[Federal Register Volume 63, Number 74 (Friday, April 17, 1998)]
[Rules and Regulations]
[Pages 19170-19174]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 98-9874]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 95-CE-92-AD; Amendment 39-10468; AD 98-08-19]
RIN 2120-AA64


Airworthiness Directives; Twin Commander Aircraft Corporation 
500, 600, and 700 Series Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Final rule.

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

SUMMARY: This amendment adopts a new airworthiness directive (AD) that 
applies to all Twin Commander Aircraft Corporation (Twin Commander) 
500, 600, and 700 series airplanes. This AD requires installing access 
holes in both wing leading edges and repetitively inspecting the 
forward attach brackets and straps for cracks. Reports of cracks in the 
wing to fuselage attachment brackets and straps, wing station (WS) 24, 
and fuselage frames prompted this action. The actions specified by this 
AD are intended to detect cracks at the wing to fuselage attach points, 
which, if not detected and corrected, could cause structural failure 
and loss of control of the airplane.

DATES: Effective May 18, 1998.
    The incorporation by reference of certain publications listed in 
the regulations is approved by the Director of the Federal Register as 
of May 18, 1998.

ADDRESSES: Service information that applies to this AD may be obtained 
from Twin Commander Aircraft Corporation, P. O. Box 3369, Arlington, 
Washington, 98223; telephone (360) 435-9797; facsimile: (360) 435-1112. 
This information may also be examined at the Federal Aviation 
Administration (FAA), Central Region, Office of the Regional Counsel, 
Attention: Rules Docket No. 95-CE-92-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: Jeffrey Morfitt, Aerospace Engineer, 
FAA, Seattle Aircraft Certification Office, 1601 Lind Ave. S.W., 
Renton, Washington, 98055-4056; telephone (425) 227-2595; facsimile 
(425) 227-1181.

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 Twin Commander 500, 
600, and 700 series airplanes was published in the Federal Register as 
a notice of proposed rulemaking (NPRM) on August 19, 1997, (62 FR 
44096). The NPRM was the result of reports of cracks in the wing to 
fuselage attachment brackets and straps, wing station (WS) 24, and 
fuselage frames. The NPRM proposed to require:

[[Page 19171]]



------------------------------------------------------------------------
                         A                  B                  C        
------------------------------------------------------------------------
Part I.........  Installing access  If cracked, prior  If no cracks,    
                  holes in left      to further         repeat the      
                  and right wing     flight,            inspection at   
                  leading edges      replacing the      regular         
                  and inspecting     brackets and       intervals until 
                  the forward        straps or          cracks are      
                  attach brackets    repairing the      found, then     
                  and straps for     part with an       accomplish Part 
                  cracks.            approved repair    II.             
                 For any airplanes   scheme. Then                       
                  that have wings    accomplish Part                    
                  modified with      II of this AD.                     
                  titanium leading                                      
                  edges through an                                      
                  STC, remove the                                       
                  wing root                                             
                  farings to                                            
                  accomplish the                                        
                  required                                              
                  inspections, in                                       
                  lieu of                                               
                  installing the                                        
                  access holes.                                         
Part II........  Inspecting for     If cracked, prior  After repairing  
                  cracks on both     to further         or replacing the
                  wing leading       flight,            damaged part,   
                  edge closeouts,    replacing any      continuing to   
                  upper & lower      cracked part or    inspect at      
                  return flange      repairing the      regular         
                  radius, fuselage   part with an       intervals.      
                  frame where tee    approved repair                    
                  bracket            scheme.                            
                  attaches,                                             
                  inboard side of                                       
                  attached bracket                                      
                  and frame tee                                         
                  bracket.                                              
Part III.......  Inspecting         If cracked, prior  If no cracks,    
                  fuselage station   to further         repeating the   
                  (f.s.) 100 for     flight,            inspection at   
                  cracks.            repairing with     regular         
                                     an approved        intervals until 
                                     repair scheme,     cracks are      
                                     and continuing     found, then     
                                     to inspect at      accomplishing   
                                     regular            Part III B of   
                                     intervals.         this AD.        
------------------------------------------------------------------------

    Accomplishment of the proposed action as specified in the NPRM 
would be in accordance with the Compliance section and Part I, II, and 
III of the ACCOMPLISHMENT INSTRUCTIONS sections of Twin Commander 
Aircraft Corporation (Twin Commander) Service Bulletin (SB) No. 223, 
dated October 24, 1996 as amended by Revision Notice No. 1, dated May 
8, 1997 and Revision Notice No. 2, dated August 18, 1997.

Comments

    Interested persons have been afforded an opportunity to participate 
in the making of this amendment. Several comments were received in 
response to the proposed action. Due consideration has been given to 
the following comments.

Turbine Engine Versus Reciprocating Engine Models

    One commenter opposes the AD for reciprocating engine powered 
models. The commenter asks if turbine models have different loads than 
reciprocating engine powered models, suggesting that the AD should 
apply only to turbine models.
    The FAA does not concur. The type of powerplant is not relevant. 
However, the turbine models are pressurized, which affects the 
configuration of the structure, and service reports indicate 
pressurization does affect cracking in the fitting. This effect is 
accounted for in the compliance times for Part III of the service 
bulletin. Cracks have been discovered in both pressurized and non-
pressurized airplanes and in every structural configuration present in 
the airplane models listed in the proposed AD. The final rule will not 
change as a result of this comment.

Low Level Survey Versus Non-Survey Operations

    Two commenters oppose the proposed action for airplanes that are 
not used for low level survey operations. The commenters ask if the 
airplanes found cracked are engaged in low level survey operations, 
suggesting that the proposed action apply only to airplanes operated in 
such a manner.
    The FAA does not concur. FAA data indicates that 6 of 47 airplanes 
inspected were in survey operations for a portion of their total hours 
of operation. All six showed cracking. The data indicates that 24 
additional airplanes were found cracked. These airplanes were not 
engaged in survey operations for a significant portion of their total 
hours of operation. The service data supports the need for the proposed 
action regardless of whether the affected airplane is used in a low 
level survey type operation. The final rule will not change as a result 
of this comment.

Evidence of an Unsafe Condition

    One commenter suggests that there is insufficient evidence of an 
unsafe condition to justify the proposed action. The commenter asks if 
the basis for this action was the 1978 Calumet, Oklahoma accident 
involving an in-flight structural breakup, suggesting that one accident 
that occurred 19 years ago does not justify an AD.
    The FAA does not concur. While this accident is a source of 
concern, there is more evidence that an unsafe condition exists. There 
have been 14 other in-flight breakups that involved leading edge 
failures, as well as 8 incidents involving in-flight damage to the wing 
leading edge. One other accident is currently under investigation by 
the National Transportation Safety Board. These accidents and incidents 
demonstrate the critical nature of the leading edge on these airplane 
models. The numerous reports of cracking (63 percent of the inspected 
airplanes) indicate that an unsafe condition exists. The final rule 
will not change as a result of this comment.

Cracks Due To Poorly Manufactured or Improperly Installed Parts

    One commenter suggests that the cracks found in the bracket were 
due to overload during installation. The commenter asks the FAA to 
conduct a metallurgical analysis of the cracked parts.
    The FAA does not concur. A metallurgical analysis has been 
conducted that shows that the crack propagation was fatigue, not 
installation overload. A developmental problem resulted in some early 
parts that did not fit correctly. However, the manufacturing process 
has been refined so that the fit problem has been alleviated. The final 
rule will not change as a result of this comment.

Airplanes Equipped With Titanium Leading Edges

    One commentor suggests that the proposed action be changed to allow 
alternative inspection techniques that would not necessitate installing 
the access doors in airplanes that have a titanium leading edge 
modification for flight into known icing conditions, or exempt these 
airplanes from the proposed action entirely. The commenter states that 
the titanium leading edges installed per Supplemental Type Certificate 
(STC) on 23 of his airplanes cannot be modified as required by the 
service bulletin. The commenter also states that the leading edge 
modifications per this STC would add significant strength to the 
leading edge, suggesting that airplanes so equipped would not be 
susceptible to cracking.

[[Page 19172]]

    The FAA partially concurs. The effect of the leading edge 
modification on the cracking, which is the subject of this AD, is 
unknown. However, stiffening of the leading edge could increase the 
load in the attachment bracket, thereby aggravating the situation. The 
unsafe condition is therefore likely to exist in airplanes with the 
titanium leading edges, and these airplanes should be included in the 
proposed action.
    The leading edge access doors are installed to make the required 
inspections easier and less time consuming. The leading edge 
modification installed on the commenter's airplanes is unique. Because 
of the small number of airplanes affected by this modification, the FAA 
can address the requests for alternative methods of compliance, as 
necessary.
    The FAA has also changed the requirement for gaining access to the 
wing leading edges for airplanes with wings modified by an STC with 
titanium leading edges. For these airplanes, the wing root farings can 
be removed to accomplish the inspections for cracks.
    The final rule will reflect these changes.

