SAF-Powered APUs Make Sense for Aviation and the Planet

Honeywell is fully onboard when it comes to shrinking the environmental footprint of air transportation, which includes actions to reduce greenhouse gas (GHG) emissions and improve air quality at the world’s airports. Airlines and airports are aggressively pursuing many GHG reduction strategies, but none will have as great a near-term impact as accelerating the transition from conventional jet fuel to sustainable aviation fuel (SAF).

Airlines are counting on SAF to contribute 65% of their GHG reduction as they pursue the goal of achieving net-zero emissions by 2050. Airports will benefit greatly from the SAF transition, which will significantly reduce the environmental impact of an aircraft using its auxiliary power unit (APU) at the gate.

APUs Leave Ground Power Units at the Gate

Studies show that running a Honeywell APU on 100% SAF will significantly reduce GHG emissions from the APU from an already low baseline. As the accompanying graph illustrates, this makes APUs a better alternative than the ground power and portable AC units some airports are using and others are exploring.

In fact, based on independent estimates using Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA) standards, a 100% SAF-powered APU will have global warming potential (GWP) impact of about 31. This compares to the average GWP impact of 68-138 for a ground power unit, depending on region, when Scope 2 emissions are considered. The high end of that range includes airports in locations where electric power largely comes from coal-fired power plants. 

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.

These findings underscore that the aviation industry is on the right track with its emphasis on SAF, which is a ready-now solution.  Emerging innovations like hydrogen fuel cells and electric propulsion show enormous promise in the longer term but their practical application may be years or even decades away.

Honeywell APUs have been certified to run on a 50-50 SAF-conventional fuel blend and we’re progressing toward 100% SAF certification  by the end of the decade.

Sustainable Aviation Fuel is the Better Investment for Aviation

Building a vibrant SAF economy will provide a better return on investment than airport spending on ground power and AC units that are a near-term solution at best.

Made from renewable sources like ethanol, biomass, used cooking oil and reclaimed carbon dioxide, SAF is a drop-in replacement with the same performance characteristics as conventional jet fuels. Many airlines already use a mixture of conventional jet fuel and SAF in their aircraft.

Honeywell has more than 15 years of direct experience in renewable fuels and our pioneering processes have been producing SAF commercially since 2016. They are currently producing SAF at six sites in Europe and the U.S., with 20 more in the planning and development stages.

As the SAF economy expands and matures, the infrastructure will grow, available volumes will increase along with demand, and prices will become more competitive. 

Auxiliary Power Units Are Flight Critical Systems

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 75 years ago.