[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: 

------------------------------------------------------------------------
                                Revision                                
                                  level                                 
           Page No.             shown on        Date shown on page      
                                  page                                  
------------------------------------------------------------------------
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