Daily Rules, Proposed Rules, and Notices of the Federal Government
You may get the service information identified in this proposed AD from Sikorsky Aircraft Corporation, Attn: Manager, Commercial Technical Support, 6900 Main Street, Stratford, Connecticut, phone (203) 383-4866, email address
We invite you to submit any written data, views, or arguments regarding this proposed AD. Send your comments to the address listed under the caption
We will post all comments we receive, without change, to
You may examine the AD docket, which contains the proposed AD, any comments, and other information, on the Internet at
A proposal to amend 14 CFR part 39 to add an AD for Sikorsky Model S-76A, B, and C helicopters with HR Textron servo actuators, part number (P/N) 76650-09805, installed, was published in the
Since issuing that NPRM, we have received comments from 10 commenters, including two separate comments from the manufacturer, and a comment from the NTSB. We have reviewed the comments on that proposed rule and further analyses and test data.
Seven commenters recommended that the NPRM be withdrawn. Another commenter recommended that no AD be published “until the FAA is absolutely certain that existing manufacturer's maintenance criteria were performed by experienced technicians.”
One of these commenters, Air Logistics, states several reasons why the NPRM should be withdrawn. First, they cite their 30 years of operational experience with Sikorsky helicopters, during which they had not experienced any servo failures. Second, they state that the results of Sikorsky testing indicates that servo actuators with leakage rates as high as 3000 cc per minute in one stage had the capacity to perform the entire mission spectrum. Third, they have conducted their own internal leak tests and hydraulic oil analyses and no defects or contaminations were found. Fourth, they state there is “no evidence” presented by the NTSB or FAA to justify the NPRM. Finally, they state that the 1,000 hour TIS reduction would impose thousands of dollars of unnecessary expense without improving safety.
Another commenter, Sikorsky Aircraft Corporation, states that the NPRM should be withdrawn for several reasons. First, they state that the scope of the NPRM is without authority because there is no unsafe condition and the NPRM is based on an NTSB recommendation founded upon “preliminary speculation” regarding the root cause of an aircraft mishap that has been shown by testing and analysis to be without merit. Second, they state that they have 28 years and 9 million servo actuator flight hours, operational testing, materials analysis, and assessments of servo actuator operation within the fleet with no related operational problems. Third, they state that the existing maintenance program is adequate to assure safe, airworthy operation of the hydraulic system and its associated hardware, “including the main rotor servo actuator, within the current defined overhaul intervals based on operator data.” “This servo design has performed for over 25 years with no service anomalies.” Fourth, they cite “extensive laboratory testing” conducted by them demonstrating that “normal servo control is maintained throughout the certified flight envelope, even with leakage and wear particle conditions up to three times the [Sikorsky S76] Maintenance Manual limits”, and state that the “servo actuator is airworthy for the entire certificated flight envelope even with significant fluid contamination and internal leakage, while operating on one stage only.” Fifth, they state that implementing the AD would create an unnecessary maintenance burden on the operators and increase fleet operating costs while providing no benefit. Additionally, the commenter provided several additional “Specific Comments”. These specific comments further argue the contention that (1) performance of the servo is compromised by internal leakage and plasma spray flaking is incorrect; (2) servo internal leakage and hydraulic fluid contamination from flaking spray could result in loss of control of the aircraft is incorrect; (3) more frequent leakage tests are required to maintain servo airworthiness is unfounded; (4) more frequent hydraulic fluid cleanliness inspections are unwarranted; and (5) reducing the servo overhaul interval is unnecessary.
Another commenter, Carl Violette, states that the NPRM should be withdrawn for several reasons. First, he cites his experience of 25 years and 60,000 flight hours of maintaining accident-free operations of the Model “S-76 variants.” Second, he states that overhauling all three Model S-76 servo actuators 1,000 hours TIS early when the leakage rates are so low is “ludicrous.” Third, he states that the 600 hour TIS inspection interval “doesn't make sense” considering the existing 100 hour TIS inspection. Fourth, he states that performing contamination inspections on the aircraft is “pointless” since the fluid is usually supplied by the hydraulic mule, which has a finer filter than the aircraft one, and therefore one would only find filtered hydraulic fluid in the aircraft. Fifth, he states that the NPRM will increase helicopter operating costs from $15 per hour to $22.50 per hour, and will cost their company an additional $9,000 per year without any failed servo actuators. Sixth, he states that the servo actuator “jump” check performed by the pilot each time the aircraft is started is a “better check” and would inform the pilots if there were any issues with the servo actuators. Seventh, he states that there is “no way” that the servo actuator could extend beyond the pilot's inputs without a mechanical breakage somewhere, and that minuscule flakes won't prevent the 3,000 PSI fluid from going where it wants to go. Eighth, Mr. Violette commented that he found it “cavalier” that so little research was done on this proposal in light of the seriousness of the incident. He questioned the proposed frequency of the leakage checks, and why this leakage prompts us to lower the overhaul interval. He further stated that if contamination checks are required, then more guidance is required. He stated, “If a patch test is done, what is the accept/reject criteria? Can I send fluid to a lab instead? What are their accept/reject criteria? When should I replace a servo?” He stated that he doesn't understand how the proposed AD makes the aircraft safer.
