WASHINGTON, Feb 2 (Reuters) - A key U.S. pilot messaging

system was experiencing a temporary outage, which could lead to

flight delays on Sunday, U.S. Transportation Secretary Sean

Duffy said late on Saturday.

The Federal Aviation Administration is working to restore

the "Notice to Air Mission" or NOTAM system, Duffy said on X.

"There is currently no impact to the National Airspace

System because a backup system is in place," Duffy said. "FAA

has set up a hotline to communicate with aviation stakeholders

and will send notices every 30 minutes with updates on the

system's status."

Duffy said the FAA "activated its contingency system to

supplement and support preflight briefings and continue flight

operations... We are investigating the root cause and we will

provide updates."

He said passengers should check with their carriers about

the status of flights on Sunday, adding "there may be some

residual delays tomorrow morning."

A January 2023 NOTAM outage led to the first nationwide U.S.

groundstop since 2001, disrupting more than 11,000 flights.

The NOTAM system provides pilots, flight crews and other

users of U.S. airspace with critical safety notices. It could

include items like taxiway lights being out at an airport,

nearby parachute activity or a specific runway being closed for

construction.

A Southwest Airlines ( LUV ) spokesperson said the carrier did not

have any measurable delays late on Saturday "and we have people

and processes in place if the situation continues into

tomorrow."

Delta Air Lines ( DAL ) and United Airlines said

they were not experiencing problems early on Sunday. "All our

operations continue as normal right now. We have up to date

NOTAM info through backup procedures," a Delta spokesperson

said.

The U.S. aviation system has faced a difficult week.

On Wednesday, an American Airlines ( AAL ) passenger jet and

a military helicopter collided near Reagan Washington National

Airport killing 67 people, the first fatal U.S. passenger

airline crash since 2009 and the deadliest U.S. air disaster in

two decades.

On Friday, a medevac plane crashed soon after takeoff in

Philadelphia with a child and five others on board. All died as

did a person on the ground, Pennsylvania Governor Josh Shapiro

said.