United Airlines had planned a dramatic flyover in Denver on Friday to mark the 25th anniversary of the 9/11 attacks, when it lost two of the four U.S. passenger jetliners hijacked by terrorists. But the airline abruptly cancelled plans late Wednesday, citing “concerns in the community.”

A United spokesperson did not immediately offer details on where the concerns had risen.

Denver Mayor Mike Johnston had already heralded the event planned for 9:03 a.m. Friday, the exact time at which a United 767 with passengers and crew had crashed into one of the World Trade Center towers in the south end of Manhattan.

The flyover had been set to feature a United Boeing 777, escorted by four F-16 fighters from the Colorado Air National Guard.

Johnston had called the planned flyover a salute to the national sacrifice and resilience that followed the attacks.

“This flyover is a powerful tribute to those we lost and a reminder that their legacy lives on in the strength of our communities and in the people who continue to serve others,” Johnston had said in a statement announcing the event.

Emergency management bulletin

The city’s Office of Emergency Management had circulated a bulletin noting that the flyover was a memorial marking the lives lost Sept. 11, 2001, and that it would have been “highly visible” and “noticeable by sound.”

The flyover had been the only public recognition planned as part of a memorial honoring crews aboard United Flight 175 and Flight 93. A private unveiling of a monument, created from steel recovered from the World Trade Center wreckage in New York, is still set for Friday morning at United’s Flight Training Center, near the former site of Stapleton Airport in Denver.

The memorial to be revealed will stand 9-foot-eleven-inches, according to United. The training center, where United’s pilots train on simulators, was to be the center point for the flyover, to have occurred at 9:03 a.m.

The four airliners hijacked 25 years ago included the two United flights and two by American Airlines. They had carried 334 passengers and crew, not counting the 19 hijackers. Including those who perished on the ground at the sites targeted, 2,977 victims died in the attacks, not counting many more who may have passed from toxin-related illnesses in the following years.

In addition to the two planes flown into the World Trade Center towers, American Airlines Flight 77 crashed into the Pentagon in Arlington, Virginia. United’s Flight 93 crashed near Shanksville, Pennsylvania, after passengers mounted a heroic fight against the hijackers.

United said that simultaneous to the private event in Denver, United and American Airlines staff have planned moments of silence and recognition on the B Concourse at DIA, that had been set for the same time as the flyover. Airport and TSA staff are planning to join in those, the statement noted.

“Twenty-five years ago, our nation was changed forever,” United Capt. Miles Morgan, managing director of the training center, had said in a statement on the planned flyover, noting that it would signify “the honor, resilience and courage that carries us forward.”