AD 96-04-09 ACTIVE

This amendment adopts a new airworthiness directive (AD), applicable to all Fokker Model F28 Mark 0100 series airplanes, that requires an inspection to detect the presence of a drain hole in certain mounting frames of the auxiliary power unit (APU). If a drain hole is present, the AD requires an inspection to detect corrosion of the mounting frame, and eventual replacement of the mounting frame. This amendment is prompted by a report indicating that corrosion was found on a number of mounting frames of the APU. The actions specified by this AD are intended to prevent such corrosion, which could lead to failure of the frame and consequently render the APU inoperative and/or create a potential fire hazard.

Final rule

96-04-09 FOKKER: Amendment 39-9521. Docket 94-NM-215-AD.
Applicability: All Model F28 Mark 0100 series 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 (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 as indicated, unless accomplished previously.

To prevent corrosion of certain mounting frames of the auxiliary power unit (APU), which could render the APU inoperative and may lead to a potential fire hazard, accomplish the following:

(a) Within 30 days after the effective date of this AD, perform a detailed visual inspection to detect the presence of a drain hole in frame member M of the mounting frames, having part number (P/N) D67050-407, of the auxiliary power unit (APU), in accordance with Fokker Service Bulletin SBF100-49-022, dated August 27, 1992.

(1) If no drain hole(s) is present, no further action is required by this AD.

(2) If any drain hole is present, prior to further flight, perform a detailed visual inspection to detect corrosion on the mounting frame of the APU, in accordance with the service bulletin.

(i) If no corrosion is detected, within 9 months after accomplishing the visual inspection, replace the mounting frame with a new mounting frame in accordance with the service bulletin.

(ii) If any corrosion is detected, within 3 months after accomplishing the visual inspection, replace the mounting frame with a new mounting frame in accordance with the service bulletin.

(b) As of the effective date of this AD, no person shall install on any airplane a mounting frame, having P/N D67050-407, that has a drain hole in frame member M.

(c) 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, Standardization Branch, ANM-113, FAA, Transport Airplane Directorate. Operators shall submit their requests through an appropriate FAA Principal Maintenance Inspector, who may add comments and then send it to the Manager, Standardization Branch, ANM-113.

NOTE 2: Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the Standardization Branch, ANM-113.

(d) Special flight permits may be issued in accordance with sections21.197 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) The inspection and replacement shall be done in accordance with Fokker Service Bulletin SBF100-49-022, dated August 27, 1992. 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 Fokker Aircraft USA, Inc., 1199 North Fairfax Street, Alexandria, Virginia 22314. Copies may be inspected at the FAA, Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, Washington; or at the Office of the Federal Register, 800 North Capitol Street, NW., suite 700, Washington, DC.

(f) This amendment becomes effective on March 25, 1996.

A proposal to amend part 39 of the Federal Aviation Regulations (14 CFR part 39) to include an airworthiness directive (AD) that is applicable to all Fokker Model F28 Mark 0100 series airplanes was published in the Federal Register on December 20, 1994 (59 FR 65514). That action proposed to require an inspection to detect the presence of a drain hole in certain mounting frames of the auxiliary power unit (APU). If a drain hole is present, the action proposed to require an inspection to detect corrosion of the mounting frame, and eventual replacement of the mounting frame.

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

One commenter supports the proposal.

Another commenter requests that the FAA withdraw the proposal for what this commenter perceives as lack of justification. This commenter purports that corrosion of the APU framewill not result in a critical safety of flight condition. The commenter contends that, even if the subject frame were to fail completely, the APU cannot fall or lean enough to sever any fuel or electrical lines; therefore, the possibility that the failure of the mounting frame could become a potential fire hazard is simply conjecture. Based on these assertions, the commenter considers that no unsafe condition exists, and requests that the FAA review its justification for the proposed rule to ensure that it is sufficient to satisfy the requirements of part 39 of the Federal Aviation Regulations (FAR).

The FAA does not concur with either the commenter's request or assertions.

First, the FAA points out that the existing design of the drain hole on certain APU mounting frames allows the accumulation of moisture on the frame. These frames have been found to be particularly sensitive to corrosion caused by such moisture accumulation. Corrosion of these frames could cause them tofail, especially when exposed to higher loads during airplane touchdown.

Second, the Rijksluchtvaartdienst (RLD) (which is the airworthiness authority for the Netherlands) and the FAA, have determined that, if a mounting frame were to fail due to associated corrosion, the APU could be displaced and consequently sever APU fuel lines located in the adjacent area. The leaking fuel could then pose a fire hazard. This is the unsafe condition that this AD intends to prevent. In addition, the APU could be rendered inoperative because of the failure of its support assembly. If it were inoperative, electrical power may not be available during flight, or both electrical and pneumatic power may not be available when the airplane is on the ground, when such power is needed via the APU.

