Brussels ? Thousands of flights are crisscrossing Europe, but things are far from normal: The cloud of volcanic ash and the nearly weeklong shutdown of air traffic have added another element of uncertainty to the hassles of flying.

There has been debate over the correct response by airlines and governments to the ash even as the world watches Iceland for any signs of another big eruption.

Just as the Sept. 11, 2001, terrorist attacks and other attempts to blow up planes heralded a new era of ultra-tight security at airports, the eruption of the Eyjafjallajokull (pronounced ay-yah-FYAH-lah-yer-kuhl) volcano that grounded much of Europe could prove to be a game-changer in the history of aviation — or at least keep things extremely unsettled for a long time.

Some people are saying they’ll think twice about taking a plane if trains — slower but more reliable — are available instead.

Harry Howelber, a 28-year-old telecommunications operator in Paris, said: “I’d just be afraid of flying into a cloud.”

Experts noted the profound psychological impact the ash cloud has had on travelers.

An aircraft passes the moon Thursday over Frankfurt, central Germany. German air traffic went back to normal Thursday following airspace closure because of the volcanic ash cloud that came from Iceland.

“There have been a number of occasions when air travel has been impacted by people’s fears of terrorist events or wars,” said David Henderson, spokesman for the Association of European Airlines. “But it’s rare for natural phenomena to cause the same reaction.”

Travel industry observers, however, do not believe the volcano will affect the way Americans travel to Europe.

“I don’t think they’ll be frightened of flying,” said longtime guidebook writer Arthur Frommer. “Look how fast we returned to flying after Sept. 11, even though the possibility of terrorists getting on a plane continued.”

The International Air Transport Association noted that passenger numbers rebounded several years after 2001.

Frommer said he and his wife are about to book tickets for a trip to Scotland. “Here I am planning to go to Europe on Aug. 16, and it never once crossed my mind,” he added.

Rudy Maxa, host of public television’s travel show “Rudy Maxa’s World,” agreed that the disruption wouldn’t affect flight bookings, particularly if people weren’t personally affected, because Americans always want to travel to Europe.

“I think it’s really a one-off. I don’t think it will be a game-changer,” Maxa said.

Adam Anderson, public relations director of Expedia.com, said the site “saw a (not unexpected) spike in cancellations for the week of April 15-20” — the week the eruption began.

“We have not, however, seen a correlative dropoff in bookings to the top 20 European destinations, when examined on a week-over-week basis,” he said. “There was a drop in London bookings, but not elsewhere. So the net is that the issue seems to have impacted existing flights, but not new ones.”

Travelocity senior editor Genevieve Shaw Brown said it was too early to gauge the long-term impact because bookings to Western Europe are made, on average, three to four months in advance.

“People traveling in the near future have had these plans in place for quite some time,” she said.

“However, time and time again, travelers prove they’re resilient, committed to taking their vacations, and because the situation seems to now be well under control, I don’t think there will be any significant long-term impact on travel to Western Europe,” Brown added.