A Denver International Airport train mishap Tuesday morning delayed hundreds of travelers from getting to their gates.

Stranded passengers took to Twitter showing pictures of the packed train platform as all trains were stopped for almost 30 minutes, causing backups at TSA security checkpoints.

“At 10:17 a.m. today, a train got stuck on Concourse A resulting in the temporarily stoppage of all trains from the terminal to the gates,” airport officials said in a statement. “The trains were stopped for approximately 28 minutes while crews worked to remove the stuck train. The trains started operating again around 10:45 a.m.”

Security checkpoint agents began metering traffic after that to allow the platforms to clear.

“The security lines were back to normal and train platforms cleared by 11:18 a.m.,” according to the statement. “The trains are operating as normal now and the issue has been resolved.”

The aging train fleet has been a concern for airport officials since at least August, when a damaged train tire caused power-line and track damage to one of the rails, crippling the system and causing hourslong delays.

Airport CEO Phil Washington acknowledged the issue during an Oct. 22 news conference.

“It’s a huge vulnerability for this airport,” Washington said. “To have one way to get people out to concourse B and C is a huge vulnerability.”

New train cars that were ordered in 2018 and supposed to arrive in May now won’t arrive until February 2023.

“Unfortunately, global supply chain delays have pushed back the delivery of the first four new train cars to February 2023,” according to a March news release. “DEN anticipates having all 26 new train cars by October 2023, with four new cars being delivered approximately every six weeks following the first delivery.”

“This delay was not welcome news. We are aware of the issues that our aging train cars are having and our crews are doing the best they can to keep these cars and associated systems in working condition for the comfort of passengers,” Washington said in the release

Airport officials collected requests for proposals for alternate ways to get passengers to the B and C gates without the trains. Travelers are only able to walk to A concourse gates.

Asked Tuesday about those proposals, a spokesperson replied via email: “At this time, we don’t plan on releasing any info regarding the RFQ. We are going to further explore design concepts as it relates to some of the proposals to get a better understanding of design and cost so that we can determine next steps.”