As the global defense market wavers between shrinkage and occasional spurts, the latter mainly due to regional crises, competition in airborne refueling for tactical and strategic aircraft remains fierce.

It's an area where Brazilian aviation manufacturer Embraer is aiming to capture a slice of the market dominated by European and U.S. manufacturers. European manufacturers aren't far behind U.S. rivals, with Airbus in the lead to compete against Boeing for airborne refueling business.

The Boeing Co., which has a regular customer in the U.S. Air Force, announced it's on track to achieve targets in a key element of airborne refueling. This relates to the airborne assembly of the refueling boom.

Boeing workers in Seattle this week took another step toward delivering next-generation aerial refueling capability to the U.S. Air Force when they began assembling the second refueling boom for the KC-46A Tanker program.

The Boeing KC-46 was developed by Boeing from its 767 jet airliner. The tanker was selected in February 2011 by USAF as the winner in the KC-X tanker competition to replace older KC-135 Stratotankers.

Success of the program is set to ensure a wider international market for Boeing.

Based on the Boeing 767 commercial airplane, the KC-46A will feature a modernized fly-by-wire boom and hose and drogue systems, making it capable of refueling any U.S. or allied fixed wing aircraft any time on any mission, Boeing said.

What's more, the KC-46 itself can be refueled in flight, adding to its substantially greater capability and mission flexibility, the company said.

"Our team is achieving significant milestones as we prepare for flight tests to begin, and we remain focused on delivering this capability on schedule," said Maureen Dougherty, KC-46 vice president and program manager. "The KC-46 boom is modeled after the proven KC-10 boom, which has performed extremely well in its 30 years of operation. We're enhancing its reliability, making it even better."

Five test booms are being built. The first will be used for risk-reducing laboratory tests scheduled to begin early next year. The second will be installed on a test aircraft to further evaluate the design.

Boeing invented the air refueling boom and has been building, upgrading and modifying it for more than 60 years. The company plans to deliver the initial 18 combat-ready KC-46As by 2017, and 179 to the U.S. Air Force by 2027.

A unit of The Boeing Co., Boeing Defense, Space and Security is one of the world's largest defense, space and security businesses specializing in innovative and capabilities-driven customer solutions, and the world's largest and most versatile manufacturer of military aircraft. With headquarters in St. Louis, Boeing Defense, Space & Security is a $33 billion business, employing 59,000 employees worldwide.

A cheaper regional rival, Brazilian company Embraer's KC-390, is a medium-size, twin-engine jet-powered military transport aircraft being developed by the Brazilian company to perform aerial refueling, transport cargo and troops, and to receive fuel in-flight.