An apparatus that runs electricity between the overhead wire and light rail trains failed on Thursday and forced the partial operation shut-down of the Regional Transportation District’s University of Colorado A-Line train between Denver International Airport and Union Station.

It was the second day in a row that passengers on the line faced lengthy delays.

The failure started just before 11 a.m. Thursday and lasted nearly 6 1/2 hours. RTD tweeted just after 5:30 p.m. that the line was running but there were still minor delays.

It wasn’t clear if the problem was related to one that caused the line to close down for several hours Wednesday after a partial power loss left a westbound train stuck on the line.

Bus shuttles again were used between the 61st and Peña Station and DIA.

Although RTD announced full service was restored at 4:45 p.m. Wednesday, at 5:15 RTD said additional repairs were needed and the A-Line was again stopped and buses ferried passengers between DIA and the 61st Street and Peña Boulevard Station.

It was not until 9:23 p.m. that RTD said the train line was back running and bus shuttles were canceled.