Llewellyn's comments come as electric auto maker Tesla prepares to unveil new battery technology that its CEO and co-founder Elon Musk has flagged will be "big", and as other airlines and Musk himself look at battery aircraft, at least for short-haul flights.
Even though all three concepts use liquid hydrogen as fuel, they employ two different means of propulsion.
Boeing's European rival Airbus has presented three concepts for the world's first zero-emission plane, a move that the company's CEO Guillaume Faury called "a historic moment for the commercial aviation sector".
The use of hydrogen had "the potential to significantly reduce aviation's climate impact", he added. Airbus estimates the Turboprop's range at 1,000 nautical miles.
The French state is backing research into low-carbon flight and sees Airbus' development of a hydrogen powered plane as the best answer to "aviation bashing", French Transport Minister Jean-Baptiste Djebbari said on LCI Television Monday. The production technology would, however, still need around five years to reach maturity, and suppliers and industrial sites would need another two to be ready, he said.
Aviation jobs across Europe face a fresh bloodbath with plane-maker Airbus and holiday company Tui flagging up brutal redundancy programmes because of Covid-19.
The turboprop design would be capable of carrying up to 100 passengers and travelling about 1,000 nautical miles. AFP Airbus
Still, Airbus managed to pull something out of its hat with one of the three new concepts.
The first "is an aircraft of classic configuration that can accommodate up to 200 seats with a range of action making it possible to cover more than 3,500 kilometres". Presumably to head off concerns about combustion, Airbus says the hydrogen will be stored at the extreme rear end of the plane: "behind the rear pressure bulkhead", CNBC reports.
"The second will be a propeller plane, capable of carrying around 100 passengers, for shorter journeys", Faury was quoted as saying. It would be powered by a modified gas-turbine running on hydrogen.
Instead of relying on the usual layout of an airliner, the French opted for a blended-wing body design.
Beyond technical developments, the regulatory framework must necessarily evolve by then to authorise the use of hydrogen in commercial aircraft, says Faury.
She also listed hydrogen's other key advantage. In its presentation, Airbus also noted that hydrogen can be used to create electricity through fuel cells, and that it would use that as a source to power electric motors. However this is now much more expensive than hydrogen produced by using fossil fuels, in addition to being less efficient.
Airbus, the French aircraft maker best known for the A380 model - the largest airliner ever in service - seems to think that hydrogen would be the flawless solution as it just released three zero-emission concept aircraft that, according to the company, could enter service by 2035.