The Rijksluchtvaartdienst (RLD), which is the airworthiness authority for the Netherlands, recently notified the FAA that an unsafe condition may exist on all Fokker Model F28 Mark 0100 and Model F28 Mark 0070 series airplanes. The RLD advises that it has received a report that a diode failed on a Fokker Model F28 Mark 0100 series airplane. The flightcrew had no indication of this failure until the battery voltage dropped below a certain value. The RLD also advises that it has received another similar report, but on a Fokker Model Mark 0070 series airplane, in which the circuit breaker of the transformer rectifier unit No. 3 of the emergency direct current (DC) bus supply tripped; this situation resulted in an oscillating behavior of the electrical relays, causing the failure of not only the systems powered by the emergency DC bus, but also of the systems powered by the emergency alternating current (AC) bus. The cause of these failures is unknown at this time.
Failure of a diode in the emergency DC bus supply could result in a battery drain, and the loss of the emergency DC bus and the subsequent loss of all systems powered by it. If the circuit breaker of the transformer rectifier unit No. 3 of the emergency DC bus supply trips, the resultant oscillations of the electrical relays could result in loss of both the emergency DC bus and emergency AC bus; this situation could lead to loss of on-side displays, autopilot, pressure control, and all communications, which could reduce the ability of the flightcrew to control the airplane.
Fokker has developed procedural information, for inclusion in the Airplane Flight Manual (AFM) of the affected airplanes, that will enable the flight crew to identify failures of the emergency DC/AC bus power supply and to take appropriate corrective actions. The RLD classified this AFM material as mandatory, and issued Dutch airworthiness directive BLA 1995-089/2 (A), dated September 29, 1995, inorder to assure the continued airworthiness of these airplanes in the Netherlands.
This airplane model is manufactured in the Netherlands and is type certificated for operation in the United States under the provisions of section 21.29 of the Federal Aviation Regulations (14 CFR 21.29) and the applicable bilateral airworthiness agreement. Pursuant to this bilateral airworthiness agreement, the RLD has kept the FAA informed of the situation described above. The FAA has examined the findings of the RLD, 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 ensure that the flightcrew is advised of the potential hazard related to failures of the emergency DC/AC bus power supply, and the procedures necessary to address it. This AD requires revising the Abnormal and Normal Procedures sections of the FAA-approved AFM to include information that will enable the flightcrew to identify failures of the emergency DC/AC bus power supply and to take appropriate procedures necessary to address it.
This is considered to be interim action. The manufacturer has advised it currently is developing a modification that will positively address the unsafe condition addressed by this AD. Once this modification is developed, approved, and available, the FAA may consider additional rulemaking.
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-179-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 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, 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), 40101, 40113, 44701.
39.13 - [Amended]
2. Section 39.13 is amended by adding the following new airworthiness directive: