AD 2017-09-12

Within 12 months after the effective date of this AD, inspect each EPSU on the airplane to determine the part number (P/N) and serial number. For any EPSU having P/N 301-3100 Amendment (Amdt) A and a serial number identified in figure 1 to paragraph (g) of this AD, and that does not have a control sticker marked with “SIL 301-3100-33-001”: Except as provided by paragraph (i) of this AD, before further flight, replace the EPSU with a serviceable unit, as specified in paragraph (h) of this AD, in accordance with the Accomplishment Instructions of ATR Service Bulletin ATR42-33-0050, Revision 03, dated May 25, 2016; or Service Bulletin ATR72-33-1043, Revision 03, dated July 20, 2016; as applicable. A review of airplane maintenance records may be done in lieu of inspection of the EPSUs on the airplane if the part number and serial number of each EPSU can be positively determined from that review.

For the purpose of this AD, a serviceable EPSU is one that meets the criteria in paragraph (h)(1), (h)(2), or (h)(3) of this AD.

(1) Has P/N 301-3100 Amdt A and a serial number that is not included figure 1 to paragraph (g) of this AD.

(2) Has P/N 301-3100 Amdt A and a serial number that is included in figure 1 to paragraph (g) of this AD, but has a control sticker marked with “SIL 301-3100-33-001.”

(3) Has P/N 301-3100 Amdt B, or later amendment.

In lieu of the replacement required by paragraph (g) of this AD, modification of an affected EPSU may be done in accordance with the Accomplishment Instructions of COBHAM Service Bulletin 301-3100-33-002, Revision 3, dated July 30, 2015.