[Federal Register Volume 59, Number 82 (Friday, April 29, 1994)]
[Unknown Section]
[Page 0]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 94-10232]
[[Page Unknown]]
[Federal Register: April 29, 1994]
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DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 39
[Docket No. 93-NM-46-AD]
Airworthiness Directives; de Havilland Model DHC-8 Series
Airplanes
AGENCY: Federal Aviation Administration, DOT.
ACTION: Supplemental notice of proposed rulemaking; reopening of
comment period.
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SUMMARY: This document revises an earlier proposed airworthiness
directive (AD), applicable to certain de Havilland Model DHC-8 series
airplanes, that would have required repetitive inspections of the
passenger service unit (PSU) printed circuit boards and power supply
connectors to detect corrosion and evidence of overheating; and repair
or replacement of the circuit boards or replacement of connectors, if
necessary. That proposal was prompted by reports that certain PSU
printed circuit boards and power supply connectors have overheated in
service. This action revises the proposed rule by adding a required
terminating action for the repetitive inspections. The actions
specified by this proposed AD are intended to prevent overheating of
the PSU printed circuit board and power supply connectors, which could
lead to a fire in the PSU.
DATES: Comments must be received by May 31, 1994.
ADDRESSES: Submit comments in triplicate to the Federal Aviation
Administration (FAA), Transport Airplane Directorate, ANM-103,
Attention: Rules Docket No. 93-NM-46-AD, 1601 Lind Avenue, SW., Renton,
Washington 98055-4056. Comments may be inspected at this location
between 9 a.m. and 3 p.m., Monday through Friday, except Federal
holidays.
The service information referenced in the proposed rule may be
obtained from de Havilland, Inc., Garratt Boulevard, Downsview, Ontario
M3K 1Y5, Canada. This information may be examined at the FAA, Transport
Airplane Directorate, 1601 Lind Avenue, SW., Renton, Washington; or at
the FAA, Engine and Propeller Directorate, New York Aircraft
Certification Office, 181 South Franklin Avenue, room 202, Valley
Stream, New York.
FOR FURTHER INFORMATION CONTACT: Michele Maurer, Aerospace Engineer,
Systems and Equipment Branch, ANE-173, FAA, Engine and Propeller
Directorate, New York Aircraft Certification Office, 181 South Franklin
Avenue, room 202, Valley Stream, New York 11581; telephone (516) 791-
6428; fax (516) 791-9024.
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 93-NM-46-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-103, Attention: Rules
Docket No. 93-NM-46-AD, 1601 Lind Avenue, SW., Renton, Washington
98055-4056.
Discussion
A proposal to amend part 39 of the Federal Aviation Regulations (14
CFR part 39) to add an airworthiness directive (AD), applicable to de
Havilland Model DHC-8 series airplanes, was published as a notice of
proposed rulemaking (NPRM) in the Federal Register on May 25, 1993 (58
FR 30001). That NPRM would have required repetitive visual inspections
of the PSU printed circuit boards and power supply connectors to detect
corrosion and evidence of overheating. If any corrosion or evidence of
overheating of the circuit board is detected, the proposed AD would
have required the repair or replacement of the circuit board. If any
corrosion or evidence of overheating of the connectors is detected, the
proposed AD would have required replacement of the affected connector.
The proposed AD would also have required that all findings of corrosion
or overheating be reported to the manufacturer. That NPRM was prompted
by reports that certain PSU printed circuit boards and power supply
connectors have overheated in service. That condition, if not
corrected, could result in overheating of the PSU printed circuit board
and power supply connectors, which could lead to a fire in the PSU.
Since the issuance of that NPRM, the manufacturer has developed a
design modification that, if installed, would eliminate the need for
the proposed repetitive inspections. De Havilland has issued Service
Bulletin 8-33-34, dated August 10, 1993, that describes installation of
Modification 8/1950. Among other things, this modification entails
reworking the PSU to include a new circuit board cover, a modified
circuit board mounting, and new wire harnesses. Transport Canada
Aviation, which is the airworthiness authority for Canada, has approved
the technical content of this service bulletin and has issued revised
Canadian AD No. CF-93-01R1, dated December 3, 1993, to include the
modification described in the service bulletin as terminating action
for that AD.
This airplane model is manufactured in Canada and is type
certificated for operation in the United States under the provisions of
Sec. 21.29 of the Federal Aviation Regulations and the applicable
bilateral airworthiness agreement. Pursuant to this bilateral
airworthiness agreement, Transport Canada Aviation has kept the FAA
informed of the situation described above. The FAA has examined the
findings of Transport Canada Aviation, reviewed all available
information, and determined that AD action is necessary for products of
this type design that are certificated for operation in the United
States.
