Ethiopian Airlines is evaluating the A350-1000 to see how the type would perform under the demanding high-altitude conditions of its Addis Ababa base.
Chief executive Tewolde Gebremariam, speaking at the Paris air show as he confirmed an agreement to take 10 more A350-900s, said the airline was still examining the -1000's capabilities.
He points out that Ethiopian is in the "unique situation" at Addis Ababa, some 2,400m above sea level. The city typically reaches its highest temperatures, up to 25C, around March-May.
"We have to see how [the -1000] performs at that altitude," says Gebremariam.
Airbus has already conducted high-elevation testing with the -1000 in South America, with take-off and landing trials at Cochabamba and La Paz.
Gebremariam points out that the A350-900 is "doing very well" under Addis Ababa's conditions. The airline operates four of the Rolls-Royce Trent XWB-powered type and is set to take a fifth in the next few days.
Ethiopian had previously ordered 14 A350s – two leased and 12 directly from Airbus – and the airframer describes the follow-on order for 10 more as an "endorsement" of the twinjet.
Airbus has confirmed that the net order book for the A350 will remain unchanged, as the 10 jets had already been listed in the backlog during April and attributed to an unidentified customer.
"We're very happy with the A350," says Gebremariam. "It's been close to a year that we've been operating the aircraft. It's exactly up to the specification, if not a little bit more."
He says the carrier is a "very satisfied customer" of the twinjet. "This is the main reason why we've decided to order more," he adds.
Gebremariam indicates that the A350 is being deployed on routes including London and destinations in China, and that the "next step" is an A350 service to Washington.