U.S. airlines are grappling with one outcome of the deep schedule cuts they’ve made in response to near-zero travel demand: Many of the flights that remain are starting to fill up, complicating social distancing guidelines and angering some passengers.

While carrier traffic is still down about 90 percent from typical levels, not everyone has stopped flying. More than 215,000 people traversed U.S. security checkpoints last Friday, the highest total since March 25, according to the Transportation Security Administration.

As air travel gradually returns in the pandemic era, airlines will face a fraught choice: Continue onboard social distancing by limiting cabin occupancy and increasing scheduled flights, or keep the number of trips in line with demand, which could lead to more crowded planes but also financially benefit cash-strapped carriers.