Airworthiness Directives; de Havilland Model DHC-8-100 Series Airplanes

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 94-NM-06-AD]

Airworthiness Directives; de Havilland Model DHC-8-100 Series

Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: This document proposes the adoption of a new airworthiness

directive (AD) that is applicable to certain de Havilland Model DHC-8-

100 series airplanes. This proposal would require modification of the

potentiometer lever stops on the nose wheel steering. This proposal is

prompted by a report that the potentiometer stops installed currently

on these airplanes are too short to limit excessive uncontrolled

potentiometer movement in the event of a mechanical link failure. The

actions specified by the proposed AD are intended to prevent the

airplane from departing the runway during takeoff or landing in the

event of the failure of the mechanical link between the rudder pedals

and the potentiometer.

DATES: Comments must be received by June 1, 1994.

ADDRESSES: Submit comments in triplicate to the Federal Aviation

Administration (FAA), Transport Airplane Directorate, ANM-103,

Attention: Rules Docket No. 94-NM-06-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 Bombardier Inc., Bombardier Regional Aircraft Division,

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, Valley Stream, New York.

FOR FURTHER INFORMATION CONTACT: Bradford Chin, Electronics 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-

6427; 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 94-NM-06-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. 94-NM-06-AD, 1601 Lind Avenue, SW., Renton, Washington

98055-4056.

Discussion

Transport Canada Aviation, which is the airworthiness authority for

Canada, recently notified the FAA that an unsafe condition may exist on

certain de Havilland Model DHC-8-100 series airplanes. Transport Canada

Aviation advises that when a Model DHC-8 series airplane is in the high

speed taxi mode during takeoff or landing, nose gear steering is

limited to 7 degrees left or right of center and is controlled through

rudder pedal movement. Rotary movement of the rudder input quadrant is

transmitted to a dual potentiometer via a mechanical link and fork

lever. The potentiometer converts this movement into electrical

signals, which are sent to an electronic control unit (ECU) located in

the nose of the airplane. Subsequently, the ECU signals the electro-

hydraulic actuator on the nose gear, thereby rotating the nose gear in

the required direction.

If the mechanical link connecting the potentiometer to the rudder

input quadrant fails, excessive uncontrolled potentiometer lever

movement is restricted by small metal stops located outside the normal

angular travel of the fork lever. These ``potentiometer stops'' limit

the size of the signal sent to the ECU only in the event of a

mechanical link failure. On certain Model DHC-8-100 series airplanes,

the currently installed potentiometer stops are too short to restrict

excessive fork lever movement in the event of a mechanical link

failure. In this case, a signal that is too large would be sent to the

ECU, which could cause the nose gear to exceed its 7-degree limitation.

This condition, if not corrected, could result in the airplane

departing the runway during takeoff or landing.

Bombardier Inc. has issued de Havilland Service Bulletin S.B. 8-32-

99, Revision `A,' dated July 26, 1993, that describes procedures for

modification of the potentiometer lever stops on the nose wheel

steering (Modification 8/1809) on certain Model DHC-8-100 and -300

series airplanes. Accomplishment of this modification will restore

overtravel protection by relocating the potentiometer lever stops.

Relocation of the stops will ensure that excessive fork lever movement

is restricted in the event of a mechanical link failure. Transport

Canada Aviation classified this service bulletin as mandatory and

issued Canadian Airworthiness Directive (AD) No. CF-93-24, dated

September 29, 1993, in order to assure the continued airworthiness of

these airplanes in Canada.

Although the effectivity of the service bulletin includes certain

Model DHC-8-100 and -300 series airplanes, Canadian AD No. CF-93-24 is

applicable only to certain Model DHC-8-100 series airplanes. The

service bulletin states that the potentiometer stops on certain Model

DHC-8-300 series airplanes are contacted by the lever prematurely,

resulting in deformation of the stops. However, the FAA has been

advised that, although deformation of the potentiometer stops on these

airplanes can occur, excessive potentiometer lever movement would still

be restricted in the event of failure of a mechanical link. In light of

this information, the FAA finds that Model DHC-8-300 series airplanes

are not subject to the addressed unsafe condition.

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 proposed AD would require modification of the

potentiometer lever stops on the nose wheel steering. The actions would

be required to be accomplished in accordance with the service bulletin

described previously.

The FAA estimates that 48 airplanes of U.S. registry would be

affected by this proposed AD, that it would take approximately 3 work

hours per airplane to accomplish the proposed actions, and that the

average labor rate is $55 per work hour. The cost for required parts

would be minimal. Based on these figures, the total cost impact of the

proposed AD on U.S. operators is estimated to be $7,920, or $165 per

airplane.

The total cost impact figure discussed above is 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.

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 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:

De Havilland, Inc.: Docket 94-NM-06-AD.

Applicability: Model DHC-8-102, -103, and -106 airplanes, serial

numbers 003 through 334 inclusive; certificated in any category.

Compliance: Required as indicated, unless accomplished

previously.

To prevent the airplane from departing the runway during takeoff

or landing, accomplish the following:

(a) Within 6 months after the effective date of this AD, modify

the potentiometer lever stops on the nose wheel steering in

accordance with de Havilland Service Bulletin S.B. 8-32-99, Revision

``A,'' dated July 26, 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, 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: Information concerning the existence of approved

alternative methods of compliance with this AD, if any, may be

obtained from the New York ACO.

(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.

Issued in Renton, Washington, on April 1, 1994.

S.R. Miller,

Acting Manager, Transport Airplane Directorate, Aircraft Certification

Service.

[FR Doc. 94-8326 Filed 4-6-94; 8:45 am]

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