Airworthiness Directives: Twin Commander Aircraft Corporation Models 500, 560A, 560E, 680, 680E, and 720 Airplanes

DEPARTMENT OF TRANSPORTATION

14 CFR Part 39

[Docket No. 92-CE-57-AD; Amdt 39-8835; AD 94-04-15]

Airworthiness Directives: Twin Commander Aircraft Corporation

Models 500, 560A, 560E, 680, 680E, and 720 Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Final rule.

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SUMMARY: This amendment adopts a new airworthiness directive (AD) that

applies to certain Twin Commander Aircraft Corporation (Twin Commander)

Models 500, 560A, 560E, 680, 680E, and 720 airplanes. This action

requires inspecting the wing front spar lower cap (spar cap) for

interference, fretting, or corrosion between the firewall flange and

spar cap flange at Wing Station (WS) 96, and clearing any interference,

repairing any fretting or corrosion damage, and replacing any cracked

spar cap. Reports of two of the affected airplanes have cracked spar

caps at WS 96 prompted this action. The actions specified by this AD

are intended to prevent failure of the wing structure caused by a

cracked spar cap at WS 96.

DATES: Effective April 12, 1994. The incorporation by reference of

certain documents listed in the regulations is approved by the Director

of the Federal Register as of April 12, 1994.

ADDRESSES: Service information that applies to this AD may be obtained

from the Twin Commander Aircraft Corporation, 19003 59th Drive, NE.,

Arlington, Washington 98223. This information may also be examined at

the Federal Aviation Administration (FAA), Central Region, Office of

the Assistant Chief Counsel, 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:

Mr. Mike Pasion, Aerospace Engineer, FAA Northwest Mountain Region,

1601 Lind Avenue SW., Renton, Washington 98055-4056; telephone (206)

277-2594; facsimile (206) 227-1181.

SUPPLEMENTARY INFORMATION: A proposal to amend part 39 of the Federal

Aviation Regulations to include an AD that applies to certain Twin

Commander Models 500, 560A, 560E, 680, 680E, and 720 airplanes was

published in the Federal Register on June 30, 1993 (58 FR 34950). The

action proposed to require inspecting the spar cap for interference,

fretting, or corrosion between the firewall flange and spar cap flange

at WS 96, and clearing any interference, repairing any fretting or

corrosion damage, and replacing any cracked spar cap. The proposed

inspection and repair, if applicable, would be accomplished in

accordance with Twin Commander SB No. 212, dated November 3, 1992.

Interested persons have been afforded an opportunity to participate

in the making of this amendment. Due consideration has been given to

the nine comments received.

Seven commenters concur with the proposal as written.

One commenter, the Civil Aviation Authority of Australia (CAA),

states that the proposal should require an eddy current inspection of

the spar cap. The CAA questions whether fretting and corrosion are the

sole contributors to fatigue damage to WS 96, or if these merely

aggravate what is already a fatigue-sensitive location. The CAA goes on

to state that, if a crack can start from a corrosion pit as small as

0.006 inches (as happened on a Swedish airplane), then there is a good

chance that even a clean airplane will crack over time. Also, the CAA

states that, if a fatigue crack has started at the base of a corrosion

pit, the blending of the corrosion will smear over the crack and

conceal it from the dye penetrant inspection (which is called for in

the SB), and that an eddy current inspection is the only method for

detection of this crack. The FAA does not concur. The proposal relates

to fretting that may occur because interference between a firewall

stiffener and the forward flange of the lower spar cap. It would

require action for fatigue cracks found as a result of this

interference and fretting. Fretting does have a synergistic

relationship with corrosion and fatigue, and its existence greatly

accelerates fatigue crack growth. The FAA has received no reports of

fatigue cracks in the affected area that were not a direct result of

fretting. Also, the spar cap at WS 96 is extremely difficult to inspect

using eddy current methods because of other structures in the area

interfering with placement of the eddy current probe. Dye penetrant

inspections are used extensively in the aviation industry and have

proved very reliable in detecting cracks. The proposed AD is unchanged

as a result of this comment.

Another commenter, the Twin Commander Aircraft Corporation states

that owners/operators should have their airplanes inspected regardless

of whether the spar cap has been replaced because interference may even

exist on a new spar. The FAA concurs that interference may exist if a

new spar is installed, unless it was installed in accordance with

replacement procedures obtained from the manufacturer through the

Manager, Seattle Aircraft Certification Office (as specified in

paragraph (a)(3) of the proposed AD). The Seattle Aircraft

Certification Office has not issued any of these procedures to airplane

owners/operators; therefore, no airplane has the spar cap replaced in

accordance with paragraph (a)(3) of the proposal and the proposal would

affect all of the airplanes listed under the Applicability section. The

proposed AD is unchanged as a result of this comment.

After careful review of all available information including the

comments referenced above, the FAA has determined that air safety and

the public interest require the adoption of the rule as proposed except

for minor editorial corrections. The FAA has determined that these

minor corrections will not change the meaning of the AD nor add any

additional burden upon the public than was already proposed.

The FAA estimates that 332 airplanes in the U.S. registry will be

affected by the proposed AD, that it will take approximately 20

workhours per airplane to accomplish the required inspection, and that

the average labor rate is approximately $55 an hour. Parts to

accomplish the required inspection cost approximately $20. Based on

these figures, the total cost impact of the inspection specified in

this AD on U.S. operators is estimated to be $371,840. One airplane

owner has already accomplished the required inspection, and found no

damage or cracks.

In addition, if the required inspection reveals cracks, or

corrosion that exceeds certain limits, replacing the spar cap would be

required at a cost of approximately $100,000, parts and labor included.

An airplane affected by this AD could have a compliance cost as low as

approximately $1,120 (labor + parts) if no cracks, interference, or

corrosion damage is found during the inspection, and as high as

approximately $101,120 (inspection + spar cap replacement) if the

operator replaces the spar cap.

Based on these airplanes having an expected average remaining

operating life of 10 years or 15 years, the annualized compliance cost

would range between:

If only inspecting the spar cap at WS 96 is necessary for

airplanes with an average remaining operating life of 10 years:

$1,120 x 0.14349 (10-year capital recovery factor at a 7 percent

interest rate)=$168 annualized cost;

If only inspecting the spar cap at WS 96 is necessary for

airplanes with an average remaining operating life of 15 years:

$1,120 x 0.11434 (15-year capital recovery factor at a 7 percent

interest rate)=$126;

If replacing the spar cap is necessary for airplanes with

an average remaining operating life of 10 years: approximately

$101,120 x 0.15349 (capital recovery factor at a 7 percent interest

rate)=$15,520; or

If replacing the spar cap is necessary for airplanes with

an average remaining operating life of 15 years: approximately

$101,120 x 0.11434 (capital recovery factor at a 7 percent interest

rate)=$11,562.

The required AD's from Dockets No. 92-CE-43-AD (for Models 500,

560A, 560E, 680, 680E, and 720) and No. 92-CE-58-AD (for Models 685,

690, 690A, and 690B) will also affect certain airplanes included in

this AD. The compliance costs of these other required AD's would add to

the cost discussed above. However, replacing the spar cap would only be

required once, so the $100,000 replacement cost, if required, would be

a one-time action.

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.

The 331 U.S.-registered airplanes affected by the required AD that

have not complied with Twin Commander SB No. 212, dated November 3,

1992, are owned according to the following breakdown: 196 by

individuals, 2 by U.S. government agencies, 7 by states or local

governments, and 126 by other entities. Six entities own 2 airplanes

each.

