[Federal Register Volume 59, Number 67 (Thursday, April 7, 1994)]
[Unknown Section]
[Page 0]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 94-8326]


[[Page Unknown]]

[Federal Register: April 7, 1994]


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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]
BILLING CODE 4910-13-U