The head of the Federal Aviation Administration said Wednesday the agency has taken steps to avoid a repeat of the technology failure last month that briefly halted all flights nationwide, but he said he couldn't promise there won't be another breakdown.

Separately, acting FAA administrator Billy Nolen defended the safety of airline travel in the United States after recent incidents at John F. Kennedy Airport in New York, in Austin, Texas, and off the coast of Hawaii. Still, Nolen said, he is putting together a team of experts to review airline safety.

"We are experiencing the safest period in aviation history, but we do not take that for granted," Nolen said during testimony before the Senate Commerce Committee. "Recent events remind us that we cannot become complacent."

The committee's hearing was billed as an examination of the failure of an FAA system that provides safety alerts to pilots, but lawmakers were most animated when they quizzed Nolen on the recent flight scares.

Sen. Ted Cruz, R-Texas, showed a video re-enactment of the Feb. 4 Austin incident in which a FedEx cargo plane flew over the top of a departing Southwest Airlines flight. Both planes had been cleared to use the same runway. The FedEx pilots aborted their landing just in time to avoid a collision.

"How can this happen?" Cruz asked. "How did air traffic control direct one plane on to the runway to take off and another plane to land, and have them both within 100 feet of each other?"

Nolen said the incident is still under investigation by his agency and the National Transportation Safety Board, but he suggested that the fact the planes did not collide should be reassuring.

"It is not what we would expect to have happened, but when we think about how we train both our controllers and our pilots, the system works as it is designed to avert what you say could have been a horrific outcome," Nolen said.

Nolen pointed out that the U.S. has not had a fatal crash involving an airline plane since 2009. Still, he said, he is forming an expert panel to review the aviation system and hold a safety summit next month to determine what steps are needed to maintain the record of recent years.

The breakdown of the FAA system of distributing alerts called NOTAMs to pilots began late on Jan. 10 when contractors accidentally deleted files, corrupting the main database and a backup, he said. Attempts to fix the problem by the next morning failed, and FAA barred all planes from taking off for nearly two hours on Jan. 11, leading to 1,300 canceled flights and 11,000 delays.

Nolen said there is now a delay in synchronizing the databases to avoid both the main and backup going down at the same time. But he can't rule out a repeat.

"Could I sit here today and tell you there will never be another issue on the NOTAM system? No, sir, I cannot," Nolen said under questioning by Cruz.

Committee chair Maria Cantwell, D-Wash., pressed Nolen to build more redundancy into the system to avoid another meltdown.

Part of the NOTAM system is 30 years old, although most airline flights use a newer system, Nolen said. But during the failure, all flights were stopped.

Nolen, a pilot and the former top safety official at FAA, has been acting administrator since the agency's last Senate-confirmed leader stepped down in March 2022, midway through his five-year term. The nomination of President Joe Biden's choice for the job, Denver International Airport CEO Phil Washington, has stalled amid questions over his thin aviation experience and involvement in a corruption investigation.