AD 98-18-08 ACTIVE

This amendment adopts a new airworthiness directive (AD) that applies to certain Bombardier Inc. (formerly deHavilland Inc) Model DHC-3 (Otter) airplanes that have been modified in accordance with A.M. Luton Supplemental Type Certificate (STC) No. SA3777NM. This AD requires modifying the airplane s electrical system. The actions specified by this AD are intended to prevent electrical system failure caused by inadequate electrical system design, which could result in the loss of the engine instruments or a possible electrical fire in the airplane s cockpit.

Final rule.

98-18-08 BOMBARDIER INC. (formerly deHavilland, Inc.): Amendment 39-10724; Docket No. 97-CE-120-AD.

Applicability: Model (Otter) DHC-3 airplanes, all serial numbers, certificated in any category, that have been modified by A.M. Luton Supplemental Type Certificate (STC) No. SA3777NM.

NOTE 1: This AD applies to each airplane identified in the preceding applicability provision that has the applicable STC incorporated, 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 (c) 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 within the next 14 calendar months after the effective date of this AD, unless already accomplished.

To prevent electrical system failure caused by inadequate electrical system requirements, which could result in the loss of the engine instruments or a possible electrical fire in the airplane's cockpit, accomplish the following:

(a) Replace the voltage regulator and the voltage-ammeter gauge, and modify the auxiliary bus systems in accordance with A.M. Luton Electrical System Schematic, Drawing 20075, Rev. G and E, Sheets 1, 2, and 3, dated May 15, 1998, which is referenced in A.M. Luton Service Information Letter No. SA-SIL-98-11-03, "Electrical Systems", Revision A, dated May 15, 1998.

(b) 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 locationwhere 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 Aircraft Certification Office (ACO), FAA, 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.

NOTE 2: Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from Seattle ACO.

(d) Questions or technical information related to A.M. Luton Electrical System Schematic, Drawing 20075, Rev. G and E, Sheets 1, 2, and 3, dated May 15, 1998, and A.M. Luton Service Information Letter No. SA-SIL-98-11-03, "Electrical Systems", Revision A, dated May 15, 1998, should be directed to A.M. Luton, 3025 Eldridge Ave., Bellingham, WA 98226; telephone: (360) 671-7817, facsimile: (360) 671-7820. This service information may be examined at the FAA, Central Region, Office of the Regional Counsel, Room 1558, 601 E. 12th Street, Kansas City, Missouri 64106.

(e) The replacements and modifications required by this AD shall be done in accordance with A.M. Luton Electrical System Schematic, Drawing 20075, Rev. G and E, Sheets 1, 2, and 3, dated May 15, 1998, which is referenced in A.M. Luton Service Information Letter No. SA-SIL-98-11-03, "Electrical Systems", Revision A, dated May 15, 1998. 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 A.M. Luton, 3025 Eldridge Ave., Bellingham, WA 98226. 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.(f) This amendment becomes effective on October 10, 1998.

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 certain Bombardier Inc. Model DHC-3 (Otter) airplanes was published in the Federal Register as a notice of proposed rulemaking (NPRM) on April 13, 1998 (63 FR 17970). The airplanes affected have electrical system modifications in accordance with A.M. Luton STC No. SA3777NM. The NPRM proposed to require replacing the voltage regulator and voltage-ammeter gauge, and modifying the auxiliary bus systems. These modifications would bring the airplane s electrical system into compliance with the current regulations.

Accomplishment of the proposed action as specified in the NPRM would be in accordance with A.M. Luton Electrical Systems Schematic Drawing 20075, Rev. G and E, Sheets 1, 2, and 3, dated May 15, 1998, which is referenced in A.M. Luton Service Information Letter SA-SIL-98-11-03, "Electrical Systems", Revision A, dated May 15, 1998.

Interested persons have been afforded an opportunity to participate in the making of this amendment. Due consideration has been given to the comments received.

