A federal source has revealed to Action News that a bullet was recovered inside the plane.
Another source tells the ABC affiliate in Charlotte the bullet was likely from a .40 caliber rifle.
Officials believe the bullet was fired in Charlotte after passengers had already exited the aircraft.
Action News, meanwhile, has learned that investigators are looking into the possibility that the bullet in question came from Charlotte Mecklenberg Training Academy, a shooting range located just south of the Charlotte-Douglas International Airport and near the path of the final approach runway.
Because of the downward trajectory of the bullet, a source says they now believe the bullet was heading back down toward the ground when it struck the plane, suggesting it may have been a stray bullet.
While sources are talking, neither the FBI or U.S. Airways have confirmed the discovery of a bullet.
Michelle Mohr, a spokeswoman for US Airways Group Inc., said the airline called the FBI because "it looked like it could have been" a bullet hole.
"It's very small," she said. "This pilot has a heck of an eye."
The hole near the rear of the plane was found after it arrived at Charlotte Douglas International Airport on Monday from Philadelphia. The airline said there were no apparent problems during the flight. Passengers who were going to be on the plane for its next flight were put on other flights, the airline said.
Mohr said the hole in the Boeing 737 is being repaired and the plane will return to flying on Wednesday. The plane seats 144 people, although it wasn't clear how many were on the flight from Philadelphia on Monday.
Transportation Safety Administration spokesman Jon Allen said his agency is cooperating with the FBI investigation. Charlotte airport director Jerry Orr and the FBI did not return messages Tuesday.
Herb Hortman, a pilot of Boeing jets for a major airline and operator of a highly regarded flight school at Northeast Airport, told Action News despite an airliner's height, a pilot out at its wing tip can spot potential trouble.
"Airliners are exactly the same, with a fairly smooth surface, you'll see your rivet lines on there, you'll see your doors, your access panels, you'll see your windows, obviously, but you're looking for any disruption in the smooth skin of the aircraft," Hortman said.
Federal Aviation Administration spokeswoman Kathleen Bergen said Tuesday that her agency also will ensure the aircraft is airworthy before it's put back in service, although that doesn't mean an FAA inspector will physically check the plane, she said.
"The airline has the mechanics. They have the manuals. They have skills and capability and authority to do those repairs. They do the required record keeping and then we can inspect that if necessary," she said.
If it does turn out to be a bullet, James Ray, head of the U.S. Airways pilots union in Charlotte says, most likely, it's nothing to worry about.
"Bottom line is, you don't have to worry about bullet holes on the side of airplanes today; it's not something that happens every day and even if it did happen to your plane tomorrow, in all likelihood, there'd be no consequences," Ray said.
While a bullet hole is rare, it's not unheard of.
Hortman says the wing of a light plane he was flying 30 years ago was hit by a bullet.
Besides bullets, holes can be caused by metal fatigue or lightning. In October, a cabin lost air pressure when a hole ripped open in the fuselage of an American Airlines flight from Miami bound for Boston. In that case, the pilot had to make an emergency landing.
The Associated Press contributed to this report.