Airworthiness Directives; Bombardier Model DHC-7 Series Airplanes

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 99-NM-165-AD]

RIN 2120-AA64

Airworthiness Directives; Bombardier Model DHC-7 Series Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: This document proposes the adoption of a new airworthiness

directive (AD) that is applicable to certain Bombardier Model DHC-7

series airplanes. This proposal would require a one-time visual

inspection to detect corrosion on the upper half of the lower longerons

on the inboard nacelles; and corrective actions, if necessary. This

proposal also would require modification of the upper and lower

longeron halves. This proposal is prompted by issuance of mandatory

continuing airworthiness information by a foreign civil airworthiness

authority. The actions specified by the proposed AD are intended to

detect and correct corrosion in the upper halves of the left and right

hand lower longerons on the inboard nacelles, which could result in a

landing gear failure.

DATES: Comments must be received by November 15, 1999.

ADDRESSES: Submit comments in triplicate to the Federal Aviation

Administration (FAA), Transport Airplane Directorate, ANM-114,

Attention: Rules Docket No. 99-NM-165-AD, 1601 Lind Avenue, SW.,

Renton, Washington 98055-4056. Comments may be inspected at this

location between 9:00 a.m. and 3:00 p.m., Monday through Friday, except

Federal holidays.

The service information referenced in the proposed rule may be

obtained from Bombardier, Inc., Bombardier Regional Aircraft Division,

Garratt Boulevard, Downsview, Ontario M3K 1Y5, Canada. This information

may be examined at the FAA, Transport Airplane Directorate, 1601 Lind

Avenue, SW., Renton, Washington; or at the FAA, Engine and Propeller

Directorate, New York Aircraft Certification Office, 10 Fifth Street,

Third Floor, Valley Stream, New York.

FOR FURTHER INFORMATION CONTACT: Franco Pieri, Aerospace Engineer,

Airframe and Propulsion Branch, ANE-171, FAA, Engine and Propeller

Directorate, New York Aircraft Certification Office, 10 Fifth Street,

Third Floor, Valley Stream, New York 11581; telephone (516) 256-7526;

fax (516) 568-2716.

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 shall 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 summarizing 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 Number 99-NM-165-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, Transport Airplane Directorate, ANM-114, Attention: Rules

Docket No. 99-NM-165-AD, 1601 Lind Avenue, SW., Renton, Washington

98055-4056.

Discussion

Transport Canada Civil Aviation (TCCA), which is the airworthiness

authority for Canada, notified the FAA that an unsafe condition may

exist on certain Bombardier Model DHC-7 series airplanes. TCCA advises

that severely corroded areas have been found in the upper halves of the

left and right lower longerons on the inboard engine nacelles. The

corrosion was caused by accumulation of moisture in the vicinity of the

longeron cavities and around or under retaining bolt seats. This

condition, if not corrected, could result in landing gear failure.

[[Page 55641]]

Explanation of Relevant Service Information

Bombardier has issued Service Bulletin S.B. 7-54-19, Revision `C,'

dated April 16, 1999, which describes procedures for a one-time visual

inspection to detect corrosion on the upper half of the lower longerons

on the inboard nacelles; and corrective actions, if necessary. The

corrective actions involve blending out corroded areas; performing a

fluorescent penetrant or eddy current inspection to detect cracks in

areas where corrosion was blended out; and repair or replacement of the

longeron with a new longeron, if necessary. The service bulletin also

describes procedures for modification of the upper and lower longeron

halves. The modification involves drilling drainage holes through the

upper and lower longeron halves; finishing all cleaned surfaces with

alodine and chromate epoxy primer; refinishing the longeron assembly

with polyurethane paint; and applying an anti-corrosion compound.

Accomplishment of the actions specified in the service bulletin is

intended to adequately address the identified unsafe condition. TCCA

classified this service bulletin as mandatory and issued Canadian

airworthiness directive CF-99-07, dated March 15, 1999, in order to

assure the continued airworthiness of these airplanes in Canada.

FAA's Conclusions

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, TCCA has kept the FAA informed of

the situation described above. The FAA has examined the findings of

TCCA, reviewed all available information, and determined that AD action

is necessary for products of this type design that are certificated for

operation in the United States.

Explanation of Requirements of Proposed Rule

Since an unsafe condition has been identified that is likely to

exist or develop on other airplanes of the same type design registered

in the United States, the proposed AD would require accomplishment of

the actions specified in the service bulletin described previously,

except as discussed below.

