Honeywell and Boeing to Develop Advanced Contrail Forecasting Sensors

Honeywell and Boeing are collaborating on a three-year research project to develop and integrate more effective humidity sensors on aircraft. The initiative, named Project MIST (Mitigation of Contrail Impact via Novel Sensing Technologies), aims to provide more accurate data for forecasting the formation of contrails, which are a significant component of aviation's climate impact.

The project is backed by funding from the UK's Aerospace Technology Institute (ATI) and includes participation from the University of Reading, a key contributor to the European Union Aviation Safety Agency's (EASA) Aviation Non-CO2 Expert Network (ANCEN). This partnership addresses the growing regulatory and scientific focus on non-CO2 emissions, which are now understood to be a major part of the industry's environmental footprint.

According to a comprehensive 2021 assessment by Manchester Metropolitan University, aviation's non-CO2 emissions, primarily from contrails and nitrogen oxides (NOx), account for approximately two-thirds of the industry's total Effective Radiative Forcing (ERF), a metric measuring net climate impact. While most contrails dissipate quickly, a small portion persist in specific atmospheric conditions, known as ice-supersaturated regions. Research from Imperial College London indicates that while only 10% to 15% of contrails are persistent, a small fraction of flights, approximately 10%, create 80% of these warming contrails.

Regulatory Drivers and Industry Response

The urgency for better contrail data is driven by new European regulations. The European Union's Monitoring, Reporting, and Verification (MRV) framework, under regulation 2018/2066, will require aircraft operators to report non-CO2 effects for flights within the European Economic Area starting January 1, 2025. The first of these reports are due by March 31, 2026. This mandate places direct pressure on airlines to accurately track and eventually mitigate emissions beyond just CO2.

Industry leaders involved in Project MIST highlighted the critical need for improved data. Anthony Florian, President of Honeywell Aerospace EMEAI, stated that enhancing aircraft-based sensing will "close critical data gaps that affect contrail forecasting." Similarly, Steph Williams of Boeing noted that maturing water vapor sensors is essential to "enable forecasting and mitigation of persistent contrails through optimized flight routes."

This project aligns with the broader industry trend of contrail avoidance routing, where airlines and Air Navigation Service Providers (ANSPs) test tactical altitude adjustments to steer aircraft around ice-supersaturated regions. However, there are concerns about potential trade-offs. The International Air Transport Association (IATA) has voiced that the MRV requirement may be premature given scientific uncertainties. Furthermore, some climate scientists have argued that rerouting flights could increase fuel burn and CO2 emissions, potentially outweighing the benefit of avoiding a short-lived contrail.

Technical Analysis and Precedents

The development of advanced sensors represents a critical step forward, building on previous research that proved the viability of contrail mitigation. A 2023 trial by Google, American Airlines, and Breakthrough Energy demonstrated a 54% reduction in contrail formation by using AI-based predictions to adjust flight paths. That trial proved the concept but also underscored the primary limitation: the lack of real-time, high-fidelity atmospheric data. Project MIST directly addresses this data gap.

This initiative follows a pattern established by earlier studies, such as the DLR and NASA ECLIF (Emission and Climate Impact of Alternative Fuels) research conducted between 2015 and 2021. Those studies established a clear link between engine soot particle emissions and contrail formation, showing that Sustainable Aviation Fuel (SAF) could reduce persistent contrails. Project MIST shifts the focus from fuel properties to atmospheric conditions, providing a complementary pathway for mitigation.

The data collected by these new sensors will have a dual benefit. For airlines, it enables compliance and climate-optimized flight routing. For meteorological agencies, the influx of high-frequency, in-flight humidity data is expected to significantly improve the accuracy of global numerical weather prediction models.

What Comes Next

The immediate focus for airlines operating in Europe is the upcoming regulatory deadline. The first reports under the non-CO2 MRV rules are due by March 31, 2026. While the initial phase involves only monitoring and reporting, the European Commission is expected to propose a measure by 2028 that could require airlines to surrender EU Emissions Trading System (ETS) allowances for their non-CO2 climate impacts. This would attach a direct financial cost to contrail formation, further incentivizing the adoption of avoidance technologies like those enabled by Project MIST.

Why This Matters

This collaboration between Honeywell, Boeing, and the University of Reading marks a pivotal shift from theoretical modeling to practical, in-flight measurement and mitigation of aviation's non-CO2 climate impact. It directly addresses a pressing regulatory demand from the EU and equips the industry with the tools needed for data-driven climate optimization. By closing a critical gap in atmospheric data, this project could enable more efficient flight routing that reduces overall climate impact, representing a significant step in the pursuit of sustainable aviation.