A proposal to amend part 39 of the Federal Aviation Regulations (14 CFR part 39) to include an airworthiness directive (AD) that is applicable to certain Saab Model SAAB SF340A and SAAB 340B series airplanes was published in the Federal Register on March 21, 1996 (61 FR 11591). That action proposed to require installation of an automatic flight idle stop on the control quadrant in the flight compartment.
Interested persons have been afforded an opportunity to participate in the making of this amendment. Due consideration has been given to the comments received.
Support for the Proposal
One commenter supports the proposal in its entirety.
Request to Extend Compliance Time
Two commenters request that the compliance time for the installation be extended beyond the proposed 12 months. One commenter suggests that the compliance time be extended to 18 months so that the installation may be performed during a regularly scheduled maintenance interval. This would preclude additional costs incurred from special scheduling and additional downtime. The other commenter requests that the compliance time be extended to 20 months because the current number of available parts and the vendor's turnaround time for delivery of parts will not be able to support the modification of the entire U.S. fleet of 230 airplanes within 12 months.
The FAA does not concur with the commenters' request. In developing a compliance time for this AD action, the FAA considered not only the degree of urgency associated with addressing the subject unsafe condition, but:
1. the recommendations for compliance time specified by the Luftfartsverket (LFV), which is the airworthiness authority for Sweden, and by the manufacturer;
2. the availability of required parts; and
3. the practical aspect of installing the required modification within an interval of time that parallels normal scheduled maintenance for the majority of affected operators.
Based on information received from the manufacturer relative to parts availability and vendor turnaround time, the FAA considers that the 12-month compliance time is adequate if operators make reasonable efforts to meet this schedule. However, under the provisions of paragraph (c) of the final rule, the FAA may approve requests for adjustments to the compliance time if data are submitted to substantiate that such an adjustment would provide an acceptable level of safety.
Request to Reference Latest Revision to Service Information
One commenter requests that the proposal be revised to cite the latest revisions to the SAAB service bulletins as the appropriate source of service information.
The FAA concurs with the commenter's request. Since issuance of the notice, SAAB has issued the following revisions to the referenced service documents:
1. Service Bulletin 340-76-031, Revision 4, dated February 25, 1996
2. Service Bulletin 340-76-032, Revision 3, dated March 25, 1996
3. Service Bulletin 340-32-100, Revision 2, dated March 25, 1996
These revised service bulletins are essentially identical to previous versions, but contain various minor editorial corrections and updated cost figures. They do not affect modifications that were accomplished in accordance with earlier versions of these service bulletins.
The FAA has revised the final rule to cite the latest versions of the service bulletins and has added information to specify that previous accomplishment of the installation in accordance with any earlier version of the service bulletin is acceptable for compliance with the applicable parts of the rule.
Request to Allow Continued Flight with Flight Idle Stop Inoperative
One commenter requests that the proposal be revised to provide relief from the Master Minimum Equipment List (MMEL) provisions to allow the airplane to continue to be operated if the flight idle (FI) stop is inoperative. In support of this request, the commenter points out that the Model SF340 automatic FI stop is unique in that, once the override mechanism is activated, the system cannot be reset without maintenance intervention. The commenter requests that the proposed AD allow affected operators to operate the airplane for at least a single additional revenue flight to a maintenance base where the FI system can be reset (or repaired, if necessary). Such relief would preclude what the commenter considers "an unreasonable exposure to loss of service" following such overrides.
The FAA concurs. In the event of a malfunction of the FI stop system, use of the FI stop override function is available to the flight crew. However, due to the redundant system design of the FI stop, the necessity for use of the override is expected to be very rare. In any case where the automatic system has malfunctioned and/or use of the override has been necessary, as the commenter correctly notes, maintenance action is required to return the FI stop system to an operational condition. If adequate maintenance support is not available upon landing, the FAA has determined that the airplane may be operated safely for one revenue flight to a location where appropriate maintenance can be performed, provided that the FI stop system has been properly deactivated and placarded for flight crew awareness in accordance with the provisions of the FAA- approved MMEL. A new paragraph has been added to the final rule to specify this.
