Transport Canada Civil Aviation (TCCA), which is the airworthiness authority for Canada, recently notified the FAA that an unsafe condition may exist on certain Bombardier Model DHC-8-400, -401, and -402 series airplanes. TCCA advises that the flight crew of a Bombardier Model DHC-8-400 series airplane experienced difficulties in extending the right main landing gear (MLG) following a gear-down selection. During that event, when subsequent use of the alternate landing gear extension procedure failed to extend the affected gear, the MLG was retracted and a second alternate gear extension was performed. This resulted in the MLG successfully extending to the down and locked position.
Inspection of the MLG revealed a groove in the lower jaw of the uplock hook on the MLG uplock assembly due to premature wear. Findings indicate that excessive wear to the uplock hook could prevent release of the roller, and the inability to extend the MLG with either the normal, or alternate, landing gear extension procedure. Findings also indicate that the low friction (black-colored) liner of the uplock rollers was omitted on a batch lot of uplock rollers, including the subject airplane.
Conditions that could cause failure of the MLG to extend, following a gear-down selection, include the absence of an uplock roller, absence of an approved liner, or presence of an unapproved or damaged uplock roller. These conditions, if not corrected, could result in the inability of the flight crew to extend the MLG, which could result in a gear-up landing and possible injury to passengers and crew.
Explanation of Relevant Service Information
Bombardier has issued DHC-8 Alert Service Bulletin A84-32-15, dated February 4, 2002, which describes procedures for a one-time inspection of the inside surface of the uplock roller on the shock strut of the MLG for the presence of an inner low friction (black-colored) liner, and corrective actions if necessary. If a low friction liner is present, operators may reinstall the existing uplock roller, or replace the uplock roller with a new uplock roller having a low friction liner. If the bore of the uplock roller has a bright metal finish, indicating the absence of a liner, operators must replace the existing uplock roller with a new uplock roller having a low friction liner. In addition, the alert service bulletin references Chapter 32-11-01, dated January 5, 2001, of Bombardier Series 400 Aircraft Maintenance Manual (AMM), PSM 1-84-2, as a secondary source of service information for replacing the MLG uplock roller with a new roller having a low friction liner.
Chapter 32-31-21, dated January 5, 2001, of Bombardier Series 400 AMM, PSM 1-84-2, describes procedures for replacing existing MLG uplock assemblies with new assemblies.
Transport Canada Civil Aviation (TCCA), which is the airworthiness authority for Canada, has issued Canadian airworthiness directive CF-2002-13, dated February 4, 2002, to assure the continued airworthiness of these airplanes in Canada. That airworthiness directive specifies procedures for revising the Airplane Flight Manual (AFM); replacing the left and right MLG uplock assemblies with new assemblies per Chapter 32-31-21 of Bombardier Series 400 AMM, PSM 1-84-2; and inspecting the uplock roller, and taking corrective action if necessary.
FAA's Conclusions
These airplane models are manufactured in Canada and are type certificated for operation in the United States under the provisions of Sec. 21.29 of the Federal Aviation Regulations (14 CFR 21.29) and the applicable bilateral airworthiness agreement. Pursuant to this bilateral airworthiness agreement, the TCCA has kept the FAA informed of the situation described above. The FAA has determined that the primary cause of the failure of the right MLG to extend and the uplock assembly to disengage, following a gear-down selection, is the design of the uplock assembly. However, we also consider that the uplock roller, which involves a quality control problem, may have contributed to such failure. The FAA has examined the findings of the TCCA, 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.
Explanation of Requirements of Rule
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 require a revision to the Limitations section, and certain paragraphs of the Normal and Alternate Extension Procedures, of the FAA-approved AFM, to advise the flight crew of appropriate procedures to follow in the event that an MLG fails to extend following a gear-down selection; replacement of the left and right MLG uplock assemblies; and a one-time inspection of the left and right MLG uplock rollers for the presence of an inner low friction liner, and corrective actions if necessary. The actions required by this AD must be accomplished per the alert service bulletin and the AMM, except as described below.
Differences Between Alert Service Bulletin, and the Canadian Airworthiness Directive and This AD
The Bombardier alert service bulletin specifies procedures only for an inspection of the left and right MLG uplock rollers, and corrective actions if necessary. However, in addition to that procedure, the Canadian airworthiness directive and this AD also specify procedures for revising the AFM and replacing the MLG uplock assemblies.
Differences Between the Canadian Airworthiness Directive and This AD
The Canadian airworthiness directive specifies inspection/replacement of the left and right MLG uplock rollers per Bombardier DHC-8 Alert Service Bulletin A84-32-15, dated February 4, 2002, "or later revisions of the alert service bulletin." However, paragraph (c) of this AD requires accomplishment of the one-time inspection of the MLG uplock rollers, and corrective actions if necessary, per the alert service bulletin, dated February 4, 2002. Where a specific service bulletin is referenced in an AD, the use of the phrase "or later revisions of the service bulletin," violates Office of the Federal Register regulations regarding approval of materials that are incorporated by reference, and, therefore may not be specified in this AD.
Interim Action
This is considered to be interim action. Bombardier has advised that it is currently evaluating a possible modification to the uplock assembly to minimize wear to the uplock hook and to ensure a more positive uplock release, which will positively address the unsafe condition addressed by this AD. Once this modification is developed, approved, and available, the FAA may consider additional rulemaking.
Determination of Rule's Effective Date
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.
Submit comments using the following format:
Organize comments issue-by-issue. For example, discuss a request to change the compliance time and a request to change the service bulletin reference as two separate issues.
For each issue, state what specific change to the AD is being requested.
Include justification (e.g., reasons or data) for each request.
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, stampedpostcard on which the following statement is made: "Comments to Docket Number 2002-NM-35-AD." The postcard will be date stamped and returned to the commenter.
Regulatory Impact
The regulations adopted herein will not have a substantial direct effect 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, it is determined that this final rule does not have federalism implications under Executive Order 13132.
The FAA has determined that this regulation is an emergency regulation that must be issued immediately to correct an unsafe condition in aircraft, and that it 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. 106(g), 40113, 44701.
Sec. 39.13 [Amended]
2. Section 39.13 is amended by adding the following new airworthiness directive: