NEW YORK — US aviation officials have taken steps to avert a repeat of January’s emergency grounding, but a top regulator said Wednesday that a meaningful system upgrade won’t be ready before 2025.

Billy Nolen, acting head of the Federal Aviation Administration, attributed the nationwide January 11 grounding of commercial planes to a mistake by a contract employee, who deleted computer files needed for a key air safety system.

The agency has taken steps, including strengthening backup systems and ensuring the presence of a second staff person during database work, that should “prevent a recurrence of what happened on January 11,” Nolen told the Senate Commerce Committee.

But Nolen said an “ongoing modernization” of the Notice to Air Missions system (NOTAM) system would take longer.

The hearing probed last month’s breakdown of the NOTAM system — a report for pilots that lists unusual flight conditions — which necessitated a temporary grounding of US flights for the first time since the September 11 attacks.

Since that time, a series of close calls at US airports in recent weeks have added to questions about whether FAA systems are too antiquated.

Nolen described NOTAM as consisting of two overlapping programs, including a portion that runs on 30-year old software and architecture that the agency is working to phase out.

While 80 percent of flights use the newer system, some key operators such as the Pentagon still utilize the older system, he said.

Nolen told the committee that “a significant portion of the modernization work” on NOTAM would be complete by mid-2025, but that he is looking at ways to accelerate that time table.

Senator Maria Cantwell, a Democrat from Washington state who chairs the panel, said the FAA needed to take steps to ensure “true redundancy” of critical systems as quickly as possible.

Senator Ted Budd, Republican of North Carolina, noted that the NOTAM reports have been criticized for burying key information, citing one 276-page report that listed a key runway closure on page 53.

Nolen said efforts are underway to make the reports more useful for pilots, adding that “we’ve got to do better.”

The hearing came as the FAA has faced scrutiny following a series of near-misses in recent weeks, such as a near-collision between a Southwest Airlines plane and a FedEx jet on February 4 in Austin, Texas.

Citing the incidents, Nolen on Tuesday announced plans for a “safety summit” in March to hear from aviation industry leaders and labor representatives.

Nolen, who said the Austin incident remains under investigation, also plans reviews of safety information sharing and of the Air Traffic Organization, writing in a memo to staff that despite FAA’s success at averting passenger jet crashes in recent times, “we must not become complacent.”