On December 5, 1996, the FAA issued AD 96-24-10, amendment 39-9850 (61 FR 66890, December 19, 1996), applicable to all Fokker Model F28 Mark 0070 and 0100 series airplanes. That AD superseded AD 96-23-16, amendment 39-9825 (61 FR 5887, November 20, 1996). AD 96-24-10 requires a revision to the Limitations Section of the FAA-approved Airplane Flight Manual (AFM) to enable the flightcrew to determine if the thrust reversers are properly stowed and locked prior to take-off by monitoring proper engagement of the autothrottle system (ATS). It also allows dispatch of the airplane with both thrust reversers inoperative provided they are deactivated and secured in the stowed position, and no operations are conducted that are predicated on thrust reverser operation. In addition, that AD requires a revision to the FAA-approved maintenance program to incorporate instructions to correct malfunctions of the secondary lock relay 1 of the thrust reversers found duringthe operational tests; to perform a daily check to detect latent failure of the secondary lock actuator switch 1; and to take corrective actions, if necessary.
That action was prompted by results of a review and safety assessment of the thrust reverser control and indication system, which indicated that a potential latent failure of the secondary lock actuator switch 1 in the open position may occur in addition to the potential failure of the secondary lock relay 1 in the energized position addressed by AD 96-23-16.
The actions required by AD 96-24-10 are intended to prevent such failures, which could result in reduced protection against inadvertent deployment of the thrust reversers during flight.
In the preamble to AD 96-24-10, the FAA indicated that the actions required by that AD were considered to be "interim action" and that further rulemaking action was being considered. The FAA now has determined that further rulemaking action is indeed necessary, and this AD follows from that determination.
New Service Information from the Manufacturer
Fokker issued Service Bulletin SBF100-78-012, dated November 22, 1996, which describes procedures for modification of the wiring of the electrical control, and indication and warning systems of the thrust reversers. This modification involves changing the wiring of the stow limit relay of the thrust reverser, which will prevent inadvertent loss of the thrust reverser stow signal during certain failure conditions (i.e., bypasses the stow limit relay to ensure that the stow solenoid is energized at all times regardless of the position of the secondary lock actuator switch 1, except during commanded deployment of the thrust reverser). This modification also involves changing the wiring of the flight warning computer (FWC), which will prevent unintended inhibition of the thrust reverser warning (i.e., bypasses the warning switch of the secondary lock relay 1). Accomplishment of this modification will eliminate the need for the revisions to the AFM and maintenance program (currently required by AD 96-24-10).
In addition, accomplishment of this modification will slightly increase the electrical loads on the emergency direct current (DC) bus on Fokker Model F28 Mark 0070 and 0100 series airplanes. The load margin for Fokker Model F28 Mark 0100 series airplanes is adequate to sustain the additional electrical loads created by accomplishment of Service Bulletin SBF100-78-012; however, Fokker Model F28 Mark 0070 series airplanes do not have an adequate load margin to sustain these additional loads. Therefore, Fokker Service Bulletin SBF100-24-034, Revision 1, dated September 12, 1996, must be accomplished on Fokker Model F28 Mark 0070 series airplanes prior to or in conjunction with Fokker Service Bulletin SBF100-78-012. Fokker Service Bulletin SBF100-24-034 describes procedures for modification of the wiring of the priority switching of the emergency inverter power supply. The modification involves reconfiguring the emergency DC bus wiring. Accomplishment of this modification will reduce the load of the emergency DC bus on Fokker Model F28 Mark 0070 series airplanes.
In addition, Fokker has also issued Service Bulletin SBF100-78-013, dated November 22, 1996. This service bulletin describes procedures for performing repetitive operational checks to detect failures of the secondary lock actuator, primary lock switch, indication and warning system, and feedback cable mechanism of the thrust reversers; and repair of the thrust reverser system, if necessary.
The Rijksluchtvaartdienst (RLD), which is the airworthiness authority for the Netherlands, classified these service bulletins as mandatory and issued Dutch airworthiness directive BLA 1996-140 (A), dated November 25, 1996, in order to assure the continued airworthiness of these airplanes in the Netherlands.
FAA's Conclusions
These airplane models are manufactured in the Netherlands and are 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.
Explanation of Requirements of the New 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 supersedes AD 96-24-10. It continues to require the following actions:
A revision to Limitations Section of the FAA-approved AFM that will enable the flightcrew to determine if the thrust reversers are properly stowed and locked prior to take-off by monitoringproper engagement of the autothrottle system (ATS); and
A revision to the FAA-approved maintenance program to incorporate instructions to correct malfunctions found during the operational tests of the secondary lock relay 1 of the thrust reversers; to perform a daily check to detect latent failure of the secondary lock actuator switch 1; and to take corrective actions, if necessary.
In addition, this AD requires performing the following new requirements:
1. Modification of the wiring of the electrical control, and indication and warning systems of the thrust reversers, which terminates the currently required AFM revision and the maintenance program revision;
2. Modification of the wiring of the priority switching of the emergency inverter power supply, for certain airplanes;
3. Repetitive operational checks to detect failures of the secondary lock actuator, primary lock switch, indication and warning system, and feedback cable mechanism of the thrust reversers; and repair of the thrust reverser system, if necessary; and
4. Submission of a report of any finding to Fokker following accomplishment of the operational checks.
These actions are required to be accomplished in accordance with the service bulletins described previously.
Operators should note that the FAA has deleted the previous allowance to dispatch with both thrust reversers inoperative, which was specified in paragraph (b) of AD 96-24-10. The FAA finds that such an allowance is unnecessary, since adequate spare parts are now available to accomplish any required part replacements as a result of the daily maintenance check.
Difference Between the AD and the Related Dutch AD
This AD differs from the Dutch airworthiness directive BLA 1996-140 (A) in that it does not address changes to the FAA Master Minimum Equipment List (MMEL), whereas the Dutch airworthiness directive changes the requirements of the Dutch MMEL for the autothrottle and the thrust reverser indicationand alerting system. The Dutch BLA allows dispatch with both autothrottle channels inoperative and both thrust reverser indication and alerting systems inoperative provided both thrust reversers are deactivated and secured in the stowed position, and no operations or procedures are predicated on their use. The FAA MMEL only allows dispatch with one autothrottle channel inoperative and does not allow dispatch with either thrust reverser indication or alerting system inoperative. The FAA finds no safety-related reason to relax these requirements.
Interim Action
This is considered to be interim action. The exact cause of the addressed unsafe condition is still unknown at this time. The reports of operational check results that are required by this AD will enable the manufacturer to obtain better insight into the nature, cause, and extent of the inadvertent thrust reverser deployment, and eventually to develop final action to address the unsafe condition. Once final action has been identified, the FAA may consider further 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 ofthe 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 96-NM-273-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 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.
39.13 - [Amended]
2. Section 39.13 is amended by removing amendment 39-9850 (61 FR 66890, December 19, 1996), and by adding a new airworthiness directive (AD), amendment 39-9866, to read as follows: