AD 97-22-02

This amendment adopts a new airworthiness directive (AD) that applies to Pilatus Britten-Norman Ltd. (PBN) BN-2, BN-2A, BN-2B, and BN-2T series airplanes. This action requires modifying the upper engine mounting brackets on the wing front spar as terminating action for the repetitive inspections that were required in AD 84-23-06. AD 84-23-06 is being revised in a separate action, deleting the Pilatus BN-2, BN-2A, BN-2B, and BN-2T series airplanes from its applicability. This AD is prompted by several reports of cracks in the upper engine mounting brackets and a new terminating action to eliminate the repetitive inspections for Pilatus BN-2, BN-2A, BN-2B, and BN-2T series airplanes. The actions specified by this AD are intended to prevent the failure of the upper engine mounting brackets on the wing mounted engines, which could possibly cause structural failure of the airplane.

Final rule.

97-22-02 PILATUS BRITTEN-NORMAN LTD.: Amendment 39-10173; Docket No. 96-CE-17-AD.

Applicability: Models BN-2 (serial numbers 1 through 2033), BN-2A and BN-2B (serial numbers 1 through 2116), and BN-2T (serial numbers 419, and 2030 through 2033) airplanes, 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 (g) 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 500 hours time-in-service (TIS) after the last inspection required by AD 84-23-06, or within the next 100 hours TIS after the effective date of this AD, whichever occurs later, unless already accomplished, and thereafter as indicated in the body of this AD.

To prevent failure of the upper mounting brackets on both wing mounted engines, which could cause structural failure of the airplane, accomplish the following:

(a) Inspect the upper mounting brackets, bolts, and bushes on both wing mounted engines in accordance with the "ACTION-Inspection" section in Pilatus Britten-Norman (Pilatus) Service Bulletin (SB) No. BN-2/SB.61, Issue 5, dated December 9, 1981, for:

(1) Cracks at the bolt holes,

(2) Elongation of the bolt holes,

(3) Fretting within the bolt holes,

(4) Cracks at the rivet holes,

(5) Distortion or delamination of the lugs, and

(6) Incorrect bearing length and threadbound bolts,

(b) If the inspection reveals any evidence of damage or defects similar to the items in paragraphs (a)(1) through (a)(6), prior to further flight, accomplish Pilatus Modification NB/M/1147 by replacing the brackets, bushes, and bolts with brackets, bushes, and bolts of improved design in accordance with paragraphs 1, 2, 3, and 5 of the "ACTION - Rectification/Modification" section in Pilatus SB No. BN-2/SB.61, Issue 5, dated December 9, 1981.

(c) If damage or defects are found on just one of the two brackets on each engine, then both brackets must be replaced, prior to further flight, in accordance with paragraph 1 of the "ACTION - Rectification/Modification" section in Pilatus SB No. BN-2/SB.61, Issue 5, dated December 9, 1981.

(d) If no damage or defects are found similar to the items in paragraphs (a)(1) through (a)(6) of this AD, continue to inspect at intervals not to exceed 500 hours TIS, until the accumulation of 2,000 hours TIS after theeffective date of this AD, at which time Modification NB/M/1147 must be accomplished on both upper mounting brackets on both engines in accordance with paragraphs 1, 2, 3, and 5 of the "ACTION - Rectification/Modification" section of Pilatus SB No. BN-2/SB.61, Issue 5, dated December 9, 1981.

(e) Accomplishing Modification NB/M/1147 in the "ACTION - Rectification/Modification" section of Pilatus SB No. BN-2/SB.61, Issue 5, dated December 9, 1981, is considered terminating action to the repetitive inspections required in paragraph (d) of this AD.

(f) 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.

(g) 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, Small Airplane Directorate, Aircraft Certification Service, FAA, 1201 Walnut, suite 900, Kansas City, Missouri 64105. The request shall be forwarded through an appropriate FAA Maintenance Inspector, who may add comments and then send it to the Manager, Small Airplane Directorate.

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

(h) The inspections and modifications required by this AD shall be done in accordance with Pilatus Britten-Norman Ltd. Service Bulletin No. BN-2/SB.61, Issue 5, dated December 9, 1981. 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 Pilatus Britten-Norman Ltd., Bembridge, Isle of Wight, United Kingdom PO35 5PR. 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.

