Mike Malik, Chief Marketing Officer, Cirium
What the Research Actually Shows
Our team at Cirium spent months analyzing this relationship across three distance bands: short-haul routes under 1,500 kilometers, medium-haul between 1,500-3,999 kilometers, and long-haul over 4,000 kilometers. We compared July 2019 operations with July 2024. The Cirium EmeraldSky platform let us track 47 operational variables across more than 100,000 daily flights. Everything from gate times and runway waits to specific aircraft configurations and passenger loads.
The correlation was consistent where operational changes occurred.
Routes with improved on-time performance showed measurable drops in flight times and emissions.
Routes with declining OTP showed the opposite: longer flights and higher emissions. The pattern held across different airlines and aircraft types.
Most emissions calculators rely on simple distance formulas. We’re tracking actual operational data. The factors that determine real fuel consumption. PwC independently verified the methodology to ISAE 3000 standards, which puts it among the most rigorous publicly available datasets on airline emissions.
Why Delays Create More Emissions
The mechanism is straightforward but often overlooked. Delayed aircraft burn fuel while accomplishing nothing productive. They sit on taxiways with engines running, waiting for clearance. They circle in holding patterns before landing. They take longer routes to dodge congestion.
Researchers Brueckner and Abreu quantified this over a 21-year study of 16 US airlines.
Each percentage point increase in flights delayed more than 15 minutes correlated with a 0.3% jump in fuel consumption and emissions.
In practice, an airline cutting its delay rate from 22% to 19% (just three percentage points) reduces fuel consumption by roughly 1%. The airlines in that study burned 13.7 billion gallons of jet fuel in 2015. At standard carbon pricing, a three-point improvement delivered $48 million in annual environmental benefits. It’s measurable impact from better operations.
Ground Operations Tell the Story
Much of the emissions penalty happens before takeoff. European air traffic management analysis (2015-2017) found that routing inefficiencies make flight paths 0.61-0.76% longer than optimal. That translated to 229,000 extra tonnes of fuel and 721,000 additional tonnes of CO₂. The equivalent of four full days of flying across the European Economic Area.
At London Heathrow during peak hours, about half the arriving aircraft enter holding patterns averaging six minutes each. During one January 2015 peak hour, those holding patterns alone produced 10 tonnes of CO₂ and 114 kilograms of nitrogen oxides.
The 20 most congested US airports generate 6 million metric tonnes of CO₂ annually just from aircraft taxiing. Research shows that eliminating taxi delays could cut overall flight fuel consumption by 1% on average, with some congested airports showing potential reductions up to 2%.
Solutions That Already Work
Continuous Descent Operations let aircraft descend smoothly with minimal engine thrust instead of the traditional step-down approach with level flight segments.
This saves an average of 51 kilograms of fuel per flight, with real-world operations achieving 3.6% fuel burn improvements.
Full deployment across Europe could deliver 350,000 tonnes in annual fuel savings.
Airport Collaborative Decision-Making systems create transparent communication between airlines, ground handlers, and air traffic control. When 17 European airports put these platforms in place in 2016, they saw 7% reductions in taxi time, 10.3% drops in air traffic delays, and 102,700 tonnes of CO₂ saved.
The Gap Between Airlines
The airline industry improved its carbon output per passenger by 12% between 2013 and 2019.
Roughly 2% per year. The variation between carriers tells an interesting story. Our 2024 Flight Emissions Review shows low-cost carriers like Wizz Air (53.9 grams CO₂ per available seat-kilometer) and Frontier (54.4 g CO₂/ASK) substantially outperforming legacy carriers.
How they run their operations explains much of this gap. Low-cost carriers typically maintain higher load factors, operate uniform fleets, fly point-to-point networks, and refine procedures more rigorously. These same factors support both on-time performance and efficiency.
Why the 3% Matters Right Now
Getting aviation to net-zero by 2050 depends heavily on sustainable aviation fuels (65% of the solution) and new propulsion technologies (13%). Operational improvements? Just 3% of the long-term plan.
Sustainable fuel production won’t reach meaningful scale until the 2030s. Hydrogen and electric aircraft remain years away from commercial deployment. That makes the 3% from operational improvements the only immediate option for emissions reduction.
Better operations are the immediate option for emissions reduction.
No new technology required, just better execution of existing procedures.
When an airline publishes its on-time performance statistics, it’s revealing more than customer service quality. Those numbers provide a window into how well the airline runs, and that directly affects environmental impact. The data proves the connection. Better on-time performance means lower emissions per passenger. It’s something airlines can improve right now.
Sources
Cirium EmeraldSky Study (2024): Short-haul route analysis comparing July 2019 to July 2024 operations, tracking 47 operational variables across 100,000+ daily flights. Methodology independently verified to ISAE 3000 standard by PricewaterhouseCoopers.
Brueckner, J.K., and Abreu, C. “Airline Fuel Usage and Carbon Emissions: Determining Factors.” Journal of Air Transport Management, Vol. 62 (2017), pp. 10-17. Study of 16 US airlines over 1995-2015 period.
EUROCONTROL Performance Review Reports (2015-2017): European air traffic management inefficiency analysis, horizontal flight efficiency data, and holding pattern emissions studies.
EUROCONTROL A-CDM Impact Assessment (2016): Analysis of 17 European airports implementing Airport Collaborative Decision Making systems. Study developed by Atlas Chase for EUROCONTROL.
Cirium Flight Emissions Review (2024): Global airline emissions rankings using flight-specific operational data. Published July 2025.
IATA Global Aviation Data (2013-2019): Historical carbon intensity trends for commercial aviation.
Air Transport Action Group (ATAG): Waypoint 2050 (2nd Edition, September 2021). Aviation industry net-zero pathway analysis and decarbonization scenarios.
