[Federal Register Volume 60, Number 155 (Friday, August 11, 1995)]
[Proposed Rules]
[Pages 41029-41033]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 95-19917]



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[[Page 41030]]


DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 91-CE-45-AD]


Airworthiness Directives; de Havilland DHC-6 Series Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: This document proposes to supersede 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. The proposed action would require 
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 the proposed 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: Comments must be received on or before October 16, 1995.

ADDRESSES: Submit comments in triplicate to the Federal Aviation 
Administration (FAA), Central Region, Office of the Assistant Chief 
Counsel, Attention: Rules Docket No. 91-CE-45-AD, Room 1558, 601 E. 
12th Street, Kansas City, Missouri 64106. Comments may be inspected at 
this location between 8 a.m. and 4 p.m., Monday through Friday, 
holidays excepted.
    Service information that applies to the proposed AD may be obtained 
from de Havilland, Inc., 123 Garratt Boulevard, Downsview, Ontario, 
Canada, M3K 1Y5. This information also may be examined at the Rules 
Docket at the address above.

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:

Comments Invited

    Interested persons are invited to participate in the making of the 
proposed rule by submitting such written data, views, or arguments as 
they may desire. Communications should identify the Rules Docket number 
and be submitted in triplicate to the address specified above. All 
communications received on or before the closing date for comments, 
specified above, will be considered before taking action on the 
proposed rule. The proposals contained in this notice may be changed in 
light of the comments received.
    Comments are specifically invited on the overall regulatory, 
economic, environmental, and energy aspects of the proposed rule. All 
comments submitted will be available, both before and after the closing 
date for comments, in the Rules Docket for examination by interested 
persons. A report that summarizes each FAA- public contact concerned 
with the substance of this proposal will be filed in the Rules Docket.
    Commenters wishing the FAA to acknowledge receipt of their comments 
submitted in response to this notice must submit a self-addressed, 
stamped postcard on which the following statement is made: ``Comments 
to Docket No. 91-CE-45-AD.'' The postcard will be date stamped and 
returned to the commenter.

Availability of NPRMs

    Any person may obtain a copy of this NPRM by submitting a request 
to the FAA, Central Region, Office of the Assistant Chief Counsel, 
Attention: Rules Docket No. 91-CE-45-AD, Room 1558, 601 E. 12th Street, 
Kansas City, Missouri 64106.

Discussion

    The FAA has determined 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 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.
    These factors have led the FAA to establish an aging commuter-class 
aircraft policy that requires incorporating a known design change when 
it could replace a critical repetitive inspection. With this policy in 
mind, the FAA conducted a review of existing AD's that apply to de 
Havilland DHC-6 series airplanes. Assisting the FAA in this review were 
(1) de Havilland; (2) the Regional Airlines Association (RAA); and (3) 
several operators of the affected airplanes.
    From this review, the FAA has identified AD 78-26-02, Amendment 39-
3370, as one that should be superseded with a new AD that would require 
a modification that could eliminate the need for short-interval and 
critical repetitive inspections. AD 78-26-02 currently requires 
repetitively inspecting the fuselage side frame flanges at Fuselage 
Station (FS) 218.125 and FS 219.525 on certain de Havilland DHC-6 
series airplanes, and repairing or replacing any cracked part.
    De Havilland Service Bulletin (SB) No. 6/371, dated June 2, 1978, 
specifies procedures for inspecting, repairing, and modifying 
(Modification Nos. 6/1461 and 6/1462) the fuselage side frame flanges 
at FS 218.125 and FS 219.525. 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.
    This airplane model is manufactured in Canada and is type 
certificated for operation in the United States under the provisions of 
Section 21.29 of the Federal Aviation Regulations (14 CFR 21.29) and 
the bilateral airworthiness agreement between the United States and 
Canada. Pursuant to this bilateral airworthiness agreement, Transport 
Canada has kept the FAA informed of the situation described above.
    Based on its aging commuter-class aircraft policy and after 
reviewing all available information, the FAA has determined that AD 
action should be taken to eliminate the repetitive short-interval 
inspections required by AD 78-26-02, Amendment 39-3370, and 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.
    Since an unsafe condition has been identified that is likely to 
exist or develop in other de Havilland DHC-6 series airplanes of the 
same type design without Modification Nos. 6/1461 and 6/1462 
incorporated, the proposed AD 

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would 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 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 would be in accordance with de 
Havilland SB No. 6/371, dated June 2, 1978.
    The FAA estimates that 94 airplanes in the U.S. registry would be 
affected by the proposed AD, that it would take approximately 300 
workhours per airplane to accomplish the proposed 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 proposed modification on U.S. operators is 
estimated to be $3,214,800 or $34,200 per airplane. This cost figure is 
based upon the assumption that none of the affected airplane owners/
operators have 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 the proposed 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 proposed AD allows 4,800 hours time-in-service (TIS) after the 
proposed AD would become effective 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 would have to accomplish the 
proposed modification within 24 to 48 calendar months after the 
proposed AD would become effective. For private owners, who typically 
operate between 100 to 200 hours TIS per year, this would allow 24 to 
48 years before the proposed modification would be mandatory.
    The following paragraphs present cost scenarios for airplanes where 
no cracks were found and where 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 TIS. A copy of the full 
Cost Analysis and Regulatory Flexibility Determination for the proposed 
action may be examined at the FAA, Central Region, Office of the 
Assistant Chief 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 
would 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 assumption that no cracks are found during the 
inspections. The proposed AD would incur the same inspections except at 
600-hour TIS intervals until 4,800 hours TIS after the proposed AD 
would become effective where the operator would have to replace the 
fuselage side frame flanges (eliminating the need for further 
repetitive inspections), which would result in a present value cost of 
$31,433. The incremental cost of the proposed AD for such an airplane 
would be $13,013 or $4,959 annualized over the three years it would 
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 would incur a present value 
incremental cost of $7,598. This would amount to a per year amount of 
$1,594 over the six years it would take to accumulate 4,800 hours TIS.
     Limited Cracking Found Scenario: Under the provisions of 
AD 78-26-02, an owner/operator of an affected de Havilland DHC-6 series 
airplane who found limited cracking (as defined in SB No. 6/371) during 
an inspection would have to inspect each 300 hours TIS or 45 days, 
whichever occurs first, and replace the part within 360 days after 
finding the cracking. The proposed AD would require inspections every 
300 hours TIS, and then require replacement at 4,800 hours TIS after 
the proposed AD would become effective. This would result in a present 
value total cost of $34,908 per airplane in scheduled service, which 
would make immediate replacement more economical ($32,400) than 
repetitively inspecting. With this scenario, the proposed AD would 
result in an incremental present value cost savings over that required 
in AD 78-26-02 of $1,491 per airplane in scheduled service (or $568 
annualized over 3 years) and $6,517 ($1,367 annualized over 6 years) 
for airplanes operating in general aviation service.
     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 would the proposed AD. The 
difference is that AD 78-26-02 requires immediate crack repair and then 
replacement within 360 days after finding the crack, and the proposed 
AD would require immediate repair and mandatory replacement of the 
fuselage side frames within 4,800 hours TIS after the proposed AD would 
become effective. This would result in a present value total cost of 
$34,709 per airplane in scheduled service, which would make immediate 
replacement more economical ($32,400) than repetitively inspecting. 
With this scenario, the proposed AD would average 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.
    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 would have a 
``significant economic impact on a substantial number of small 
entities,'' and, in cases where they would, 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 proposed 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. 

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    Of the 94 U.S.-registered airplanes affected by the proposed AD, 4 
airplanes are owned by the federal government. 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 the proposed 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 would 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, the 
proposed AD would not have a ``significant economic impact on a 
substantial number of small entities.''
    The regulations proposed herein would 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 
proposal would 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) if promulgated, 
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 draft regulatory evaluation 
prepared for this action has been placed 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, Safety.

The Proposed Amendment

    Accordingly, pursuant to the authority delegated to me by the 
Administrator, the Federal Aviation Administration proposes to amend 
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 AD 78-26-02, Amendment 39-
3370, and adding the following new AD to read as follows:

De Havilland: Docket No. 91-CE-45-AD. Supersedes AD 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: 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 use the authority 
provided in paragraph (e) of this AD to request approval from the 
FAA. This approval may address either no action, if the current 
configuration eliminates the unsafe condition, or different actions 
necessary to address the unsafe condition described in this AD. Such 
a request should include an assessment of the effect of the changed 
configuration on the unsafe condition addressed by this AD. In no 
case does the presence of any modification, alteration, or repair 
remove any airplane from the applicability of this AD.

    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 Fuselage Station (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, dated June 2, 1978. Utilize the following chart to 
determine which fuselage stations are affected:

------------------------------------------------------------------------
                                                             Fuselage   
                                          Modification 6/    stations   
               Serial Nos.                     1553       affected (both
                                           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 2: Modification 6/1553 incorporates fuselage side frames of 
improved stress corrosion resistant material at FS 218.125.

    (1) If cracks are found that exceed the limits specified in 
Figure 3 of de Havilland SB No. 6/371, 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, dated 
June 2, 1978. 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, dated June 2, 1978. 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 cracks are found that are within the limits specified in 
Figure 3 of de Havilland SB No. 6/371, reinspect at intervals not to 
exceed 300 hours TIS until the modification specified in paragraph 
(b) of this AD is incorporated.
    (3) 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.
    (b) Within the next 4,800 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, dated June 2, 1978. This consists of 
replacing all fuselage side frames required as specified in the 
following chart:

------------------------------------------------------------------------
                                                             Fuselage   
                                          Modification 6/    stations   
               Serial Nos.                     1553       affected (both
                                           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.
    (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 

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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. 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.

    Note 3: Information concerning the existence of approved 
alternative methods of compliance with this AD, if any, may be 
obtained from the New York ACO.

    (f) All persons affected by this directive may obtain copies of 
the document referred to herein upon request to de Havilland, Inc., 
123 Garratt Boulevard, Downsview, Ontario M3K 1Y5 Canada; or may 
examine this document at the FAA, Central Region, Office of the 
Assistant Chief Counsel, Room 1558, 601 E. 12th Street, Kansas City, 
Missouri 64106.
    (g) This amendment supersedes AD 78-26-02, Amendment 39-3370.

    Issued in Kansas City, Missouri, on August 7, 1995.
Gerald W. Pierce,
Acting Manager, Small Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 95-19917 Filed 8-10-95; 8:45 am]
BILLING CODE 4910-13-U