Passengers on a flight to South Korea were left feeling sick after a terrifying discovery forced the plane to turn around. As the plane soared to 10,000 feet, someone realized that one of the doors had not been sealed all the way shut. Footage of the heart-pounding moment is captured in the cell phone video above, where noise resembling that of an air vent can be heard. That sound is what alerted the aircrew to turn around to Cebu, Philippines, according to local outlet Yonhap News Agency. About 163 people were aboard the flight, operated by Korean Air’s low-cost subsidiary Jin Air. No injuries were reported, but some passengers later said they had been sick with worry.