Federal Aviation Administration, DOT.
Final rule; request for comments.
This amendment adopts a new airworthiness directive (AD) for the specified Bell Helicopter Textron (Bell) model helicopters. This action requires certain checks and inspections of each tail rotor blade assembly (T/R blade) at specified intervals and repairing or replacing, as applicable, any unairworthy T/R blade. This amendment is prompted by three failures of a T/R blade occurring during flight and a recent incident of a cracked T/R blade discovered during a scheduled visual inspection. The actions specified in this AD are intended to detect damage to a T/R blade that could lead to cracking of a T/R blade and subsequent loss of control of the helicopter.
Effective May 21, 2008.
Comments for inclusion in the Rules Docket must be received on or before July 7, 2008.
Use one of the following addresses to submit comments on this AD:
- Federal eRulemaking Portal: Go to http://www.regulations.gov. Follow the instructions for submitting comments.
- Fax: 202-493-2251.
- Mail: U.S. Department of Transportation, Docket Operations, M-30, West Building Ground Floor, Room W12-140, 1200 New Jersey Avenue, SE., Washington, DC 20590.
- Hand Delivery: U.S. Department of Transportation, Docket Operations, M-30, West Building Ground Floor, Room W12-140, 1200 New Jersey Avenue, SE., Washington, DC 20590, between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays.
You may get the service information identified in this AD from Bell Helicopter Textron, Inc., P.O. Box 482, Fort Worth, Texas 76101, telephone (817) 280-3391, fax (817) 280-6466.
Examining the Docket: You may examine the docket that contains the Start Printed Page 24859AD, any comments, and other information on the Internet at http://www.regulations.gov, or in person at the Docket Operations office between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays. The Docket Operations office (telephone (800) 647-5527) is located in Room W12-140 on the ground floor of the West Building at the street address stated in the ADDRESSES section. Comments will be available in the AD docket shortly after receipt.Start Further Info
FOR FURTHER INFORMATION CONTACT:
Michael Kohner, Aviation Safety Engineer, FAA, Rotorcraft Directorate, Rotorcraft Certification Office, Fort Worth, Texas 76193-0170, telephone (817) 222-5447, fax (817) 222-5783.End Further Info End Preamble Start Supplemental Information
A proposal to amend 14 CFR part 39 to include an AD for the specified model helicopters was published in the Federal Register as Docket No. FAA-2006-26219, Directorate Identifier 2004-SW-49-AD on November 2, 2006 (71 FR 64484). That Notice of Proposed Rulemaking (NPRM) was prompted by eight reports of fatigue cracking of T/R blades installed on Bell Model 212 and 412 helicopters (three failures on the Bell Model 212 and five failures on the Bell Model 412) with a blade assembly, part number (P/N) 212-010-750-009, -105, and -107. Six of the cracks initiated between blade stations 30 to 33.5; one crack initiated at blade station 21.9; and one crack initiated at blade station 27.6. Three of these T/R blades failed during flight and all were installed on Bell Model 412 series helicopters. In one of the in-flight failures, the T/R blade failed due to a fatigue crack that initiated in the blade skin from a nick .060 inches long by .008 inches deep. The initial damage was above the maximum allowable damage limit for the blade skin provided in the maintenance manual. That failed blade had accumulated 1,478 hours time-in-service (TIS). In another in-flight failure, a section of the T/R blade separated from the helicopter during cruise flight at 5,500 feet. The helicopter was reported to have violently turned down and to the left. The helicopter “leveled out” at approximately 1,000 feet before setting down in the water. The blade failed due to a cracked stainless steel leading edge spar that originated from a corrosion pit .001 inches deep. The corrosion area extended .003 inches along the surface of the origin location. That blade had accumulated 4,643 hours TIS. In the third in-flight failure, sanding on the spar and chem-milling was found during a post-accident investigation. The crack had initiated at blade station 21.9 and the blade had accumulated 1,232 hours TIS. Also, the following blades were found cracked:
|Model||Year||P/N 212-010-750-||Hours TIS||Blade station (in.)||Crack length (in.)||Initial damage part and type||Initial damage size|
|212||1973||−009||3,224||32.2||6.5||Skin—Corrosion||.030 in. wide.|
|212||1985||−009||279||31.5||13.0||Spar—Manufacturing Notch||.090 in. wide.|
|212||1991||−105||423||30.8||8.0||Skin—Non Sharp Dent||.75 in. long.|
|412||1996||−105||1,235||30.0||8.3||Skin—Scratch||.45 in. long by .005 in. deep.|
The NPRM proposed to require the following interim actions until either a more rigorous inspection is developed or a new blade that is more damage tolerant is designed:
- Before each start of the engines, visually checking each T/R blade for a crack;
- Within 25 hours TIS or 15 days, whichever occurs first, and thereafter at intervals not to exceed 25 hours TIS or 15 days, whichever occurs first, cleaning and visually inspecting each T/R blade for a crack, corrosion, nick, scratch, or dent using a 3-power or higher magnifying glass and a bright light;
- If certain damage is found, inspecting for a crack or corrosion using a 10-power or higher magnifying glass and measuring the depth of any damage; and
- Before further flight, replacing any cracked T/R blade and repairing or replacing any otherwise unairworthy T/R blade.
Since the issuance of that NPRM, we were notified that a crack was found on another T/R blade, P/N 212-010-750-105 FM, installed on a Bell Model 412EP helicopter. The crack was discovered while the helicopter was on the ground during a scheduled visual inspection. The T/R blade is now being examined at the manufacturer's field investigation lab. The crack is located approximately in the center of the TR blade span and extends across the majority of the chord. The T/R blade had accumulated 2,076 hours TIS. Because P/N 212-010-750-105 FM was not included in the applicability of the NPRM, and because a crack growth analysis using the striation count data from one of the failed T/R blades predicted a crack propagation rate of approximately 77 hours TIS from damage initiation to blade failure, we will withdraw that NPRM and issue this AD as a Final rule; request for comments. This AD contains the proposed requirements from the NPRM; however, we've included additional P/Ned blades and made other changes based on the comments to the NPRM. In response to the NPRM we received several comments from 4 commenters; the manufacturer, the Canadian National Defence Headquarters, and 2 individuals.
Two commenters suggest changing the compliance time for the proposed actions. One of the commenters suggests changing the proposed initial inspection from 25 hours TIS or 15 days to 25 hours TIS or 30 days and changing the recurring inspection from 25 hours TIS or 15 days to 25 hours TIS or 30 days. The other commenter believes that a visual inspection before the first flight of each day would be adequate and that a limit of 10 hours between visual inspections in any one day could be added. The same commenter states that it is not always practical (e.g. carrying a suitable safe ladder for conducting an adequate inspection and carry passengers) and might also be hazardous (e.g. doing an inspection from an offshore oil field platform where there is no ladder or stand available or where there is restricted space and the possibility of high wind speeds) to do a visual inspection before each engine start. Finally, one commenter, the manufacturer, states that it is impractical to require inspection of the T/R blades before each flight or engine start unless we are referring to a ground-level visual inspection because a ladder, which is not available in the field, would be required for a hands-on inspection. It recommends an Start Printed Page 24860inspection in accordance with the maintenance manual. The manufacturer further recommends an inspection for more than just “cracks”, that is, any damage beyond limits in accordance with the published schedule and requirements in the maintenance manual.
We concur with the recommendation to change the initial and recurring inspections from 25 hours TIS or 15 days to 25 hours TIS or 30 days. The 15-day interval was originally proposed because a corrosion pit was the initiation point for one of the failures and that interval is consistent with FAA advisory material relating to the detection of corrosion. Since the proposal was published, we have reevaluated the need for the interval and determined that a 30-day interval is adequate for this inspection and the AD is revised accordingly. We do not concur that a visual inspection before the first flight of each day would be adequate and that a limit of 10 hours between visual inspections in any one day should be added. Additionally, we do not agree with the manufacturer that a 60-day interval would be appropriate because of the quick degradation in the T/R blade strength. However, we do agree that it is not always practical to require a detailed visual inspection of the T/R blades using a ladder before each flight or engine start. The proposed owner/operator (pilot) check was only intended to be a “walk around” check to detect any large cracks. Although the Canadian commenter states that their inspection from the ground is not considered effective, we have received reports that two cracked blades were discovered during checks performed from the ground. The initial and recurring inspections performed by a mechanic are detailed, up-close inspections.
One commenter also suggests that instead of requiring a mandatory daily log book entry stating compliance with the AD that “the blade inspection be made a required preflight checklist item with no daily log book entry required.” If a logbook entry is required, the commenter suggests that it be a separate entry made at the time the 25 hour is signed off. We have determined that this critical check needs to be mandated. This determination is based on the critical nature of this failure and that the length of a crack is predicted to grow quickly once it is detectable based on the service history of these T/R blades. All required inspections, including the pilot checks specifically approved by this AD, must be recorded at the time they are performed. That recording evidences that the required AD actions have been performed. If it is not recorded, the aircraft is not in compliance with the AD and is unairworthy.
In addition to comments regarding the inspection times and types, the manufacturer provided other comments to the NPRM. Those comments and our responses follow:
|The AD lists a 1991 Model 212 with a .75″ crack * * * that Bell questions since they have no conclusive technical data on it. They also question our references to a 77 hour crack propagation from striation count and state that the 77 hour value is actually from a crack growth analysis that simply includes striation count data. Bell also states that they are aware of only 4, not 8, existing M205Bs that are of FAA certified configuration||The cracked T/R blade in question is found in the FAA service difficulty database. An approximate 8-inch crack was found in the T/R blade installed on a Bell Model 212 helicopter during a daily inspection. The crack was located 20.25 inches inboard from the tip of the T/R blade running through a .75 inch long smooth dent. The part number of the T/R blade was 212-010-750-105 with a total time of 423 hours. We agree with the comment about the reference to the 77 hour crack propagation and the number of existing M205B helicopters and have revised this AD accordingly.|
|The listed tail rotor dash numbers appear to be incorrect. The Model 204B does not use the 212-010-750 tail rotor blade and there also appears to be several of the later dash numbers missing from various models||While the standard Model 204B helicopter may not use this particular T/R blade, the 212-010-750 T/R blade may be on a modified Model 204B helicopter that does use this blade. To assure that we have covered all affected blades, the applicability now encompasses all affected dash-numbered T/R blades.|
|Recommend changing areas called out for special attention to Stations 25.0 to 35.0 (both sides) for damage/corrosion and include inboard blade butt area surrounding balance weights/screws for cracks||Agree with this change and have revised this AD accordingly.|
|There have not been eight reported failures, there have been three. All others are reported cracks in the blade skin, not “failures.” The term “failure” can be misleading||A crack in a blade makes that blade unable to safely perform its intended function. Thus, there are now 9 T/R blades that meet that criteria.|
|Bell objects to our statement in the NPRM that “The requirements of the proposed AD would be interim actions until either a more rigorous inspection is developed or a new blade that is more damage tolerant is designed.” Bell states “Although we are in concept discussions with DND, completion and certification of this blade is many months away and could be misleading to the commercial community.”||As we understand this objection by the manufacturer, it believes that a redesigned blade is unnecessary and that the current inspections are adequate. We do not agree. Based on the fracture analysis, once the crack reaches a size that is detectable by inspection, it is predicted to grow quickly. Therefore, for the affected T/R blades, it is critical to find a crack or damage that could lead to a crack at the earliest opportunity. The service history of these affected T/R blades has shown that the current inspections are inadequate to reveal these cracks before blade failure. One T/R blade failed and another one cracked because of manufacturing damage on the inside of the T/R blade. That damage was not initially detectable by external inspection. Another T/R blade failed during flight due to cracking that initiated from a corrosion pit in the leading edge spar that was too small to be readily detected. Therefore, replacing the affected T/R blades with a redesigned, more damage-tolerant T/R blade is anticipated as terminating action for the requirements of this AD.|
Another commenter, the Canadian National Defence Headquarters, views the proposed actions as a “good first step” but offers several recommendations. Those recommendations and our responses follow: Start Printed Page 24861
|“Promulgate to other aviation regulation agencies worldwide because there are many more airframes affected than the ‘388 helicopters of U.S. registry’.”||Our standard practice is to send our ADs to aviation authorities with which we have a bilateral agreement. In turn, it is then at their discretion whether or not to follow up with similar action.|
|Adjust the inspection frequency as a function of the operations environment, e.g., a 12.5 hours inspection frequency using the 10x magnification (noting that deployments of small numbers of aircraft take the minimum support equipment required) visual inspection for operations using “harsh & rough” landing fields and an interval of 25 hours inspection for paved landing fields||We agree that the risk of incurring damage in the T/R blade would be less for those helicopters operated on paved landing fields versus “harsh & rough” landing fields. Defining and enforcing such an inspection interval, however, would be difficult because helicopters operate in so many varied environments. We believe the commet to use a 10-power magnifying glass may be a typographical error because the Canadian National Defense uses a 2-power magnifying glass and a good source of light every 12.5 hours TIS for the visual inspection of the T/R blades on their Model 412CF helicopters. Regardless, we have determined that a 25-hour TIS inspection using a 3x or higher magnifying glass is best for the overall safe operation of these helicopters in the U.S.|
|Specify that the visual check be carried out by an appropriately qualified person||We do not believe that further information regarding who can carry out this visual check is necessary. The visual check is only intended to detect a large-scale crack and we believe an owner/operator (pilot) is qualified to perform this “walk-around” function.|
|Define what constitutes a “bright light”||The illumination levels are historically not given for visual inspections that are mandated by an AD. We believe what constitutes a bright light can be adequately determined by the individuals who are qualified to do the inspection. We also did not want to create additional calibration and recordkeeping requirements.|
|Implement damage mapping as a means to increase detectability of new damage and decrease the maintenance burden||Inspection of the T/R blade records and recording any damage found within the repair limits are in the maintenance instructions for the T/R blade inspection on the applicable helicopters. These steps are currently in the applicable maintenance procedures. Operators are free to implement such mapping if they believe it will reduce their maintenance burden.|
|Carry out a Type 1, Method C, Level III dye-penetrant inspection in cases where difficulties are encountered in determining the presence of a crack by visual inspection||We believe the requirement to use of a 10-power magnifying glass is adequate.|
We have reviewed the following Bell documents:
- Operations Safety Notice OSN 205-02-37, OSN 205B-02-10, OSN 212-02-39, OSN 412-02-25, OSN 412CF-02-05, and OSN UH-1H-II-02-3, dated August 27, 2002. These Operations Safety Notices apply to all owners and operators of Bell 205, 205B, 212, 412, 412CF, and UH-1H-II helicopters and were written to remind operators of the following:
- The importance of accomplishing a complete inspection of the T/R blades at specified inspection intervals;
- That the blades must be cleaned in order to perform an adequate visual inspection to determine their condition; and
- That maintenance manuals and component repair and overhaul manuals are to be consulted for damage limits and repair criteria as required.
- Alert Service Bulletin No. 412CF-03-20, dated February 6, 2003, which applies to Model 412CF helicopters and provides instructions for doing a visual inspection of certain T/R blades immediately and every 25 hours TIS in accordance with the Model 412CF maintenance manual and instructions for sending the affected tail rotor blade to DND “Calgary Supply Center” for refinishing and reidentification.
- Bell Maintenance Document C-12-146-000/MF-001, Mod 4, dated February 12, 2004, which applies to Model 412CF helicopters and specifies a tail rotor blade damage records check and a visual inspection for dents, nicks, cracks, paint chips, or blisters using a 2-power magnifying glass and a good source of light in specified areas of the tail rotor blades (reference 64-00-00, section 64-38, page 42).
This unsafe condition is likely to exist or develop on other helicopters of these same type designs. Therefore, this AD is being issued to detect damage to a T/R blade that could lead to cracking of a T/R blade and subsequent loss of control of the helicopter. This AD requires:
- Before each start of the engines, visually checking each T/R blade for a crack. An owner/operator (pilot) holding at least a private pilot certificate may perform this visual check and must enter compliance with paragraph (a) of this AD into the aircraft maintenance records in accordance with 14 CFR 43.11 and 91.417(a)(2)(v). A pilot may do this check because it requires no special tools and can be performed equally well by a pilot or a mechanic.
- Within 25 hours TIS or 30 days, whichever occurs first, unless accomplished previously, and thereafter at intervals not to exceed 25 hours TIS or 30 days, whichever occurs first, cleaning and visually inspecting the T/R blade skins, leading edge spar, doublers, grip plates, and trailing edge for a crack, corrosion (may be indicated by blistering, peeling, flaking, bubbling, or cracked paint) and any other damage (including a nick, scratch, or dent) using a 3x or higher magnifying glass.
- If certain damage is found, inspecting the affected area using a 10-power or higher magnifying glass and measuring the depth of the damage.
- Before further flight, repairing or replacing, as applicable, any unairworthy T/R blade. The short compliance time involved is required because a cracked or damaged T/R blade creates an unsafe condition that can adversely affect the structural integrity and controllability of the helicopter. Therefore the required actions within the specified short time intervals require that this AD be issued immediately.
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.
We estimate that this AD will affect 384 helicopters of U.S. registry. There Start Printed Page 24862are approximately 184 Model 205A and 205A-1 helicopters, 4 Model 205B helicopters, 101 Model 212 helicopters, 80 Model 412, 412CF, and 412EP helicopters, and 15 modified Model 204B helicopters. Each visual check will take .125 hours, each visual inspection will take .5 hours, and 6 hours to remove and replace each T/R blade assembly, if necessary. The average labor rate is $80. Replacement parts will cost $11,243 for each T/R blade assembly. Based on these figures, the estimated cost impact of the AD for all of the affected models will be $1,828,855 assuming an average of 600 hours TIS per year for each helicopter resulting in 365 visual checks, 24 inspections, and 5 T/R blade assembly replacements for the total fleet.
This AD is a final rule that involves requirements that affect flight safety and was not preceded by notice and an opportunity for public comment; however, we invite you to submit any written data, views, or arguments regarding this AD. Send your comments to an address listed under ADDRESSES. Include “Docket No. FAA-2008-0490; Directorate Identifier 2008-SW-26-AD” at the beginning of your comments. We specifically invite comments on the overall regulatory, economic, environmental, and energy aspects of the AD. We will consider all comments received by the closing date and may amend the AD in light of those comments.
We will post all comments we receive, without change, to http://www.regulations.gov, including any personal information you provide. We will also post a report summarizing each substantive verbal contact with FAA personnel concerning this AD. Using the search function of our docket Web site, you can find and read the comments to any of our dockets, including the name of the individual who sent the comment. You may review the DOT's complete Privacy Act Statement in the Federal Register published on April 11, 2000 (65 FR 19477-78).
We have determined that this AD will not have federalism implications under Executive Order 13132. This AD 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.
For the reasons discussed above, I certify that the 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 an economic evaluation of the estimated costs to comply with this AD. See the AD docket to examine the economic evaluation.
Authority for This Rulemaking
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.Start List of Subjects
List of Subjects in 14 CFR Part 39End List of Subjects
Adoption of the AmendmentStart Amendment Part
Accordingly, pursuant to the authority delegated to me by the Administrator, the Federal Aviation Administration amends part 39 of the Federal Aviation Regulations (End Amendment Part Start Part
PART 39—AIRWORTHINESS DIRECTIVESEnd Part Start Amendment Part
1. The authority citation for part 39 continues to read as follows:End Amendment Part
2. Section 39.13 is amended by adding a new airworthiness directive to read as follows:End Amendment Part
2008-10-03 Bell Helicopter Textron: Amendment 39-15509. Docket No. FAA-2008-0490; Directorate Identifier 2008-SW-26-AD.
The following model helicopters, with the specified tail rotor blade assembly (T/R blade) installed, certificated in any category:
|Helicopter model||With T/R blade, part number (P/N)|
|204B, 205A, 205A-1, 212, 412, 412CF, and 412EP||212-010-750-(all dash numbers).|
|205B||212-010-750-(all dash numbers). 212-015-501-(all dash numbers).|
|210||210-010-001-(all dash numbers). 212-010-750-(all dash numbers).|
Required as indicated.
To detect any damage in a T/R blade, prevent cracking of a T/R blade leading to failure from static overload, and subsequent loss of control of the helicopter, accomplish the following:
(a) Before each start of the engines, visually check both sides of each T/R blade for a crack. An owner/operator (pilot) holding at least a private pilot certificate may perform this visual check and must enter compliance with this paragraph into the aircraft maintenance records in accordance with 14 CFR 43.11 and 91.417(a)(2)(v).
(b) Within 25 hours time-in-service (TIS) or 30 days, whichever occurs first, unless accomplished previously, and thereafter at intervals not to exceed 25 hours TIS or 30 days, whichever occurs first:
(1) Clean each T/R blade by hand using a mild degreaser and water to remove soot and grime on both sides of the blade using a coarse, loosely woven cotton cloth in a spanwise direction. Use a cloth with a color that contrasts with the color of the T/R blade so that a snag will be visible.
(2) Using a 3-power or higher magnifying glass and a bright light, visually inspect the T/R blade skins, leading edge spar, doublers, grip plates, and trailing edge for a crack, corrosion (may be indicated by blistering, peeling, flaking, bubbling, or cracked paint) and any other damage (including a nick, scratch, or dent). See Figure 1 of this AD. Pay particular attention to both sides of the T/R blade in the area located 16 to 26 inches from the T/R blade tip (blade station 25 to 35—the T/R blade tip is located at blade station 51) and to the inboard blade butt area near the attachment of the external balance weights Start Printed Page 24863and screws. Also pay particular attention to any blade surface that was snagged by the cloth, as that may be an indication of a crack or paint chip that could lead to corrosion.
(3) If any blistering, peeling, flaking, bubbling, or cracked paint is detected, remove the paint from the affected area and visually inspect the affected area for corrosion or a crack using a 10-power or higher magnifying glass. If any corrosion is found, measure the depth of the corrosion (a digital optical micrometer is one tool that can be used for this measurement).
(4) If a nick, scratch, or dent is found, visually inspect for a crack using a 10-power or higher magnifying glass and measure the depth of the damage (a digital optical micrometer is one tool that can be used for this measurement).
(c) Before further flight:
(1) Replace any T/R blade that has a crack with an airworthy blade.
(2) Replace any T/R blade that has any corrosion, nick, scratch, dent, or other damage that exceeds any maximum repair limit with an airworthy blade.
The maximum repair limits are specified in the applicable maintenance manual.
(3) Repair or replace with an airworthy blade any T/R blade that has any corrosion, nick, scratch, dent or other damage that is within the maximum repair limits.
The repair procedures are specified in the applicable maintenance manual and component repair and overhaul manuals.
(d) 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, Rotorcraft Certification Office, Rotorcraft Directorate, FAA, ATTN: Michael Kohner, Aviation Safety Engineer, Fort Worth, Texas 76193-0170, telephone (817) 222-5447, fax (817) 222-5783, for information about previously approved alternative methods of compliance.
(e) This amendment becomes effective on May 21, 2008.Start Signature
Issued in Fort Worth, Texas, on April 22, 2008.
Mark R. Schilling,
Acting Manager, Rotorcraft Directorate, Aircraft Certification Service.
BILLING CODE 4910-13-P
BILLING CODE 4910-13-CStart Printed Page 24864
[FR Doc. E8-9790 Filed 5-5-08; 8:45 am]
BILLING CODE 4910-13-P