But it was illusory. The crowds were caused by hastily introduced security measures, and the traffic was mostly outward, with people heading for international destinations and in no hurry to return.
There was little of the bustle normally associated with JFK. Instead there was anxiety, gloom and confusion. Computers were malfunctioning and the security system sometimes failed.
The searches were haphazard. Monica Rojas, who was returning to Mexico City with her two young sons, said: "They took away my nail clippers and nail file from one bag, but I had a pair of scissors in another where they did not even look."
A security guard flicked his thumb at a pile of suitcases. "All kind of stuff could well be getting through, we have to depend on the X-ray Machines. If they miss things we haven't got the manpower to search through everything."
The airlines in America usually make about 40,000 flights a day and last year carried almost 650 million passengers. But when Wall St reopened on Monday some airline shares dropped 50 per cent and about $US12 billion was wiped off their value.
Now the carriers face the extra costs of security. John Ashcroft, the Attorney-General, has already moved to assign a number of agents from other law enforcement bodies to a Federal Aviation Administration scheme for marshals.
Beyond the crowds at the entrance and beyond the security bottlenecks came the strange sight of domestic terminals virtually deserted. They would normally be full of business travellers.
Thirty-five minutes before flight DL6182 was due to take off for Boston there were six people waiting to board, including the two United employees who were discussing whether they would still have a job at the end of the month.
On board, the stewardess said: "Spread yourself out, there is plenty of room." Later, handing out coffees and soft drinks, she confided: "Lucky this is not lunchtime. We won't be able to serve wine. I don't think we have a corkscrew on board ... we don't know whether it's a dangerous instrument."
At Boston, James Forino, an accountant, said some of his colleagues had decided against flying for the time being. "I don't know whether this will last. Americans are so used to flying, it will be a life change for them not to," he said.
And then Mr Forino asked about a return flight to New York. "No problem, they are wide open," said the woman from Delta.
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