Airworthiness Directives; de Havilland Model DHC-8 Series Airplanes

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.

-----------------------------------------------------------------------

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