Just as Americans begin jetting away for summer vacation come two episodes that could rattle fliers, a spate of bomb threats against planes and an embarrassing report about undercover agents easily smuggling weapons past security.

Threats were called in Tuesday morning against at least five airliners. Government sources told NBC News that the threats were not credible. Four of the planes landed safely, and the fifth was scheduled to land by mid-afternoon.

Hours earlier, the acting chief of the Transportation Security Administration was reassigned after undercover agents managed to get weapons, explosives and other contraband past TSA agents in 67 out of 70 tests.

John Pistole, a former TSA administrator, told NBC News that the failure rate was disturbing, especially at a time of "a continuing drumbeat of interests by terrorist groups."

The unsettling news came at the start of what is expected to be a record summer for air travel. The industry estimates that 222 million people will crowd into planes from June 1 through Aug. 31, about 2.4 million every day.

Almost a dozen flights have been threatened over the past two weeks, mostly flights coming into the United States from other countries. All have proved to be hoaxes. Last week, the FBI looked into threats of chemical weapons on board planes.

On Tuesday, Matt Tremaine took a flight from San Diego to Philadelphia after visiting friends. When the plane touched down, he looked outside to and saw emergency crews.

"Then the pilot made an announcement that there were threats made against several planes and that our plane was one of them," he said. "The pilot said he was told about it after we landed and said, 'If I knew earlier I would have let you know about it.'"

Police and bomb-squad dogs searched the plane, US Airways Flight 648, and police gave the all-clear.

The other flights were Delta 55, from Los Angeles to Atlanta; United 995, from San Francisco to Chicago; and Volaris 939, from Portland, Oregon, to Guadalajara, Mexico. Korean Airlines 23, from Seoul to San Francisco, was scheduled to land in the afternoon.

Tremaine said that the threats against planes didn't faze him. He said he was more concerned about the TSA report.

"I feel fine flying," he said. "If anything it would be the report about the TSA and how 95% of things make it through that worries me more about flying," he said.

Airline stocks dropped sharply in the morning, the threats were made public just before the opening bell, before recovering most of their losses.

Brett Snyder, who runs the popular airline industry blog The Cranky Flier, told NBC News in an email that he doesn't think the episodes will have an impact on summer travel demand.

The threats were "hoaxes as usual," he said, and he pointed out that TSA breaches have been exposed many times before.

"If there was an actual bomb found on an aircraft, then that would potentially change things," he said. "I really don't think this is going to impact how people feel about flying. It'll just increase the anger at the government for how security is run." (Source: NBC News)

US airport security reforms ordered

A top US official has pledged reforms after tests found that airport screeners allowed mock explosives and weapons through security checkpoints 95% of the time.

Homeland Security Secretary Jeh Johnson on Monday called for revised security procedures in airports across the US.

In one test, a screener failed to find a fake bomb taped to an agent's back despite patting the man down.

The acting head of the agency responsible has been moved elsewhere.

Transportation Security Administration's Melvin Carraway has been reassigned to a different job in the Department of Homeland Security.

Acting Deputy Director Mark Hatfield will now lead the agency until a new boss comes in.

The results of tests were first reported by ABC News, which said the tests were carried out at 70 US airports but only three were able detect the banned weapons.

Mr Johnson said security officers should be retrained and scanning equipment should be retested. He said he was taking the results of tests "very seriously".

"The numbers in these reports never look good out of context but they are a critical element in the continual evolution of our aviation security," he said.

"We take these findings very seriously in our continued effort to test, measure and enhance our capabilities and techniques as threats evolve."

Mr Johnson said the results of the report were classified, but he said there would be more random covert testing at checkpoints. (Source: BBC News)

Story Date: June 3, 2015