The FAA cannot determine the sizes of all the affected non-

individual owner entities nor the relative significance of the costs

estimated above. Because of these uncertainties, no cost thresholds for

significant economic impact can be reasonably determined. Based on the

possibility that this AD could have a significant impact on a

substantial number of small entities, the FAA conducted a regulatory

flexibility analysis. A copy of this analysis may be obtained by

contacting the Rules Docket at the location provided under the caption

``ADDRESSES''.

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 significant under DOT Regulatory Policies and Procedures (44 FR

11034, February 26, 1979) because of substantial public interest; and,

(3) may have a significant economic impact on a substantial number of

small entities. The FAA has conducted an Initial Regulatory Flexibility

Determination and Analysis and has considered alternatives to this

action that could minimize the impact on small entities. A copy of this

analysis may be obtained by contacting the Rules Docket at the location

provided under the caption ``ADDRESSES''. After careful consideration,

the FAA has determined that the required action is the best course to

achieve the safety objective of returning the airplane to its original

certification level of safety.

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 14 CFR part

39 of the Federal Aviation Regulations 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 adding the following new AD to read

as follows:

94-04-15 Twin Commander Aircraft Corporation: Amendment 39-8835;

Docket No. 92-CE-57-AD.

Applicability: The following model and serial number airplanes

that do not have the wing front spar lower cap replaced in

accordance with procedures specified in paragraph (a)(3) of this AD,

certificated in any category:

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Model Serial No.

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500.............................. 618 through 750.

560A............................. 231 through 450.

560E............................. 433 through 750.

680.............................. 242 through 658.

680E............................. 623 through 750.

720.............................. 501 through 750.

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Compliance: Required within the next 50 hours time-in-service

after the effective date of this AD, unless already accomplished.

To prevent failure of the wing structure caused by a cracked

wing front spar lower cap at Wing Station (WS) 96, accomplish the

following:

(a) Inspect the wing front spar lower cap of each wing for

corrosion or interference between the firewall flange and spar

flange in accordance with the ACCOMPLISHMENT INSTRUCTIONS section of

Twin Commander Service Bulletin (SB) No. 212, dated November 3,

1992.

(1) If any interference is found between the firewall flange and

spar flange, prior to further flight, clear this interference in

accordance with the ACCOMPLISHMENT INSTRUCTIONS section of Twin

Commander SB No. 212, dated November 3, 1992.

(2) If any corrosion damage is found, prior to further flight,

repair any corrosion damage to the wing front spar lower cap in

accordance with the ACCOMPLISHMENT INSTRUCTIONS section of Twin

Commander SB No. 212, dated November 3, 1992.

(3) If any cracks are found, prior to the further flight,

replace the wing front spar lower cap in accordance with replacement

procedures obtained from the manufacturer through the Manager,

Seattle Aircraft Certification Office (ACO), at the address

specified in paragraph (c) of this AD.

(b) Special flight permits may be issued in accordance with 14

CFR 21.197 and 21.199 to operate the airplane to a location where

the requirements of this AD can be accomplished.

(c) An alternative method of compliance or adjustment of the

compliance time that provides an equivalent level of safety may be

approved by the Manager, Seattle ACO, FAA, Northwest Mountain

Region, 1601 Lind Avenue SW., 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 ACO, FAA, Northwest Mountain Region.

Note: Information concerning the existence of approved

alternative methods of compliance with this AD, if any, may be

obtained from the Seattle ACO, FAA, Northwest Mountain Region.

(d) The inspection and repair required by this AD shall be done

in accordance with Twin Commander Service Bulletin No. 212, dated

November 3, 1992. 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, 19003 59th Drive, NE., Arlington, Washington

98223. Copies may be inspected at the FAA, Central Region, Office of

the Assistant Chief 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.

(e) This amendment (39-8835) becomes effective on April 12,

1994.

Issued in Kansas City, Missouri, on February 14, 1994.

Barry D. Clements,

Manager, Small Airplane Directorate, Aircraft Certification Service.

[FR Doc. 94-3840 Filed 2-18-94; 8:45 am]

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