[Federal Register Volume 59, Number 209 (Monday, October 31, 1994)]
[Unknown Section]
[Page 0]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 94-26877]


[[Page Unknown]]

[Federal Register: October 31, 1994]


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


DEPARTMENT OF TRANSPORTATION
14 CFR Part 39

[Docket No. 91-CE-21-AD]

 

Airworthiness Directives; de Havilland DHC-6 Series Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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

SUMMARY: This document proposes to supersede Airworthiness Directive 
(AD) 73-05-03, which currently requires repetitively inspecting the 
rear spar cap for cracks on certain de Havilland DHC-6 series 
airplanes, and 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 wing rear spar support as terminating action for the 
currently required repetitive inspections. The actions specified in the 
proposed AD are intended to prevent cracking of the top flange of the 
wing rear spar attachment caps, which could result in loss of control 
of the airplane.

DATES: Comments must be received on or before January 4, 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-21-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, 181 South Franklin Avenue, Room 
202, Valley Stream, New York 11581; telephone (516) 791-6220; facsimile 
(516) 791-9024.

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-21-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-21-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 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.
    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 recently 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 73-05-03, Amendment 39-
1658, as one that should be superseded with a new AD that would 
eliminate short-interval and critical repetitive inspections. AD 73-05-
03 currently requires repetitively inspecting the wing rear spar cap 
for cracks on certain de Havilland DHC-6 series airplanes, and 
replacing any cracked part.
    De Havilland, Inc. (formerly Boeing of Canada, Ltd.) has issued 
Service Bulletin (SB) No. 6/295, Revision D, dated December 20, 1991. 
This service bulletin specifies procedures for installing wing rear 
spar attachment caps that are manufactured from a material having 
improved stress corrosion resistant properties. This installation is 
known as Modification 6/1301.
    As a result of the previously discussed AD review, Transport Canada 
considers Modification 6/1301 mandatory and has issued Transport Canada 
AD CF-73-03R1 in order to assure the continued airworthiness of these 
airplanes in Canada.
    This airplane model is manufactured in Canada and is type 
certificated for operation in the United States under the provisions of 
Sec. 21.29 of the Federal Aviation Regulations (14 CFR 21.29) and the 
applicable bilateral airworthiness agreement. 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 73-05-03, Amendment 39-1658, and to prevent 
cracking of the top flange of the wing rear spar attachment caps, which 
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 that do not have Modification No. 6/1301 incorporated, 
the proposed AD would supersede AD 73-05-03 with a new AD that would 
(1) initially retain the requirement of repetitively inspecting the 
wing rear spar cap for cracks and replacing any cracked part; and (2) 
eventually require installing wing rear spar attachment caps that are 
manufactured from a material having improved stress corrosion resistant 
properties (Modification 6/1301) as terminating action for the 
repetitive inspections. The proposed actions would be accomplished in 
accordance with de Havilland SB No. 6/295, Revision D, dated December 
20, 1991.
    The FAA estimates that 82 airplanes in the U.S. registry would be 
affected by the proposed AD, that it would take approximately 22 
workhours per airplane to accomplish the proposed modification, and 
that the average labor rate is approximately $60 an hour. Parts cost 
approximately $6,350 per airplane. Based on these figures, the total 
cost impact of the proposed AD on U.S. operators is estimated to be 
$629,432. This figure is based upon the assumption that none of the 
affected airplane owners/operators have incorporated Modification 6/
1301.
    The intent of the FAA's aging commuter airplane program is to 
ensure safe operation of commuter-class airplanes that are in 
commercial service without adversely impacting private operators. Of 
the approximately 82 airplanes in the U.S. registry that 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 following paragraphs present cost scenarios for airplanes where 
no cracks were found and where certain category cracks were found, 
utilizing an average remaining airplane life of 15 years and 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-21-AD, Room 
1558, 601 E. 12th Street, Kansas City, Missouri.
     No Cracks Scenario: Under the provisions of AD 73-05-03, 
an owner/operator of an affected de Havilland DHC-6 series airplane in 
scheduled service who operates an average of 1,600 hours TIS annually 
would inspect every 26 weeks. This would amount to a remaining airplane 
life (estimated 15 years) cost of $14,058; this figure is based on the 
assumption that no cracks are found during the inspections. The 
proposed AD would incur the inspection at one 1,200-hour TIS interval 
and then, at 2,400 hours TIS, the operator would have to replace the 
top flange of the wing spar attachment caps (eliminating the need for 
further repetitive inspections). This would result in a present value 
cost of $8,331, which would be a present value cost savings of $5,727 
or $4,154 annualized over the 1.5 years it would take to accumulate 
2,400 hours TIS. An owner of a general aviation airplane who operates 
800 hours TIS annually without finding any cracks during the 1,200-hour 
TIS inspection would incur a present value cost savings of $6,430. This 
would amount to a per year savings of $2,450 over the 1.5 years it 
would take to accumulate 2,400 hours TIS.
     Category I cracks found scenario: These are spanwise 
cracks that are inboard of the third rivet, or spanwise cracks that 
exceed 50 inches, or any chordwise cracks: Under the provisions of AD 
73-05-03, an owner/operator who found cracks under this scenario would 
have to immediately repair the cracked part and repetitively inspect 
every 26 weeks. The proposed AD would require immediate replacement as 
terminating action for the repetitive inspections, which would result 
in present value compliance costs of $8,355. The present value cost 
savings for this scenario would be $6,300 for airplanes in scheduled 
service and $6,295 per general aviation airplane.
     Category II cracks found scenario: These are spanwise 
cracks that are outboard of the 10th rivet and within the limits of 
paragraph (b) of the service bulletin: Under the provisions of AD 73-
05-03, an owner/operator who found cracks under this scenario would 
have to repetitively inspect every 13 weeks. This would result in 
present value compliance costs of $27,625. The proposed AD would 
require repetitive inspections every 600 hours TIS until replacement of 
the top flange of the wing rear spar attachment caps at 2,400 hours TIS 
as terminating action for the repetitive inspections. This would result 
in present value compliance costs of $9,700. Immediate replacement of 
the top flange would be more economical; present value costs would be 
$8,355. The present value cost savings for this scenario would be 
$19,272 per airplane in scheduled service and $19,269 per general 
aviation airplane.
     Category III cracks found scenario: These are spanwise 
cracks that are outboard of the 10th rivet and within the limits of 
paragraph (c) of the service bulletin: Under the provisions of AD 73-
05-03, an owner/operator who found cracks under this scenario would 
have to repetitively inspect every 2 weeks. This would result in 
present value compliance costs of $175,000. The proposed AD would 
require repetitive inspections every 100 hours TIS until replacement of 
the top flange of the wing rear spar attachment caps at 2,400 hours TIS 
as terminating action for the repetitive inspections. This would result 
in present value compliance costs of $13,965. Immediate replacement of 
the top flange would be more economical; present value costs would be 
$8,355. The present value cost savings for this scenario would be 
$166,075 per airplane in scheduled service and $166,784 per general 
aviation airplane.
     Category IV cracks found scenario: These are spanwise 
cracks that are outboard of the 10th rivet and exceed the limits of 
paragraph (b) or (c) of the service bulletin. Also included are cracks 
in the splice plates of the vertical and horizontal legs of the rear 
spar or elongated rivet holes: Under the provisions of AD 73-05-03, an 
owner/operator who found cracks under this scenario would have to 
immediately repair any crack and then repetitively inspect every 26 
weeks. This would result in present value costs of $14,500. The 
proposed AD would require immediate crack repair, an inspection at 
1,200 hours TIS, and replacement of the top flange of the wing rear 
spar attachment caps at 2,400 hours TIS as terminating action for the 
repetitive inspections. This would result in present value compliance 
costs of $8,929. Immediate replacement of the top flange would be more 
economical; present value costs would be $8,355. The present value cost 
savings for this scenario would be $6,040 per airplane in scheduled 
service and $6,430 per general aviation airplane.
     Category V cracks found scenario: These are spanwise 
cracks that are between the third and tenth rivet: Under the provisions 
of AD 73-05-03, an owner/operator who found cracks under this scenario 
would have to immediately repair any crack, repetitively inspect every 
2 weeks, replace the top flange of the wing rear spar attachment caps, 
and repetitively inspect every 26 weeks. This would result in present 
value compliance costs of about $30,000. The proposed AD would require 
immediate crack repair, repetitive inspections every 50 hours TIS, and 
replacement of the top flange of the wing rear spar attachment caps at 
2,400 hours TIS as terminating action for the repetitive inspections. 
This would result in present value compliance costs of $38,988. 
Immediate replacement of the top flange would be more economical; 
present value costs would be $8,355. The present value cost savings for 
this scenario would be $19,356 per airplane in scheduled service and 
$26,367 per general aviation airplane.
     Category VI cracks found scenario: These are spanwise 
cracks that have a total length exceeding 30 inches but not exceeding 
50 inches: Under the provisions of AD 73-05-03, an owner/operator who 
found cracks under this scenario would have to immediately repair any 
crack, replace the top flange of the wing rear spar attachment caps at 
26 weeks, and repetitively inspect thereafter every 26 weeks. This 
results in present value compliance costs of about $21,200. The 
proposed AD would require immediate crack repair, repetitive 
inspections every 600 hours TIS, and replacement of the top flange of 
the wing rear spar attachment caps at 2,400 hours TIS as terminating 
action for the repetitive inspections. This would result in present 
value compliance costs of $10,289. Immediate replacement of the top 
flange would be more economical; present value costs would be $8,355. 
The present value cost savings for this scenario would be $12,707 per 
airplane in scheduled service and $13,028 per general aviation 
airplane.
    The Regulatory Flexibility Act of 1980 (RFA) was enacted by 
Congress to ensure that small entities are not unnecessarily or 
disproportionally burdened by government regulations. The RFA requires 
government agencies to determine whether rules 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 $4,850 for unscheduled 
operators.
    Of the 82 U.S.-registered airplanes affected by the proposed AD, 
three airplanes are owned by the federal government. Of the other 79, 
one business owns 24 airplanes, one business owns 7 airplanes, one 
business owns 6 airplanes, one business owns 3 airplanes, 6 businesses 
own 2 airplanes each, and twenty-seven businesses own 1 airplane each.
    As presented in the crack scenario discussion, replacing the top 
flange of the wing rear spar attachment caps immediately or within 
2,400 hours TIS is more economical in all scenarios than continuing to 
repetitively inspect the part for the life of the airplane. Therefore, 
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 on a substantial number of 
small entities. 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. App. 1354(a), 1421 and 1423; 49 U.S.C. 
106(g); and 14 CFR 11.89.


