American Airlines continued to heap misery on to its passengers yesterday as the US carrier scrapped a further 900 flights from vital hub airports across the United States over safety concerns and gave warning that there would be further cancellations today.

The groundings amounted to almost half of American’s flights and left about 100,000 passengers stranded yesterday at airports such as Dallas-Forth Worth and Chicago, as well as La Guardia, Kennedy and Newark in the New York area.

They marked the third day of significant cancellations for American, which has collectively grounded nearly 2,500 flights and disrupted about 250,000 passengers.

The airline cancelled the flights after the US aviation regulator raised concerns that its aircraft repair crews and government inspectors had been lax in their inspections of its ageing fleet of Boeing MD80 jets.

The fear was that insufficient safety checks on electrical wires could spark fires on board the aircraft.

The cancellations are the worst in at least 30 years, apart from those inflicted by severe weather conditions and the September 11 terrorist attacks. Alan Bender, a professor of airline economics at Embry Riddle Aeronautical University in Daytona Beach, Florida, expects this week’s cancellations to lose the airline “tens of millions of dollars”.

These losses will be particularly harmful to American since, like its rivals, the airline is already struggling with an 85 per cent rise in the cost of jet fuel in the past year on the back of the rising oil price. The group is also facing a recession which would reduce demand for overseas holidays.

Dan Garton, executive vice president of American Airlines, said: “This couldn’t have come at a worse time. If there is any good news, it’s that this is a relatively concentrated, one-time event, unlike the price of jet fuel.”

American’s share price tumbled by $1.15, or 11 per cent, to $9.17 on Wednesday as the extent of the damage from the increased regulatory scrutiny came to light. The shares recovered some ground yesterday, trading $0.50 higher, at $9.67, in midday trading.

Dallas-Fort Worth, one of the hub airports that has been most affected by the groundings, has tried to soothe passengers by opening restaurants late and handing out nappies and baby formula to families in need.

The more planes that are grounded, the harder it is to put stranded passengers on alternative connecting flights because the remaining capacity has already been used up.

Yesterday, tempers were fraying as lengthy waits took their toll of passengers. “I’m quite angry,” said Brad Weiss, a lawyer, waiting at Reagan National Airport in Virginia. Mr Weiss’s flight had been cancelled and he was worried about making it home to Chicago to watch his nine-year-old daughter present a school science fair project.

Rebekah Matter, 26, another lawyer, was trying to visit her family in New Mexico. But her first morning flight to Chicago was cancelled. The airline put her on an alternative route, stopping at St Louis and Dallas-Fort Worth, but cancelled what was to be the final leg to Albuquerque.

Standing in a long line as she waited to rearrange the last leg of her voyage, Ms Matter said: “I’m perturbed. I should have been at work today. I feel like I’m in limbo. I’m not travelling and I’m not at work. It was just a wasted day.”

Alaska, Delta and Southwest have also cancelled a smaller number of flights for the same reason, as the US Congress stepped up its scrutiny of the US regulator, the Federal Aviation Administration, after a series of revelations about these increasingly lax oversights. These include the recent finding that Southwest had failed to stop 40 flights by planes that had not been properly inspected.

In New York, disgruntled passengers were united in their view that the situation “sucked”. “On a scale of one to ten, as far as rubbish goes, this is a 15,” said Paul King, 28, of Dallas, who had been on line at New York’s La Guardia airport for six hours.

“This is really not good. It basically ruins my week,” said Yoree Koh, 25, a resident of New York’s Upper East side who was heading to a postgraduate orientation evening at the University of Chicago.

American Airlines said it expected to have all of its MD80 liners back in service by tomorrow night.

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