[Federal Register Volume 62, Number 61 (Monday, March 31, 1997)]
[Proposed Rules]
[Pages 15129-15133]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 97-7967]


=======================================================================
-----------------------------------------------------------------------

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 91-CE-45-AD]
RIN 2120-AA64


Airworthiness Directives; de Havilland DHC-6 series Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Supplemental notice of proposed rulemaking (NPRM); Reopening of 
the comment period.

-----------------------------------------------------------------------

SUMMARY: This document proposes to revise an earlier proposed 
airworthiness directive (AD), which would have superseded AD 78-26-02. 
That AD 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 previous document would have

[[Page 15130]]

required 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. As currently written, the document allows 
continued flight if cracks are found in the fuselage side frames that 
do not exceed certain limits. Since publication of that proposal, the 
Federal Aviation Administration (FAA) has established a policy to 
disallow airplane operation when known cracks exist in primary 
structure (the fuselage area is considered primary structure). The 
actions specified by 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. Since the comment period for the original proposal has closed 
and the change described above goes beyond the scope of what was 
originally proposed, the FAA is allowing additional time for the public 
to comment.

DATES: Comments must be received on or before June 13, 1997.

ADDRESSES: Submit comments in triplicate 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. 
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 Supplemental NPRM

    Any person may obtain a copy of this supplemental 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

    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.

The FAA's Aging Commuter-Class Aircraft Policy

    The actions specified in the NPRM 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.

Events Leading to the Issuance of This Supplemental NPRM

    As currently written, the existing 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. Since issuing the NPRM, the FAA has 
established a policy to disallow 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 has determined that the crack limits contained in the 
NPRM and AD 78-26-02 should be eliminated, and that AD action should be 
taken to require immediate replacement of any cracked fuselage flange.

Explanation of the Provisions of the Proposed AD

    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 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,

[[Page 15131]]

as applicable, and repairing or replacing any cracked part (except that 
the repair or replacement would be required prior to further flight); 
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 prepared a Regulatory Flexibility Determination and 
Analysis for the original proposal. This analysis is unchanged and is 
repeated in this supplemental NPRM.

Cost Impact

    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 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 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.
    <bullet> 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 presumption that no cracks are found during the 
inspections. The proposed AD would require 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.
    <bullet> Cracks found 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 three years) for each airplane operated in scheduled service, and 
$6,607 ($1,386 annualized over six 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 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 
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 the proposed AD, 
four airplanes are owned by the federal government. Of the other 90 
airplanes, 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

[[Page 15132]]

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.''

Regulatory Impact

    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 USC 106(g), 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:

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

------------------------------------------------------------------------
                                                       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.     
------------------------------------------------------------------------

    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, 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 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 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 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. 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. 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) 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

[[Page 15133]]

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 March 24, 1997.
Henry Armstrong,
Acting Manager, Small Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 97-7967 Filed 3-28-97; 8:45 am]
BILLING CODE 4910-13-U