Millennium, a science fiction film from 1989 that stars Kris Kristofferson. Kristofferson plays a government inspector who heads up investigations into plane crashes. While investigating a major crash that seem to have some subtle anomalies, he learns that people from Earth’s future are traveling back to our time to rescue people who would have otherwise died in plane crashes. These time travelers put everyone on the plane in a sort of limbo, remove those who were about to die in seconds, and replace them with look-a-like bodies. Then they unfreeze time and the crash occurs as it was meant to.
They are doing this because Earth in the future is dying. The planet is horribly polluted, people are in terrible health, and many cannot reproduce. They are re-populating future Earth with healthy people from our time who otherwise would have died without their intervention. They are doing it in a clandestine way, so as to not alter the future by changing things in the past.
One of the memorable details you may remember is that the time travelers hiding among us are all chain smokers. Earth of the future is so badly polluted, that our cleaner air is alien to them. They chain smoke to fill their lungs with toxins to create a more familiar atmosphere.