More than 3,700 U.S. flights have been canceled due to the cold weather.

Officials say one out of every 10 flights from the Midwest to Boston had to be canceled on Monday. Airport workers could only stay outside for a matter of minutes and de-icing fluids were freezing at airports where the record low was minus 16 degrees.

United Airlines says its jet fuel is pumping slowly because of the cold.

Meanwhile, JetBlue flights took off again on Tuesday, after grounding hundreds of flights in and out of the Northeast.

The airline is trying to accommodate passengers who were stranded at Logan Airport for two days and had to sleep on cots and chairs.