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-8-102, -103, and -106 series airplanes equipped with Safe Flight stall warning computers having part number (P/N) 3605-4, -5, or -6, and on which Modification 8/2072 has not been installed. Transport Canada Aviation advises that, during a routine "air mode" test of the stall warning system, the stick shakers did not activate. Investigation revealed that the weight-on-wheels relay contacts within the stall warning computer had become contaminated. This condition, if not corrected, could lead to incorrect logic detection of the weight-on-wheels signal, and subsequent loss of the stick shaker function.
Bombardier has issued Alert Service Bulletin S.B. A8-27-73, dated November 25, 1993, which describes procedures for repetitive operational testing to ensure activation of the stick shakers of the No. 1 and No. 2 stall warning computers, and replacement of non-operational stall warning computers with new or serviceable units. Transport Canada Aviation classified the alert service bulletin as mandatory and issued Canadian airworthiness directive CF-95-06, dated April 10, 1995, in order to assure the continued airworthiness of these airplanes in Canada.
Bombardier has also issued Service Bulletin S.B. 8-27-76, dated October 31, 1994, which describes procedures for replacing Safe Flight stall warning computers having P/N 3506-5, -6, or -7 with new stall warning computers having P/N 3506-8 (Modification 8/2072). The new stall warning computers have additional internal monitoring; installation of the new computers will increase reliability. Accomplishment of this replacement would eliminate the need for the repetitive operational tests.
This airplane model is manufactured in Canada and is type certificated for operation in the United States under the provisionsof section 21.29 of the Federal Aviation Regulations (14 CFR 21.29) 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, this AD is being issued to detect contamination of the weight-on-wheels relay contacts in the stall warning computer; such contamination could lead to incorrect logic detection of the weight-on-wheels signal, and subsequent loss of the stick shaker function. This AD requires repetitive operational testing of the No. 1 and No. 2 stall warning computers to ensure activation of the associated stick shaker, and replacement of non-operational stall warning computers with new units. This AD also provides an optional terminating action for the repetitive operational test requirements. The actions are required to be accomplished in accordance with the service bulletins described previously.
The FAA is considering further rulemaking action to require the replacement of Safe Flight stall warning computers with units having P/N 3506-8. However, the proposed compliance time (6 months) for this replacement is sufficiently long so that notice and time for public comment would be practicable.
As a result of recent communications with the Air Transport Association (ATA) of America, the FAA has learned that, in general, some operators may misunderstand the legal effect of AD's on airplanes that are identified in the applicability provision of the AD, but that have been altered or repaired in the area addressed by the AD. TheFAA points out that all airplanes identified in the applicability provision of an AD are legally subject to the AD. If an airplane has been altered or repaired in the affected area in such a way as to affect compliance with the AD, the owner or operator is required to obtain FAA approval for an alternative method of compliance with the AD, in accordance with the paragraph of each AD that provides for such approvals. A note has been included in this rule to clarify this long-standing requirement.
Since a situation exists that requires the immediate adoption of this regulation, it is found that notice and opportunity for prior public comment hereon are impracticable, and that good cause exists for making this amendment effective in less than 30 days.
Comments Invited
Although this action is in the form of a final rule that involves requirements affecting flight safety and, thus, was not preceded by notice and an opportunity for public comment, comments are invited on this rule.Interested persons are invited to comment on this 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 under the caption "ADDRESSES." All communications received on or before the closing date for comments will be considered, and this rule may be amended in light of the comments received. Factual information that supports the commenter's ideas and suggestions is extremely helpful in evaluating the effectiveness of the AD action and determining whether additional rulemaking action would be needed.
Comments are specifically invited on the overall regulatory, economic, environmental, and energy aspects of the rule that might suggest a need to modify the 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 that summarizes each FAA-public contact concerned with the substance of this AD will be filed in the Rules Docket.
Commenters wishing the FAA to acknowledge receipt of their comments submitted in response to this rule must submit a self-addressed, stamped postcard on which the following statement is made: "Comments to Docket Number 95-NM-104-AD." The postcard will be date stamped and returned to the commenter.
The regulations adopted herein will 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 final rule does not have sufficient federalism implications to warrant the preparation of a Federalism Assessment.
The FAA has determined that this regulation is an emergency regulation that must be issued immediately to correct an unsafe condition in aircraft, and thatit is not a "significant regulatory action" under Executive Order 12866. It has been determined further that this action involves an emergency regulation under DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979). If it is determined that this emergency regulation otherwise would be significant under DOT Regulatory Policies and Procedures, a final regulatory evaluation will be prepared and placed in the Rules Docket. A copy of it, if filed, may be obtained from the Rules Docket at the location provided under the caption "ADDRESSES."
List of Subjects in 14 CFR Part 39
Air transportation, Aircraft, Aviation safety, Incorporation by reference, Safety.
Adoption of the Amendment
Accordingly, pursuant to the authority delegated to me by the Administrator, the Federal Aviation Administration amends 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.
39.13 - [Amended]
2. Section 39.13 is amended by adding the following new airworthiness directive: