European aircraft maker Airbus believes the United States will be the biggest customer for its A400M military transport plane, despite a fatal crash involving one of them during a test flight last month.

"By the next decade at the latest, the US armed forces will be the biggest customer for the aircraft," Airbus chief executive Tom Enders told the weekly magazine WirtschaftsWoche in an interview.

Despite its current technical problems, there was no other rival product at the moment, Enders argued.

Boeing's C-17 was larger and Lockheed Martin's C-130 was smaller.

"But a lot of countries don't want either extreme. For the next few years, there will only be one alternative, the A400M, which is also a lot more fuel-efficient and more versatile," he said.

An A400M plane crashed during a test on May 9 near Seville in Spain, killing four of the six people on board and seriously injuring the two others.

The A400M, a large, propeller-driven transport aircraft, was launched in 2003 and is assembled in Seville. But Britain, Germany, Turkey, Malaysia and Spain grounded their A400M planes after the crash.

An initial analysis of the black boxes revealed that three of the aircraft's four engines failed, Airbus has said.

Enders said Airbus was sticking to its sales and earnings targets for this year, despite the crash.

"We're on the right path to achieve our published goals for 2015," the CEO said.

Airbus is looking to increase both sales and earnings this year.

"In 2014, our operating profit was four billion euros on sales of 60 billion euros," he said. Cash flow was positive, at 88 million euros, compared with a negative cash flow of around one billion euros in 2013.

Turning to the possibility of upgrading its super jumbo A380, Enders said a decision would be reached by the end of this year.

"The administrative board will need until the end of the year to get a full picture of the situation and to reach a decision," Enders said.

"It is one of the most difficult product decisions of the last few years. But it's clear: there won't be an A380 with new engines for just one customer."

Dubai's Emirates Airline in particular is pushing for a more fuel-efficient variant of the superjumbo.

Enders said Airbus had succeeded in reducing fuel consumption of the A380 by several percent even without the engines.

"One option I'm concretely thinking about would be innovations in the cabin," he said, adding that new engines would be one of a number of possible engines.