Discussion
What Events Have Caused This AD?
Reports of excessive backlash in the flap actuators of the internal gear system on certain Pilatus Models PC-12 and PC-12/45 airplanes caused FAA to issue AD 99-19-32, Amendment 39-11319 (64 FR 50439, September 17, 1999).
AD 99-19-32 currently requires you to inspect the flap actuator internal gear system for correct end-play and backlash measurements and accomplish any corrective adjustments, as necessary.
The Federal Office for Civil Aviation (FOCA), which is the airworthiness authority for Switzerland, recently notified FAA of the need to change AD 99-19-32. The FOCA reports that Pilatus has identified modifications for the flap system and designed and manufactured a new flap control and warning unit (FCWU) that permits the flap power drive-unit circuit breaker to close during flight.
The previous FCWU does not allow the pilot to close the flap power drive-unit circuit breaker during flight and the FCWU cannot sense when a single actuator becomes worn. This could result in flap panel distortion. The incorporation of these modifications to the flap system and the installation of the new design FCWU, Pilatus part number FCWU 99-3, make the current end-play and backlash measurement procedures incorrect.
Pilatus has also identified quality deficiencies with serial numbers less than 100,001 of Pilatus part number FCWU 99-3.
In addition, the FOCA reports that electrical surges in the flap system can decrease the electrical life of the flap power drive-unit motor contactor. At the 40-degree flaps position, the flaps-down limit switch (S035) operates before the flap control warning unit can stop the extend command, which causes the flap power drive-unit's Up/Down relay (K32) to change from the extend to the retract position. The current in the field winding then goes in the opposite direction while a current still flows to the motor. Electrical current to the flappower drive-unit motor and field windings remains when the circuit breaker (CB034) closes and the motor contactor (K31 or K670) stays closed.
Has FAA Taken Any Action to This Point?
We issued a proposal to amend part 39 of the Federal Aviation Regulations (14 CFR part 39) to include an AD that would apply to all Pilatus PC-12 and PC-12/45 airplanes. This proposal was published in the Federal Register as a notice of proposed rulemaking (NPRM) on September 20, 2001 (66 FR 48381). The NPRM proposed to supersede AD 99-19-32 and proposed to require you to accomplish the following:
-Repetitively inspect the flap actuator internal gear system for correct end-play and backlash measurements with any necessary corrective adjustments;
-Incorporate certain modifications to the flap system and install a new design FCWU with a serial number of 100,001 or higher, or FAA-approved equivalent part number; and
-Modify the flap control wiring and install a flap power drive-unit field control panel.
Accomplishment of these proposed actions as specified in the NPRM would be required in accordance with the following:
-Pilatus PC-12 Service Bulletin No. 27-008, which incorporates the following pages:
Effective pages
Revision level
Date
1, 2, and 11
2
September 13, 2000.
3 through 10 and 12 through 114
1
June 26, 2000
-Pilatus PC-12 Service Bulletin No. 27-012, dated September 13, 2000;
-Pilatus PC-12 Maintenance Manual Temporary Revision No. 27-13, dated April 30, 2000; and
-Pilatus PC-12 Service Bulletin No. 27-011, Revision No. 1, dated January 26, 2001.
Note: We added to the final rule Pilatus PC-12 Maintenance Manual Temporary Revision No. 27-14 (which superseded Temporary Revision No. 27-13), dated December 4, 2000, and Pilatus PC-12 Aircraft Maintenance Manual 27-50-03, pages 601 through 608, dated April 30, 2000.
What Is the Potential Impact if FAA Took No Action?
These conditions, if not corrected, couldcause the flap power drive-unit circuit breaker to not close during flight and cause current surges in the flap control system. Both conditions have the potential for flap system failure with consequent reduced or loss of control of the airplane.
Was the Public Invited To Comment?
The FAA encouraged interested persons to participate in the making of this amendment. The following presents the comments received on the proposal and FAA's response to each comment:
Comment Issue No. 1: The AD Is not Necessary
What is the commenter's concern? Several commenters state that the AD is not necessary and the actions that are currently required by AD 99-19-32 are sufficient. The commenters request that FAA withdraw the NPRM.
