But United took significantly longer to recover than other airlines from the same set of storms, and some have suggested the airline’s internal processes for the crew are to blame. Ken Diaz, president of the United chapter of the Association of Flight Attendants, has criticized United for its crew scheduling system, saying that the problems were so acute over the holiday week that schedulers weren’t even sure where some of its crews were located.

Kirby also panned offsets, a long-time favorite environmental program for airlines that involves planting or saving trees and counting that against their carbon emissions, which Kirby said the “vast majority of ... frankly are fraud.”

“They are either forests that were never going to be cut down or trees that were going to be planted anyway,” he said.

The University of Berkeley’s Goldman School of Public Policy conducted a study covering 293 forest management carbon offset projects and found that many of them had dubious benefits. Delta Air Lines was sued in May after a California-based plaintiff argued that the airline’s offsets were insufficient to reduce emissions. Dutch Airline KLM was accused last year of breaching Dutch consumer law with its CO2 compensation marketing.

Kirby said instead of planting trees, United is focused on expanding the use of sustainable aviation fuel, which Kirby called currently “uneconomic and expensive.” Sustainable aviation fuel is an umbrella term for clean-burning biofuels manufactured from a range of organic matter such as corn, algae or other items.

Beyond being expensive to produce, there are additional concerns that the biomass needed for many industries, including aviation, is itself not sustainable. In any case, Kirby noted that widespread usage is decades away and will require billions in government support to expand SAF-related supply chains and infrastructure.

Kirby compared the development of SAF to the solar and wind power industries around 20 years ago, arguing that years of government investments were needed to spur alternatives to coal and natural gas. Meanwhile, climate change is making disruptive weather events that cause airlines to cancel and delay millions of flights more common.

“It’s not going to happen tomorrow,” Kirby said. But he noted that the Inflation Reduction Act makes it closer to reality since it included a per-gallon tax credit of up to $1.75 on sustainable aviation fuels that reduce greenhouse gas emissions by at least 50 percent.

“Pre-IRA we didn’t think we could get to 100 percent SAF, now we think we can get to 100 percent SAF,” Kirby said, adding that 2046 is United’s target for universal SAF usage.

SAF production rapidly expanded in 2022 to 15.8 million gallons, according to a Government Accountability Office report, but that is a literal drop in the bucket, accounting for less than 0.1 percent of the total jet fuel used by major U.S. airlines last year.

The FAA set an original 2012 goal for U.S. airlines to use at least 1 billion gallons of sustainable aviation fuel annually by 2018 but the proposal was never acted upon by the Trump administration. The Biden administration upped the target in 2021 to 3 billion gallons per year by 2030.

Kirby added that competitors in the industry are now embracing SAF usage and tax credits in a way they weren’t two or three years ago, but the conversation on offsets is just beginning.

“The good news is when I said things like that two to three years ago I got a lot of pushback from my peers,” Kirby said. “SAF has moved, the carbon offset conversation hasn’t moved as much.”