Events Leading to This AD
The FAA has received several reports of the parking brake valve inadvertently slipping to the "PARK" position during flight on Air Tractor Models AT-250, AT-300, AT-301, AT-302, AT-400, AT-400A, AT-401, AT-402, AT-501, and AT-502 airplanes. When the parking brake is in the "PARK" position, a constant pressure is applied to the brakes, which cannot be relieved or reduced when the pilot removes pressure from the brake pedals. This pressure builds to the point that when the pilot applies the brake upon landing to slow the airplane, the airplane overturns.
The airplanes in the incidents described above were equipped with Gerdes part number (P/N) A-850-5 or Cleveland P/N 60-9 parking brake valves. The FAA has determined that these Gerdes or Cleveland parking brake valves should be replaced with Scott parking brake valves, P/N 4500A-2, on certain Air Tractor Models AT-250, AT-300, AT-301, AT-302, AT-400, AT-400A, AT-401, AT-402,AT-501, and AT-502 airplanes.
Applicable Service Information
Air Tractor has issued Snow Engineering Co. Service Letter #76, dated December 12, 1988, which specifies replacing Gerdes part number A-850-5 and Cleveland P/N 60-9 parking brake valves with Scott parking brake valves, P/N 4500A-2. Air Tractor Service Letter #76 Instructions specify procedures for accomplishing this parking brake valve replacement.
The FAA's Determination
After examining the circumstances and reviewing all available information related to the incidents described above, including the referenced service information, the FAA has determined that AD action should be taken to prevent the airplane from overturning because of extreme pressure applied to the brake if the parking brake valve inadvertently slips to the "PARK" position during flight.
Explanation of the Provisions of This AD
Since an unsafe condition has been identified that is likely to exist or develop in other Air Tractor Models AT-250,AT-300, AT-301, AT-302, AT-400, AT-400A, AT-401, AT-402, AT-501, and AT-502 airplanes of the same type design that are equipped with a Gerdes (P/N) A-850-5 or Cleveland P/N 60-9 parking brake valve, the FAA is implementing AD action. This AD requires replacing these Gerdes or Cleveland parking brake valves with a Scott P/N 4500A-2 parking brake valve. Accomplishment of this replacement is in accordance with Air Tractor Service Letter #76 Instructions, as referenced in Snow Engineering Co. Service Letter #76, dated December 12, 1988.
Since a situation exists (possibility of the airplane overturning during landing) that requires the immediate adoption of this regulation, it is found that notice and opportunity for public prior 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 immediate flight safety and,thus, was not preceded by notice and opportunity to 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 should 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 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 forexamination 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 No. 96-CE-49 -AD." The postcard will be date stamped and returned to the commenter.
Regulatory Impact
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 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 (otherwise, an evaluation is not required). A copy of it, if filed, may be obtained from the Rules Docket.
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 USC 106(g), 40113, 44701.
Section 39.13 - [AMENDED]
2. Section 39.13 is amended by adding a new airworthiness directive (AD) to read as follows: