On April 12, 2002, the FAA published AD 2001-24-51, Amendment 39-12706 (67 FR 17934), applicable to MDHI Model 600N helicopters, that had been issued on November 28, 2001, to all known operators. That AD requires, within 5 hours time-in-service (TIS), inspecting both upper tailboom attachment fittings, nut plates, and both angles for a crack or thread damage, and repairing or replacing any cracked or damaged part before further flight. That AD also requires replacing the upper right tailboom attachment bolt with a new bolt, and if the upper right tailboom attachment bolt is broken, replacing the three remaining attachment bolts with airworthy attachment bolts before further flight. Adding a washer to each bolt and modifying both access covers was also required. Thereafter, inspecting the upper tailboom attachments at intervals not to exceed 25 hours TIS and repairing or replacing any cracked part is required by that AD. That AD was prompted by the discovery of a cracked attachment bolt on a helicopter. That condition, if not corrected, could result in failure of a tailboom attachment, loss of the tailboom, and subsequent loss of control of the helicopter.
Since issuing that AD, on March 21, 2006, an accident occurred in Alberta, Canada, involving an MDHI Model 600N helicopter, resulting in one fatality. That accident may have been caused by failure of the thread engagement between the nut plate and bolt, and/or by cracking in the attachment bathtub fitting. This condition, if not corrected, could result in failure of the tailboom attachment fittings, separation of the tailboom from the helicopter, and subsequent loss of control of the helicopter.
On February 2, 2005, we issued a notice of proposed rulemaking (NPRM), applicable to MDHI Model 600N helicopters, to supersede AD 2001-24-51. That NPRM, Docket No. 2004-SW-16-AD (70 FR 7065, February 10, 2005), proposed to require the same actions required by AD 2001-24- 51, and also proposed to require, before further flight, installing six additional inspection holes in the aft fuselage skin panels. The NPRM also proposed to require, within 100 hours TIS, inspecting the lower tailboom attachment fittings, inspecting the upper longerons at intervals not to exceed 1,200 flight hours, and additionally proposed a terminating action of modifying the fuselage aft section to strengthen the tailboom attachments and longerons. We anticipate withdrawing that NPRM. We also anticipate issuing a subsequent AD to require, within 24 months TIS, modifying the aft fuselage to strengthen the tailboom attachments and the longerons.
We have reviewed the following MDHI service information:
MD Helicopters Service Bulletin SB600N-036, dated November 2, 2001, which describes procedures for inspecting the tailboom attachment fittings, repairing damaged fittings, and installing inspection holes in the upper right and upper left access covers;
MD Helicopters Service Bulletin SB600N-039, dated December 9, 2003, which describes procedures for installing additional inspection holes in the fuselage, and also describes procedures for recurring inspections of the tailboom attachment fittings and of the upper longerons for cracks; and
MD Helicopters Service Bulletin SB600N-043, dated April 13, 2006, which describes procedures for inspecting the tailboom attachment fittings and attachment bolts, and replacing the nut plates, attachment fittings, and attachment bolts, if necessary.
MD Helicopters Technical Bulletin TB600N-007, Revision 1, dated April 13, 2006, which describes procedures for modifying the fuselage aft section to strengthen tailboom attachment fittings and upper longerons.
Since an unsafe condition has been identified that is likely to exist or develop on other MDHI Model 600N
helicopters of the same type design, this AD supersedes AD 2001-24-51 to require, within 5 hours TIS, installing six inspection holes in the aft fuselage skin panels. Then, using a borescope, inspect all four tailboom attachment fittings and the surrounding areas, the upper longerons, the upper nut plates and the upper angles for cracks. Add a washer to each bolt between the tailboom and the NAS1587 countersunk washer. If a crack is found on a right-hand angle, before further flight, install a new clip. If a crack is found on the left-hand angle, before further flight, replace the angle with an airworthy angle, or repair the angle in accordance with FAA-approved procedures. Finally, replacing the upper RH tailboom attachment bolt with a new bolt, and if the upper right attachment bolt is broken, replacing the three remaining attachment bolts with airworthy attachment bolts before further flight is required. Within 25 hours TIS, the following actions are also required:
Inspecting all attachment fittings and surrounding areas;
Replacing the upper right tailboom attachment fitting with an airworthy fitting;
Painting the inspectionarea;
Inspecting the attachment bolts for wear or damage;
Replacing worn or damaged attachment bolts; and
Replacing all existing nut plates with airworthy nut plates. Thereafter, inspect the upper tailboom attachment fittings, angles, and nut plates at intervals not to exceed 25 hours TIS, and inspect the lower tailboom attachment fittings, angles and nut plates at intervals not to exceed 100 hours TIS. Modifying the aft fuselage to strengthen the tailboom attachments and the longerons constitutes a terminating action for the requirements of this AD. Accomplish the actions by following the specified portions of the service and technical bulletins described previously.
The short compliance time involved is required because the previously described critical unsafe condition can adversely affect the controllability and structural integrity of the helicopter. A portion of the helicopters operated in this fleet have high utilization rates. Drilling inspection holes and inspecting the tailboom attachment fittings and surrounding areas for cracks are required within 5 hours TIS, therefore this AD must 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.
The FAA estimates that this AD will affect 18 helicopters, and:
Initial inspections will take approximately 2 work hours;
Repetitive inspections will take approximately 24 work hours; and
The initial modification will take approximately 25 work hours for a total of 51 work hours per helicopter to accomplish at an average labor rate of $80 per work hour. Required parts will cost approximately $2,050 for each tailboom attachment fitting (1 per helicopter) and $26 for 4 nut plates and 4 rivet collars per helicopter. Based on these figures, which assume a rateof utilization of 600 hours TIS per year, resulting in 24 repetitive inspections per year, we estimate the total cost impact of the AD on U.S. operators to be approximately $6,156 per helicopter, or $110,808, for the fleet, to perform the inspections and replacements.
Comments Invited
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-2006-24518; Directorate Identifier 2006-SW-10-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://dms.dot.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), or you may visit http://dms.dot.gov .
Regulatory Findings
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 DMS 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.
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.
Sec. 39.13 [Amended]
2. Section 39.13 is amended by removing Amendment 39-12706 (71 FR 17934, April 12, 2002), and by adding a new airworthiness directive (AD), Amendment 39-14569, to read as follows: