Passengers of American Airlines are expected to face more travel troubles on Friday as the company announced it would cancel another 570 flights to continue to inspect wiring on some of its jets for a fourth straight day.

On Thursday, the airline cancelled 933 flights, on top of the almost 1,100 cancelled Wednesday, and more than 700 earlier in the week.

Passengers wait in line at O'Hare International Airport in Chicago on Wednesday.
(Paul Beaty/Associated Press)

The cancellations stem from inspections of U.S. planes being carried out by the Federal Aviation Administration. The inspections were sparked by a congressional hearing last week that found Southwest Airlines had kept 40 planes in the air that hadn't been properly inspected. 

Airline industry observers said it is one of the biggest disruptions to air travel since the Sept. 11, 2001, attacks.

The airline estimated Wednesday that more than 100,000 travellers were affected by the cancellations — with airports in Dallas and Chicago hardest hit.

Some Canadian airports were affected as well, as Thursday flights between Calgary and Dallas were cancelled. Six flights from Toronto were also cancelled, while Montreal had four cancellations.

The airline says it has been providing vouchers for later flights, as well as meals, hotels and ground transportation for stranded passengers, though some travellers including, Mary Rickert, complained of chaos.

"It's an absolute disaster," Rickert said of the lines at Chicago's O'Hare Airport. "It's a four-hour wait just to get to the ticket counter. Shoot me now."

The FAA's second round of checks are expected to continue through June.

The FAA is investigating American Airlines' aging MD-80 jets, which make up almost half its fleet. Federal inspectors say they have found problems with the spacing and direction of cords used to secure bundles of wires in the planes' auxiliary hydraulic systems.

If the wiring rubs together, the fear is it could ignite fuel vapours and cause an explosion in the fuel tank, which could bring down a plane.

American Airlines CEO Gerard Arpey said Thursday that the cancellations will cost the company tens of millions of dollars, but he says American can withstand the losses.

Wiring didn't meet FAA standards

A spokesman for the airline said an FAA inspector checked several MD-80s Monday and found that some of the wiring work performed two weeks ago didn't meet FAA standards. The next day, American began taking planes out of service so that wiring bundles could be inspected and stowed properly in the wheel wells.

Despite the problems found by inspectors, American has said that passenger safety was never jeopardized. Arpey said he takes full responsibility for the airline's failure to comply with the federal safety rule.

While other airlines have also had to ground planes, the cancellations at American Airlines are by far the most severe. Midwest Airlines said Thursday personnel were reinspecting wiring harnesses on 13 planes.

The cancellations and resulting loss of revenue come as American faces high fuel prices and a weakening economy.

The airline's parent company, AMR, is scheduled to report first-quarter earnings in two weeks, and analysts are forecasting a loss of more than $300 million, according to a survey by Thomson Financial.

With files from the Associated Press