Differences Between Proposed Rule and Service Bulletin

Operators should note that, although the service bulletin specifies

that the manufacturer may be contacted for disposition of certain

cracks, this proposal would require the repair of those conditions to

be accomplished in accordance with a method approved by either the FAA,

or TCCA (or it's delegated agent). In light of the type of repair that

would be required to address the identified unsafe condition, and in

consonance with existing bilateral airworthiness agreements, the FAA

has determined that, for this proposed AD, a repair approved by either

the FAA or TCCA (or it's delegated agent) would be acceptable for

compliance with this proposed AD.

Cost Impact

The FAA estimates that 32 airplanes of U.S. registry would be

affected by this proposed AD.

It would take approximately 8 work hours per airplane to accomplish

the proposed inspection, at an average labor rate of $60 per work hour.

Based on these figures, the cost impact of the proposed AD on U.S.

operators is estimated to be $15,360, or $480 per airplane.

It would take approximately 12 work hours per airplane to

accomplish the proposed modification, at an average labor rate of $60

per work hour. Based on these figures, the cost impact of the

modification proposed by this AD on U.S. operators is estimated to be

$23,040, or $720 per airplane.

The cost impact figures discussed above are based on the assumption

that no operator has yet accomplished any of the proposed requirements

of this AD action, and that no operator would accomplish those actions

in the future if this AD were not adopted.

Regulatory Impact

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 proposed

regulation (1) Is not a ``significant regulatory action'' under

Executive Order 12866; (2) is not a ``significant rule'' under the 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 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, 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. 106(g), 40113, 44701.

Sec. 39.13 [Amended]

2. Section 39.13 is amended by adding the following new

airworthiness directive:

Bombardier, Inc. (Formerly de Havilland, Inc.): Docket 99-NM-165-AD.

Applicability: Model DHC-7 series airplanes, serial numbers 004

through 113 inclusive, except serial numbers 037 and 061;

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 (d) 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, unless accomplished

previously.

To detect and correct corrosion in the upper halves of the left and

right hand lower longerons on the inboard nacelles, which could result

in a landing gear failure, accomplish the following:

Inspection

(a) Within 6 months after the effective date of this AD, perform

a visual inspection to detect corrosion on the upper half of the

[[Page 55642]]

lower longerons on the inboard nacelles in accordance with

Bombardier Service Bulletin S.B. 7-54-19, Revision `C,' dated April

16, 1999.

Modification

(b) If no corrosion is detected, prior to further flight, modify

the upper and lower longeron halves in accordance with Bombardier

Service Bulletin S.B. 7-54-19, Revision `C,' dated April 16, 1999.

Corrective Action

(c) If any corrosion is detected, prior to further flight,

accomplish the actions specified in paragraph (c)(1) or (c)(2) of

this AD, as applicable, in accordance with Bombardier Service

Bulletin S.B. 7-54-19, Revision `C,' dated April 16, 1999.

(1) For corrosion that is within the limits specified in the

service bulletin: Accomplish the corrective actions specified in the

service bulletin, and perform a fluorescent penetrant inspection or

high frequency eddy current inspection to detect cracks in areas

where corrosion was blended out. The corrective actions and

inspections shall be done in accordance with the service bulletin.

(i) If no crack is detected, prior to further flight, modify the

upper and lower longeron halves in accordance with the service

bulletin.

(ii) If any crack is detected, prior to further flight,

accomplish the actions required by paragraphs (c)(1)(ii)(A) and

(c)(1)(ii)(B) of this AD.

(A) Either replace the longeron with a new longeron in

accordance with the service bulletin, or repair in accordance with a

method approved by either the Manager, New York Aircraft

Certification Office (ACO), FAA, Engine and Propeller Directorate;

or Transport Canada Civil Aviation (or it's delegated agent). For a

repair method to be approved by the Manager, New York ACO, as

required by this paragraph, the Manager's approval letter must

specifically reference this AD.

(B) Modify the upper and lower longeron halves in accordance

with the service bulletin.

(2) For corrosion that exceeds the limits specified in the

service bulletin: Accomplish the actions required in paragraphs

(c)(1)(ii)(A) and (c)(1)(ii)(B) of this AD.

Alternative Methods of Compliance

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

compliance time that provides an acceptable level of safety may be

used if approved by the Manager, New York ACO, FAA, Engine and

Propeller Directorate. Operators shall submit their requests through

an appropriate FAA Principal 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.

Special Flight Permits

(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.

Note 3: The subject of this AD is addressed in Canadian

airworthiness directive CF-99-07, dated March 15, 1999.

Issued in Renton, Washington, on October 7, 1999.

D.L. Riggin,

Acting Manager, Transport Airplane Directorate, Aircraft Certification

Service.

[FR Doc. 99-26870 Filed 10-13-99; 8:45 am]

BILLING CODE 4910-13-P