Small altitude adjustments on business aviation flights could make a big difference in the environmental impacts of contrails—the condensation trails of aircraft—without CO2 emission tradeoffs. That's the assessment of a just-concluded environmental study conducted by aviation sustainability company 4Air has found that
The study, conducted over one year, encompassed 16,000 flights and more than 27,000 flight hours. It found that adjustments on even 50 flights out of 16,888 would have reduced the non-CO2 emission impact from the sample by more than 50%.
“The results of this study demonstrate both the challenges and opportunities with reducing aviation’s footprint from contrails,” said 4Air president Kennedy Ricci. “Effectively reducing our contrail warming impact requires considering contrails on every flight, but successfully avoiding on just a handful of flights would have a major impact, potentially without CO2 tradeoffs.”
Contrails are produced when hot water vapor emitted from aircraft engines rapidly cool at higher altitudes. Depending on the time of day, contrails can linger and absorb heat that would normally radiate back into space. Some studies suggest that contrails have a bigger impact on the environment than CO2 emissions and can contribute to two-thirds of the aviation industry’s warming impact.
Contrails can be formed at the upper end of a commercial aircraft’s service ceiling. Business aircraft, which have higher service ceilings, are able to fly higher than the formation region. This can reduce CO2 emissions and their contrail impact.
Of the 23 flights in the study with the highest contrail impact—which in total accounted for 35% of the total impact—65% of those flights could have minimized or avoided it by flying at a higher altitude. Eighteen percent of the flights surveyed created a contrail.
The average contrail was estimated to persist for around 2.5 hours, but more impactful warming came from contrails that lasted around 6.5 hours, according to the study.
4Air has also completed six months of a contrail avoidance pilot program in collaboration with Flexjet. That program focused on contrail forecasts and optimizing flight paths to minimize the time flights spend in contrail-forming regions. Flight paths were then adjusted to modify cruising altitudes—with notes shared among pilots to calibrate climbs and descents with the intent of minimizing time in contrail regions.
The company has offered what it calls “science-based goals and independently verified results” as a framework for private aviation operators to pursue sustainability options. It has offered a four-tier rating system for companies looking to verifiably reduce their emissions impact through means of becoming emission-neutral or negative through carbon credits and offsets and encouraging funding of the Aviation Climate Fund.