Request to Allow Continued Flight if Anti-Skid System is Inoperative
This same commenter requests that the proposal be revised to provide MMEL relief to allow dispatch of an airplane equipped with an automatic FI stop system when the anti-skid system is inoperative. The commenter states that, while the quadruple redundancy of the "release" signal to the FI stop solenoid will minimize system faults that cause the solenoid to not release, this redundancy will result in the inability to defer the anti-skid system.
The FAA does not consider that additional revision of the proposed rule is necessary. The FI stop system uses wheel-spin-up signals from the anti-skid system to drive the FI stop to the "open" position. Other signals, such as weight-on-wheels signals, are also used to drive the FI stop to the "open" position, thus providing a redundant system design of the FI stop. However, the Abnormal Procedures specified in the FAA-approved Airplane Flight Manual (AFM) that relate to in-flight failure of the anti-skid system may include instructions for the flight crew to activate override of the FI stop upon landing. This use of the FI stop override then requires maintenance action to reset and, as discussed in the previous issue, the FAA has determined that a single flight for return of the aircraft to a location for maintenance will meet acceptable safety levels. Since the most restrictive requirements take precedence in the determination of dispatch relief, other equipment, such as the anti-skid system, may also be required to be repaired to support the requirements for the FI stop system.
Request to Provide Flight Crew with Indication of Status of FI System
One commenter supports the intent of the proposal, but requests that it be revised to include a requirement to provide the flight crew with adequate indication of the system status and failure annunciation, as well as a means to verify that the system is operational while in flight. The commenter considers that a status indicator is required to inform the flight crew of the mode of the lockout system. As a minimum, this indicator should inform the crew of two conditions:
1. the system has experienced a failure of some type, and
2. ground idle will not be available when it should be.
This commenter also considers that a means is necessary to allow the crew to test (fault check) and verify the system status and operability. Accurate knowledge of the system's status can be critical to the safety of the operation.
The FAA concurs partially with the commenter's statements about the need for adequate status indication and crew verification. The automatic FI stop system has been designed to provide status indication to the flight crew. The position of the FI stop in either the "open" position (no blocking of power levers into beta) or "closed" position is provided by means of indications on the top of the Flight Status Panel (FSP) as follows:
o FI stop (blue): FI stop is open and landing gear is down and locked. This is the normal indication when the airplane is electrically powered on the ground. The blue light normally will turn off when the landing gear is retracted after takeoff, and it does not illuminate for the duration of the flight. If the landing gear is not retracted following takeoff, the light will stay on, and the FI stop will remain open, until all wheels have spun down to less than 9 knots, which may take up to 90 seconds.
oFI stop open (amber): This light indicates an abnormal situation, showing that the FI stop is open, although landing gear is not down and locked. The amber light will appear if the FI stop fails to close after takeoff when the landing gear is retracted, indicating that there is no protection against movement of the power levers into beta during flight. This light also will appear if the manual override knob is pulled, causing the FI stop to open. This status indication is intended to alert the flight crew when FI stop protection is not available; therefore, increased crew awareness is necessary to prevent inadvertent placement of the power levers into beta mode during flight.
These status indications do not, however, predict an upcoming failure of the FI stop to open correctly upon landing. Due to the redundant system design of the FI stop, and based on the failure analysis probabilities, malfunction of the FI stop system that would result in the system remaining closed after touchdown is predicted to be very infrequent. In the event of a malfunction or if adverse runway conditions result in the FI stop remaining closed upon touchdown, the override mechanism is always available to the flight crew. Operators may refer to SAAB 340 Operations Bulletin No. 52, which describes procedures to be followed in such an event.
As for the commenter's request for a means to allow the flight crew to test (fault check) and verify the system status and operability, the FAA points out that the FI stop lights on the FSP, as described above, provide an accurate indication of the system operation; in light of this, the FAA does not consider it necessary to add a flight crew test in addition to this status information. Additionally, lamp checks may be performed by the flight crew to ensure that the FI stop indication lights themselves are operational.
Request to Include Provisions to Minimize Compound System Failures
The same commenter requests that the proposal be revised to include provisions to minimize or exclude compound systems failures, and to ensure that the flight crew is able to override the automatic system if it becomes necessary to do so. If these features are not available, the commenter requests that the FI stop system be changed to incorporate them. To support its request, the commenter states that provisions must be made to eliminate failure modes that would result in certain systems being simultaneously disabled. The primary concern is the controllability of the airplane on the ground. Inability to select ground idle after landing may seriously degrade the airplane's stopping performance. If a failure that prevents access to ground idle also disables other ground operation related systems (such as nose wheel steering), the stopping capability and/or the controllability of the airplane could be seriously compromised. In order to further improve the reliability and independence of the FI stop installation, this commenter urges incorporation of three specific design considerations:
1. the ability to tap the spin-up signal in its rawest usable form, prior to it being processed by any digital/control component, to avoid its loss if that component should fail;
2. a redundant, parallel spin-up signal provided in case of a failure or lack of signal from one sensor;
3. a revision to the system operation that will address the possibility of reduced wheel spin- up (i.e., hydroplaning).
Related to the possibility of such failures, this commenter also states that provisions must be made to enable the flight crew to deliberately and rapidly override the FI stop system. This is necessary to prevent a system failure from creating a potentially hazardous situation when the crew is attempting to stop the airplane. The commenter states that, if power cannot be reduced below flight idle during the landing roll-out, the stopping capability of the airplane will be significantly degraded, potentially resulting in a runway overrun.
The FAA concurs with this commenter's statements, but finds that no revision to the rule is necessary because the design features suggested by the commenter already have been incorporated into the FI stop system. The quadruple redundancy of the "release" signal to the FI stop solenoid has been designed in order to minimize system faults that would cause the solenoid to not release. If the left or right landing gear is extended, and if any one of the left or right inboard or outboard wheel speed signals is greater than 25 knots, or if the left or right weight-on- wheels signal is true, then the FI stop system is opened, permitting unrestricted movement of the power levers.
Additionally, in the unlikely event that this combination of data fails to drive the FI stop to the "open" position, a manual override knob is also available to the flight crew. When this override knob is pulled, the FI stop will be mechanically forced to the "open" position. This combination of the redundant signal inputs and the override knob was intentionally designed into the FI stop system to enable selection of beta modes when necessary for slowing action.
Conclusion
After careful review of the available data, including the comments noted above, the FAA has determined that air safety and the public interest require the adoption of the rule with the changes previously described. The FAA has determined that these changes will neither increase the economic burden on any operator nor increase the scope of the AD.
Cost Impact
The FAA estimates that 224 airplanes of U.S. registry will be affected by this proposed AD. Accomplishment of the required installations will take between 122 and 142 work hours per airplane, depending upon the configuration of the airplane. The average labor rate is $60 per work hour. Required parts will cost approximately $9,300 per airplane. Based on these figures, the cost impact of this AD on U.S. operators is estimated to be between $3,722,880 and $3,991,680 (or between $16,620 and $17,820 per airplane).
The cost impact figure discussed above is based on assumptions that no operator has yet accomplished any of the requirements of this AD action, and that no operator would accomplish those actions in the future if this AD were not adopted.
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.
For the reasons discussed above, I certify that this action (1) is not a "significant regulatory action" under Executive Order 12866; (2) is not a "significant rule" under DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979); and (3) will not have a significant economic impact, positive or negative, on a substantial number of small entities under the criteria of the Regulatory Flexibility Act. A final evaluation has been prepared for this action and it is contained in the Rules Docket. A copy of it 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 addingthe following new airworthiness directive: