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Honeywell Innovations Reduce the Environmental Impact of Flight

Honeywell Innovations Reduce the Environmental Impact of Flight

  • Making our flight-critical auxiliary power units cleaner and more efficient 

The future of humanity depends on the health of the planet and right now the Earth’s well-being and our own long-term survival is threatened by global climate change. 97% of publishing scientists conclude that humans are a primary cause of climate change as we burn fossil fuels for electricity, heating and cooling, and transportation.

In 2018, aircraft were responsible for about 3% of total U.S. carbon dioxide emissions and nearly 9% of greenhouse gas emissions from the U.S. transportation sector. Globally, airline emissions account for 2% of greenhouse gas emissions, but, without action, that number could triple by 2050. Led by the International Civil Aviation Organization (ICAO), the aviation industry is taking action to manage aviation’s carbon footprint.

Reducing emissions and improving air quality at airports

Honeywell supports Biden Administration policies designed to help drive emissions reductions in the air transportation sector, which include efforts to reduce emissions and improve air quality around airports.  

Recently, the FAA awarded $20.4 million in grants to fund zero-emission airport vehicles, including their electric charging infrastructure and electrify the ramp equipment used to service planes at the gate. Included is an examination of the use of auxiliary power units (APUs) at the gate and on the ramp.

APUs are small, onboard turbine engines that usually reside in the aircraft’s tail section. They generate the power needed to run the air conditioning, lights, communications systems and cockpit displays while the aircraft is on the ground.

When needed, an APU can restart an engine or provide power to the cabin and cockpit during flight, as in the famous “Miracle on the Hudson” landing that made Capt. Sully Sullenberger a household name. The APU is a flight-critical system required for aircraft to meet ETOPS (Extended-range Twin-engine Operations Performance Standards) for flight over water and remote areas.

Honeywell has produced more APUs than anyone else – more than 100,000 since we introduced the first one in the mid-1950s.

Improving the APU’s environmental performance

When conventional fossil fuel is used, APUs contribute a small fraction (less than 1%) of the total greenhouse gas footprint left by a typical commercial aircraft. To mitigate the environmental impact of APUs, Honeywell is working aggressively to modify its APUs to operate on sustainable aviation fuel (SAF). We estimate that running engines on 100% SAF will reduce greenhouse gas emissions from Honeywell APUs by 60%-80%.

Honeywell is the leading developer and licensor of technologies to produce SAF. Our technology converts fats, oils and grease to fuels that are essentially a drop-in replacement for conventional aviation fuels. The technology is currently in use at four SAF plants worldwide, including two in the U.S. and two in Italy.

Meanwhile, Honeywell engineers are constantly looking for innovations that improve the fuel efficiency of our APUs. For example, the HGT1700 APU that flies on the Airbus A350 is more powerful, efficient and reliable than previous generations of systems. The HGT1700 features variable speed capability to increase starting power while lowering specific fuel consumption by 6%-10%.

In addition, Honeywell recently introduced a fuel-saving feature for the world’s most utilized APU, the 131-9 for narrowbody aircraft. The new High Efficiency Mode (HEM) upgrade improves performance and reliability, while also delivering fuel-efficiency improvements of close to 2%.

Airports consider alternative methods for ground power and AC

Airport authorities in the U.S. and elsewhere are considering alternatives to the APU for providing electric power and cabin air conditioning for aircraft at the gate and on the ramp. Most commonly mentioned are remote power and AC units, which already are being used at several Chinese airfields.

The hypothesis behind this regulatory push is that ground power and remote air conditioning would produce lower emissions than operating the APU at the gate. To make an accurate comparison through an environmental lens, it’s important to trace how the electricity consumed by ground power and remote air conditioning systems was generated. For example, 63% of the energy used in the U.S. comes from power plants that burn fossil fuels like coal, natural gas and petroleum. That number is higher still in some other countries, like China (86%).

So, while reducing the use of APUs may contribute to a reduction in a particular airport’s environmental impact, it would likely have an overall negative affect on the planet overall, compared to use of a modern, efficient APU running on sustainable aircraft fuels.

The comparison should also include the duplicate effort involved in manufacturing, operating and maintaining these ground solutions. Since the APU is still required for backup power, the environmental impact of these alternative solutions would be incremental. Due to ETOPS requirements, the APU will still need to be powered-up before each flight for testing purposes.

In summary, we believe equipping airports worldwide with ground power and remote air conditioning capabilities reflects a short-term view with little or no potential return on investment.  

Making a difference where it matters most

While we fully support Biden Administration and aviation-industry initiatives aimed at reducing this global industry’s environmental impact, Honeywell believes government funds can have much greater effect in other areas.

APU technology has efficiently and reliably provided aircraft power and cabin cooling for close to six decades. We’re dedicated to continuous improvement and innovation that will make APUs more efficient, sooner rather than later, while we expand their ability to run on sustainable fuels.

Funds earmarked for this effort can be better used for other purposes, such as accelerating production of Sustainable Aviation Fuels and making improvements to the Air Traffic Management system, which would enable more direct flights and greater fuel economy. These solutions provide clear net emissions benefit and support airport and airline requirements well into the future.

Greater use of artificial intelligence and advanced data analytics, exemplified by our unique Honeywell Forge Flight Efficiency platform, deliver the capabilities airlines and other operators need to save fuel.


At Honeywell, we have pledged to be carbon neutral in all our facilities and operations by 2035. We are building on enormous progress made over the last two decades, which has reduced our greenhouse gas intensity by more than 90%. As a global corporate leader in sustainability, we are accelerating our activities and will tackle even more energy-savings projects, convert to renewable energy sources, complete capital improvement projects at our sites, electrify our fleet of company vehicles and use credible carbon offsets.

Even more impactfully, we will continue to develop and deploy innovative products, services and software solutions to help our customers in core industries – like aerospace and defense – achieve their own sustainability goals.

Honeywell Aerospace is uniquely positioned to make an impact at a global level, with production and development programs spanning a wide range of planet-positive technologies. In addition to APUs and sustainable aviation fuels, examples include class-leading, fuel-efficient gas turbine propulsion engines, electric power-generation and distribution systems, fuel cells and electric propulsion systems.

David Shilliday
Vice President and General Manager, UAM/UAS, Honeywell Aerospace Technologies


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