Airworthiness Directives; de Havilland DHC-6 Series Airplanes

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 91-CE-46-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) 83-18-03, which currently requires repetitively inspecting the

tailplane outboard hinge assembly 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

eventually modifying the tailplane outboard hinge arm and tailplane

hinge plate as terminating action for the currently required repetitive

inspections. The actions specified in the proposed AD are intended to

prevent tailplane failure caused by cracks in either the outboard hinge

arm or the hinge plate.

DATES: Comments must be received on or before January 4, 1995.

ADDRESSES: Submit comments on the proposal in triplicate to the Federal

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

Chief Counsel, Attention: Rules Docket No. 91-CE-46-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, M3K1Y5. 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-46-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-46-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) Transport Canada, which is the airworthiness authority

for Canada; (2) de Havilland, Inc.; (3) the Regional Airlines

Association (RAA); and (4) several U.S. and foreign operators of the

affected airplanes.

From this review, the FAA has identified AD 83-18-03, Amendment 39-

1658, as one that should be superseded with a new AD that would

eliminate short-interval and critical repetitive inspections. AD 83-18-

03 currently requires repetitively inspecting the tailplane outboard

hinge assembly 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. 6/421, Revision B, dated November 11, 1983.

This service bulletin specifies procedures for replacing the tailplane

outboard hinge arm and tailplane hinge plate with parts of improved

design. This replacement is known as Modification No. 6/1799.

As a result of the previously discussed AD review, Transport Canada

considers Modification 6/1799 mandatory and has issued Transport Canada

AD CF-83-11 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

Section 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 including that received from

Transport Canada, the FAA has determined that AD action should be taken

to eventually eliminate the repetitive short-interval inspections

required by AD 83-18-03, and to prevent tailplane failure caused by

cracks in either the outboard hinge arm or the hinge plate.

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, the proposed AD would supersede AD 83-18-03 with a

new AD that would (1) initially retain the requirement of repetitively

inspecting the tailplane outboard hinge assembly for cracks, and

replacing any cracked part; and (2) eventually require modifying the

tailplane outboard hinge arm and tailplane hinge plate with parts of

improved design (Modification No. 1799) as terminating action for the

currently required repetitive inspections. The proposed actions would

be accomplished in accordance with de Havilland SB No. 6/421, Revision

B, dated November 11, 1983.

The FAA estimates that 141 airplanes in the U.S. registry would be

affected by the proposed AD, that it would take approximately 35

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

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

approximately $4,400 per airplane. Based on these figures, the total

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

$916,500. This figure is based on the assumption that no affected

airplane owner/operator has accomplished the proposed action.

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

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

40 percent are operated in scheduled passenger service. A significant

number of the remaining 60 percent are operated in other forms of air

transportation such as air cargo and air taxi.

The proposed AD allows 2,400 hours time-in-service (TIS) before

mandatory accomplishment of the design modification. The average

utilization of the fleet for those airplanes in commercial commuter

service is approximately 25 to 50 hours TIS per week. Based on these

figures, operators of commuter-class airplanes involved in commercial

operation would have to accomplish the proposed modification within 12

to 24 calendar months after the proposed AD would become effective. For

private owners, who typically operate between 100 to 200 hours TIS per

year, this would allow 12 to 24 years before the proposed modification

would be mandatory.

The following paragraphs present cost scenarios for airplanes where

no cracks are found and where cracks are 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-46-AD, Room 1558, 601 E.

12th Street, Kansas City, Missouri.

No Cracks Scenario: Under the provisions of AD 83-18-03,

an owner/operator of a de Havilland DHC-6 series airplane in scheduled

service who operates an average of 1,600 hours TIS annually would

inspect every 1,200 hours TIS. This would amount to a remaining

airplane life (estimated 15 years) amount of $4,769; this figure is

based on the assumption that no cracks are found during the

inspections. The proposed AD would incur the same 1,200-hour TIS

inspection until 2,400 hours TIS where the operator would have to

replace the tailplane outboard hinge arm assembly (eliminating the need

for further repetitive inspections), which would result in a present

value cost of $6,574. The incremental cost of the proposed AD for such

an airplane would be $1,805 ($6,574-$4,769) or $1,309 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 inspections would incur a

present value incremental cost of $3,843 ($5,990-$2,507). This would

amount to a per year amount of $1,327 over the three years it would

take to accumulate 2,400 hours TIS.

