A proposal to amend part 39 of the Federal Aviation Regulations (14 CFR part 39) to include an AD that would apply to certain de Havilland DHC-6 series airplanes without Modification No. 6/1301 incorporated was published in the Federal Register on October 31, 1994 (59 FR 54415). The action proposed to supersede AD 73-05-03 with a new AD that would (1) initially retain the requirement of repetitively inspecting the wing rear spar cap for cracks and replacing any cracked part; and (2) eventually require installing wing rear spar attachment caps that are manufactured from a material having improved stress corrosion resistant properties (Modification 6/1301) as terminating action for the repetitive inspections. Accomplishment of the proposed actions would be in accordance with de Havilland Service Bulletin No. 6/295, Revision D, dated December 20, 1991.
Interested persons have been afforded an opportunity to participate in the making of this amendment. Nocomments were received on the proposed rule or the FAA's determination of the cost to the public.
After careful review of all available information related to the subject presented above including the referenced service information, the FAA has determined that air safety and the public interest require the adoption of the rule as proposed except for minor editorial corrections. The FAA has determined that these minor corrections will not change the meaning of the AD and will not add any additional burden upon the public than was already proposed.
The FAA estimates that 82 airplanes in the U.S. registry will be affected by this AD, that it will take approximately 22 workhours per airplane to accomplish the required modification, and that the average labor rate is approximately $60 an hour. Parts cost approximately $6,350 per airplane. Based on these figures, the total cost impact of this AD on U.S. operators is estimated to be $628,940. This figure is based upon the assumption that no affected airplane owner/operator has incorporated Modification 6/1301.
The intent of the FAA's aging commuter airplane program is to ensure safe operation of commuter-class airplanes that are in commercial service without adversely impacting private operators. Of the approximately 82 airplanes in the U.S. registry that will be affected by this AD, the FAA has determined that approximately 45 percent are operated in scheduled passenger service. A significant number of the remaining 55 percent are operated in other forms of air transportation such as air cargo and air taxi.
The following paragraphs present cost scenarios for airplanes where no cracks were found and where certain category cracks were found during the inspections, and where the remaining airplane life is 15 years with an average annual utilization rate of 1,600 hours time-in-service (TIS). A copy of the full Cost Analysis and Regulatory Flexibility Determination for the required action may be examined at the FAA, Central Region, Office of the Assistant Chief Counsel, Attention: Rules Docket No. 91-CE-21-AD, Room 1558, 601 E. 12th Street, Kansas City, Missouri.
o No Cracks Scenario: Under the provisions of AD 73-05-03, an owner/operator of an affected de Havilland DHC-6 series airplane in scheduled service who operates an average of 1,600 hours TIS annually will inspect every 26 weeks. This amounts to a remaining airplane life (estimated 15 years) cost of $14,058; this figure is based on the assumption that no cracks are found during the inspections. This AD will incur the inspection at one 1,200-hour TIS interval and then, at 2,400 hours TIS after the effective date of the AD, the operator has to replace the top flange of the wing spar attachment caps (eliminating the need for further repetitive inspections). This results in a present value cost of $8,331, which is a present value cost savings over that required in AD 73-05-03 of $5,727 or $4,154 annualized over the 1.5 years it will take to accumulate 2,400 hours TIS. An owner of a general aviation airplane who operates 800 hours TIS annually without finding any cracks during the 1,200-hour TIS inspection will incur a present value cost savings over that required in AD 73-05-03 of $6,430. This amounts to a per year savings of $2,450 over the 1.5 years it takes to accumulate 2,400 hours TIS.
o Category I cracks found scenario: These are spanwise cracks that are inboard of the third rivet, or spanwise cracks that exceed 50 inches, or any chordwise cracks. Under the provisions of AD 73-05-03, an owner/operator who finds cracks during an inspection under this scenario has to immediately repair the cracked part and repetitively inspect every 26 weeks. This AD will require immediate replacement as terminating action for the repetitive inspections, which results in present value compliance costs of $8,355. The present value cost savings over that required in AD 73-05-03 for this scenario is $6,300 for airplanes in scheduled service and $6,295 per general aviation airplane.
o Category II cracks found scenario: These are spanwise cracks that are outboard of the 10th rivet and within the limits of paragraph (b) of the service bulletin. Under the provisions of AD 73-05-03, an owner/operator who finds cracks during an inspection under this scenario has to repetitively inspect every 13 weeks. This results in present value compliance costs of $27,625. This AD would require repetitive inspections every 600 hours TIS until replacement of the top flange of the wing rear spar attachment caps at 2,400 hours TIS after the effective date of the AD as terminating action for the repetitive inspections. This results in present value compliance costs of $9,700. Immediate replacement of the top flange is more economical than repetitively inspecting; present value costs are $8,355. The present value cost savings over that required in AD 73-05-03 for this scenario is $19,272 per airplane inscheduled service and $19,269 per general aviation airplane.
o Category III cracks found scenario: These are spanwise cracks that are outboard of the 10th rivet and within the limits of paragraph (c) of the service bulletin. Under the provisions of AD 73-05-03, an owner/operator who finds cracks during an inspection in this scenario has to repetitively inspect every 2 weeks. This results in present value compliance costs of $175,000. This AD requires repetitive inspections every 100 hours TIS until replacement of the top flange of the wing rear spar attachment caps at 2,400 hours TIS after the effective date of the AD as terminating action for the repetitive inspections. This results in present value compliance costs of $13,965. Immediate replacement of the top flange is more economical than repetitively inspecting; present value costs are $8,355. The present value cost savings over that required in AD 73-05-03 for this scenario is $166,075 per airplane in scheduled serviceand $166,784 per general aviation airplane.
o Category IV cracks found scenario: These are spanwise cracks that are outboard of the 10th rivet and exceed the limits of paragraph (b) or (c) of the service bulletin. Also included are cracks in the splice plates of the vertical and horizontal legs of the rear spar or elongated rivet holes. Under the provisions of AD 73-05-03, an owner/operator who finds cracks during an inspection under this scenario has to immediately repair any crack and then repetitively inspect every 26 weeks. This results in present value costs of $14,500. This AD requires immediate crack repair, then an inspection after accumulating 1,200 hours TIS, and replacement of the top flange of the wing rear spar attachment caps at 2,400 hours TIS after the effective date of the AD as terminating action for the repetitive inspections. This results in present value compliance costs of $8,929. Immediate replacement of the top flange is more economical than repetitively inspecting; present value costs are $8,355. The present value cost savings over that required in AD 73-05-03 for this scenario is $6,040 per airplane in scheduled service and $6,430 per general aviation airplane.
o Category V cracks found scenario: These are spanwise cracks that are between the third and tenth rivet. Under the provisions of AD 73-05-03, an owner/operator who finds cracks during an inspection under this scenario has to immediately repair any crack, repetitively inspect every 2 weeks, replace the top flange of the wing rear spar attachment caps, and repetitively inspect thereafter every 26 weeks. This results in present value compliance costs of about $30,000. This AD requires immediate crack repair, repetitive inspections every 50 hours TIS, and replacement of the top flange of the wing rear spar attachment caps at 2,400 hours TIS after the effective date of the AD as terminating action for the repetitive inspections. This results in present value compliancecosts of $38,988. Immediate replacement of the top flange is more economical than repetitively inspecting; present value costs are $8,355. The present value cost savings over that required in AD 73-05-03 for this scenario are $19,356 per airplane in scheduled service and $26,367 per general aviation airplane.
o Category VI cracks found scenario: These are spanwise cracks that have a total length exceeding 30 inches but not exceeding 50 inches. Under the provisions of AD 73-05-03, an owner/operator who finds cracks during an inspection under this scenario has to immediately repair any crack, replace the top flange of the wing rear spar attachment caps at 26 weeks, and repetitively inspect thereafter every 26 weeks. This results in present value compliance costs of about $21,200. This AD requires immediate crack repair, repetitive inspections every 600 hours TIS, and replacement of the top flange of the wing rear spar attachment caps at 2,400 hours TIS after the effective dateof the AD as terminating action for the repetitive inspections. This results in present value compliance costs of $10,289. Immediate replacement of the top flange is more economical than repetitively inspecting; present value costs are $8,355. The present value cost savings over that required in AD 73-05-03 for this scenario is $12,707 per airplane in scheduled service and $13,028 per general aviation airplane.
The Regulatory Flexibility Act of 1980 (RFA) was enacted by Congress to ensure that small entities are not unnecessarily or disproportionally burdened by government regulations. The RFA requires government agencies to determine whether rules could have a "significant economic impact on a substantial number of small entities," and, in cases where they could, conduct a Regulatory Flexibility Analysis in which alternatives to the rule are considered. FAA Order 2100.14A, Regulatory Flexibility Criteria and Guidance, outlines FAA procedures and criteria for complying with the RFA. Small entities are defined as small businesses and small not-for-profit organizations that are independently owned and operated or airports operated by small governmental jurisdictions. A "substantial number" is defined as a number that is not less than 11 and that is more than one-third of the small entities subject to a rule, or any number of small entities judged to be substantial by the rulemaking official. A "significant economic impact" is defined by an annualized net compliance cost, adjusted for inflation, which is greater than a threshold cost level for defined entity types. FAA Order 2100.14A sets the size threshold for small entities operating aircraft for hire at 9 aircraft owned and the annualized cost thresholds, adjusted to 1994 dollars, at $69,000 for scheduled operators and $5,000 for unscheduled operators.
Of the 82 U.S.-registered airplanes affected by this AD, three airplanes are owned by the federal government. Of the other 79, one business owns 24airplanes, one business owns 7 airplanes, one business owns 6 airplanes, one business owns 3 airplanes, 6 businesses own 2 airplanes each, and twenty-seven businesses own 1 airplane each.
As presented in the crack scenario discussion, replacing the top flange of the wing rear spar attachment caps immediately or within 2,400 hours TIS after the effective date of this AD is more economical in all scenarios than continuing to repetitively inspect the part for the life of the airplane. Therefore, this AD will not have a "significant economic impact on a substantial number of small entities."
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 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, 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 USC 106(g), 40101, 40113, 44701.
Section 39.13 - [AMENDED]
2. Section 39.13 is amended by removing Airworthiness Directive (AD) 73-05-03, Amendment 39-1658, and adding a new AD to read as follows: