default
(5) In the event of a default, a plan sponsor may require immediate payment of the outstanding amount of an employer’s withdrawal liability, plus accrued interest on the total outstanding liability from the due date of the first payment which was not timely made. For purposes of this section, the term “default” means— (A) the failure of an employer to make, when due, any payment under this section, if the failure is not cured within 60 days after the employer receives written notification from the plan sponsor of such failure, and (B) any other event defined in rules adopted by the plan which indicates a substantial likelihood that an employer will be unable to pay its withdrawal liability.