Need for Terminating Action

    One commenter suggests that the proposed action be changed to 
include a modification that terminates the repetitive inspection 
requirements.
    The FAA partially agrees. A modification to the airplane to 
terminate the repetitive inspections that are proposed would be 
desirable. However, neither the manufacturer, nor any other party has 
proposed a permanent fix to the cracking. The unsafe condition 
necessitates that the proposed action be taken at this time. If a 
terminating action should become available in the future, the FAA would 
incorporate it into a superseding AD. The final rule will not change as 
a result of this comment.

Work To Be Done at a Twin Commander Service Center

    One commenter states that the service bulletin recommends that the 
work be done at a Twin Commander service center which could be 
difficult to schedule, given the limited service centers and the number 
of airplanes affected. The commenter states that requiring the 
modification be accomplished at these Twin Commander service centers 
would be a hardship for some owners.
    The FAA partially agrees that it may be difficult for all of the 
owners/operators to schedule the work at a Twin Commander service 
center. Revision Notice No. 1 is included in the service bulletin that 
is incorporated by reference into the proposed action. This revision 
clarifies that it is recommended by the manufacturer, but not required, 
that the work be done by a Twin Commander service center. The final 
rule will not change as a result of this comment.

Projected Cost Impact Unrealistically Low

    One commenter argues that the economic analysis reflected the cost 
per side, not the total cost and that the total cost quoted was 
unrealistically low.
    The FAA does not concur. The type certificate holder verified that 
the hours quoted were for the entire airplane, not one side. The total 
inspection hours are based on two prototype installations. The cost 
impact provided in the NPRM presents a conservative estimate of the 
time required for a mechanic to install two access doors and conduct a 
dye penetrant inspection. There will be additional cost if the 
inspection turns up cracked fittings or leading edge ribs. The 
additional cost of repairing damaged wing structure found by the 
inspections cannot be determined, since it depends on the magnitude of 
the damage found and the repair technique used. The final rule will not 
change as a result of this comment.

The FAA's Determination

    After careful review of all available information related to the 
subject presented above, including the related service information, the 
FAA has determined that air safety and the public interest require the 
adoption of the rule as proposed, except for the changes discussed 
above and minor editorial corrections. The FAA has determined that 
these changes and minor corrections will not change the meaning of the 
AD and will not add any additional burden upon the public than was 
already proposed.

Cost Impact

    The FAA estimates that 1,464 airplanes in the U.S. registry will be 
affected by this AD, that it will take approximately 82 workhours for 
PART I; 100 workhours for PART II (if required); and 7 workhours for 
PART III per airplane (if required) to accomplish this action. The 
average labor rate is approximately $60 an hour. Parts cost 
approximately $410 for PART I and approximately $450 for PART II (if 
required) per airplane. Based on these figures, the total cost impact 
for PART I will be $5,330 per airplane, PART II (if required) will be 
$6,450 per airplane, and PART III will be $420 per airplane (if 
required). The U.S. fleet cost is estimated to be $11,127,650, or 
$5,950 per airplane if no damage is found; and $23,021,400 for the U.S. 
fleet, or $12,200 per airplane if damage is found. For purposes of 
estimating the cost of this AD, the FAA is presuming that none of the 
owners/operators have had any of the actions accomplished on any of the 
affected airplanes. In addition, the cost impact does not take into 
consideration the costs of the repetitive inspections. The FAA has no 
way of determining the number of repetitive inspections that may be 
incurred over the life of the airplane.