Since an unsafe condition has been identified that is likely to
exist or develop on other airplanes of the same type design registered
in the United States, the FAA has determined that the previously
proposed AD must be revised to require the installation of Modification
8/1950 as terminating action for the proposed repetitive inspections of
the PSU.
This determination to mandate installation of the modification is
based on the FAA's finding that long term continued operational safety
will be better assured by design changes to remove the source of the
problem, rather than by repetitive inspections. Long term inspections
may not be providing the degree of safety assurance necessary for the
transport airplane fleet. This, coupled with a better understanding of
the human factors associated with numerous continual inspections, has
led the FAA to consider placing less emphasis on inspections and more
emphasis on design improvements. The proposed modification requirement
is in consonance with these considerations.
Since this change expands 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.
Additionally, due consideration has been given to the following
comments received in response to the original notice:
Two commenters suggest that issuance of the proposed rule is
unnecessary. The commenters contend that the criteria for issuing a
regulation under Federal Aviation Regulations 39.1 (14 CFR 39.1),
specifically that the addressed condition ``is likely to exist or
develop on other airplanes of the same type,'' has not been met. These
commenters also report that their experience to date does not support
the need for issuance of this proposed rule. One of these commenters
suggests that the occurrences of overheated PSU's appear to have been
limited to only a few units and, possibly, to only one non-U.S.
operator that is operating in a unique environment. The commenter
questions whether there were any other factors that could have effected
the failure of these units, such as missing or improperly installed
insulation blankets, previous maintenance performed on the subject
units, etc.
The FAA does not concur with the commenters' suggestion that this
rule is unnecessary. Results of the investigation of the failure
scenarios, as performed by de Havilland, revealed that the ingress of
moisture through the PSU connectors is a situation that is not unique
to a specific airplane or operator; it is a situation that is common to
all Model DHC-8 airplanes due to their common design. It is true that
the one non-U.S. operator that experienced the failure does operate in
a high humidity environment, which may have contributed to creating the
worst corrosion/overheat incident reported to date. Operation of any
aircraft in that type of environment increases the chance of moisture
ingress that could lead to corrosion on the printed circuit board or
connectors, and to an excessive overheat condition or a potential fire
hazard, should such corrosion go undetected. Although the commenters
may not yet have experienced a severe corrosion problem in their
current operating environment, there is nothing restricting Model DHC-8
aircraft from being operated in an environment that is more conducive
to a moisture ingress and corrosion problem. The FAA concludes that,
based on the design of the Model DHC-8, the addressed unsafe condition
is likely to exist or develop on other airplanes of this same type.
One commenter requests that the proposed compliance time of 300
hours time-in-service or 30 days (whichever occurs later) for the
initial inspection be extended to at least 600 hours time-in-service.
The commenter considers the proposed compliance time to be too
stringent, especially in light of the fact that the PSU circuit board
overheat problem was first reported four years ago, in 1990. The FAA
does not concur. The addressed overheating problem is the result of
corrosion of the printed circuit board pins and connector interfaces.
Since corrosion is an agent that acts over time, it is important that
operators assess the severity of the corrosion on each applicable
airplane as expeditiously as possible; therefore, the initial
inspection interval of 300 hours time-in-service, as proposed, is
appropriate. The FAA does consider that operators who have performed
the initial action within the last 12 months should be provided
``credit'' for such action and has revised the proposed initial
compliance time to provide such credit.
Two commenters suggest that the proposed repetitive inspection
interval of 600 hours time-in-service is too conservative and should be
extended. These commenters request that the interval be changed to at
least 12 months. The commenters state that the addressed corrosion
situation results from condensation-induced moisture collecting on the
connector; however, since a water dispersing dielectric grease (a
corrosion inhibiting compound) is applied after the initial inspection,
it would serve to protect the area from any further corrosion for some
time. One of these commenters considers that any significant changes in
the corrosion status of the circuit board would be insignificant at the
proposed 600-hour interval (which equates to approximately 60 days for
most affected operators). One of these commenters indicates that it
already has completed the initial inspection of its fleet of 22 Model
DHC-8's and its findings have revealed that the corrosion is minor and
is not rapidly generated. The FAA concurs with the commenters' request,
based on the information provided. The notice has been revised to
specify a repetitive inspection interval of 12 months.
One commenter requests that the proposed rule provide a description
of the overheat damage for which inspection is made. The commenter
notes that there is a distinction between normal in-service
discoloration and overheat damage. The circuit board produces heat
through its normal operation, which causes a discoloration of the
circuit board's coating. Overheating would cause the board to show
exposed fibers and/or melted parts. The FAA concurs with the
commenter's request. A note has been added to the proposed rule to
describe the appearance of overheat damage.
