29 C.F.R. § 4043.61

(a) In general. Unless a waiver or extension applies with respect to the plan, each contributing sponsor of a plan is required to notify PBGC no later than 30 days before the effective date of a reportable event described in this subpart C if the contributing sponsor is subject to advance reporting for the reportable event. If there is a change in contributing sponsor, the responsibility for any failure to file or defective filing lies with the person who is the contributing sponsor of the plan on the notice date.

(b) Persons subject to advance reporting. A contributing sponsor of a plan is subject to the advance reporting requirement under paragraph (a) of this section for a reportable event if —

(c) Funding determinations. For purposes of paragraph (b) of this section, the aggregate unfunded vested benefits, aggregate value of plan assets, and aggregate premium funding target are determined by aggregating the unfunded vested benefits, values of plan assets, and premium funding targets (respectively), as determined in accordance with part 4006 of this chapter for purposes of the variable-rate premium for the plan year preceding the effective date of the event, of plans maintained (on the notice date) by the contributing sponsor and any members of the contributing sponsor's controlled group, disregarding plans with no unfunded vested benefits (as so determined).

(d) Shortening of 30-day period. Pursuant to § 4043.3(d), PBGC may, upon review of an advance notice, shorten the notice period to allow for an earlier effective date.