"This is huge," said Marco Caceres, senior analyst and director of space studies at Teal Group. "It would break up a monopoly and has the potential to save the taxpayer an awful lot of money."

Richard Aboulafia, an analyst at the Teal Group, said: "Delta's established a rich pattern for buying older planes. The only surprise here is that they actually went ahead with their order. They were the least enthusiastic about new-generation airplanes."

Delta declined to say how much it would pay for the planes, which have a list price of more than $13 billion. But a single bulk order effectively guarantees it will receive a steep discount.

"You get half off just for showing up," Mr. Aboulafia said.

"This tells us three things: One, this new export campaign is an export of an export; two, they don't have the technology themselves; and three, they're relying on Russian engines, which are no great prize," says Richard Aboulafia, VP of Analysis at the Teal Group Corporation.

He also has numerous questions about what's inside the FC-31. For example, how advanced are the jet's active electronically scanned array (AESA) radars, electronic warfare systems, and sensor fusion? "That's a big capability—fusing all the sensor inputs together into an air combat management picture for the pilot," Aboulafia says. "That's huge. It's one of the key enablers in fighter technology."

He doubts there's much of a foreign market for the FC-31, especially not in China-leery East Asia. And while the Chinese could begin serial production of their own J-31 fighter in five years, "it's not really clear what they get out of that," he says. By the end of the decade, the United States would have already rolled out hundreds of Joint Strike Fighters, which, development problems aside, will be superior planes.

This is not the first time the Russian-made AJ26 engines have caused problems, Marco Caceres, an analyst at Teal Group Corp., wrote in an Oct. 31 note. In 2007, the Sea Launch Zenit 3SL exploded because of an engine clogging and SpaceX failed to launch its Falcon 1 in March 2006 due to engine failure, he wrote.

If the engine proves to have been at fault in the latest explosion, it would be easier for Orbital to replace them rather than to attempt a repair, Caceres said in a phone interview today. "Their confidence in the engine was never high," he said.

Orbital's stock dropped 15 percent after the accident, and the company will likely have to postpone its resupply launches while it figures out what went wrong. If the problem can't be quickly fixed, according to Marco Caceres, director of space studies at the defense consultancy the Teal Group, Orbital may have to delay for several years while it works on a replacement, at which point it would risk losing its NASA contract.