Regulatory Flexibility Act Economic Analysis

    Because the estimated cost for the inspection and possible repairs 
are expensive, the FAA conducted a Cost Analysis and Initial Regulatory 
Flexibility Determination and Analysis for this AD.
    The Regulatory Flexibility Act of 1980 (RFA) was enacted by 
Congress to assure that small entities are not unnecessarily and 
disproportionately burdened by Government regulations. The RFA requires 
agencies to review rules that may have a ``significant economic impact 
on a substantial number of small entities,'' and, in cases where they 
would, to conduct a Regulatory Flexibility Analysis in which 
alternative actions are considered.
    FAA Order 2100.14A, Regulatory Flexibility Criteria and Guidance, 
defines ``significant economic impact'' as an annualized net compliance 
cost, adjusted for inflation, which is greater than a threshold cost 
level for defined entity types. A ``substantial number'' is defined as 
a number that is at least eleven and that is more than one-third of the 
small entities subject to a rule, or any number of small entities 
subject to a rule which is substantial in the judgment of the 
rulemaking official. ``Small entities'' are defined as small 
businesses, small not-for-profit organizations which are independently 
owned and operated, or airports operated by small governmental 
jurisdictions.
    With limited information available to airplane specific costs, a 
range of per airplane costs can be estimated by constructing 
hypothetical low-and high-cost scenarios. These scenarios are based on 
three general presumptions: first, that these airplanes have 
accumulated 6,000 hours TIS and are subject to this AD within the next 
100 hours TIS; second, that all of these airplanes are at the minimum 
and maximum extremes of annual TIS (200 or 300 hours) with a remaining

[[Page 19173]]

operating life of 10 and 20 years, and the extent of cracking is 
unknown (no cracking or cracking in the inspected areas); and third, 
that these airplanes are of the model types incurring either the lowest 
or highest costs.
    The total low-cost scenario in 1997 dollars will be $5,570 ($4,805 
discounted) per airplane over 10 years, with $5,330 of the costs 
incurred in the first year. The annualized cost (again over 10 years) 
will be $641 per airplane.
    The total high-cost scenario in 1997 dollars will be $25,285 per 
airplane ($16,487 discounted) over 30 years, with $15,865 of the costs 
incurred in the first year. The annualized cost (again over 30 years) 
will be $1,556.
    This AD will affect approximately 1,464 airplanes, of which 366 are 
owned by individuals, 38 are owned by federal and state agencies, and 
847 are owned by 697 separate entities. Of the 697 entities, one entity 
owns 28 airplanes, three entities own between 10 and 12 airplanes, 
nineteen separate entities own between 3 and 9 airplanes, thirty-two 
entities own 2 airplanes, and six-hundred forty-two entities own 1 
airplane each. The FAA cannot determine the size of all 697 owner 
entities, or the type of business each entity is engaged in. The FAA 
also cannot conclusively determine the costs of this AD. For 
illustration purposes, it has been calculated that the AD will have 
hypothetical annualized costs between $641 (the low-cost scenario) and 
$1,556 (the high-cost scenario) per airplane. Due to the uncertainties 
involved with these calculations, as well as with the ownership 
information, no determinations can be made regarding ``significant 
economic impact on a substantial number of small entities.''
    The FAA has considered three alternatives to this AD: (1) take no 
federal action and rely on voluntary compliance with the Twin Commander 
Service Bulletin No. 223. The FAA finds this alternative unacceptable 
because of the consequences that could result, if the unsafe condition 
is not eliminated; (2) mandate inspecting fewer parts, and at longer 
intervals in the areas where the wings attach to the fuselage. This 
alternative is unacceptable because less stringent inspections could 
fail to locate cracking in key parts of the airplane for too long a 
period of time; (3) defer Federal action pending review of additional 
data to determine whether to require the specified inspections. This 
alternative is unacceptable because evidence already exists of cracking 
in the wing and fuselage at the attach points which would be considered 
structural failure.
    Consequently, the FAA is unable to conclusively make an economic 
impact evaluation based on information available.

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) could have a 
significant economic impact, positive or negative, on a substantial 
number of small entities under the criteria of the Regulatory 
Flexibility Act. A copy of the final evaluation prepared for this 
action is contained in the Rules Docket. A copy of it may be obtained 
by contacting the Rules Docket at the location provided under the 
caption ADDRESSES.

List of Subjects in 14 CFR Part 39

    Air transportation, Aircraft, Aviation safety, Incorporation by 
reference, Safety.

Adoption of the Amendment

    Accordingly, pursuant to the authority delegated to me by the 
Administrator, the Federal Aviation Administration amends part 39 of 
the Federal Aviation Regulations (14 CFR part 39) as follows:

PART 39--AIRWORTHINESS DIRECTIVES

    1. The authority citation for part 39 continues to read as follows:

    Authority: 49 U.S.C. 106(g), 40113, 44701.


Sec. 39.13  [Amended]

    2. Section 39.13 is amended by adding a new airworthiness directive 
(AD) to read as follows:

98-08-19  Twin Commander Aircraft Corporation: Amendment 39-10468; 
Docket No. 95-CE-92-AD.

