(1) (A) (i) Except as provided in subparagraphs (B) and (D) of this paragraph and in paragraphs (4) and (5), an employer shall pay the amount determined under section 1391 of this title , adjusted if appropriate first under section 1389 of this title and then under section 1386 of this title over the period of years necessary to amortize the amount in level annual payments determined under subparagraph (C), calculated as if the first payment were made on the first day of the plan year following the plan year in which the withdrawal occurs and as if each subsequent payment were made on the first day of each subsequent plan year. Actual payment shall commence in accordance with paragraph (2). (ii) The determination of the amortization period described in clause (i) shall be based on the assumptions used for the most recent actuarial valuation for the plan. (B) In any case in which the amortization period described in subparagraph (A) exceeds 20 years, the employer’s liability shall be limited to the first 20 annual payments determined under subparagraph (C). (C) (i) Except as provided in subparagraph (E), the amount of each annual payment shall be the product of— (I) the average annual number of contribution base units for the period of 3 consecutive plan years, during the period of 10 consecutive plan years ending before the plan year in which the withdrawal occurs, in which the number of contribution base units for which the employer had an obligation to contribute under the plan is the highest, and (II) the highest contribution rate at which the employer had an obligation to contribute under the plan during the 10 plan years ending with the plan year in which the withdrawal occurs. For purposes of the preceding sentence, a partial withdrawal described in section 1385(a)(1) of this title shall be deemed to occur on the last day of the first year of the 3-year testing period described in section 1385(b)(1)(B)(i) of this title . (ii) (I) A plan may be amended to provide that for any plan year ending before 1986 the amount of each annual payment shall be (in lieu of the amount determined under clause (i)) the average of the required employer contributions under the plan for the period of 3 consecutive plan years (during the period of 10 consecutive plan years ending with the plan year preceding the plan year in which the withdrawal occurs) for which such required contributions were the highest. (II) Subparagraph (B) shall not apply to any plan year to which this clause applies. (III) This clause shall not apply in the case of any withdrawal described in subparagraph (D). (IV) If under a plan this clause applies to any plan year but does not apply to the next plan year, this clause shall not apply to any plan year after such next plan year. (V) For purposes of this clause, the term “required contributions” means, for any period, the amounts which the employer was obligated to contribute for such period (not taking into account any delinquent contribution for any other period). (iii) A plan may be amended to provide that for the first plan year ending on or after September 26, 1980 , the number “5” shall be substituted for the number “10” each place it appears in clause (i) or clause (ii) (whichever is appropriate). If the plan is so amended, the number “5” shall be increased by one for each succeeding plan year until the number “10” is reached. (D) In any case in which a multiemployer plan terminates by the withdrawal of every employer from the plan, or in which substantially all the employers withdraw from a plan pursuant to an agreement or arrangement to withdraw from the plan— (i) the liability of each such employer who has withdrawn shall be determined (or redetermined) under this paragraph without regard to subparagraph (B), and (ii) notwithstanding any other provision of this part, the total unfunded vested benefits of the plan shall be fully allocated among all such employers in a manner not inconsistent with regulations which shall be prescribed by the corporation. Withdrawal by an employer from a plan, during a period of 3 consecutive plan years within which substantially all the employers who have an obligation to contribute under the plan withdraw, shall be presumed to be a withdrawal pursuant to an agreement or arrangement, unless the employer proves otherwise by a preponderance of the evidence. (E) In the case of a partial withdrawal described in section 1385(a) of this title , the amount of each annual payment shall be the product of— (i) the amount determined under subparagraph (C) (determined without regard to this subparagraph), multiplied by (ii) the fraction determined under section 1386(a)(2) of this title .
29 USC § 1399(c)(1)
None identified, default scope is assumed to be the parent (part 1) of this section.