WASHINGTON -- America's airlines marked a year of emotional and financial agony Wednesday, one year after terrorists used four passenger planes to slaughter thousands.

Cabin staff will wear commemorative pins, pilots will ask passengers to remember those killed, and airlines will hold private, low-key services, spokesmen for the major carriers said.

The painful memories are compounded by the industry's struggle to emerge from heavy economic losses.

After axing 80,000 people in the aftermath of the attacks, many more jobs are still being lost, and now many of the carriers are meeting resistance from unions to more cuts. "The short-term outlook is not terrific," said John Ash, head of Global Aviation Associates. "The airline cost structure is too high to support the kind of fares that people are willing to pay."

One airline, U.S. Airways, has filed for bankruptcy.

United Airlines lost two planes -- one tearing into the World Trade Center and another crashing into a Pennsylvania field. Now it is contemplating filing for bankruptcy protection in the face of stiff union opposition to its tight-fisted reform program.

The American Airlines jets also were turned into missiles -- one ploughed into the twin towers and another into the Pentagon. Now, it is sacking 7,000 people in a struggle to turn a profit.

The terrorist attacks had a terrible impact on an industry that was already struggling, experts said.

Before the attacks, the 10 biggest carriers had expected a collective loss of 3.0 billion to 3.5 billion dollars in 2001.

The plunge in traffic after the attacks, in which hijackers used four passenger planes as missiles, more than doubled the forecast losses to an unprecedented 7.7 billion dollars.

This year, they may lose five billion dollars, ash said. next year, if they are lucky, the airlines could lose one billion dollars.

"The attacks basically exacerbated an already seriously-deteriorating industry," he said.

But the ensuing lengthy security procedures and heightened fears also had a longer-lasting effect. "It has produced an environment that has not been conducive to travel," Ash said.

Traffic was still down 8.4 percent from last year in July, the Air Transport Association said.

The industry had been improving slightly as passenger numbers climbed and airlines cut capacity, Air Transport Association economist David Swierenga said.

But in March this year the improvement was cut short as the economic recovery began to weaken, hurting business travel, which is the most profitable area for carriers.

A surge in costs linked to tighter security measures and heightened competition from low-cost operators such as southwest, aggravated the pain and forced major airlines to slash prices.

"The industry is going through probably the toughest time that it has ever seen and it is unlikely that next year will see a return to profitability, although I am sure carriers will reduce the size of their losses," Swierenga said.

The earliest date for a return to normality was 2004, he forecast.