Daniel K. Inouye International Airport in Honolulu, Hawaii

Editor’s Note: Sign up for Unlocking the World, CNN Travel’s weekly newsletter. Get news about destinations opening, inspiration for future adventures, plus the latest in aviation, food and drink, where to stay and other travel developments.

CNN  — 

Federal safety investigators have opened an inquiry into a third runway close-call involving an airliner in less than a month.

The National Transportation Safety Board said Wednesday it is investigating a January 23 incident involving a United Airlines 777 jet and a smaller, single-engine cargo plane at the Honolulu airport.

The United jet improperly crossed a runway at the Daniel K. Inouye International Airport while the cargo aircraft was landing, the Federal Aviation Administration said. At the closest point, the aircraft were separated by 1,170 feet.

United referred questions to the NTSB.

The cargo aircraft involved in the incident is a smaller Cessna 206 turboprop operated by Kamaka Air, which ferries goods between the Hawaiian islands. The airline did not immediately respond to a request for comment.

The NTSB announced the investigation the day after Billy Nolen, the acting FAA administrator, directed his agency in a memo to “mine the data to see whether there are other incidents that resemble ones we have seen in recent weeks.”

2 other runway incidents

There two other runway incursions that occurred within a month’s time.

One included an American Airlines jetliner that crossed a runway at New York’s JFK International Airport where a Delta Air Lines flight was taking off on January 13.

The NTSB said in a preliminary report that the American crew did not have clearance to cross the runway, and it has issued a subpoena to compel the crew’s testimony.

The second incident occurred on February 5, when a FedEx pilot narrowly averted landing in Austin, Texas, atop a departing Southwest Airlines flight cleared to use the same runway. The planes were at one point about 100 feet apart, the NTSB said.

Testimony before Senate committee

Unlike in those two instances where one of the planes needed to abort, in the Honolulu incident, the Cessna came to a stop before reaching the spot where the United 777 had crossed.

Nolen testified before the Senate Commerce Committee on Wednesday that the Austin incident was “not something that we expected to take place.”

The investigation is ongoing, he said.

“The tower visibility was zero. It was a low, low visibility day,” Nolen said. “But when we think about the controls, how we train both our controllers and our pilots, the system works as it’s designed to avert what you say could have been a horrific outcome.”

Plunge toward the ocean