One commenter states that the economic impact data presented in the
preamble to the NPRM was not completely accurate. This commenter notes
that the number of work hours necessary to perform the proposed
inspections is two work hours per aircraft, not per PSU, as the notice
indicated. The FAA acknowledges this correction, and has revised the
economic impact information, below, accordingly.
The FAA estimates that 133 Model DHC-8 series airplanes of U.S.
registry would be affected by this proposed AD.
The proposed inspections would take approximately 2 work hours per
airplane to accomplish, at an average labor rate of $55 per work hour.
Based on these figures, the total cost impact of the proposed
inspections on U.S. operators is estimated to be $14,630, or $110 per
airplane, per inspection.
The proposed modification would require approximately 2.25 work
hours per PSU to accomplish, at an average labor cost of $55 per work
hour. Required parts would cost approximately $61.50 per PSU. Each
airplane is equipped with between 18 and 26 PSU's. Based on these
figures, the total cost impact of the proposed modification on U.S.
operators is estimated to be $185.25 per PSU, or between $3,334.50 and
$4,816.50 per airplane.
The total 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. However, the
FAA has been advised that the proposed initial inspection has already
been accomplished on approximately 22 airplanes; therefore the future
economic impact of this proposed rule is reduced by at least $2,420.
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. 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:
De Havilland, Inc.: Docket 93-NM-46-AD.
Applicability: Model DHC-8 series airplanes, equipped with
passenger service units have part numbers 10-1418-1/2 and 10-1081-3/
-4/-5/-6; certificated in any category.
Compliance: Required as indicated, unless accomplished
previously. -
To prevent overheating of the passenger service unit (PSU)
printed circuit board and power supply connectors, which could lead
to a fire in the PSU, accomplish the following:
(a) Within 300 hours time-in-service after the effective date of
this AD, or within 30 days after the effective date of this AD, or
within 12 months after any previous inspection conducted prior to
the effective date in accordance with this paragraph, whichever
occurs later: Conduct a visual inspection of all PSU printed circuit
boards and power supply connectors to detect corrosion and evidence
of overheating, in accordance with paragraph III. of de Havilland
Alert Service Bulletin S.B. A8-33-30, Revision `A', dated December
18, 1992.
Note 1: The overheat condition referred to in this paragraph is
the discoloration of the printed circuit board around the connector
interfaces, and not the light conformal coating discoloration
resulting from the normal operation of high current devices mounted
on the printed circuit board.
(1) If no corrosion or evidence of overheating is detected,
repeat the inspection at intervals not to exceed 12 months.
(2) If any corrosion or evidence of overheating of the PSU
printed circuit board is detected as a result of any inspection,
prior to further flight, either repair or replace the PSU printed
circuit board in accordance with the service bulletin. Thereafter,
repeat the inspection at intervals not to exceed 12 months.
(3) If any corrosion or evidence of overheating of the power
supply connectors is detected as a result of any inspection, prior
to further flight, replace the affected power supply connector in
accordance with the service bulletin. Thereafter, repeat the
inspection at intervals not to exceed 12 months.
(b) Within 10 days after accomplishing each inspection required
by paragraph (a) of this AD, notify de Havilland, Inc., of all
findings of corrosion or overheating, in accordance with de
Havilland Alert Service Bulletin S.B. A8-33-30, Revision `A', dated
December 18, 1992. Information collection requirements contained in
this regulation have been approved by the Office of Management and
Budget (OMB) under the provisions of the Paperwork Reduction Act of
1980 (44 U.S.C. 3501 et seq.) and have been assigned OMB Control
Number 2120-0056.
(c) Within 24 months after the effective date of this AD,
install Modification 8/1950 in accordance with de Havilland Service
Bulletin 8-33-34, dated August 10, 1993. Installation of this
modification constitutes terminating action for the repetitive
inspections required by paragraph (a) of this AD.
(d) 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, New York Aircraft Certification
Office (ACO), FAA, Engine and Propeller Directorate. Operators shall
submit their requests through an appropriate FAA Principal
Maintenance Inspector, who may add comments and then send it to the
Manager, New York ACO.
Note 2: Information concerning the existence of approved
alternative methods of compliance with this AD, if any, may be
obtained from the New York ACO.
(e) Special flight permits may be issued in accordance with
Secs. 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 April 22, 1994.
S.R. Miller,
Acting Manager, Transport Airplane Directorate, Aircraft Certification
Service.
[FR Doc. 94-10232 Filed 4-28-94; 8:45 am]
BILLING CODE 4910-13-U
