With a bill to make daylight saving time permanent moving through Congress, airlines are warning that permanently changing the nation’s clocks could take years to implement and require costly operational changes.

Daylight saving time is one step closer to becoming the year-round standard after the House voted in favor of a bill that would keep clocks permanently shifted ahead. The legislation now heads to the Senate, where it must pass before it would land on President Trump’s desk for his signature. Its future remains up in the air. 

Advocates for the bill say making DST permanent would reduce energy use because the sun would set later in the winter, while detractors say it could create more cold, dark mornings and lead to negative health outcomes. 

The aviation industry says permanent DST would be very disruptive to the sector, requiring up to 24 months to adjust airlines’ scheduling systems. The change would impact everything from “crew and aircraft positioning” to “domestic and international connectivity issues,” according to Airlines for America, or A4A, the trade association representing leading carriers.

“Airlines operate expansive interconnected domestic and global networks that are reliant on stability and predictability. Any changes would need an implementation timeline that reflects these global complications,” the group said.

Other businesses that depend on consistent scheduling, such as trucking and railroad companies, would also require time to adjust, experts say.

In a statement to CBS News, A4A said that if the bill becomes law, lawmakers “should allow for a significant amount of time to adjust airline schedules, websites, reservation systems, crew scheduling, payroll and the implementation of IT fixes both at the air carriers and any impacted vendors prior to implementation of DST changes.”

Business challenges

The aviation industry is unique given its reliance on complex scheduling, and for the fact that tickets can be reserved well in advance of the date of travel, said aviation industry analyst Henry Harteveldt, founder of Atmosphere Research Group.

Trucking and railroad companies, which are also timetable dependent, will have to make significant operational changes if the bill becomes law, Harteveldt added. 

“They would all have to make changes to their software programs if we abandon the practice of daylight saving time,” he said. 

But, he added, airlines may only require six months to a year to adjust, rather than up to two years. 

“There are a lot of different software systems that may need to be reprogrammed within an airline, including reservation, crew scheduling and maintenance, which will have to be adjusted,” he said. “But I don’t think it’s going to be a two-year time frame. That seems extreme.”

He said the twice-yearly clock changes already illustrate how even minor disruptions can affect daily routines. “And though under normal circumstances airlines send out emails and text alerts, and make announcements, passengers show up for flights at the wrong time,” he said.