Airlines canceled more than 4,400 flights as extreme cold in the U.S. Midwest and Northeast froze fuel lines to airplanes and posed exposure hazards for employees working on the tarmac.
JetBlue Airways took the most drastic step of any airline by suspending all flights at New York and Boston airports on Monday, with plans to gradually resume them on Tuesday.
The brunt of Monday's 4,400 cancellations was felt in such areas as Chicago, Minneapolis and Cleveland, according to the FlightAware.com tracking service. More than 1,600 flights were halted at Chicago O'Hare, an airport that typically has 2,400 daily flights, according to city officials.
"Even though there is not a lot of precipitation falling, extreme cold weather can severely impact operations," Andrea Huguely, a spokeswoman for American Airlines Group, said in an email.
American and American Eagle canceled more than 500 flights on Monday, roughly 14 percent of their typical daily count. At O'Hare, American had "minimal operations" and canceled nearly 380 flights, including American Eagle flights.
"The problem we—and other carriers—faced very early is the fueling pumper trucks wouldn't work," said American spokeswoman Mary Frances Fagan. "Parts were frozen. Fuel nozzles were also frozen and had to be taken to a hangar to thaw out. It's slow going."
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JetBlue said halting its flights at John F. Kennedy International, LaGuardia, Newark Liberty and Boston Logan airports would allow time to position flight crews and take other steps to recover from snowstorms that had struck the Midwest and parts of the Northeast. It said it would add extra flights on Tuesday and Wednesday to accommodate passengers whose plans were disrupted.
"It's a combination of everything that has had a domino effect the last few days," JetBlue spokesman Anders Lindstrom said. "As one of the largest carriers in the Northeast, weather in this area impacts our entire route network and operations."
JetBlue, which has nearly 80 percent of its operations in the Northeast, canceled 108 flights from JFK, LaGuardia and Newark Liberty airports on Monday, nearly half of the 220 daily departures it typically has at those locations.
Winter and accompanying storms are a major issue for U.S. airlines in the first quarter. Airlines typically will proactively cancel flights during big storms to minimize disruptions.
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David Fintzen, an airline analyst with Barclays, said it was too soon to comment on financial impact from the flight cancellations.
"With U.S. airlines in much stronger financial positions and investors increasingly focused on the bigger industry picture, severe weather in any one quarter is increasingly looked through by the markets," Fintzen said in a statement to Reuters.
"Moreover, short-term weather impact is disruptive to passengers but financially is a minor factor for earnings versus trends in the overall economy or fuel prices," Fintzen added.
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Stephen Sigmund, executive director of the Global Gateway Alliance nonprofit group of leaders from business and other sectors, said JetBlue's Monday shutdown pointed to a need to bolster U.S. investment in the NextGen program that would shift air traffic control systems to global positioning satellites from radar.
"It doesn't solve the problem of terrible weather," Sigmund said. "But what it would do is allow for better management during weather events, so you don't have the kind of compounding problem that you had this week."
Shares of JetBlue fell 4.3 percent to $8.66 on Monday as most U.S. airlines ended lower. Southwest fell 1.4 percent to $19.15. American Airlines gained 1.8 percent to $27.03.