Cracks Found Scenario: Under the provisions of AD 83-18-

03, an owner/operator of a de Havilland DHC-6 series airplane who found

cracks during an inspection would have to repair the crack prior to

further flight and resume inspections every 1,200 hours TIS. The

proposed AD would require immediate replacement of the arm assembly if

cracks were found as terminating action for the repetitive inspection

requirement. The repair cost is the same as the replacement except that

the repair does not terminate the inspection requirement. For this

reason, the proposed AD would result in present-day cost savings, which

would continue to grow over the remaining life of the airplane since

repetitive inspections would not be required. Using the assumed 15-year

remaining life, the cost savings would be $4,409 for scheduled service

airplane owners/operators and $2,149 for general aviation airplane

owners/operators.

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

airplanes are owned by the federal government. Of the other 135, one

business owns 26 airplanes, one business owns 9 airplanes, one business

owns 8 airplanes, 1 business owns 7 airplanes, one business owns 4

airplanes, two businesses own 3 airplanes each, thirteen business own 2

airplanes each, and forty-nine businesses each own 1 airplane.

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

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

utilizes the worst case scenario using the lower annualized cost

threshold of $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 64 entities owning 3 or fewer

airplanes would not experience a ``significant economic impact'' as

defined by FAA Order 2100.14A. Since the remaining five entities do not

constitute a ``substantial number'' as defined in the Order, the

proposed AD would not have a ``significant economic impact on a

substantial number of small entities.''

The regulations proposed herein would not have substantial direct

effects on the States, on the relationship between the national

government and the States, or on the distribution of power and

responsibilities among the various levels of government. Therefore, in

accordance with Executive Order 12612, it is determined that this

proposal would not have sufficient federalism implications to warrant

the preparation of a Federalism Assessment.

For the reasons discussed above, I certify that this action (1) is

not a ``significant regulatory action'' under Executive Order 12866;

(2) is not a ``significant rule'' under DOT Regulatory Policies and

Procedures (44 FR 11034, February 26, 1979); and (3) if promulgated,

will not have a significant economic impact, positive or negative, on a

substantial number of small entities under the criteria of the

Regulatory Flexibility Act. A copy of the draft regulatory evaluation

prepared for this action has been placed in the Rules Docket. A copy of

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

provided under the caption ADDRESSES.

List of Subjects in 14 CFR Part 39

Air transportation, Aircraft, Aviation safety, Safety.

The Proposed Amendment

Accordingly, pursuant to the authority delegated to me by the

Administrator, the Federal Aviation Administration proposes to amend

part 39 of the Federal Aviation Regulations (14 CFR part 39) as

follows:

PART 39--AIRWORTHINESS DIRECTIVES

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

Authority: 49 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 83-18-03, Amendment 39-

4719, and adding a new AD to read as follows:

De Havilland: Docket No. 91-CE-46-AD. Supersedes AD 83-18-03,

Amendment 39-4719.

Applicability: Models DHC-6-1, DHC-6-100, DHC-6-200 and DHC-300

airplanes (serial numbers 1 to 810), certificated in any category,

that have not incorporated Modification 6/1799 in accordance with

the ACCOMPLISHMENT INSTRUCTIONS, Replacement, section of de

Havilland Service Bulletin (SB) No. 6/421, Revision B, dated

November 11, 1983.

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

already accomplished.

To prevent tailplane failure caused by cracks in either the

outboard hinge arm or the hinge plate, accomplish the following:

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

effective date of this AD or within the next 1,200 hours TIS after

the last inspection accomplished in accordance with superseded AD

83-18-03, Amendment 39-4719, whichever occurs later, inspect the

tailplane outboard hinge arm assembly for cracks in accordance with

the ACCOMPLISHMENT INSTRUCTIONS, Inspection, section of de Havilland

SB No. 6/421, Revision B, dated November 11, 1983.

(1) If cracks are not found, reinspect every 1,200 hours TIS

until Modification 6/1799 (tailplane outboard hinge arm and

tailplane hinge plate) is installed as required by paragraph (b) of

this AD.

(2) If cracks are found, prior to further flight, replace the

tailplane outboard hinge arm assembly with Modification 6/1799 in

accordance with the ACCOMPLISHMENT INSTRUCTIONS, Replacement,

section of de Havilland SB No. 6/421, Revision B, dated November 11,

1983.

(b) Within 2,400 hours TIS after the effective date of this AD,

replace the tailplane outboard hinge arm assembly with Modification

6/1799 in accordance with the ACCOMPLISHMENT INSTRUCTIONS,

Replacement, section of de Havilland SB No. 6/421, Revision B, dated

November 11, 1983, unless already accomplished in accordance with

paragraph (a)(2) of this AD.

(c) Compliance with paragraph (a)(2) or (b) of this AD is

considered terminating action for the inspection requirements 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: 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.

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

John R. Colomy,

Acting Manager, Small Airplane Directorate, Aircraft Certification

Service.

[FR Doc. 94-26876 Filed 10-28-94; 8:45 am]

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