Chicago Department of Aviation officials said Friday afternoon they're still investigating why runway lights at
shut off overnight, causing the airport to close for almost four hours and 85 flights to be canceled or diverted.
A problem with an airfield's lighting vault reportedly cut power to the lights, but officials could offer no further explanation. The aviation department is conducting an "extensive investigation" into the matter, said spokeswoman Karen Pride.
Just after the airport closed at 9:10 p.m., extra crews and staff were brought onto the airfield to restore the power to the airfield's electrical system, which Pride described as complex. The runway lights went on around 1:19 a.m. -- well in advance of this morning's scheduled air service, Pride said.
Midway Airport has multiple backup equipment for the airfield's electrical system, which kicked in at the time of the outage, "but was unable to sustain the runways lights for long enough periods of time to ensure the safety of aircraft, passengers and employees at the airport," Pride said.
Had the lights turned off as a plane prepared to land on the runway, the airline and
would decide if the plan could safely land or should be diverted to another airport, Pride said.
She added it was unknown if Thursday's extreme heat had anything to do with the power outage. ComEd officials on Friday said the equipment that failed belonged to the airport, and not the electrical company.