2 planes aborted landings in San Francisco when a Southwest jet taxied across their runways

The Federal Aviation Administration said Thursday that the Southwest plane cleared the runways when the other planes passed directly overhead, and the decision to abort the landings was "precautionary."

"The FAA looked into the events and determined the appropriate steps were taken to ensure safe operations," the agency said.

The National Transportation Safety Board said it is not investigating the matter.

The incident comes after a half-dozen close calls in recent months that are being investigated by safety officials. Those include one in February in which a FedEx plane flew about 100 feet (30 meters) over the top of a Southwest jet in Austin, Texas, after an air traffic controller cleared both planes to use the same runway.

In the incident this month, an inbound United Airlines plane flew as low as a few hundred feet (100 meters) over San Francisco Bay before pilots saw the Southwest jet on the same runway and decided to abandon their landing.

Shortly after that, the crew of an incoming Alaska Airlines plane saw the same Southwest jet crossing a second, parallel runway, and the pilots aborted their landing too.

Both the United and Alaska planes circled around and landed safely.

The air traffic controller told the crew of the Southwest jet, "You shouldn't be on the runway," according to a recording captured by LiveATC.com. When one of the pilots tried to explain, the controller cut him off, saying, "I don't need an argument."

The incident was first reported by the San Francisco Chronicle. The San Francisco airport was the scene of a frightening near-disaster in 2017, when pilots of an Air Canada jet mistook a taxiway for their runway and nearly landed on top of four other planes waiting to take off.

Despite recent close calls, the acting head of the FAA has said the nation's air-traffic system is safe, pointing to the lack of a fatal crash involving a U.S. airline since 2009.

However, concern about the close calls led the FAA to hold a "safety summit" in March. The agency said this week it is investing $100 million in improvements at 12 airports — but not San Francisco — to reduce the number of "runway incursions," when a plane or airport vehicle is on a runway when it should not be.