(i) This amendment becomes effective on November 24, 1997.

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 Pilatus BN-2, BN-2A, BN-2B, and BN-2T series airplanes was published in the Federal Register on March 10, 1997 (62 FR 10754). The action proposed to require initially inspecting the upper engine mounting brackets on the wing mounted engines for:

(1) Cracks at the bolt-holes,

(2) Elongation of the bolt holes,

(3) Fretting within the holes,

(4) Cracks at the rivet holes,

(5) Distortion or delamination of the lugs, and that

(6) The bearings are the correct length and the bolts are not threadbound.

If there is no evidence of damage or defects similar to any of the above-mentioned items, the proposed AD would require repetitive inspections at regular intervals until the accumulation of 2,000 hours time-in-service after the effective date of the AD, at which time the AD would require accomplishing Pilatus Modification NB/M/1147.

If any damage or defects are found similar to any of the six items previously mentioned, this action would require immediately accomplishing Pilatus Modification NB/M/1147. This modification consists of replacing damaged brackets, bolts, and bushes with parts of an improved design. Accomplishing this modification is considered a terminating action to the repetitive inspections. Accomplishment of the AD would be in accordance with Pilatus Britten-Norman Service Bulletin No. BN-2/SB.61, Issue 5, dated December 9, 1981.

Interested persons have been afforded an opportunity to participate in the making of this amendment. No comments were received on the proposed rule or the FAA's determination of the cost to the public.

The FAA's Aging Aircraft Policy
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 if the known problem is not detected during the inspection; (2) the probability of the problem not being detected during the inspection; (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.

For Pilatus BN-2, BN-2A, BN-2B, and BN-2T series airplanes, the manufacturer has incorporated a design change that would replace damaged bolts, brackets, and bushes with parts of improved design, which would terminate the repetitive inspections of the upper engine mounting brackets on the wing mounted engines required by AD 84-23-06. It is AD 84-23-06 that required the repetitive inspections on the Pilatus BN-2, BN-2A, BN-2B, and BN-2T series airplanes and the Pilatus BN-2A MK. 111 series airplanes. A separate action (Docket 84-CE-18-AD) is being published concurrently with this AD, and revises AD 84-23-06 so that the BN-2A MK. 111 series airplanes will be the only airplanes to which AD 84-23-06 applies.

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 modify the upper engine wing mounting brackets of the affected airplanes to eliminate the repetitive short-interval inspections, and to prevent failure of the upper engine wing mounting brackets on wing mounted engines, which could possibly cause structural failure of the airplane.

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 minor editorial corrections. The FAA has determined that these 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 112 airplanes in the U.S. registry will be affected by the AD, that it will take approximately 37 workhours per airplane to accomplish the initial inspection and modification, and that the average labor rate is approximately $60 an hour. Parts cost approximately $800 per airplane to accomplish the modification. Based on these figures, the total cost impact of the AD on U.S. operators is estimated to be $338,240 or $3,020 per airplane. This figure is based on the initial inspection and modification only. It does not take into account the cost for the repetitive inspections that may be incurred over the life of the airplane until the modification is accomplished.The FAA has no way of determining how many owners/operators have accomplished the proposed action and, therefore assumes that none of the owners/operators of the affected airplanes have accomplished the proposed action.

The AD Action's Impact Utilizing the FAA's Aging Commuter Class Aircraft Policy
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 112 airplanes in the U.S. registry that will be affected by this AD, the FAA has determined that approximately 18 percent are operated in scheduled passenger service by 11 different operators. A significant number of the remaining 82 percent are operated in other forms of air transportation such as air cargo and air taxi.

This AD allows 2,000 hours time-in-service (TIS) after the effective date of the AD before mandatory accomplishment of the design modification. Theaverage 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 will have to accomplish the modification within 10 to 20 calendar months after the effective date of the AD. For private owners, who typically operate between 100 to 200 hours TIS per year, this will allow 5 to 10 years before the modification will be mandatory.

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 USC 106(g), 40113, 44701.

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