A loaded handgun fell out of a checked bag Tuesday as it was being loaded onto a US Airways flight departing from Charlotte.

The incident illustrates what some safety experts have called a potential weakness in federal safety precautions: Checked bags are examined for explosives but not for loaded guns.

Under federal rules, passengers can carry firearms in checked luggage, provided the guns are unloaded and are in locked, hard-sided cases. The gun found Tuesday was not in a locked, hard-sided case, according to a US Airways employee who asked not to be named because he isn’t authorized to talk with the press.

The handgun – a .25-caliber semiautomatic – had a bullet in the chamber and a fully loaded clip when it was found inside the airplane’s baggage compartment, the employee said. The gun fell from an unzipped outer pocket of a bag, landing on the floor near two US Airways employees who were loading the plane, he said. The gun’s safety switch was on.

“Let’s assume the gun didn’t have a safety on, and it discharged,” the employee said. “What if a stray bullet hits a US Airways employee in the chest and kills them?”

US Airways spokeswoman Michelle Moore confirmed that employees found a gun that fell out of a bag that had been checked on to Flight 381. That flight departed Charlotte Douglas International Airport for Las Vegas at about 6:50 p.m. Tuesday.

Jon Allen, a spokesperson for the Transportation Security Administration, declined to say whether TSA officials should have caught the gun or whether the agency would investigate.

But he added that the machines that scan checked bags are designed to screen for the sorts of explosives that can take down a plane. TSA officials say they are not required to look for loaded guns in checked bags.

Until about six years ago, aviation security consultant Quinten Johnson said, TSA officials used to examine the X-ray images of every checked bag. That changed in 2006. Under the new system, Johnson said, TSA officials don’t manually inspect a bag unless the alarm sounds on an automated explosive-detection device.

Johnson said he thinks that change made sense because loaded weapons in checked bags pose little risk to the flying public. He said he’s aware of just one instance – on an Alaska Airlines flight in 2000 – where a firearm in a checked bag accidentally discharged. The bullet went through the cabin floor and lodged in a diaper bag without injuring anyone.

“The risk is incredibly low compared to the effort it would take to have people looking at every bag going through,” said Johnson, a former TSA federal security director at four airports in the Southeast.

Other experts, however, say they’re troubled by the potential dangers.

“There’s nothing to say that weapon won’t go off,” said aviation security consultant Glen Winn. “A bullet could go into the aircraft and hit a passenger or sever a line and cause that plane to crash. … If you interrupt the electrical system on an airplane of today with something like a round going off, you’ve got a problem.”

Winn, a former airline security director, said crew members have in the past been injured by guns in checked bags that accidentally went off. In the 1970s, he recalled, a gun discharged inside a plane at Denver’s airport, injuring a crew member who was loading the plane.

Winn said he thinks TSA employees working near the screening machines should have caught the gun that fell out of the bag in Charlotte. “In my book, somebody wasn’t paying attention,” he said.

Allen, the TSA spokesman, said it’s the responsibility of passengers to declare any weapons they are carrying in checked luggage. Passengers who violate security rules can face civil penalties, he said.