Airlines in Europe this winter are flying passenger planes that are at times nearly empty in order to hold onto coveted take-off and landing spots at airports during a time of lower travel demand.

Recent publicity around this usage requirement has sparked controversy and anger at a time of growing international concern over climate change and the carbon emissions created by the aviation industry.

Airport industry representatives, meanwhile, are defending it, arguing for the need to maintain commercial viability, connectivity and competitiveness.

Airlines have expressed frustration over so-called “use it or lose it” slot rules established by the European Commission, the EU’s executive arm, which was suspended in March 2020 as the industry was floored by the Covid-19 pandemic. It has since been brought back incrementally to now require airlines to use 50% of their allocated airport slots. That figure is scheduled to increase to 80% this summer.

German carrier Lufthansa is among those airlines, and is already cutting some 33,000 flights over the winter season as the omicron variant hobbles demand. Still, it has to make 18,000 flights over the winter season to meet its slot use requirement, its CEO said. Its subsidiary Brussels Airlines is having to make 3,000 almost-empty flights by the end of March.

“Due to the weak demand in January, we would have reduced significantly more flights,” Lufthansa Group CEO Carsten Spohr told a German newspaper in late December. “But we have to make 18,000 additional, unnecessary flights in winter just to secure our take-off-and-landing rights.”

He added: “While climate-friendly exemptions were found in almost all other parts of the world during the time of the pandemic, the EU does not allow this in the same way. That harms the climate and is exactly the opposite of what the EU Commission wants to achieve with its ‘Fit for 55’ program.”

The “Fit for 55” program was adopted by Commission in July of 2021 to meet the new EU goal of reducing greenhouse gas emissions by a minimum of 55% by 2030.

In the face of criticism from airlines and environmentalists, airport industry representatives are pushing back, saying there is “no reason” why the thousands of near-empty flights should be reality.

Airport industry body Airports Council International (ACI) expressed support for the European Commission’s position, arguing that its lowering of the airport slot use threshold to 50% was “designed to reflect the uncertainties of a badly hit market and fragile recovery for aviation.”

“A few airlines are claiming they are forced to run high volumes of empty flights in order to retain airport slot usage rights. There is absolutely no reason why this should be the reality,” Olivier Jankovec, Director General of ACI Europe, said in a statement in early January.

He rejected the notion of completely empty “ghost flights” being flown, as have the airlines themselves, who say that rather than being completely empty, the flights often have very few passengers and would otherwise be canceled if it weren’t for the slot use requirement.

“Low load factors have of course been a reality throughout the pandemic,” Jankovec said, “but the retention of vital air connectivity for both economic and societal imperatives is well documented … Balancing commercial viability alongside the need to retain essential connectivity and protect against anti-competitive consequences is a delicate task.”

Environmental activists are not impressed. “‘Brussels Airlines makes 3,000 unnecessary flights to maintain airport slots’,” Swedish climate activist Greta Thunberg wrote on Twitter last week, citing a headline of a Belgian newspaper. “The EU surely is in a climate emergency mode…”

The aviation sector creates about 14% of the carbon emissions from overall transport, making it the second-biggest source of transport greenhouse gas emissions after road travel, according to the commission, which also says that if global aviation were a country, it would rank in the top 10 emitters.

The European Commission says on its own website that “aviation is one of the fastest-growing sources of greenhouse gas emissions” and that it “is taking action to reduce aviation emissions in Europe.” 

Belgian mobility minister Georges Gilkinet described the institution’s flight requirements as “environmental, economic and social nonsense.” He wrote to the European Commission this month to demand more flexibility for airlines to keep insufficiently booked planes on the ground.

But a Commission spokesman said that the current 50% threshold is a sufficient reduction that reflects consumer demand and offers “much needed continued air connectivity to citizens.”

Lufthansa spokesman Boris Ogursky told CNBC on Wednesday that he believed the commission’s slot rule of 80% use for summer 2022 is “appropriate.” However, he noted, “air traffic has however still not normalized yet. Due to the development of new virus variants and the resulting travel restrictions, the situation remains volatile, so exemptions are still necessary.”

“Not only next summer 2022, but also now in the current winter flight schedule 21/22, more flexibility would be needed in a timely manner,” Ogursky said. “Without these crisis-related flexibilities, airlines are forced to fly with almost empty planes just to secure their slots.”

He added that this practice is not in place in regions outside of Europe. “Other regions of the world are taking a more pragmatic approach here, for example by temporarily suspending slot rules due to the current pandemic situation. That benefits the climate and the airlines.”

ACI’s Jankovec highlighted a provision called “Justified Non-Use of Slots”, which allows airlines to present the case to their slot-coordinators, “allowing them to effectively use their allocated airport slots for less than 50% of the time,” he said.

For Lufthansa, this provision isn’t very helpful, as it only allows airlines to exempt single flight connections, according to Ogursky: “This option cannot be applied to the majority of our weekly booked flights, resulting in the end to 18,000 unnecessary flights during the current winter schedule (Nov 21 – Mar 22),” he said.

Brussels Airlines media relations manager Maaike Andries also clarified that the flights taking off to meet the airport slot use threshold are not empty; rather, for the coming winter season, some of the airline’s flights “are insufficiently filled to be profitable.”

“These flights would normally be cancelled by us to make sure we don’t operate unnecessary flights from both an ecological and an economical point of view,” Maaike added. “However if we would cancel all those flights, this would mean we pass under the minimum limit to keep our slots. The same issue is valid for all carriers in Europe, as this is a European law.”

“In other continents there have been made appropriate exceptions to the normal regulations, avoiding these unnecessary flights, but in Europe we are still in need of more flexibility.”