Airworthiness Directives; de Havilland DHC-6 Series Airplanes

DEPARTMENT OF TRANSPORTATION

14 CFR Part 39

[Docket No. 91-CE-22-AD]

Airworthiness Directives; de Havilland DHC-6 Series Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: This document proposes to supersede Airworthiness Directive

(AD) 81-10-11, which currently requires repetitively inspecting the

elevator root ribs for cracks on 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 elevator root rib as

terminating action for the repetitive inspections that are currently

required by AD 81-10-11. The actions specified in the proposed AD are

intended to prevent failure of the elevator root rib, 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-22-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-22-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-22-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 81-10- 11, Amendment

39-4112, as one that should be superseded with a new AD that would

require a modification that could eliminate the need for short-interval

and critical repetitive inspections. AD 81-10-11 currently requires

repetitively inspecting the elevator root rib for cracks on certain de

Havilland DHC-6 series airplanes, and replacing any cracked part.

De Havilland has issued Service Bulletin (SB) No. 6/399, Revision

E, dated May 25, 1984, which specifies procedures for (1) inspecting

the elevator root rib; and (2) modifying the elevator root rib

(Modification No. 6/1769). Modification No. 6/1769 consists of pulling

back the elevator skins, removing the torque tube assembly, replacing

the root rib assembly and doubler, replacing the second outboard nose

rib, installing a new intercostal, and reinstalling the torque tube

assembly and new skin.

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 81-10-11, and to prevent failure of the

elevator root rib, 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. 6/1769 incorporated,

the proposed AD would supersede AD 81-10-11 with a new AD that would

(1) retain the current requirement of inspecting the elevator root rib

for cracks, and replacing any cracked part; and (2) require modifying

the elevator root rib (Modification 6/1769) as terminating action for

the repetitive inspections. The proposed actions would be accomplished

in accordance with de Havilland SB No. 6/399, Revision E, dated May 25,

1984.

The FAA estimates that 169 airplanes in the U.S. registry would be

affected by the proposed AD, that it would take approximately 54

workhours per airplane to accomplish the proposed action, and that the

average labor rate is approximately $60 an hour. Parts cost

approximately $4,200 per airplane. Based on these figures, the total

cost impact of the proposed AD on U.S. operators is estimated to be

$1,257,360. This figure is based upon the assumption that none of the

affected airplane owners/operators have incorporated Modification 6/

1769.

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 169 airplanes in the U.S. registry that would be

affected by the proposed AD, the FAA has determined that approximately

50 percent are operated in scheduled passenger service. A significant

number of the remaining 50 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 cracks were found, utilizing an average

remaining airplane life of 15 years and an average annual utilization

rate of 1,600 hours TIS. De Havilland Models DHC-6-100 and DHC-6-200

airplanes have probably already accumulated 15,000 hours TIS;

therefore, those airplanes would have 100 hours TIS after the effective

date of the AD to incorporate Modification 6/1769. Some Model DHC-6-300

airplanes have not yet accumulated 15,000 hours TIS. This analysis is

based upon the assumption that these airplanes yet to accumulate 15,000

hours TIS have 10,000 hours TIS if operated in scheduled service and

5,000 hours TIS if operated in general aviation. 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-22-AD, Room

1558, 601 E. 12th Street, Kansas City, Missouri.

No Cracks Scenario for Models DHC-6-100 and DHC-6-200:

These airplanes would be inspected at 50 hours TIS after the effective

date and modified within 100 hours TIS after the effective date. The

incremental present value cost of the proposed AD over that required by

AD 81-10-11 is $5,919 for an airplane utilized in sheduled service, and

$6,642 for an airplane utilized in general aviation.

No Cracks Scenario for Model DHC-6-300 Airplanes: These

airplanes would be inspected at 50 hours TIS after the effective date

and thereafter at 600-hour TIS intervals until the elevator root rib is

replaced upon the accumulation of 15,000 hours TIS. The incremental

present value cost of the proposed AD over that required by AD 81-10-11

is $4,962 for an airplane utilized in sheduled service, and $3,099 for

an airplane utilized in general aviation.

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 169 U.S.-registered airplanes affected by the proposed AD, 6

airplanes are owned by the federal government. Of the other 163, one

business owns 26 airplanes, two businesses own 9 airplanes each, one

business owns 8 airplanes, one business owns 7 airplanes, one business

owns 5 airplanes, four businesses own 3 airplanes each, sixteen

businesses own 2 airplanes each, and fifty-five businesses own 1

airplane each.

Because the FAA has no readily available means of obtaining data on

the sizes of these entities, the economic analysis for the proposed AD

utilizes the worst case scenario using the lower annualized cost

threshold of $4,850 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 proposed AD could have a

significant impact on a substantial number of small entities. Because

of this, 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 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, 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

proposal 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 proposed action is the

best course to achieve the safety objective of returning the airplane

to its original certification level of safety.

Alternative actions and views are solicited from interested persons

and will be considered by the FAA in the development of the final rule.

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 81-10-11, Amendment 39-

4112, and adding a new AD to read as follows:

De Havilland: Docket No. 91-CE-22-AD. Supersedes AD 81-10-11,

Amendment 39-4112.

Applicability: Models DHC-6-1, DHC-6-100, DHC-6-200, and DHC-6-

300 airplanes (all serial numbers), certificated in any category,

that do not have Modification No. 6/1769 incorporated.

Compliance: Required as indicated in the body of the AD, unless

already accomplished.

To prevent failure of the elevator root rib, which could result

in loss of control of the airplane, accomplish the following:

(a) Within the next 50 hours time-in-service (TIS) after the

effective date of this AD, unless already accomplished (compliance

with AD 81-10-11), inspect the elevator root rib, part number (P/N)

C6TE1022, for cracks in accordance with the ACCOMPLISHMENT

INSTRUCTIONS section of de Havilland Service Bulletin (SB) No. 6/

399, Revision E, dated May 25, 1984.

(1) If any crack is found, prior to further flight, accomplish

one of the following:

(i) Replace the cracked part with an airworthy part and

reinspect thereafter at intervals not to exceed 600 hours TIS until

the modification required in paragraph (b) of this AD is

incorporated; or

(ii) Incorporate Modification 6/1769 in accordance with the

ACCOMPLISHMENT INSTRUCTIONS section of de Havilland SB No. 6/399,

Revision E, dated May 25, 1984.

Note 1: Modification 6/1769 consists of pulling back the

elevator skins, removing the torque tube assembly, replacing the

root rib assembly and doubler, replacing the second outboard nose

rib, installing a new intercostal, and reinstalling the torque tube

assembly and new skin.

(2) If no cracks are found, reinspect thereafter at intervals

not to exceed 600 hours TIS until the modification required in

paragraph (b) of this AD is incorporated.

(b) Upon the accumulation of 15,000 hours TIS or within the next

100 hours TIS after the effective date of this AD, whichever occurs

later, unless already accomplished in accordance with paragraph

(a)(1)(ii) of this AD, incorporate Modification 6/1769 in accordance

with the ACCOMPLISHMENT INSTRUCTIONS section of de Havilland SB No.

6/399, Revision E, dated May 25, 1984.

(c) Incorporating Modification 6/1769 as specified in paragraphs

(a)(1)(ii) and (b) of this AD is considered terminating action for

the inspection requirement of this AD.

(d) Special flight permits may be issued in accordance with

sections 21.197 and 21.199 of the Federal Aviation Regulations (14

CFR 21.197 and 21.199) to operate the airplane to 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, 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.

(f) All persons affected by this directive may obtain copies of

the document referred to herein upon request to de Havilland, Inc.,

123 Garratt Boulevard, Downsview, Ontario M3K 1Y5 Canada; or may

examine this document at the FAA, Central Region, Office of the

Assistant Chief Counsel, Room 1558, 601 E. 12th Street, Kansas City,

Missouri 64106.

(g) This amendment supersedes AD 81-10-11, Amendment 39-4112.

Issued in Kansas City, Missouri, on October 25, 1994.

John R. Colomy,

Acting Manager, Small Airplane Directorate, Aircraft Certification

Service.

[FR Doc. 94-26878 Filed 10-28-94; 8:45 am]

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