Retroactive Modification of Travel Orders

An employee appealed a settlement, claiming additional per diem payments in connection with an Intergovernmental Personnel Act assignment in a city other than his permanent station. The employee was on this assignment for 6 months, but travel orders were not issued because of administrative oversight. Retroactive modification of the travel orders to authorize a higher per diem rate is permitted since there were no travel orders at the time travel was performed under which a particular per diem rate would be vested.