Discussion
What Events Have Caused This AD?
The Civil Aviation Authority (CAA), which is the airworthiness authority for the United Kingdom, recently notified FAA that an unsafe condition may exist on all Pilatus Britten-Norman BN-2, BN-2A, BN-2B, BN-2T, and BN2A MK. III series airplanes. The CAA reports two occurrences of extensive cracks being found on the bottom corner of the engine mount bracket between the attachment flange and the main bracket. The cracks were found during regular scheduled maintenance.
The manufacturer has determined that this condition is a result of the reinforcing doubler being too close to the flange.
What Is the Potential Impact if FAA Took No Action?
This condition, if not detected and corrected, could result in failure of the engine mount. Such failure could result in the engine separating from the airplane and lead to loss of control of the airplane.
Has FAA Taken Any Action to This Point?
Weissued a proposal to amend part 39 of the Federal Aviation Regulations (14 CFR part 39) to include an AD that would apply to all Pilatus Britten-Norman BN-2, BN-2A, BN-2B, BN-2T, and BN2A MK. III series airplanes. This proposal was published in the Federal Register as a notice of proposed rulemaking (NPRM) on August 22, 2002 (67 FR 54384). The NPRM proposed to require you to repetitively inspect the bottom corner of the engine mount bracket for cracks, replace any cracked bracket, return the removed bracket(s) to Pilatus Britten-Norman, and report the return to FAA.
Are There Differences Between This AD, the Service Information, and the CAA AD?
The CAA AD and the service information allow continued flight if cracks are found in the engine mount bracket that do not exceed certain limits. The applicable service bulletin specifies replacement of the engine mount bracket only if cracks are found exceeding this limit, as does CAA AD 005-11-2001. This AD does not allow continued flight if any crack is found. FAA policy is to disallow airplane operation when known cracks exist in primary structure, unless the ability to sustain ultimate load with these cracks is proven. The engine mount bracket is considered primary structure, and the FAA has not received any analysis to prove that ultimate load can be sustained with cracks in this area.
Is There a Modification I Can Incorporate Instead of Repetitively Inspecting the Engine Mount Brackets?
The FAA has determined that long-term continued operational safety will be better assured by design changes that remove the source of the problem rather than by performing repetitive inspections. With this in mind, we will continue to work with Pilatus Britten-Norman in collecting information to determine whether a future design change may be necessary.
Was the Public Invited To Comment?
The FAA encouraged interested persons to participate in the making of this amendment. We did not receive any comments on theproposed rule or on our determination of the cost to the public.
FAA's Determination
What is FAA's Final Determination on This Issue?
After careful review of all available information related to the subject presented above, we have determined that air safety and the public interest require the adoption of the rule as proposed except for minor editorial corrections. We have determined that these minor corrections:
--Provide the intent that was proposed in the NPRM for correcting the unsafe condition; and
--Do not add any additional burden upon the public than was already proposed in the NPRM.
Cost Impact
How Many Airplanes Does This AD Impact?
We estimate that this AD affects 126 airplanes in the U.S. registry.
What Is the Cost Impact of This AD on Owners/Operators of the Affected Airplanes?
We estimate the following costs to accomplish the inspection for BN-2, BN-2A, BN-2B, and BN2A MK. III series airplanes:
Labor cost
Parts cost
Total cost per airplane
4 workhours x $60 per hour = $240
$10
$250
We estimate the following costs to accomplish the inspection for BN-2T series airplanes:
Labor cost
Parts cost
Total cost per airplane
8 workhours x $60 per hour = $480
$10
$490
We estimate the following costs to accomplish any necessary replacements for BN-2, BN-2A, BN-2B, and BN-2T series airplanes that will be required based on the results of the inspection. We have no way of determining the number of airplanes that may need such replacement:
Labor cost
Parts cost per bracket
Total cost per bracket
48 workhours x $60 per hour = $2,880 per bracket (2 brackets per engine, 2 engines per airplane).
$1,295
$2,880 + $1,295 = $4,175.
We estimate the following costs to accomplish any necessary replacements for BN2A MK. III series airplanes that will be required based on the results of the inspection. We have no way of determining the number of airplanes that may need such replacement:Labor cost
Parts cost per bracket
Total cost per bracket
48 workhours x $60 per hour = $2,880 per bracket (2 brackets per engine, 2 engines per airplane).
$714
$2,880 + $714 = $3,594.
What Is the Compliance Time of This AD?
The compliance time of this AD is "within the next 500 hours time-in-service (TIS) or within the next 24 calendar months after the effective date of this AD, whichever occurs first."
Why Is The Compliance Time of This AD Presented in Both Hours TIS and Calendar Time?
We have established the compliance time of this AD in both hours TIS and calendar time. The unsafe condition is dependent upon repetitive airplane operation. However, the recommended maintenance program specifies other actions in this area at intervals not to exceed 2 years. Therefore, the compliance time will ensure that high-time airplanes are inspected within a certain amount of hours TIS and the lower time airplanes would be inspected at the next maintenance event in the affected area. We have determined that this compliance time:
--Will ensure that the unsafe condition is addressed in a timely manner on all affected airplanes; and
--Will not inadvertently ground any of the affected airplanes.
Regulatory Impact
Does This AD Impact Various Entities?
The regulations adopted herein will not have a substantial direct effect 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, it is determined that this final rule does not have federalism implications under Executive Order 13132.
Does This AD Involve a Significant Rule or Regulatory Action?
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, under 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. FAA amends 39.13 by adding a new AD to read as follows: