Gallery: Rush To Retrofit Aircraft For Hydrogen-Electric Propulsion

As the push for sustainable aviation gains traction, airlines, OEMs, startups and operators are turning to hydrogen-electric propulsion as a way to reduce the climate effects of aviation. Read on to find out more about some of the efforts currently underway to retrofit commercial aircraft with hydrogen-electric power trains.

German propulsion startup H2Fly has partnered with Deutsche Aircraft to develop a hydrogen propulsion demonstrator based on the Dornier 328 40-seat regional turboprop. The project is funded by Germany’s Ministry of Economic Affairs and Climate Action. H2Fly will develop the megawatt-class fuel-cell powertrain and liquid-hydrogen storage system. First flight is planned for 2025 and would be followed by certification of hydrogen-powered version of the D328eco.

One of the leading pioneers in the segment is startup ZeroAvia, which has secured a flurry of investments and orders from big names in the aviation and venture capital industries. It is currently developing a zero-emission power train through support from the UK government under the HyFlyer II program.

The startup is preparing to perform flight tests of its modified Dornier 228 hydrogen-electric propulsion system testbed, which initially will have one of its two Honeywell TPE331 turboprop engines replaced by an electric motor and control electronics. It will be powered by a fuel-cell system and hydrogen tanks mounted in the fuselage.

In December 2021, United Airlines invested in ZeroAvia as part of its goal to reduce greenhouse gas emissions 100% by 2050. United says it expects to buy up to 100 of ZeroAvia’s new ZA2000 zero-emission, hydrogen-electric engines, which could be retrofitted to existing United Express aircraft—such as the 50-seat Bombardier CRJ-550—as early as 2028.

A few months earlier, Alaska Air Group partnered with ZeroAvia to develop a liquid-hydrogen fuel-cell power train to power part of Alaska Airlines’ fleet of 76-seat De Havilland Canada Dash 8-400 regional turboprops. The airline has secured options for up to 50 kits to begin converting its regional aircraft to hydrogen-electric power.

ZeroAvia also signed a memorandum of understanding with De Havilland Canada in December 2021 to offer its hydrogen-electric powertrain for retrofit or production-line installation in Dash 8-400 aircraft. The aircraft will be powered by a version of ZeroAvia’s planned ZA2000 propulsion system, which will be comprised of scalable configurations that can power aircraft ranging from the ATR 42/72 and Dash 8-200/300 up to the CRJ regional jet.

In October 2021, ZeroAvia partnered with Mitsubishi’s CRJ support division, MHI RJ Aviation (MHIRJ), to develop and certify a conversion of the CRJ regional jet. MHIRJ is providing engineering services to support FAA Part 33 certification of ZeroAvia’s propulsion system, and the companies are working together to evaluate the feasibility of a retrofit program for regional aircraft.

In November 2021, ZeroAvia signed an agreement with Irish cargo airline ASL Aviation Holdings to develop hydrogen-electric engine conversions for ATR 72 freighters. Under the agreement, ASL Airlines Ireland will provide a retired ATR 72 freighter for the program development, which will then be used as a demonstrator. ASL plans to convert a number of its owned aircraft for hydrogen-electric powered operations starting in 2026.

ASL has also signed a similar letter of intent with startup Universal Hydrogen, which is developing conversion kits to retrofit regional aircraft with hydrogen-electric power trains. The agreement covers the provision of an ATR 72 for use as a test and certification aircraft, as well as a potential order for kits to retrofit aircraft with a hydrogen-electric power train.

Universal Hydrogen is developing lightweight, modular capsules to retrofit aircraft to hydrogen fuel-cell propulsion. The capsules are designed to be transported via the existing global intermodal container network and loaded with existing airport equipment into aircraft that have been minimally modified to operate on hydrogen.

The California-based startup has also secured a wide range of deals with airlines looking to convert their fleets to hydrogen-electric propulsion, as well as interest from ATR.

ACIA Aero Leasing signed a letter of intent with Universal Hydrogen in November 2021 to convert up to 30 turboprops. The lessor, which operates a portfolio of ATR 42/72s and Dash 8-400s, expects to place 10 firm orders for Universal Hydrogen’s ATR 72 conversion, with purchase rights for 20 additional kits for various turboprop types.

Irish aircraft lessor Elix Aviation has signed a letter of intent with Universal Hydrogen to acquire 10 conversion kits for its current and future leased fleet. Under the agreement, Universal Hydrogen has given Elix the flexibility to select any combination of its Dash 8-300 or ATR 72-500/600 conversion kits.

In February, Universal Hydrogen also took delivery of its first test aircraft from Elix—a Dash 8-300.

Earlier in 2021, Universal Hydrogen signed agreements with Air Nostrum, Icelandair and Ravn Alaska to retrofit ATR 72s and Dash 8 regional turboprops with hydrogen fuel-cell power trains. The Icelandair agreement covers conversion of its domestic Dash 8 fleet, and Ravn Alaska has committed to purchasing five conversion kits for its Dash 8 fleet. Air Nostrum, which currently operates five ATR 72s on behalf of Iberia, has signaled intent to purchase 11 conversion kits for its existing and future fleet.

Most recently, U.S. startup carrier Connect Airlines signed a letter of intent with Universal Hydrogen in early December 2021. It plans to purchase 24 hydrogen conversion power kits to power its 12 Dash 8 aircraft and has secured purchase rights for 12 additional kits of other unspecified aircraft types. Universal Hydrogen expects to complete installation of the conversion kits by 2025.

Focusing on hydrogen-electric propulsion conversions for smaller aircraft is Spanish/Australian startup Dante Aeronautical. Volotea and Air Nostrum are partnered with the startup to convert the Cessna Grand Caravan to hydrogen fuel-cell propulsion, with the first flight planned for early 2024. In November 2021, regional aircraft lessor Montrose Global Aircraft Management signed a memorandum of understanding with Dante to retrofit turboprop aircraft with hydrogen-electric powertrains.

To prepare for this whirlwind of conversion activity, Lufthansa Technik is working with the German Aerospace Center, the Center for Applied Aeronautical Research and the Hamburg Airport to develop maintenance and ground processes for hydrogen-powered aircraft. The partners are creating a pioneering demonstrator from an Airbus A320 and a digital twin to map ground processes. The project will take place over the next two years, with operation of the demonstrator starting this year.