Third, although there have been no reported cases of inoperative APU's or fuel leakage caused by the problems associated with the failure of the APU mounting frames, the potential for them to occur stillexists. In fact, when Fokker examined the subject APU mounting frames removed from in-service airplanes, it found that up to 73% of the thickness at the place of the drain holes in these frames was fretted away. This reduced thickness, which is attributed to the typical effects of corrosion, weakens the integrity of the frames and, consequently, can lead to their failure.

Finally, according to section 39.1 of the FAR (14 CFR 39.1), the issuance of an AD is based on the finding that an unsafe condition exists and that condition is likely to exist or develop in aircraft of a particular type design. The responsibilities placed on the FAA by the Federal Aviation Act do not limit it from making any unsafe condition the proper subject of an AD -- regardless of whether or not the unsafe condition has actually occurred in service and led to an incident or accident. When sufficient data exist to demonstrate that an unsafe condition is likely to exist or develop on other products of thesame type design, the issuance of an AD is appropriate in order to address that potential unsafe condition and to prevent its occurrence.

This same commenter also requests clarification as to the applicability of the proposed rule. The commenter points out that, although both the proposed AD and the parallel Dutch AD are applicable to all Fokker Model F28 Mark 0100 series airplanes, the referenced Fokker service bulletin calls out only certain airplanes (serial numbers 11244 through 11402) in its effectivity listing. This commenter knows of four airplanes on which the suspect frames were found, but these airplanes were not included in the service bulletin's effectivity listing. The commenter believes that the service bulletin should be revised to specify that all airplanes must be inspected.

The FAA does not concur that additional action is necessary. Since in-service experience has shown that APU mounting frames are regularly removed from and (re-) installed on aircraft upon removal of the APU, the FAA has determined that the suspect frames could be installed on any Fokker Model F28 Mark 0100 airplane. In light of this, the applicability of the AD, which makes all airplanes subject to the requirements, is correct. In any case, where there are differences between the AD and the service bulletin, the AD prevails.

One commenter requests that the rule be revised to extend the compliance time for replacement of the mounting frames from the proposed 30 days or 90 days (depending upon the results of the inspection for corrosion) to one year for all cases. The commenter states that Fokker has indicated that it has only 2 frames in stock to support the replacement requirement. In addition, the lead time for procurement of a replacement frame is minimum of 127 days.

The FAA concurs that some adjustment to this compliance time can be made. Reports received by the FAA indicate that most airplanes already have been inspected in accordance with the requirements of this AD, and have been found not to have the suspect APU mounting frames installed. Therefore, the FAA considers that only a limited number of replacement mounting frames actually will be required. However, the FAA acknowledges that timely parts availability may be a problem for some operators. In light of this, the FAA finds that the compliance time for replacement of the frame can be extended to 9 months for cases where no corrosion is found on the frame, and to 3 months for cases where corrosion is found. The FAA finds that safety will not be compromised by the extension of these compliance times. The final rule has been revised accordingly.

After careful review of the available data, including the comments noted above, the FAA has determined that air safety and the public interest require the adoption of the rule with the change previously described. The FAA has determined that this change will neither increase the economic burden on any operator nor increasethe scope of the AD.

The FAA estimates that 119 airplanes of U.S. registry will be affected by this AD, that it will take approximately 13 work hours per airplane to accomplish the required actions, and that the average labor rate is $60 per work hour. Based on these figures, the cost impact of the AD on U.S. operators is estimated to be $92,820, or $780 per airplane.

The cost impact figure discussed above is based on assumptions that no operator has yet accomplished any of the requirements of this AD action, and that no operator would accomplish those actions in the future if this AD were not adopted.

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 final evaluation has been prepared for this action and it is contained in the Rules Docket. A copy of it may be obtained from 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 the following new airworthiness directive:

The service information referenced in this AD may be obtained from Fokker Aircraft USA, Inc., 1199 North Fairfax Street, Alexandria, Virginia 22314. This information may be examined at the Federal Aviation Administration (FAA), Transport Airplane Directorate, Rules Docket, 1601 Lind Avenue, SW., Renton, Washington; or at the Office of the Federal Register, 800 North Capitol Street, NW., suite 700, Washington, DC.

Tim Dulin, Aerospace Engineer, Standardization Branch, ANM-113, FAA, Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, Washington 98055-4056; telephone (206) 227-2141; fax (206) 227-1149.