WASHINGTON _ Delta Air Lines' meltdown is nowhere close to being over.
The Atlanta-based carrier canceled more than 620 flights by late afternoon Tuesday, after scrubbing around 1,000 flights a day earlier, and disgruntled passengers howled over disrupted summer travel plans.
More pain awaits passengers as Delta struggles to restore service, the second reminder in less than a month that America's air transportation avenues are dependent on computerized systems that can fail when a single piece of hardware doesn't do its job. In July, a similar outage disrupted Southwest Airlines' operations for days when a single computer router failed.
For the second day in a row, Delta offered scant details about what caused the electrical outage and what triggered the widespread knock-on effects. The utility that powers the headquarters, Georgia Power, has said it was an internal piece of electrical equipment, akin to a homeowner's fuse box, that failed. The equipment was owned by Delta and placed within the carrier's facilities, the utility said.
Aviation consultant Mike Boyd, based in Evergreen, Colo., said it would take Delta another 36 hours to return to anything resembling a normal schedule.
"It's a mess," he said. "It's going to take a few days to sort out."
The problems for Delta, which began at 2:30 a.m. EDT Monday with a power outage at an Atlanta facility that affected the airline's worldwide reservations system, cascaded around the globe as airliners and crews remained out of place, forcing new cancellations and delays.
Passengers slept on airport floors as far away as Tokyo and Madrid. The airline handed out sleeping mats for stranded passengers in Minneapolis. At San Francisco's airport, the line for limited Delta flights Tuesday stretched from Terminal 1 to Terminal 2.
At Baltimore's Thurgood Marshall International Airport, both passengers' and Delta staff's nerves were frayed. One woman who had been told her bag was too large to carry on board the plane complained that she had been waiting to board her flight for two days. "I've been working since 2 a.m.," the Delta worker responded.
Delta, the second-largest U.S. airline by numbers of passengers offered only limited refunds and fee waivers for the thousands of passengers inconvenienced by delays and cancellations.
In a statement Wednesday, the airlines' chief operating officer, Gil West, attributed the problem to the malfunction of "a power control module" at the Atlanta headquarters. The malfunction caused a "surge to the transformer and a loss of power," and even though power was quickly restored, "critical systems and network equipment didn't switch over to backups."
"Similar to what happens after a severe weather event, it is not unusual for a global airline to take more than 24 hours to return to full reliability," West said. Delta is doing "everything possible to return the operation to normal," he added, without specifying when full service would be re-established.
In its statement, Delta noted that flight crews have also been thrown off kilter by the outage, unable _ like passengers _ to get where they need to be. The airline is juggling legal restrictions on how long flight crews can be on duty without rest with rescheduling rotations of flight crews, it added.
"Multiplied across tens of thousands of pilots and flight attendants and thousands of scheduled flights," West said, "rebuilding rotations is a time-consuming process."
The meltdown hit Delta at a summer travel peak when many passengers were boarding aircraft with non-refundable tickets on leisure trips, industry experts said.
"With the exception of the day before Thanksgiving, this is the protracted peak," said Robert W. Mann, a former executive with American, Pan Am and TWA who is now an airline industry analyst based at Port Washington, N.Y.
"It is a huge black eye" for the airline, Mann said. "It is less of a financial black eye than a reputational black eye."
Passengers voiced anger and dismay at the disruptions.
"Come on Delta. No pilots for our flight?!? Unreal," tweeted passenger Laurin Goff of New York City.
Another passenger, Marty Maceda, tweeted: "Beginning to feel like #tomhanks in that movie where he lives in an airport. #Delta #DeltaOUTRAGE."
Mann said he believed Delta's global data and operations center had three different power systems. When utility power would go out, a transfer switch would shift power to a bank of batteries. Once independent diesel generators had cranked up, power would be switched from the batteries to that third system, he said.
"I suspect it (the transfer switch) failed when they were testing it," Mann said.
The meltdown was a setback to an airline that had experienced a long stretch with not a single canceled flight due to aircraft maintenance issues, he said.
"All those 'Attaboys!' got wiped off the board with this," he said.
While Delta struggled to get flights back in the air, the issue of its treatment of affected passengers lingered.
While Delta extended its offer for passengers to waive its flight change fees for Monday and Tuesday tickets and offered those delayed more than three hours $200 travel vouchers and hotel rooms where available, Boyd said customers ought to be able to request a full refund.
"If I missed the wedding, I don't want to go now," Boyd said. "Many trips are time-definite."
In spite of years of airline consolidation reducing the overall number of carriers, passengers still have a choice in many cases, and Delta customers might fly with someone else next time.
"You want to smooth this over as quickly as you can," Boyd said.
