[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