANM-113,
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,
Standardization Branch, ANM-113.
Note: Information concerning the existence of approved
alternative methods of compliance with this AD, if any, may be
obtained from the Standardization Branch, ANM-113.
(c) Special flight permits may be issued in accordance with
Federal Aviation Regulations (FAR) 21.197 and 21.199 to operate the
airplane to a location where the requirements of this AD can be
accomplished.
(d) The modification shall be done in accordance with British
Aerospace Service Bulletin SB.24-91-70488B&C, Revision 1, dated
March 29, 1993; or British Aerospace Service Bulletin SB.24-91-
70488B&C, Revision 2, dated July 19, 1993, which contains the
following list of effective pages:
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Revision
level
Page No. shown on Date shown on page
page
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1............................. 2 July 19, 1993
2............................. 2 (none)
3-10.......................... 1 (none)
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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 British Aerospace, PLC,
Librarian for Service Bulletins, P.O. Box 17414, Dulles
International Airport, Washington, DC. 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.
(e) This amendment becomes effective on April 22, 1994.
Issued in Renton, Washington, on February 25, 1994.
Darrell M. Pederson,
Acting Manager, Transport Airplane Directorate, Aircraft Certification
Service.
[FR Doc. 94-4835 Filed 3-22-94; 8:45 am]
BILLING CODE 4910-13-U