    Applicability: Models 500, 500A, 500B, 500S, 500U, 520, 560, 
560A, 560E, 560F, 680, 680E, 680F, 680FL, 680FLP, 680FP, 680T, 680V, 
680W, 681, 685, 690, 690A, 690B, 690C, 690D, 695, 695A, 695B and 720 
airplanes, all serial numbers, certificated in any category.

    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 request approval for an 
alternative method of compliance in accordance with paragraph (f) 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 in the body of this AD after 
the effective date of this AD, unless already accomplished.
    To prevent cracks at the wing to fuselage attach points, which, 
if not detected and corrected, could cause structural failure and 
loss of control of the airplane, accomplish the following:
    (a) For all models except Models 520, 560, 690C and 695, 
accomplish the actions in the following table in accordance with the 
Compliance section and Part I, I, and III of the ACCOMPLISHMENT 
INSTRUCTIONS sections of Twin Commander Service Bulletin No. 223, 
dated October 24, 1996 as amended by Revision Notice No. 1, dated 
May 8, 1997 and Revision Notice No. 2, dated August 18, 1997:

[[Page 19174]]



------------------------------------------------------------------------
                         A                  B                  C        
------------------------------------------------------------------------
Part I.........  Upon the           If cracked, prior  If no cracks are 
                  accumulation of    to further         found, repeat   
                  6,000 hours        flight, replace    inspection at   
                  total time-in-     the brackets and   1,000 hour (hr.)
                  service (TIS) or   straps or repair   intervals until 
                  within the next    the part by an     cracks are      
                  100 hours TIS,     approved repair    found, replace  
                  whichever occurs   scheme (see        the cracked part
                  later, install     paragraph (b) of   or repair by an 
                  access holes in    this AD). Then,    approved repair 
                  left and right     accomplish PART    scheme (see     
                  wing leading       II of this AD..    paragraph (b) of
                  edges and         (Accomplish in      this AD), then  
                  inspect the        accordance with    accomplish PART 
                  forward attach     PART I of          II.             
                  brackets and       Compliance        (Accomplish in   
                  straps for         Section in Twin    accordance with 
                  cracks.            Commander SB       PART I of       
                 For any airplanes   223, dated Oct.    Compliance      
                  that have wings    24, 1996 as        Section in Twin 
                  modified with      amended by         Commander SB    
                  titanium leading   Revision Notice    223, dated Oct. 
                  edges through an   No. 1, dated May   24, 1996 as     
                  STC, remove the    8, 1997 and        amended by      
                  wing root          Revision Notice    Revision Notice 
                  farings to         No. 2, dated       No. 1, dated May
                  accomplish the     August 18,         8, 1997 and     
                  required           1997.)             Revision Notice 
                  inspections, in                       No. 2, dated    
                  lieu of                               August 18,      
                  installing the                        1997.)          
                  access holes.                                         
                 (Accomplish in                                         
                  accordance with                                       
                  PART I of                                             
                  Compliance                                            
                  Section in Twin                                       
                  Commander SB                                          
                  223, dated Oct.                                       
                  24, 1996 as                                           
                  amended by                                            
                  Revision Notice                                       
                  No. 1, dated May                                      
                  8, 1997 and                                           
                  Revision Notice                                       
                  No. 2, dated                                          
                  August 18,                                            
                  1997.)                                                
Part II........  Inspect for        If cracked, prior  After repair or  
                  cracks at the      to further         replacement is  
                  wing leading       flight, replace    accomplished,   
                  edge close-outs,   any cracked part   continue to     
                  upper & lower      or repair the      inspect at 6,000
                  return flange      part with an       hr. intervals.  
                  radius, fuselage   approved repair   (Accomplish in   
                  frame where tee    scheme (see        accordance with 
                  bracket            paragraph (b) of   PART II of      
                  attaches,          this AD). If no    Compliance      
                  inboard side of    cracks are         Section in Twin 
                  attach bracket     found, continue    Commander SB    
                  and frame tee      to repetitively    223, dated Oct. 
                  bracket.           inspect at 1,000   24, 1996 as     
                 (Accomplish in      hour TIS           amended by      
                  accordance with    intervals.         Revision Notice 
                  PART II of        (Accomplish in      No. 1, dated May
                  Compliance         accordance with    8, 1997 and     
                  Section in Twin    PART II of         Revision Notice 
                  Commander SB       Compliance         No. 2, dated    
                  223, dated Oct.    Section in Twin    August 18,      
                  24, 1996 as        Commander SB       1997.)          
                  amended by         223, dated Oct.                    
                  Revision Notice    24, 1996 as                        
                  No. 1, dated May   amended by                         
                  8, 1997, and       Revision Notice                    
                  Revision Notice    No. 1, dated May                   
                  No. 2, dated       8, 1997 and                        
                  August 18,         Revision Notice                    
                  1997.)             No. 2, dated                       
                                     August 18,                         
                                     1997.)                             
Part III.......  For pressurized    If cracked, prior  If no cracks,    
                  airplanes, at      to further         repeat          
                  6,000 hr. total    flight, repair     inspection at   
                  TIS or within      with an approved   1,000 hr.       
                  the next 100       repair scheme      intervals until 
                  hours TIS          (see paragraph     cracks are      
                  whichever occurs   (b) of this AD),   found, then     
                  later, inspect     and continue to    accomplish PART 
                  fuselage station   inspect at 1,000   III B of this   
                  (F.S.) 100 for     hr. intervals.     AD.             
                  cracks.           (Accomplish in     (Accomplish in   
                 For non-            accordance with    accordance with 
                  pressurized        PART III of        PART III of     
                  airplanes, at      Compliance         Compliance      
                  12,000 hr. total   Section in Twin    Section in Twin 
                  TIS or within      Commander SB       Commander SB    
                  the next 100       223, dated Oct.    223, dated Oct. 
                  hours TIS          24, 1996 as        24, 1996 as     
                  whichever occurs   amended by         amended by      
                  later, inspect     Revision Notice    Revision Notice 
                  F.S. 100 for       No. 1, dated May   No. 1, dated May
                  cracks.            8, 1997 and        8, 1997 and     
                 (Accomplish in      Revision Notice    Revison Notice  
                  accordance with    No. 2, dated       No. 2, dated    
                  PART III of        August 18,         August 18,      
                  Compliance         1997.)             1997.)          
                  Section in Twin                                       
                  Commander SB                                          
                  223, dated Oct.                                       
                  24, 1996 as                                           
                  amended by                                            
                  Revision Notice                                       
                  No. 1, dated May                                      
                  8, 1997 and                                           
                  Revision Notice                                       
                  No. 2, dated                                          
                  August 18,                                            
                  1997.)                                                
------------------------------------------------------------------------

    (b) Obtain a FAA-approved repair scheme from the manufacturer 
through the Manager of the Seattle Aircraft Certification Office at 
the address specified in paragraph (f) of this AD.
    (c) For Twin Commander Models 520 and 560 airplanes, upon the 
accumulation of 6,000 hours total TIS or within the next 100 hours 
TIS, whichever occurs later, accomplish PART II of the table in 
paragraph (a) of this AD. Accomplish PART III in accordance with the 
compliance times in the above table of paragraph (a). These models 
are excluded from the wing leading edge access hole installation in 
PART I of the table in paragraph (a) of this AD.
    (d) For Twin Commander Models 690C and 695 airplanes, accomplish 
PARTS I and II in accordance with the compliance times in the above 
table of paragraph (a). These Models are excluded from PART III of 
the table in paragraph (a) 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, Seattle Aircraft 
Certification Office, 1601 Lind Ave. S.W., Renton, Washington, 
98055-4056. The request shall be forwarded through an appropriate 
FAA Maintenance Inspector, who may add comments and then send it to 
the Manager, Seattle Aircraft Certification Office.

    Note 2: Information concerning the existence of approved 
alternative methods of compliance with this AD, if any, may be 
obtained from the Seattle Aircraft Certification Office.

    (g) The inspections and installations required by this AD shall 
be done in accordance with the Twin Commander Service Bulletin No. 
223, dated October 24, 1996 as amended by Revision Notice No. 1, 
dated May 8, 1997 and Revision Notice No. 2, dated August 18, 1997. 
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 Twin Commander Aircraft Corporation, 
P.O. Box 3369, Arlington, Washington, 98223. 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, suite 700, 
Washington, DC.
    (h) This amendment becomes effective on May 18, 1998.

    Issued in Kansas City, Missouri, on April 3, 1998.
Michael Gallagher,
Manager, Small Airplane Directorate, Aircraft Certificate Service.
[FR Doc. 98-9874 Filed 4-16-98; 8:45 am]
BILLING CODE 4910-13-U