DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2016-9139; Directorate Identifier 2016-CE-023-AD]
RIN 2120-AA64

Airworthiness Directives; Mitsubishi Heavy Industries, Ltd. Airplanes

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Proposed rule; withdrawal.

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SUMMARY: The FAA is withdrawing a notice of proposed rulemaking (NPRM)
that proposed to adopt a new airworthiness directive (AD) that would
have applied to certain Mitsubishi Heavy Industries, Ltd. Models MU-2B-
10, MU-2B-15, MU-2B-20, MU-2B-25, MU-2B-26, MU-2B-26A, MU-2B-30, MU-2B-
35, MU-2B-36, MU-2B-36A, MU-2B-40, and MU-2B-60 airplanes. The NPRM
resulted from mandatory continuing airworthiness information (MCAI)
originated by an aviation authority of another country to identify and
correct an unsafe condition on an aviation product and would have
required repetitively inspecting the wing spacer plates for cracks
until they were replaced with an improved design wing spacer plates.
Since issuance of the NPRM, we determined that damage is contained to
the wing spacer plate with no evidence that primary structure is
affected. Accordingly, the NPRM is withdrawn.

DATES: As of February 28, 2019, the proposed rule, which published in
the Federal Register on September 16, 2016 (81 FR 63725), is withdrawn.

FOR FURTHER INFORMATION CONTACT: Bang Nguyen, Aerospace Engineer, FAA,
Fort Worth ACO Branch, 10101 Hillwood Pkwy., Fort Worth, Texas 76177;
telephone: (817) 222-4973; fax: (817) 222-5785; email:
bang.nguyen@faa.gov.

SUPPLEMENTARY INFORMATION:

Discussion

We issued an NPRM that proposed to amend 14 CFR part 39 to add an
AD that would apply to the specified products. The NPRM was published
in the Federal Register on September 16, 2016 (81 FR 63725). The NPRM
was prompted by the Japan Civil Aviation Bureau (JCAB), which is the
aviation authority for Japan, AD No. TCD-8783-2016, dated June 28, 2016
(referred to after this as "the MCAI"), to correct an unsafe
condition for certain Mitsubishi Heavy Industries (MHI) Models MU-2B-20,
MU-2B-25, MU-2B-26, MU-2B-30, MU-2B-35, and MU-2B-36 airplanes.

As part of the MHI MU-2B aging aircraft program, one-piece and
three-piece main wings were subjected to detailed teardown inspections,
and cracks were found in the wing spacer plates attached to the forward
lower spar area at wing station 580. It was determined that the cracks
resulted from fatigue caused by flight loads.

Japan is the State of Design for the MHI airplane models that the
MCAI AD applies to: Models MU-2B-20, MU-2B-25, and MU-2B-26 with serial
numbers (S/Ns) 102 and 121 through 347, except 313 and 321; and Models
MU-2B-30, MU-2B-35, and MU-2B-36 with S/Ns 502 through 696, except 652
and 661. The United States is the State of Design for MHI Models MU-2B-
10, MU-2B-15, MU-2B-25, MU-2B-26, MU-2B-26A, and MU-2B-40 with S/Ns
313SA, 321SA, and 348SA through 459SA; and Models MU-2B-36A and MU-2B-
60 with S/Ns 661SA and 697SA through 1569SA airplanes. Japan is the
State of Design for Models MU-2B-10 and MU-2B-15 airplanes, but has
recently removed these models from the MHI Japanese type certificate.
These models remain on the FAA type certificate; however, none of these
airplanes are currently on the U.S. registry.

The NPRM proposed to require repetitively inspecting the wing
spacer plates for cracks until they were replaced with an improved
design wing spacer plates. The proposed actions were intended to detect
and correct cracks in the wing spacer plates, which could result in
reduced structural integrity of the wings and loss of control.

Actions Since the NPRM Was Issued

Since issuance of the NPRM, we have received data from operators
who completed the inspections specified in MHI MU-2 Service Bulletin
No. 245, dated April 21, 2016, and MU-2 Service Bulletin No. 107/57-
005, dated May 3, 2016. During the inspections, no cracking in a
primary wing structure has been detected. We have determined that
damage is contained to the wing spacer plates without affecting the
primary structure. Our analysis of fleet data also demonstrates that
the wing spar and the wing spar cap maintains conformity with the
structural requirements of the type certificate after complete fracture
of the wing spacer plate. Neither the JCAB nor the manufacturer has
provided the FAA with sufficient data that an unsafe condition exists.
Therefore, we have determined that AD action is not appropriate, and
the NPRM should be withdrawn.

After we received numerous comments on the NPRM stating there is no
unsafe condition, we requested additional information from JCAB to
demonstrate that the cracks found in the spacers reduce the structural
integrity of primary structure. JCAB replied that it took AD action
because it is uncertain how the fatigue strength will be affected over
the life of the airplane. In addition to the lack of conclusive data
that there is an unsafe condition, we considered that removing the wing
in order to perform the proposed corrective action may be more
detrimental to the aircraft than the cracks themselves.

Withdrawal of this NPRM constitutes only such action and does not
preclude the agency from issuing future rulemaking on this issue, nor
does it commit the agency to any course of action in the future.

Regulatory Findings

Since this action only withdraws an NPRM, it is neither a proposed
nor a final rule and therefore, not covered under Executive Order
12866, the Regulatory Flexibility Act, or DOT Regulatory Policies and
Procedures (44 FR 11034, February 26, 1979).

List of Subjects in 14 CFR Part 39

Air transportation, Aircraft, Aviation safety, Incorporation by
reference, Safety.