Something unexpectedly broke the hum of a routine meeting of federal aviation and law enforcement officials at Manchester Airport.

“All of a sudden everyone’s pager went off just simultaneously,” recalled then-Assistant Airport Director Brian O’Neill. “We stopped the meeting and there were multiple requests for a television, so they could watch the news.”

People made it into the airport director’s office just in time to see a hijacked plane hit the second World Trade Center tower in New York City on Sept. 11, 2001.

What would happen next?

“No one really knew what was going on,” O’Neill said last week in a phone interview from Mesa, Ariz., where today he is executive director and CEO of the Phoenix-Mesa Gateway Airport Authority.

“It was really a helpless feeling,” O’Neill said.

On that morning of uncertainty, Kevin Dillon, then head of Manchester’s airport, talked with the city’s emergency management chief.

“Should there be something done in terms of evacuation of buildings in downtown Manchester?” Dillon recalled asking. The answer was no, partly because “we didn’t want to set off a panic.”

On Friday, the country will mark the 20th anniversary of the terrorist attacks that killed nearly 3,000 people and shut down commercial air travel for days, changing how people — and their bags — made it on to airplanes.

“I think what it did for many air travelers now is there is a new sense of individual vigilance,” O’Neill said. “Everyone is part of the air transportation security system.”

Reinforced cockpit doors, enhanced screening at airport checkpoints and limits to how much liquid you could bring on-board were among the safety changes that followed the hijackings.

Today, all bags are screened for explosives before being loaded onto planes, said Dillon, now executive director of the Connecticut Airport Authority, which oversees several airports, including Bradley International north of Hartford.

“I think the effort of the federal government and the airlines and the airports really was able to rebuild consumer confidence in air travel after September 11 although it still haunts many of us every single day.” O’Neill said.

He counts himself among them.

“There’s something every single day that comes up that is a direct result of what happened on September 11,” O’Neill said.

Take workers delivering Diet Coke to be sold at airport gift shops.

“Before (9/11), it was just driving up to a gate or a door and unloading,” he said. “Now, all the product goes through the equipment at the security checkpoint,” he said.

A beautiful day darkened

“I always say the same thing most people say about September 11: It was such an amazing weather day,” Dillon said.

“I remember driving into work that day. What a great time of the year fall is,” he said. “What an amazing weather day it was.”

The day soon darkened — American Airlines Flight 11 out of Boston hit the World Trade Center at 8:46 a.m., followed by United Flight 175, also from Boston, striking the second tower 17 minutes later.

“Naturally, when the second plane hit the building, I — like most other folks — realized this was something much, much bigger,” Dillon said.

Authorities later determined that two terrorists flew out of Portland, Maine, to connect in Boston with other hijackers.

“I think every airport director in the country probably thought of that: We could have been the launching point for part of this attack,” Dillon said.

The FAA ordered all commercial planes to land at the nearest airport, grounding flights for at least three days.

When airports reopened, “You could see the suspicion in people, eyeing fellow passengers in the airport,” he said.

For Dillon, the World Trade Center wasn’t a mere tourist destination.

During the 1980s, Dillon worked there as an operations services supervisor. His duties included responding to fire alarms in the building.

“To be honest with you, I was shocked that building was capable of collapsing like that,” said Dillon, who ran Manchester’s airport until 2007.

He recalled thinking of “so many coworkers in those positions there and having a pretty good understanding of what they were doing at the time.”

The Port Authority of New York and New Jersey lost 84 members in the attack on the World Trade Center.

“Certainly there were a number of them I did work with that did perish in the attack,” Dillon said.

For Dillon, every Sept. 11 remains a solemn one.

“That is a day I typically spend by myself,” he said.

“It’s more of a day of solitude” for him to remember “what those folks experienced that day,” Dillon said.

“I certainly reflect on that history and the friends that were lost.”