Bomb threats made against 5 airline companies

Bomb threats made against five different airlines come amid a host of troubling airline security news.

Government sources told NBC News that bomb threats were called in Tuesday morning against US Airways, Delta Airlines, United Airlines, Volaris and Korean Air flights originating in the U.S. Or landing in the U.S. Sources say the threats don't seem credible, all the flights except Korean Air have already landed.

US Airways Flight 648 landed in Philadelphia and was met by a police bomb squad who found no evidence of explosive material and called the threat a hoax.

There have been a number of hoax bomb threats called in over the past two weeks, but most have regarded flights coming into the U.S. from other countries.

In other scary travel news, United Airlines briefly grounded all of their planes Tuesday morning after unspecified issues with "dispatching information" on the planes' computers.

"United began delaying flights at approximately 8 a.m. CT to ensure aircraft departed with proper dispatching information," a spokesperson for the airline said. "We resumed departures at about 8:40 CT and are accommodating our customers to their destinations."

All of this comes just a day after the acting head of the TSA was reassigned following a Department of Homeland Security investigation found a number of security failures in some of the United States' busiest airports.

More from AOL.com:
Some GOP donors willing to give to many, just not Paul
Boston Marathon bomber's college pal gets 6 years in prison
Survey: Most Americans with disabilities 'striving to work'