(CNN/RNN) – Delta Air Lines dealt with a brief computer system outage Tuesday evening.
Passengers were complaining on Delta's Twitter page, saying they couldn't sign in or access their boarding pass on the app.
The airline grounded flights during the outage.
Around 8:30 p.m. ET, Delta told those passengers the issue was with the airline's computer system, but did not elaborate, saying only that technical support was working to fix the issue.
About an hour later, the airline tweeted: "Delta teams have restored all IT systems after a technology issue briefly affected some of our systems this evening. All groundstops have been lifted."
.@Delta teams have restored all IT systems after a technology issue briefly affected some of our systems this evening. All groundstops have been lifted.— Delta News Hub (@DeltaNewsHub) September 26, 2018
Delta said flights already in the air during the outage weren't affected.
Late Tuesday night, the airline released another statement: "There are currently no Delta flight cancellations following a brief technology issue that prompted an hour-long groundstop for U.S. mainline Delta flights this evening. Additional flight delays and the impact on Wednesday morning's schedule are expected to be minimal. Delta apologizes to its customers for this inconvenience."
In the statement, Delta advised customers flying Tuesday night or Wednesday to check their flight status on delta.com or on the Fly Delta app, assuring them that "all of Delta's customer tools are fully functional."
According to Delta, the impact of the outage was limited to the U.S., and there was "no safety impact on any Delta flights."
The airline is investigating the cause of the outage.
Copyright 2018 CNN. Raycom News Network contributed to this report. All rights reserved.