FRANKFURT - Berlin’s new international airport said on Monday that engineering group Imtech had promised under a new agreement to complete work it had been contracted to do at the airport, after its German unit filed for insolvency this month. Berlin airport had feared a further delay to its opening, originally planned for 2012, due to the insolvency. The airport said on Monday the new agreement would allow Imtech to continue its work on heating and ventilation systems. Payments for Imtech’s services will be made to a special account.