Airworthiness Directives; British Aerospace Model BAe 146-100A, - 200A, and -300A Series Airplanes

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