Comment No. 1: Change in Compliance Time

Three commenters state that the proposed compliance of 100 hours time-in-service (TIS) would be an economic hardship because of the way they operate the affected airplanes. Some operators utilize their airplanes more than 100 hours in a month s time, with many in revenue operations, i.e., air taxi, etc. One operator estimates losing as much as $50,000 if the airplanes had to be out of service for approximately three days to accomplish the proposed modification. All of the commenters state that their fleets have not had any service history problems related to electrical fires and proposed that the compliance time be lengthened to coincide with the next annual inspection.

The FAA concurs. In reviewing the service history of the U.S. registered fleet and the operational levels of the affected airplanes, the FAA has determined that the compliance time should coincide with the airplanes annual maintenance programs. For this reason, the compliance time of the proposed AD is changed from 100 hours TIS after the effective date of the AD to 14 calendar months after the effective date the AD. This will give all owners/operators of the affected airplanes the opportunity to schedule the actions specified in this AD to coincide with regularly scheduled maintenance. The final rule will be changed accordingly.

Comment No. 2: Circuit Breaker Requirement

One commenter states that there isn t a need for the installation of a circuit breaker on the wire to the auxiliary bus. The commenter expresses that the components drawing from the auxiliary bus utilize individual circuit breakers, and there are other distribution wires in the original electrical system that are not protected by a circuit breaker that have not had any adverse affects.

The FAA does not concur. The subject of this AD addresses the electrical system changes affected by STC SA3777NM. As installed, the electrical system is not in compliance with part 23 of the Federal Aviation Regulations (14 CFR part 23). The electrical distribution bus was added as part of STC SA3777NM to provide electrical power to the additional engine-related electrical loads. This distribution bus is connected to the battery through the master solenoid with a 10-gauge wire. If a fault in this wire should occur, a hazard in the form of smoke or fire in the cockpit could result. If a determination is made that the original electrical system is similarly protected and poses a safety hazard, then another NPRM may be issued to address that condition. The final rule will not change as a result of this comment.

Comment No. 3: Loadmeter vs. Ammeter

A commenter states that installing a loadmeter should not be mandatory. The commenter states that the ammeter is more useful to pilots and mechanics in performing their duties.

The FAA does not concur. In the original, unmodified electrical system, the ammeter shunt is placed between the battery and the electrical distribution busses, so it properly indicates the current load. With the incorporation of STC SA3777NM, the additional engine-related electrical loads were added to the battery side of the shunt. As a result, the ammeter does not indicate the total and actual electrical load from (and to) the battery. The ammeter is providing misleading information. The loadmeter was proposed by the STC holder as a solution and as a means to keep the disturbance to existing wiring to a minimum. If the commenter wants to use an ammeter in lieu of a loadmeter, he/she may submit the appropriate information and apply for an alternative method of compliance (AMOC), as specified in paragraph (c) of the AD. The final rule will not change as a result of this comment.

CommentNo. 4: Over-voltage protection

Two commenters agree with the proposal and state that addressing over-voltage protection is a necessity for the voltage regulator.

The FAA's Determination

After careful review of all available information related to the subject presented above, the FAA has determined that air safety and the public interest require the adoption of the rule as proposed except for the change in compliance time and minor editorial corrections. The FAA has determined that the compliance time change and the 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 17 airplanes in the U.S. registry will be affected by this AD, that it will take approximately 20 workhours per airplane to accomplish this action, and that the average labor rate is approximately $60 an hour. Parts cost approximately $2,000 per airplane. Based on these figures, thetotal cost impact of this AD on U.S. operators is estimated to be $54,400, or $3,200 per airplane.

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) 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 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.

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

Service information that applies to this AD may be obtained from A.M. Luton, 3025 Eldridge Avenue, Bellingham, Washington 98225; telephone: 360) 671-7817, facsimile: (360) 671-7820. This information may also be examined at the Federal Aviation Administration (FAA), Central Region, Office of the Regional Counsel, Attention: Rules Docket No. 97-CE-120-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.

Mr. Mike Pasion, Aerospace Engineer, Seattle Aircraft Certification Office, FAA, 1601 Lind Avenue, SW, Renton, Washington 98055-4056; telephone: (425) 227-2594; facsimile: (425)227-1181.