AD 97-23-09 — Aircraft-logs.com

97-23-09 DE HAVILLAND: Amendment 39-10197; Docket No. 91-CE-45-AD. Supersedes 78-26-02, Amendment 39-3370.

Applicability: Models DHC-6-1, DHC-6-100, DHC-6-200, and DHC-6-300 airplanes (serial numbers 1 through 411), certificated in any category, that do not have Modification Nos. 6/1461 and 6/1462 incorporated.

NOTE 1: Modification No. 6/1461 introduces fuselage side frames manufactured from material having improved stress corrosion properties at Fuselage Station (FS) 218.125, and Modification No. 6/1462 introduces fuselage side frames of this material at FS 219.525.

NOTE 2: This AD applies to each airplane identified in the preceding applicability provision, regardless of whether it has been modified, altered, or repaired in the area subject to the requirements of this AD. For airplanes that have been modified, altered, or repaired so that the performance of the requirements of this AD is affected, the owner/operator must request approval for an alternative method of compliance in accordance with paragraph (e) of this AD. The request should include an assessment of the effect of the modification, alteration, or repair on the unsafe condition addressed by this AD; and, if the unsafe condition has not been eliminated, the request should include specific proposed actions to address it.

Compliance: Required as indicated, unless already accomplished.

To prevent failure of the fuselage because of cracks in the fuselage side frames, which, if not detected and corrected, could result in loss of control of the airplane, accomplish the following:

(a) Within the next 200 hours time-in-service (TIS) after the effective date of this AD, unless already accomplished (compliance with AD 78-26-02), and thereafter as indicated below, inspect the fuselage side frames for cracks at FS 218.125 and FS 219.525, as applicable (see chart below) in accordance with the ACCOMPLISHMENT INSTRUCTIONS section of de Havilland Service Bulletin (SB) No. 6/371,which incorporates the following pages:

Pages
Revision Level
Date
1, 2, 5, through 10,
13, 14, 19, 20, and 23
Original Issue
June 2, 1978
3, 4, 11, 12, 15, 16, 17,
18, 21, and 22
Revision A
May 18, 1979

Utilize the following chart to determine which fuselage stations are affected:

Serial
Numbers
Modification 6/1553
Incorporated
Fuselage Stations
Affected (both sides)
1 through 395
No
218.125 and 219.525
1 through 395
Yes
219.525 only
396 through 411
N/A
219.525 only

NOTE 3: Modification 6/1553 incorporates fuselage side frames of improved stress corrosion resistant material at FS 218.125.

(1) If any crack is found during any inspection required by this AD, prior to further flight, accomplish one of the following:

(i) Repair the cracks in accordance with the ACCOMPLISHMENT INSTRUCTIONS: REPAIR: section of de Havilland SB No. 6/371. Reinspect thereafter at intervals not to exceed 600 hours TIS until the modification specified in paragraph (b) of this AD is incorporated; or

(ii) Replace the cracked fuselage side frame in accordance with the ACCOMPLISHMENT INSTRUCTIONS: REPLACEMENT: section of de Havilland SB No. 6/371. Reinspect any fuselage side frame not replaced at intervals not to exceed 600 hours TIS until the modification specified in paragraph (b) of this AD is incorporated.

(2) If no cracks are found, reinspect thereafter at intervals not to exceed 600 hours TIS until the modification specified in paragraph (b) of this AD is incorporated, provided no cracks are found during an inspection. If cracks are found, prior to further flight, repair or replace and reinspect as specified in paragraph (a)(1) of this AD.

(b) Within the next 4,800 hours TIS after the effective date of this AD, incorporate Modification Nos. 6/1461 and 6/1462 in accordance with the ACCOMPLISHMENT INSTRUCTIONS: REPLACEMENT: section of de Havilland SB No. 6/371. This consists of replacing all fuselageside frames required as specified in the following chart:

Serial
Numbers
Modification 6/1553
Incorporated
Fuselage Stations
Affected (both sides)
1 through 395
No
218.125 and 219.525
1 through 395
Yes
219.525 only
396 through 411
N/A
219.525 only

(c) Incorporating Modification Nos. 6/1461 and 6/1462 as specified in paragraph (b) of this AD is considered terminating action for the inspection requirement of this AD. The modifications may be incorporated at any time prior to the next 4,800 hours TIS after the effective date of this AD, at which time they must be incorporated.

(d) Special flight permits may be issued in accordance with sections 21.197 and 21.199 of the Federal Aviation Regulations (14 CFR 21.197 and 21.199) to operate the airplane to a location where the requirements of this AD can be accomplished.

(e) An alternative method of compliance or adjustment of the initial or repetitive compliance times that provides an equivalent level of safety may be approved by the Manager, New York Aircraft Certification Office (ACO), FAA, 10 Fifth Street, 3rd Floor, Valley Stream, New York 11581.

(1) The request shall be forwarded through an appropriate FAA Maintenance Inspector, who may add comments and then send it to the Manager, New York Aircraft ACO.

(2) Alternative methods of compliance approved in accordance with AD 78-26-02 are not considered approved as alternative methods of compliance with this AD.

NOTE 4: Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the New York ACO.

(f) The inspections and modifications required by this AD shall be done in accordance with de Havilland Service Bulletin (SB) No. 6/371, which incorporates the following pages:

Pages
Revision Level
Date
1, 2, 5, through 10,
13, 14, 19, 20, and 23
Original Issue
June 2, 1978
3, 4, 11, 12, 15, 16, 17,
18, 21, and 22
RevisionA
May 18, 1979

This incorporation by reference was approved by the Director of the Federal Register in accordance with 5 U.S.C. 552(a) and 1 CFR part 51. Copies may be obtained from de Havilland, Inc., 123 Garratt Boulevard, Downsview, Ontario M3K 1Y5 Canada. Copies may be inspected at the FAA, Central Region, Office of the Regional Counsel, Room 1558, 601 E. 12th Street, Kansas City, Missouri, or at the Office of the Federal Register, 800 North Capitol Street, NW., 7th Floor, suite 700, Washington, DC.

(g) This amendment (39-10197) supersedes AD 78-26-02, Amendment 39-3370.

(h) This amendment becomes effective on December 22, 1997.

Events Leading to the Issuance of This AD

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 Nos. 6/1461 and 6/1462 incorporated was published in the Federal Register as a notice of proposed rulemaking (NPRM) on August 11, 1995 (60 FR 41030). The NPRM proposed to supersede AD 78-26-02 with a new AD that would (1) retain the current requirement of repetitively inspecting the fuselage side frame flanges at Fuselage Station (FS) 218.125 and FS 219.525, as applicable, and repairing or replacing any cracked part; and (2) require modifying the fuselage side frame flanges in the referenced FS areas (Modification Nos. 6/1461 and 6/1462), as terminating action for the repetitive inspections. Accomplishment of the proposed actions as specified in the NPRM would be in accordance with de Havilland Service Bulletin (SB) No. 6/371, dated June 2, 1978.

Modification No. 6/1461 introduces fuselage side frames manufactured from material having improved stress corrosion properties at FS 218.125, and Modification No. 6/1462 introduces fuselage side frames of this material at FS 219.525.

Interested persons have been afforded an opportunity to participate in the making of this amendment. No comments were received on the proposed rule or the FAA's determination of the cost to the public.

As written, the original NPRM (as does AD 78-26-02) allows continued flight if cracks are found in the fuselage side frames that do not exceed certain limits. Extensive analysis of the consequences of flying with known cracks in primary structure prompted the FAA to establish a policy that disallows airplane operation when known cracks exist in primary structure, unless the ability to sustain ultimate load with these cracks is proven. The fuselage structure is considered primary structure, and the FAA has not received any analysis to prove that ultimate load can be sustained with cracks in this area.

For this reason, the FAA determined that the crack limits contained in the original NPRM and AD 78-26-02 should be eliminated, and that the NPRM should be revised to propose immediate replacement of any cracked fuselage flanges. Since revising the proposed AD to require immediate replacement of any cracked fuselage flanges went beyond the scope of what was presented in the original NPRM, the FAA published a supplemental NPRM in the Federal Register on March 31, 1997 (62 FR 15129).

Interested persons were again afforded an opportunity to participate in the making of this amendment. No comments were received regarding the substance of the supplemental NPRM or the FAA's determination of the cost to the public.

The FAA's Determination

After careful review of all available information related to the subject presented above, the FAA has determined that air safety and the public interest require theadoption of the AD as proposed in the supplemental NPRM, 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's Aging Commuter-class Aircraft Policy

The actions specified in this AD are part of the FAA's aging commuter class aircraft policy, which briefly states that, when a modification exists that could eliminate or reduce the number of required critical inspections, the modification should be incorporated. This policy is based on the FAA's determination that reliance on critical repetitive inspections on aging commuter-class airplanes carries an unnecessary safety risk when a design change exists that could eliminate or, in certain instances, reduce the number of those critical inspections. In determining what inspections are critical, the FAA considers (1) the safety consequences of the airplane if the known problem is not detected by the inspection; (2) the reliability of the inspection such as the probability of not detecting the known problem; (3) whether the inspection area is difficult to access; and (4) the possibility of damage to an adjacent structure as a result of the problem.

The alternative to modifying the fuselage side frames at FS 218.125 and FS 219.525 would be to rely on the repetitive inspections required by AD 78-26-02 to detect cracks in these areas.

Cost Impact

The FAA estimates that 94 airplanes in the U.S. registry will be affected by this AD, that it will take approximately 300 workhours per airplane to accomplish the required modification, and that the average labor rate is approximately $60 an hour. Parts cost approximately $16,200 (average) per airplane. Based on these figures, the total cost impact of the required modification on U.S. operators is estimated to be $3,214,800 or $34,200 per airplane. This cost figure is based upon the presumption that no affected airplane owner/operator has incorporated Modification Nos. 6/1461 and 6/1462.

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 94 airplanes in the U.S. registry that would 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.

This AD allows 4,800 hours time-in-service (TIS) after the effective date of the AD before mandatory accomplishment of the design modification. The average utilization of the fleet for those airplanes in commercial commuter service is approximately 25 to 50 hours TIS per week. Based on these figures, operators of commuter-class airplanes involved in commercial operation have to accomplish the required modification within 24 to 48 calendar months after this AD becomes effective. For private owners, who typically operate between 100 to 200 hours TIS per year, this allows 24 to 48 years before the required modification is required.

The following paragraphs present cost scenarios for airplanes where no cracks are found and where cracks are found during the inspections, and where the remaining airplane life is 15 years with an average annual utilization rate of 1,600 hours TIS. A copy of the full Cost Analysis and Regulatory Flexibility Determination for this action may be examined at the FAA, Central Region, Office of the Regional Counsel, Attention: Rules Docket No. 91-CE-45-AD, Room 1558, 601 E. 12th Street, Kansas City, Missouri.

- No Cracks Scenario: Under the provisions of AD 78-26-02, 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 400 hours TIS. This would amount to a remaining airplane life (estimated 15 years) cost of $18,420; this figure is based on the presumption that no cracks are found during the inspections. This AD requires the same inspections except at 600-hour TIS intervals until 4,800 hours TIS after the effective date of the AD when the operator has to replace the fuselage side frame flanges (eliminating the need for further repetitive inspections), which results in a present value cost of $31,433. The incremental cost of this AD for such an airplane is $13,013 or $4,959 annualized over the 3 years it will take to accumulate 4,800 hours TIS. An owner of a general aviation airplane who operates 800 hours TIS annually without finding any cracks during the 600-hour TIS inspections will incur a present value incremental cost of $7,598. This amounts to a per year amount of $1,594 over the 6 years it takes to accumulate 4,800 hours TIS.

- Excessive cracking scenario: AD 78-26-02 requires repairing or replacing the fuselage side frames if excessive cracking is found (as defined by SB No. 6/371), as will this AD. The difference is that AD 78-26-02 requires immediate crack repair and then replacement within 360 days after finding the crack, and this AD requires immediate repair and mandatory replacement of the fuselage side frames within 4,800 hours TIS after the effective date of the AD. This results in a present value total cost of $34,709 per airplane in scheduled service, which makes immediate replacement more economical ($32,400) than repetitively inspecting. With this scenario, this AD averages a present value cost savings over that required in AD 78-26-02 of $2,083 ($794 annualized over 3 years) for each airplane operated in scheduled service, and $6,607 ($1,386 annualized over 6 years) for each airplane operated in general aviation service.

Regulatory Flexibility Determination and Analysis

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 required rule, or any number of small entities judged to be substantial by the rulemaking official. A "significant economic impact" is defined by an annualized netcompliance 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 nine 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 94 U.S.-registered airplanes affected by this AD, the federal government owns 4 airplanes. Of the other 90, one business owns 26 airplanes, two businesses own 7 airplanes each, one business owns 3 airplanes, seven businesses own 2 airplanes each, and thirty-three businesses own 1 airplane each.

Because the FAA has no readily available means of obtaining data on sizes of these entities, the economic analysis for this AD utilizes the worst case scenario using the lower annualized cost threshold of $5,000 for operators in unscheduled service instead of $69,000 for operators in scheduled service. With this in mind andbased on the above ownership distribution, the 33 entities owning two or fewer airplanes will not experience a "significant economic impact" as defined by FAA Order 2100.14A. Since the remaining 11 entities do not constitute a "substantial number" as defined in the Order, this AD will not have a "significant economic impact on a substantial number of small entities."

Regulatory Impact

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.

39.13 [Amended]
2.Section 39.13 is amended by removing Airworthiness Directive (AD) 78-26-02, Amendment 39-3370, and adding the following new AD to read as follows:

AD Number	97-23-09	Status	Active
Effective Date	December 22, 1997	Issue Date	Not specified
Docket Number	91-CE-45-AD	Amendment	39-10197
Product Type	["Aircraft"]	Product Subtype	["Small Airplane"]
CFR Part	--- - Part 39 [62 FR 60451 NO. 217 11/10/97]	CFR Section	N/A
Citation	Federal Register: November 10, 1997 (Volume 62, Number 217)

Manufacturer(s)	Viking Air Limited
Model(s)	DHC-6-1 DHC-6-100 DHC-6-200 DHC-6-300

AD 97-23-09 ACTIVE