ATLANTA -- Hundreds of people are waking up at Hartsfield-Jackson Atlanta International Airport after Delta and American Airlines cancelled flights for safety re-inspections. If you're headed to the airport today, officials warn of longer than normal lines.

Delta Air Lines is voluntarily re-inspecting wiring on 133 MD-88 and MD-90 airplanes but had no estimate on how many flights it might have to cancel during the process, a spokeswoman said.

Delta spokeswoman Chris Kelly said officials are expecting heavy volumes at Hartsfield-Jackson Atlanta International Airport on Thursday. She said both Delta and the Transportation Security Administration are bringing in extra staff to handle the crowd of travelers.

American Airlines canceled about 325 flights Wednesday so its crews could inspect some wire bundles aboard its MD-80 aircraft.

READ: Delta's Full Statement

"We take airworthiness directives very seriously," Delta spokesman Kent Landers said.

Delta said its 117 MD-88 and 16 MD-90 planes were inspected earlier this year but the airline is "proactively and voluntarily revalidating" compliance with an Airworthiness Directive from the Federal Aviation Administration in cooperation with the FAA.

The review is expected to be completed by Saturday, and the airline is contacting passengers whose flights might be cancelled in order to rebook them on other aircraft, spokeswoman Katie Connell said.

Overnight, Hartsfield-Jackson Atlanta International Airport became the home to sleepy, frustrated and stranded passengers.

"It's not pleasant," said traveler Jerry Brereton. "It's not a pleasant way to travel. But sometimes you get to a place where you kind of expect it."

A check of Hartsfield's arrivals and departures screen showed the word "cancelled" popping up quite a bit.

"And now we're here at 1:30 in the morning with two toddlers -- so, we're thrilled with it," traveler Deidra Ricci told Channel 2.

It would be incorrect to say the planes were "grounded" because all 133 aircraft will not be out of service during the re-inspection process, Connell said.

American Airlines spokesman Tim Wagner said the carrier's entire fleet of MD-80s was being inspected.

The need for the new inspections became known during an audit of American by a joint team of inspectors from the FAA and the Fort Worth-based airline, Wagner said.

The inspection involves proper spacing between two bundles of wires in the plane's auxiliary hydraulic system, Wagner said. It must be installed "exactly according to the directive," he said.