Presidential candidate Mitt Romney greets firefighters on the anniversary of 9/11 before boarding his campaign plane. (Photo by Bill O'Leary/The Washington Post)

At 8:46 a.m. Eastern, a couple dozen Chicago firefighters stood on the tarmac of Chicago O'Hare International Airport, a few hundred yards from Mitt Romney's parked campaign plane, for a moment of silence observing the 11-year anniversary of the first plane that hit the World Trade Center.

Romney, the Republican presidential candidate, was en route in the back seat of a Chevy Suburban on some highway somewhere in the suburbs of Chicagoland. He was missing an impromptu photo opportunity.

But Romney arrived at O'Hare about 10 minutes later. He walked along the tarmac to greet the firemen, who had already folded up their American flag but remained standing in a line in front of their flashing emergency vehicles.

Romney shook their hands one by one, although reporters could not hear what he said. Then Romney boarded his plane and, minutes later, was wheels up en route to Reno, Nev., where he is set to address the National Guard Association convention.

Romney was never planning to arrive by the moment of silence, a campaign aide said, but since the firefighters were observing the anniversary near his plane, he decided to walk over and greet them.