More than 5,000 completely empty passenger flights have flown to or from UK airports since 2019, the Guardian can reveal. A further 35,000 commercial flights have operated almost empty since 2019, with fewer than 10% of seats filled, according to analysis of data from the Civil Aviation Authority (CAA). This makes a total of about 40,000 “ghost flights”. In one quarter, for example, 62 empty planes left Luton airport for Poland, while in another, Heathrow saw 663 almost empty flights going to and from the US. Both quarters were during the Covid-19 pandemic. Air travel results in more carbon emissions an hour than any other consumer activity and is dominated by a minority of frequent flyers, making it a focus of climate campaigners. They called the ghost flight revelations “shocking” and said a jet fuel tax was needed and airport expansion plans should be questioned. The UK government describes ghost flights as “environmentally damaging”. Why ghost flights operate remains unclear. Only airlines know the reasons but they do not publish data that explains the practice. Ghost flights may run to fulfil “use-it-or-lose-it” airport slot rules, though these were suspended during the height of the pandemic. Other reasons cited by airlines include Covid repatriation flights or the repositioning of aircraft. But these cannot be verified and campaigners said more transparency was needed. The new data gives the fullest picture to date of the number of UK ghost flights, as previous data only counted international departures. It now includes international arrivals and flights within the UK. The CAA will now publish this data quarterly, as a result of a series of FoI requests by the Guardian. “Publication of this data is a step in the right direction, but we need more transparency to understand why these inefficient, polluting practices continue, and to hold the main airline culprits to account,” said Tim Johnson at the Aviation Environment Federation. “Given the climate emergency, the revelation that so many near empty planes have been burning fossil fuels and adding to the CO2 building up in the atmosphere is pretty shocking.” A spokesperson for the Department for Transport said it would work with the CAA to monitor aircraft occupancy and seek greater transparency on the issue of ghost flights. The data shows an average of 130 completely empty flights a month since 2019. The number of empty flights remained at a similar level before, during and after pandemic travel restrictions, with the second highest level in the second quarter of 2022. This suggests the reason the airlines chose to fly empty planes was not related to the impact of Covid on aviation. Half of the empty flights were within the UK and the top seven airports accounted for two-thirds of the total, led by Birmingham with 1,455, Luton (1,307) and Bristol (758). The number of empty flights did not correlate with the total number of flights at each airport, suggesting they may reflect issues on specific routes. There have been an average of 1,200 almost empty ghost flights a month since the start of 2020, when numbers jumped at the start of the Covid pandemic. Most of these – about 80% – were to or from foreign destinations. Eight airports, among the busiest in the UK, accounted for about two-thirds of the almost empty flights since 2019, led by Heathrow (10,467), Manchester (3,309), Gatwick (2,766) and Stansted (2,197). Edinburgh and Glasgow both had more than 1,500 almost empty flights. Alethea Warrington, at the climate charity Possible, said: “This shocking new data on ghost flights is yet another example of how the aviation industry cannot be trusted to get its emissions on track to tackle the climate crisis.” “Following a summer of record-breaking, runway-melting heat, this wanton waste of carbon by airlines flies in the face of those feeling the full brunt of our warming world,” she said. “To end this for good, it’s time to start taxing kerosene to discourage unnecessary emissions.” A spokesperson for Airlines UK said: “Millions of flights arrived and departed the UK between 2019 and 2022, with only a tiny fraction operating without or with few passengers and for a variety of operational reasons driven by the pandemic.” Airlines have denied operating ghost flights to retain slots. The normal 80:20 rule, meaning 80% of flights on a route must operate to retain the valuable slots, only applies to the busiest airports and was suspended from the end of March 2020 because of the pandemic. It was reintroduced as a 50:50 rule in October 2021 and rose to 70:30 from the end of March 2022. Some airlines have said that some ghost flights took place during the pandemic to fly in Covid-related supplies on passenger planes. However, the CAA data records fewer than 300 flights since the start of 2020 carrying cargo but no passengers. A spokesperson for Birmingham airport said: “Flight occupancy fell during the pandemic due to travel restrictions. During this time flights into Birmingham included British nationals returning from ‘red list’ countries, PPE and Afghan refugees.” A Luton airport spokesperson said the reasons for the high number of ghost flights included Covid travel restrictions and regulatory requirements regarding aircraft airworthiness and pilot licensing. “Following the removal of all travel restrictions, average passenger loads per flight have returned to 88% this summer,” he said. Repositioning of aircraft and maintenance was among the reasons given by Bristol airport for its ghost flights. Heathrow is the UK’s busiest airport and had the highest number of almost empty flights. A Heathrow spokesperson said: “At a time [during the pandemic] when the industry was losing billions, no operator would have been flying a plane without it being commercially viable or without an operational need. As borders closed to passengers, airlines switched to cargo operations, delivering vital medical supplies for the country.” Anna Hughes, at the Flight Free UK campaign group, said: “Putting tens of thousands of empty or near-empty planes in the air during a climate crisis is a vast waste of money and a needless source of emissions. It makes a mockery of people’s efforts to reduce their own emissions. If it makes business sense for the airlines to do this, there’s something badly wrong with the business model.” The spokesperson for Airlines UK said: “UK airlines are fully committed to achieving net zero emissions by 2050. Alongside filling our flights as much as possible, we are making ‘jet zero’ a reality by modernising our airspace to further reduce inefficiencies, using at least 10% sustainable aviation fuel by 2030 and driving the development of zero emission commercial aircraft.” Johnson said: “Several reasons have been put forward for near empty flights during the pandemic, but the provision of 2019 data – a record year for airport passengers in the UK – highlights a wider problem. The data also shows that 50,000 aircraft arrived or departed from Heathrow and Gatwick alone in 2019 less than half full. This must cast doubt both on these airports’ claims that they are effectively full and need to expand and on their claims to be responding to the urgency of the climate challenge.” All the flights in the CAA data are commercial passenger flights and air crew training flights are not included. There were thousands of ghost flights to oil rigs but these were not included in the Guardian analysis. The CAA data also lists Bournemouth airport as having 933 empty flights, but the airport said the vast majority of these were non-commercial flights run by a company that is a tenant at the airport.