Sec. 39.13  [Amended]

    2. Section 39.13 is amended by removing AD 73-05-03, Amendment 39-
1658, and adding a new AD to read as follows:

De Havilland: Docket No. 91-CE-21-AD. Supersedes AD 73-05-03, 
Amendment 39-1658.

    Applicability: Models DHC-6-1, DHC-6-100, DHC-6-200, and DHC-6-
300 airplanes (serial numbers 1 to 330), certificated in any 
category, that have not incorporated Modification 6/1301 in 
accordance with the instructions in Part C of de Havilland Service 
Bulletin (SB) 6/295, Revision D, dated December 20, 1991.
    Compliance: Required as indicated in the body of this AD, unless 
already accomplished.
    To prevent cracking of the top flange of the wing rear spar 
attachment caps, which could result in loss of control of the 
airplane, accomplish the following:
    (a) Within the next 100 hours time-in-service (TIS) after the 
effective date of this AD, inspect both wing rear spar attachment 
caps, part number (P/N) C6WM1032, for cracks in accordance with 
paragraph A of the Accomplishment Instructions section of de 
Havilland SB No. 6/295, Revision D, dated December 20, 1991. The 
exposure time of Inspection Method A.1 (Radiographic) shall be 120 
seconds instead of 60 seconds for the inboard X-ray tube location, 
and the X-ray beam angle shall be decreased from 10 degrees to 5 
degrees for all X-ray tube locations.
    (1) If cracking is not detected, reinspect each cap every 1,200 
hours TIS until a Modification 6/1301 spar cap is installed as 
required by paragraph (c) of this AD.
    (2) If spanwise cracking is detected outboard of the 10th rivet, 
accomplish the following:
    (i) For cracks that have the following (the criteria of 
paragraph (c) in the Compliance section of de Havilland SB No. 6/
295, Revision D, dated December 20, 1991): 