Another commenter, Helicopter Support, Inc., states that the NPRM should be withdrawn for several reasons. First, in 20 years of overhaul and repair experience, they found flaking of the Model S-76 servo actuator piston plasma spray in only extremely rare circumstances. Second, Sikorsky testing showed “no connection between internal leakage of the main rotor servo actuator and subsequent loss of control of the helicopter.” Third, a reduction in the overhaul interval from 3,000 to 2,000 hours TIS would impose an unnecessary financial burden, and would increase maintenance costs and negatively impact flight availability. Fourth, the maintenance procedures called out in Chapters 5 29 of the Sikorsky S-76 Maintenance Manual “are sufficient to identify leakage and contamination” in the servo actuator system. Fifth, performing the leakage rate check is subjective and can lead to costly false removals of the servo actuator. Sixth, the 600 hours TIS patch test can be addressed by the 12 month
Another commenter, Aero Med Spectrum Health, cited their 14 or more years of operating both Model S-76A and Model S-76B helicopters without any operational problems or internal failures of the servo actuators, or anomalies reported by the crew, as evidence that the AD is unnecessary.
Another commenter, HR Textron, stated that the AD is unnecessary because the NPRM is based on “speculation of an NTSB investigator” with respect to a Model S-76 helicopter accident that has been shown to be “without substance or merit,” and extensive testing by HR Textron and Sikorsky have demonstrated that “internal leakage and/or plasma spray flaking do not create an unsafe condition.” Further, information on the flight data recorder of the accident helicopter “do not support the theory that a mechanical malfunction of the servo caused the mishap.”
Another commenter, Jay Deering, feels that the AD is “unnecessary” and will cause undue hardship for the operator.
Another commenter, Steve Strollo, states that the “AD should not be published until the FAA is absolutely certain that existing manufacturer's maintenance criteria were performed by experienced technicians.” He further states that in his 26 years as an AP mechanic, he has seen only one serious servo actuator failure due to “tissue thin wall thickness along the entire length of the tube” and the pilots were unaware of the malfunction. He has never experienced excessive contamination of a hydraulic system, or a failed patch test. Also, he believes that degradation of the accident servo “did not occur overnight” and that if the 300 hours TIS inspection is performed correctly, damage to the servo actuator can be easily spotted.
Regarding Mr. Strollo's comment referencing the 300 hours TIS inspection, that is an inspection pertaining to “noticeable wear of the chrome plating on the visible surface” of the servo actuator piston that is not required by an AD and is not relevant to this proposal.
Two commenters, Copterline Oy (Copterline) and the NTSB, supported the NPRM.
One commenter, Copterline, was the operator of the Sikorsky Model S-76 helicopter that crashed shortly after taking off in Estonia in 2005 and prompted the NTSB safety recommendation. Copterline states that the NPRM should be adopted in its entirety and expanded to include other servo actuators in which there is “a possibility for manufacturing process error” which can cause plasma coating to delaminate and block the servo actuator return ports, leading to loss of control of the helicopter. They state that “the reason why the Plasma coating flakes off remains unaddressed.” They state that the NPRM should be expanded to include additional testing—for example, x-ray, ultrasonic, or other appropriate testing—to confirm that the plasma coating has adhered to the servo actuator pistons, which will further reduce risk. This commenter states that the NPRM should be more comprehensive. Copterline also states that the NPRM should propose a reduction in the servo actuator piston life limit until the plasma spray flaking problem has been resolved. Copterline cites NTSB laboratory findings and states that it agrees with Sikorsky that when one of the two return flow ports is blocked, safe operations can be conducted. However, if both return ports of the control valve have been blocked, the bypass function is not available and the blocked side will jam the other stage. They state that the “laboratory testing results justify the NTSB's concern.” Copterline also states that the proposed AD actions and even the additional requirements that they propose “would not adversely affect the S-76 operators and, in practise, [sic] would not materially increase operating costs of the S-76 fleet.” This commenter also states that continued accidents would be reflected in increased insurance premiums that would more than offset any short term savings associated with not taking appropriate action.
Additionally, this commenter attached a copy of its “Detailed Comments to Sikorsky's Comments on FAA and AOL” Web sites. These comments are consistent with those made to the NPRM.
Another commenter, the NTSB, also supports the NPRM, and states that “results of the Safety Board and Sikorsky tests demonstrate the need for issuance of a final rule consistent with the proposed AD as soon as possible.”
Based on the comments summarized previously and our re-evaluation of the published proposal, we agree with various portions of the comments proposing withdrawal of the NPRM and portions of those supporting the NPRM. With respect to those comments citing operational experience, lack of supportive evidence by the FAA or NTSB, testing results, adequacy of existing maintenance programs, imposition of costly procedures without an increase in safety, and inappropriateness of the proposed procedures as evidence supporting withdrawal, we have determined that portions of the initial proposal are unnecessary to correct the unsafe condition, although there is still uncertainty about the root cause of the accident. Based on our reevaluation, we continue to believe that servo actuator pistons may experience piston head seal leakage and plasma spray flaking, but this does not justify the full scope of the initial proposal. We believe that the piston head seal leakage and plasma spray flaking can be addressed adequately by leakage rate inspections and replacement of the current servo actuator pistons with an improved design not as susceptible to plasma spray flaking. The reduction in the overhaul interval from 3,000 to 2,000 hours TIS is not necessary if the leakage rate inspection is performed, and the leakage rate inspection is a better way of determining servo actuator condition than the hydraulic fluid patch test. Therefore, in order to prevent degraded servo actuator performance as a result of piston head seal leaking and plasma spray flaking, which may result in subsequent loss of control of the helicopter, we are revising the proposed rule by removing the requirement to inspect the hydraulic fluid for contamination using a patch test kit or an independent laboratory analysis method; removing the requirement to reduce the interval for overhauling an affected servo actuator from 3,000 to 2,000 hours TIS; revising the initial inspection time; and removing the 600 hours TIS repetitive hydraulic fluid leak inspection. We are proposing to add a 2,250 hours TIS hydraulic fluid leakage inspection to the currently required 1,500 hours TIS hydraulic fluid leakage inspection; and proposing to add a requirement to either install a new design servo actuator, Sikorsky part number (P/N) 76650-09805-111 (HR Textron P/N 3006760-111), or replace the servo actuator pistons, P/N 41004321 with P/N 41012001 or P/N 41012001-001, in servo actuators, Sikorsky P/N 76650-09805-109 and -110 (HR Textron P/N 3006760-109 and -110), either because of excessive leakage at the 1,500 or 2,250 hours TIS leakage inspection, or upon reaching the 3,000 hours TSN or TSO maintenance interval.
Regarding the comments in opposition to our proposal because of the cost, we agree that the initial proposal and these revised proposals would increase the operator's maintenance costs. While the total estimated cost amount of the impact contained in the economic evaluation in
Since we believe that the proposed leakage rate check and incorporation of the new servo actuator piston design are sufficient to address degraded servo actuator performance as a result of piston head seal leakage and plasma spray flaking, Copterline's proposed additional x-ray, ultrasonic, or other appropriate tests to verify adhesion of the piston plasma coating are not necessary, and would increase the operators' costs without an increased level of safety. Furthermore, we have determined, as previously mentioned, that we need to address degraded servo actuator performance due to internal leakage and piston head plasma spray flaking, which could potentially lead to loss of control of the helicopter. Therefore, we are revising the initial proposal to require only the leakage rate inspections and replacement of the servo actuators, Sikorsky P/N 76650-09805-109 and -110, with servo actuators, Sikorsky P/N 76650-09805-111, or replacement of servo actuator pistons, P/N 41004321, with P/N 41012001 or P/N 41012001-001, in Sikorsky servo actuators, P/N 76650-09805-109 and -110.
Copterline also states that inconclusive investigations into previous “unsolved accidents” involving Sikorsky Model S-70, S-76, and H-53 helicopters should be re-examined to determine if there is any relationship between those accidents and the more recent accident involving the Copterline helicopter that prompted issuing the NPRM.
We do not agree that additional review of previous accidents involving Sikorsky helicopter models is necessary. Investigations of previous Model S-76 helicopter accidents indicated no evidence of involvement of the servo actuators, therefore, we believe there is no relationship to the Copterline accident. Moreover, these servo actuators on those other Sikorsky model helicopters are significantly different in design, not susceptible to the same plasma flaking and seal leakage problems as the Model S-76 servo actuator, and would not provide useful information for evaluating the failure modes of the Model S-76 servo actuator.
Copterline expressed concern that the servo actuator does not meet the part 29 certification requirements to be a “fail-safe component”, and that it was not designed for the situation in which both return ports are blocked, which could cause the servo actuator to jam. As previously noted, they cite the NTSB laboratory findings as evidence that this dual blockage occurred, leading to the accident. Copterline states that the manufacturer of the servo actuator or the helicopter must demonstrate and prove that the servo actuator is a fail-safe component and that the Model S-76 helicopter meets all the type certification requirements.
We disagree with Copterline's statement that the S-76 servo actuator does not meet part 29 certification requirements. The design of the affected Model S-76 helicopter servo actuator meets the fail-safe design regulatory requirements that were in effect at the time of initial certification of the Model S-76 helicopter. The inspection requirements of this revised proposal will assure that the Model S-76 servo actuator remains airworthy.
Copterline states that “the FAA should require Sikorsky to make all Servo testing reports available without delay.” Copterline also states that “servo testing results and findings for cases where both return flow ports are blocked should be released immediately, if they exist.” Also, Copterline states that the “specially manufactured and modified servo used in the Sikorsky testing” did not demonstrate conclusively what happened in the accident servo actuators. They further state that the Sikorsky testing does not establish that a servo actuator on the helicopter involved in the accident did not malfunction.
We agree with the comment that all testing results and findings should be released and to our knowledge, all relevant and requested FAA agency records have been made available. With respect to the comment that Sikorsky did not demonstrate conclusively what happened in the accident, the parties involved in the accident investigation have conducted extensive investigations to determine the cause of the accident. Although the Estonian authorities have released a final report identifying a cause of the accident, these parties have not and may not ever agree on the cause of the accident. As previously mentioned, the FAA has determined, based on further information obtained from the Copterline accident investigation and other test and service history data since we issued the NPRM, that a need exists to address degraded servo actuator performance due to internal leakage and piston head plasma spray flaking. This is reflected in this proposal.
Sikorsky states with respect to the accident, that the physical evidence does not support the theory that a mechanical malfunction of the servo caused the accident, and that it is physically impossible for the Model S-76 helicopter to perform these maneuvers without being influenced by an external force such as a waterspout. Copterline states Sikorsky's comment is incorrect when it states that it is physically impossible for the Model S-76 helicopter to perform the maneuvers recorded on its own even if the servo actuator malfunctioned, and cites the accident helicopter's flight data recorder (FDR) data as evidence that the accident helicopter stalled at 130 knots, and this stall is the external force that explains the maneuvers. They also state that if there had been any weather related cause to the accident, that it could have been read from the FDR data, and that there isn't any data to support Sikorsky's theory of a waterspout.
The weather data and laboratory test data are inconclusive. We have determined that the Model S-76 servo actuator pistons may experience piston head seal leakage and plasma spray flaking, and are proposing the 1,500 and 2,250 hours TIS leakage inspections and servo actuator replacement to address this unsafe condition.
Finally, Sikorsky, in a second comment, states that the comments submitted by the NTSB in response to the previously issued NPRM are inaccurate or inconsistent with physical evidence or recorded test data. Sikorsky states that the Sikorsky testing fully demonstrated that all flight loads can be sustained in a triple “failure” condition, and that a “combined failure” with high leakage rates (3 times the in-service allowable leakage), 100 percent blockage of one of the two C3 ports, and loads associated with high airspeeds (and more significantly, the entire certified flight spectrum), will not overpower the servo actuator. They further state that they have briefed the NTSB and FAA on results of these tests and maintain that the testing demonstrates that the servo actuator design is safe and robust.
As stated previously, the final report on the accident investigation has been released, and the parties involved in the investigation have not and may never agree on the cause of the accident. However, we have determined that there
Since this proposal changes the scope and the requirements of the originally proposed rule, we have determined that it is necessary to reopen the comment period to provide additional opportunity for public comment.
We estimate that this proposed AD would affect 300 helicopters (900 servo actuators) of U.S. registry. We also estimate that the leakage rate inspection would take about 1 work hour per servo actuator at an average labor rate of $80 per work hour, and the two leakage rate inspections on 900 servo actuators would cost about $144,000. We estimate that 6 servo actuators, Sikorsky P/N 76650-09805-109 or -110, would need to be replaced with servo actuators, Sikorsky P/N 76650-09805-111. Assuming an estimated 8 work hours per servo actuator for installation and a cost of $57,000 per servo actuator, the total cost of installing these servo actuators would be $345,840. We estimate that the cost of replacing the pistons in the remaining 894 servo actuators would cost $7,259,280, assuming 14 work hours to replace the pistons and install the servo actuator, and a cost of $3,500 per piston (2 pistons per servo). Therefore, the total estimated cost of this proposal is $7,749,120.
We have determined that this proposed AD would not have federalism implications under Executive Order 13132. Additionally, this proposed AD would 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.
For the reasons discussed above, I certify that the proposed regulation:
1. Is not a “significant regulatory action” under Executive Order 12866;
2. Is not a “significant rule” under the 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.
We prepared a draft economic evaluation of the estimated costs to comply with this proposed AD. See the AD docket to examine the draft economic evaluation.
Title 49 of the United States Code specifies the FAA's authority to issue rules on aviation safety. Subtitle I, Section 106, describes the authority of the FAA Administrator. Subtitle VII, Aviation Programs, describes in more detail the scope of the Agency's authority.
We are issuing this rulemaking under the authority described in Subtitle VII, Part A, Subpart III, Section 44701, “General requirements.” Under that section, Congress charges the FAA with promoting safe flight of civil aircraft in air commerce by prescribing regulations for practices, methods, and procedures the Administrator finds necessary for safety in air commerce. This regulation is within the scope of that authority because it addresses an unsafe condition that is likely to exist or develop on products identified in this rulemaking action.
Air transportation, Aircraft, Aviation safety, Safety.
Accordingly, pursuant to the authority delegated to me by the Administrator, the Federal Aviation Administration proposes to amend part 39 of the Federal Aviation Regulations (14 CFR part 39) as follows:
1. The authority citation for part 39 continues to read as follows:
49 U.S.C. 106(g), 40113, 44701.
2. Section 39.13 is amended by adding a new airworthiness directive to read as follows:
To detect leaking in a servo actuator, which could lead to degraded servo actuator performance and subsequent loss of control of the helicopter, do the following:
(a) For a servo actuator with 1,500 or less hours time-in-service (TIS) since new (TSN) or TIS since overhaul (TSO), determine the leakage rate on or before reaching 1,500 hours TSN or TSO.
(b) For a servo actuator with 2,250 or less hours TSN or TSO, but more than 1,500 hours TSN or TSO, determine the leakage rate on or before reaching 2,250 hours TSN or TSO.
(c) If the leakage rate in any servo actuator exceeds 700 cc per minute when performing the leakage rate inspection specified in paragraph (a) or (b) of this AD, then:
(1) Replace that servo actuator piston, HR Textron P/N 41004321, with a servo actuator piston, P/N 41012001 or P/N 41012001-001, and re-identify the servo actuator on the servo actuator data plate as Sikorsky P/N “76650-09805-111” and HR Textron P/N “3006760-111” using a metal stamp method; or
(2) Replace the servo actuator with an airworthy servo actuator, Sikorsky P/N 76650-09805-111, HR Textron P/N 3006760-111.
(d) On or before 3,000 hours TSN or TSO, whichever occurs first, replace each servo actuator piston and re-identify the servo actuator as specified in paragraph (c)(1) of this AD or replace each servo actuator as specified in paragraph (c)(2) of this AD.
(e) Modifying and re-identifying each servo actuator as specified in paragraph (c)(1) of this AD or replacing each servo actuator as specified in paragraph (c)(2) of this AD is terminating action for the requirements of this AD for the modified and re-identified or replaced servo actuator.
(f) To request a different method of compliance or a different compliance time for this AD, follow the procedures in 14 CFR 39.19. Contact the Manager, Boston Aircraft Certification Office, FAA, ATTN: Terry Fahr, Aviation Safety Engineer, 12 New England Executive Park, Burlington, MA 01803, telephone (781) 238-7155, fax (781) 238-7170, for information about previously approved alternative methods of compliance.