[Federal Register Volume 62, Number 217 (Monday, November 10, 1997)]
[Rules and Regulations]
[Pages 60451-60454]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 97-29534]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 91-CE-45-AD; Amendment 39-10197; AD 97-23-09]
RIN 2120-AA64


Airworthiness Directives; de Havilland DHC-6 Series Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Final rule.

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[[Page 60452]]

SUMMARY: This amendment supersedes Airworthiness Directive (AD) 78-26-
02, which currently requires repetitively inspecting the fuselage side 
frame flanges at Fuselage Station (FS) 218.125 and FS 219.525 for 
cracks on certain de Havilland DHC-6 series airplanes, and repairing or 
replacing any cracked part. The Federal Aviation Administration's 
policy on aging commuter-class aircraft is to eliminate or, in certain 
instances, reduce the number of certain repetitive short-interval 
inspections when improved parts or modifications are available. This AD 
requires modifying the fuselage side frames at the referenced FS areas 
as terminating action for the repetitive inspections that are currently 
required by AD 78-26-02. The actions specified in this AD are intended 
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.

DATES: Effective December 22, 1997.
    The incorporation by reference of certain publications listed in 
the regulations is approved by the Director of the Federal Register as 
of December 22, 1997.

ADDRESSES: Service information that applies to this AD may be obtained 
from de Havilland, Inc., 123 Garratt Boulevard, Downsview, Ontario, 
Canada, M3K 1Y5. This information may also be examined at the Federal 
Aviation Administration (FAA), Central Region, Office of the Regional 
Counsel, Attention: Rules Docket 91-CE-45-AD, Room 1558, 601 E. 12th 
Street, Kansas City, Missouri 64106; or at the Office of the Federal 
Register, 800 North Capitol Street, NW., suite 700, Washington, DC.

FOR FURTHER INFORMATION CONTACT: Jon Hjelm, Aerospace Engineer, FAA, 
New York Aircraft Certification Office, 10 Fifth Street, 3rd Floor, 
Valley Stream, New York 11581; telephone (516) 256-7523; facsimile 
(516) 568-2716.

SUPPLEMENTARY INFORMATION:

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 the adoption 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

[[Page 60453]]

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 
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 
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 and based 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.

[[Page 60454]]

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), 40101, 40113, 44701.


Sec. 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:
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,  Original Issue....  June 2, 1978.     
 20, and 23.                                                            
3, 4, 11, 12, 15, 16, 17, 18,     Revision A........  May 18, 1979.     
 21, and 22.                                                            
------------------------------------------------------------------------

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

------------------------------------------------------------------------
                                                       Fuselage stations
           Serial No.               Modification 6/     affected (both  
                                  1553  incorporated        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 
fuselage side frames required as specified in the following chart:

------------------------------------------------------------------------
                                                       Fuselage stations
           Serial Nos.              Modification 6/     affected (both  
                                  1553  incorporated        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,  Original Issue....  June 2, 1978.     
 20, and 23.                                                            
3, 4, 11, 12, 15, 16, 17, 18,     Revision A........  May 18, 1979.     
 21, and 22.                                                            
------------------------------------------------------------------------

    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 (39-10197) becomes effective on December 22, 
1997.

    Issued in Kansas City, Missouri, on October 31, 1997.
James E. Jackson,
Acting Manager, Small Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 97-29534 Filed 11-7-97; 8:45 am]
BILLING CODE 4910-13-U