First to tenth    No cracks.                                            
 rivet.                                                                 
11th to 29th      One cracked pitch (the distance between adjacent rivet
 rivet.            holes) in ten pitches with four uncracked pitches    
                   minimum between cracks.                              
30th to 69th      Two cracked pitches in ten pitches with four uncracked
 rivet.            pitches minimum between cracks.                      
70th to 74th      One cracked pitch.                                    
 (end).                                                                 
                                                                        

Repeat the inspection specified in paragraph (a) of this AD at 
intervals not to exceed 100 hours TIS until a Modification 6/1301 
spar cap is installed as required by paragraph (c) of this AD.
    (ii) For cracks found outboard of the 10th rivet that run only 
between two adjacent rivets provided not more than four such cracks 
exist in an attachment cap and a minimum of two rivet pitch lengths 
of uncracked material separates cracks ( the criteria of paragraph 
(b) in the Compliance section of de Havilland SB No. 6/295), repeat 
the inspection specified in paragraph (a) of this AD at intervals 
not to exceed 600 hours TIS until a Modification 6/1301 spar cap is 
installed as required by paragraph (c) of this AD.
    (iii) For cracks that meet or exceed the criteria of paragraphs 
(b) or (c) in the Compliance section of de Havilland SB No. 6/295, 
prior to further flight, reinforce the spar cap in accordance with 
paragraph B of the Accomplishment Instructions section of de 
Havilland SB No. 6/295, Revision D, dated December 20, 1991, and 
reinspect thereafter at intervals not to exceed 1,200 hours TIS 
until a Modification 6/1301 spar cap is installed as required by 
paragraph (c) of this AD.
    (3) If spanwise cracking is detected inboard of the third rivet, 
or if a chordwise crack is detected, or if the total length of 
cracks on a cap exceeds 50 inches, prior to further flight, replace 
the spar cap with a Modification 6/1301 cap in accordance with 
paragraph C of the Accomplishment Instructions section of de 
Havilland SB No. 6/295, Revision D, dated December 20, 1991.
    (4) If spanwise cracking is detected between the third and tenth 
rivet, prior to further flight, reinforce the spar cap in accordance 
with paragraph B of the Accomplishment Instructions section of de 
Havilland SB No. 6/295, Revision D, dated December 20, 1991, and 
reinspect inboard of the alter attachment caps at intervals not to 
exceed 50 hours TIS until a Modification 6/1301 spar cap is 
installed as required by paragraph (c) of this AD.
    (5) If cracking exceeds 30 inches but does not exceed 50 inches, 
prior to further flight, reinforce the spar cap in accordance with 
paragraph B of the Accomplishment Instructions section of de 
Havilland SB No. 6/295, Revision D, dated December 20, 1991, and 
reinspect the spar cap at intervals not to exceed 600 hours TIS 
until a Modification 6/1301 spar cap is installed as required by 
paragraph (c) of this AD.
    (b) Within 100 hours after the effective date of this AD and 
thereafter at intervals not to exceed 1,200 hours TIS until a 
Modification 6/1301 spar cap is installed as required by paragraph 
(c) of this AD, inspect the splice plates of the vertical and 
horizontal legs of the rear spar fitting at Wing Stations 87 to 91 
for cracks or elongated rivet holes. Prior to further flight, 
replace any part that is cracked or has elongated rivet holes with a 
serviceable part.
    (c) Within 2,400 hours TIS after the effective date of this AD, 
replace both wing rear spar caps with a Modification 6/1301 spar cap 
in accordance with paragraph C of the Accomplishment Instructions in 
de Havilland SB No. 6/295, Revision D, dated December 20, 1991, 
unless already accomplished in accordance with paragraph (a) (3) of 
this AD.
    (d) Incorporating Modification 6/1301 on both wing rear spar 
caps in accordance with paragraph C of the Accomplishment 
Instructions in de Havilland SB No. 6/295, Revision D, dated 
December 20, 1991, is considered terminating action for the 
inspection requirements of this AD.
    (e) 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.
    (f) 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, 181 South Franklin Avenue, Room 
202, 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 ACO.

    Note 2: Information concerning the existence of approved 
alternative methods of compliance with this AD, if any, may be 
obtained from the New York ACO.

    (g) 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.

    Issued in Kansas City, Missouri, on October 25, 1994.
John R. Colomy,
Acting Manager, Small Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 94-26877 Filed 10-28-94; 8:45 am]
BILLING CODE 4910-13-P