What is FAA's response to the concern? We do not concur that this AD is not necessary. As previously discussed, the unsafe conditions specified in this document, if not corrected, could cause the flap power drive-unit circuit breaker to not close duringflight and cause current surges in the flap control system. If the pilot cannot close the circuit breaker during flight, the flight control and warning unit (FCWU) would not sense a worn actuator. Current surges in the flap control system could decrease the electrical life of the flap power drive-unit motor contactor. Both conditions have the potential for flap system failure with consequent reduced or loss of control of the airplane.
We are not changing the final rule as a result of these comments.
Comment Issue No. 2: Change the Compliance Time
What is the commenter's concern? One commenter suggests that FAA change the repetitive inspection interval for the actuator backlash from 100 hours time-in-service (TIS) to 600 hours TIS. This would coincide with Pilatus PC-12 Service Bulletin No. 27-008 and Pilatus PC-12 Maintenance Manual Temporary Revision No. 27-14 (which superseded Temporary Revision No. 27-13), dated December 4, 2000, or Pilatus PC-12 Aircraft Maintenance Manual 27-50-03, pages 601 through 608, dated April 30, 2000.
What is FAA's response to the concern? We concur with this comment. Our intent was to make the repeat inspections at 600-hour TIS intervals once the improved design actuators were installed.
We are changing the final rule to reflect:
--The change in repeat inspections from 100-hour TIS to 600-hour TIS intervals; and
--Reference to Pilatus PC-12 Maintenance Manual Temporary Revision No. 27-14 (which superseded Temporary Revision No. 27-13), dated December 4, 2000, or Pilatus PC-12 Aircraft Maintenance Manual 27-50-03, pages 601 through 608, dated April 30, 2000.
FAA's Determination
What Is FAA's Final Determination on This Issue?
We carefully reviewed all available information related to the subject presented above and determined that air safety and the public interest require the adoption of the rule as proposed except for the changes discussed above and minor editorial questions. We have determined that these changes and minor corrections:
--Provide the intent that was proposed in the NPRM for correcting the unsafe condition; and
--Do not add any additional burden upon the public than was already proposed in the NPRM.
Cost Impact
How Many Airplanes Does This AD Impact?
We estimate that this AD affects 135 airplanes in the U.S. registry.
What Is the Cost Impact of This AD on Owners/Operators of the Affected Airplanes?
We estimate the following costs to accomplish the initial inspection of the flap actuator internal gear system for end-play and backlash measurements. We have no way of determining the number of corrective adjustments each owner/operator of the affected airplanes would need to accomplish, the nature of such adjustments, or the number of repetitive inspections each owner/operator would incur. Therefore, the cost estimate only takes into account the cost of the proposed initial inspection:
Labor cost
Parts cost
Total cost per airplane
Total cost on U.S. operators
6 workhours x $60 per hour = $360
Not Applicable
$360
$48,600
We estimate the following costs to incorporate certain modifications to the flap system and install a new design FCWU with a serial number of 100,001 or higher:
Labor cost
Parts cost
Total cost per airplane
Total cost on U.S. operators
70 workhours x $60 per hour = $4,200
Pilatus will provide parts at no cost to the owner/operator.
$4,200
$567,000
We estimate the following costs to modify the flap control wiring and install a flap power drive-unit field control panel:
Labor cost
Parts cost
Total cost per airplane
Total cost on U.S. operators
5 workhours x $60 per hour = $300
Pilatus will provide parts at no cost to the owner/operator.
$300
$40,500
Regulatory Impact
Does This AD Impact Various Entities?
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.
Does This AD Involve a Significant Rule or Regulatory Action?
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 copy of the final evaluation prepared for this action is contained in the Rules Docket. A copy of it may be obtained by contacting 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, under 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. FAA amends Sec. 39.13 by removing Airworthiness Directive (AD) 99-19-32, Amendment 39-11319 (64 FR 50439, September 17, 1999), and adding a new AD to read as follows: